Communication device

Abstract

A communication device is described that comprises a first data unit buffer for holding data units of a first communication protocol and a second data unit buffer for holding data units of a second communication protocol. The first communication protocol is a communication protocol suitable for transmitting data units from a sending peer of the first communication protocol to a receiving peer of the first communication protocol over one or more relay peers of the first communication protocol. The first communication protocol provides for at least a first type (RACK) of receipt information that is indicative of a correct receipt at a relay peer and a second type (ACK) of receipt information that is indicative of a correct receipt at the receiving peer. The second communication protocol can be a conventional ARQ protocol or a protocol using the two types of receipt information.

Claims

The invention claimed is: 1. A communication device, comprising a first data unit buffer for holding data units of a first communication Relay-Automatic Retransmission Request (ARQ) protocol, where said first communication Relay-ARQ protocol is a communication protocol suitable for transmitting data units from a sending peer of said first communication Relay-ARQ protocol to a receiving peer of said first communication Relay-ARQ protocol over one or more relay peers of said first communication Relay-ARQ protocol, providing for feedback messages sent in a direction to said sending peer of said first communication Relay-ARQ protocol, where said feedback messages carry information on a receipt of said data units of said first communication Relay-ARQ protocol, said first communication Relay-ARQ protocol providing for at least a first type and a second type of receipt information, said first type (RACK) of receipt information being indicative of a correct receipt at a relay peer and said second type (ACK) of receipt information being indicative of a correct receipt at said receiving peer, and where said first communication Relay-ARQ protocol provides that said sending peer of said first communication Relay-ARQ protocol uses a sending peer control procedure for controlling a transmission based on said feedback messages of said first communication Relay-ARQ protocol, and each relay peer of said first communication Relay-ARQ protocol uses a relay peer control procedure for controlling a transmission based on said feedback messages of said first communication Relay-ARQ protocol, a second data unit buffer for holding data units of a second communication protocol that at least has ARQ functionality, where said second communication ARQ-functional protocol is a communication protocol suitable for transmitting data units from a sending peer of said second communication ARQ-functional protocol to a receiving peer of said second communication ARQ-functional protocol, which provides for feedback messages sent in a direction to said sending peer of said second communication ARQ-functional protocol, where said feedback messages of said second communication ARQ-functional protocol carry information on a receipt of said data units of said second communication ARQ-functional protocol, said second communication ARQ-functional protocol providing for a specific type of receipt information that is indicative of a correct receipt at said receiving peer of said second communication ARQ-functional protocol, and where said second communication ARQ-functional protocol provides that said sending peer of said second communication ARQ-functional protocol uses a control procedure for controlling a transmission based on said feedback messages of said second communication ARQ-functional protocol and the receipt information contained therein, and a control system arranged to control a generation of said data units of said second communication ARQ-functional protocol such that a data symbol stream carried in said data units of said first communication Relay ARQ protocol is also carried in said data units of said second communication ARQ-functional protocol, said control system being arranged to implement the control procedure for controlling a transmission of said data units of said first communication Relay ARQ protocol in such a way that if all the data symbols of said data symbol stream contained in a given data unit of said first communication Relay ARQ protocol are successfully transferred into said second data unit buffer, then said control procedure for controlling a transmission of said data units of said first communication Relay ARQ protocol acts as if said first type (RACK) of receipt information had been received for said given data unit, whereby said control system implements the control procedure according to the first communication Relay-ARQ protocol using RACKs and ACKs and couples logic of the first communication Relay-ARQ protocol to the second communication ARQ-functional protocol by exploiting the ARQ functionality of the second communication ARQ-functional protocol to simplify handling of the data units of said first communication Relay-ARQ protocol by temporarily passing responsibility of further forwarding the data units of said first communication Relay-ARQ protocol by using said second data unit buffer of the second communication ARQ-functional protocol. 2. The communication device according to claim 1 , wherein said control system is arranged to implement a sending peer control procedure of said first communication Relay-ARQ protocol for performing a first retransmission control procedure for a data unit that has been sent but for which no first type (RACK) receipt information has been received, performing a second retransmission control procedure if said first type (RACK) receipt information has been received for said data unit that has been sent, and holding said data unit that has been sent at least until having received said second type (ACK) of receive information. 3. The communication device according to claim 1 , wherein said control system is arranged to implement a relay peer control procedure of said first communication Relay-ARQ protocol for: performing a first retransmission control procedure for a data unit that has been sent but for which no first type (RACK) receipt information has been received, performing a second retransmission control procedure if said first type (RACK) receipt information has been received for said data unit that has been sent, holding said data unit that has been sent until a predetermined deletion condition is fulfilled, and after receiving said second type (ACK) of receipt information for said data unit that has been sent, sending to a sender-side peer of said first communication Relay-ARQ protocol a feedback message of said first communication Relay-ARQ protocol carrying said second type (ACK) of receipt information for said data unit that has been sent. 4. The communication device according to claim 1 , wherein said first communication Relay-ARQ protocol and said second communication ARQ-functional protocol are at the same communication layer. 5. The communication device according to claim 1 , wherein said first communication Relay-ARQ protocol is at a first communication layer, and said second communication ARQ-functional protocol is at a second communication layer below said first communication layer. 6. The communication device according to claim 1 , wherein said feedback messages of said first communication Relay-ARQ protocol are embedded in data units of said second communication ARQ-functional protocol received by said communication device from a peer of said second communication ARQ-functional protocol, and said control system is arranged to extract said feedback messages of said first communication Relay-ARQ protocol from said received data units of said second communication ARQ-functional protocol. 7. The communication device according to claim 1 , wherein said control system is arranged to, identify receipt information associated with data units of said first communication Relay-ARQ protocol on the basis of receipt information associated with data units of said second communication ARQ-functional protocol contained in feedback messages of said second communication ARQ-functional protocol. 8. The communication device according to claim 7 , wherein said control system is arranged to implement said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol such that if said specific receipt information is received for all of the one or more data units of said second communication ARQ-functional protocol that carry all of the data symbols of said data symbol stream that are contained in a given data unit of said first communication Relay-ARQ protocol, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said first type (RACK) of receipt information had been received for said given data unit of said first communication Relay-ARQ protocol. 9. The communication device according to claim 7 , wherein said control system is arranged to implement said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol such that if said specific receipt information is received for all of the one or more data units of said second communication ARQ-functional protocol that carry all of the data symbols of said data symbol stream that are contained in a given data unit of said first communication Relay-ARQ protocol, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said second type (ACK) of receipt information had been received for said given data unit of said first communication Relay-ARQ protocol. 10. The communication device according to claim 7 , wherein said second communication ARQ-functional protocol is a communication protocol suitable for transmitting data units from a sending peer of said second communication ARQ-functional protocol to a receiving peer of said second communication ARQ-functional protocol over one or more relay peers of said second communication ARQ-functional protocol, and said second communication ARQ-functional protocol providing for at least said first type and said second type of receipt information, where said control system is arranged to implement said control procedure for controlling a transmission of said data units of said first communication protocol such that if said second type of receipt information is received for all of the one or more data units of said second communication ARQ-functional protocol that carry all of the data symbols of said data symbol stream that are contained in a given data unit of said first communication Relay-ARQ protocol, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said second type (ACK) of receipt information had been received for said given data unit of said first communication Relay-ARQ protocol. 11. The communication device according to claim 7 , wherein said first Relay-ARQ communication protocol and said second communication ARQ-functional protocol provide for a third type (NACK) of receipt information that is indicative of an incorrect receipt, where said control system is arranged to implement said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol such that if said third type (NACK) of receipt information is received for one of the one or more data units of said second communication ARQ-functional protocol that carry all of the data symbols of said data symbol stream that are contained in a given data unit of said first communication Relay-ARQ protocol, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said third type (NACK) of receipt information had been received for said given data unit of said first communication Relay-ARQ protocol. 12. A method of controlling a communication device, said device comprising a first data unit buffer for holding data units of a first communication Relay-Automatic Retransmission Request (ARQ) protocol and a second data unit buffer for holding data units of a second communication protocol that at least has ARQ functionality, where said first communication Relay-ARQ protocol is a communication protocol suitable for transmitting data units from a sending peer of said first communication Relay-ARQ protocol to a receiving peer of said first communication Relay-ARQ, protocol over one or more relay peers of said first communication Relay-ARQ protocol, which provides for feedback messages sent in a direction to said sending peer of said first communication Relay-ARQ protocol, where said feedback messages carry information on a receipt of said data units of said first communication Relay-ARQ protocol, said first communication Relay-ARQ protocol providing for at least a first type and a second type of receipt information, said first type (RACK) of receipt information being indicative of a correct receipt at a relay peer and said second type (ACK) of receipt information being indicative of a correct receipt at said receiving peer, and where said first communication Relay-ARQ protocol provides that said sending peer of said first communication Relay-ARQ protocol uses a sending peer control procedure for controlling a transmission based on said feedback messages of said first communication Relay-ARQ protocol, and each relay peer of said first communication Relay-ARQ protocol uses a relay peer control procedure for controlling a transmission based on said feedback messages of said first communication Relay-ARQ protocol, and where said second communication ARQ-functional protocol is a communication protocol suitable for transmitting data units from a sending peer of said second communication ARQ-functional protocol to a receiving peer of said second communication ARQ-functional protocol, which provides for feedback messages sent in a direction to said sending peer of said second communication ARQ-functional protocol, where said feedback messages of said second communication ARQ-functional protocol carry information on a receipt of said data units of said second communication ARQ-functional protocol, said second communication ARQ-functional protocol providing for a specific type of receipt information that is indicative of a correct receipt at said receiving peer of said second communication ARQ-functional protocol, and where said second communication ARQ-functional protocol provides that said sending peer of said second communication ARQ-functional protocol uses a control procedure for controlling a transmission based on said feedback messages of said second communication ARQ-functional protocol and the receipt information contained therein, said method comprising the steps of: generating said data units of said second communication ARQ-functional protocol such that a data symbol stream carried in said data units of said first communication Relay-ARQ protocol is also carried in said data units of said second communication ARQ-functional protocol, operating the control procedure for controlling a transmission of said data units of said first, communication Relay-ARQ protocol in such a way that if all the data symbols of said data symbol stream contained in a given data unit of said first communication Relay-ARQ protocol are successfully transferred into said second data unit buffer, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said first type (RACK) of receipt information had been received for said given data unit, where the control procedure is implemented according to the first communication Relay-ARQ protocol using RACKs and ACKs and couples logic of the first communication Relay-ARQ protocol to the second communication ARQ-functional protocol by exploiting the ARQ functionality of the second communication ARQ-functional protocol to simplify handling of the data units of said first communication Relay-ARQ protocol by temporarily passing responsibility of further forwarding the data units of said first communication Relay-ARQ protocol by using said second data unit buffer of the second communication ARQ-functional protocol. 13. The method according to claim 12 , further comprising: implementing a sending peer control procedure of said first communication Relay-ARQ protocol for: performing a first retransmission control procedure for a data unit that has been sent but for which no first type (RACK) receipt information has been received, performing a second retransmission control procedure if said first type (RACK) receipt information has been received for said data unit that has been sent, and holding said data unit that has been sent at least until having received said second type (ACK) of receive information. 14. The method according to claim 12 , further comprising: implementing a relay peer control procedure of said first communication Relay-ARQ protocol for: performing a first retransmission control procedure for a data unit that has been sent but for which no first type (RACK) receipt information has been received, performing a second retransmission control procedure if said first type (RACK) receipt information has been received for said data unit that has been sent, holding said data unit that has been sent until a predetermined deletion condition is fulfilled, and after receiving said second type (ACK) of receipt information for said data unit that has been sent, sending to a sender-side peer of said first communication Relay-ARQ protocol a feedback message of said first communication Relay-ARQ protocol carrying said second type (ACK) of receipt information for said data unit that has been sent. 15. The method according to claim 12 , wherein said first communication Relay-ARQ protocol and said second communication ARQ-functional protocol are at the same communication layer. 16. The method according to claim 12 , wherein said first communication Relay-ARQ protocol is at a first communication layer, and said second communication ARQ-functional protocol is at a second communication layer below said first communication layer. 17. The method according to claim 12 , wherein said feedback messages of said first communication Relay-ARQ protocol are embedded in data units of said second communication ARQ-functional protocol received by said communication device from a peer of said second communication ARQ-functional protocol, said method further comprising the step of extracting said feedback messages of said first communication Relay-ARQ protocol from said received data units of said second communication ARQ-functional protocol. 18. The method according to claim 12 , further comprising: identifying receipt information associated with data units of said first communication Relay-ARQ protocol on the basis of receipt information associated with data units of said second communication ARQ-functional protocol contained in feedback messages of said second communication ARQ-functional protocol. 19. The method according to claim 18 , further comprising: operating said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol such that if said specific receipt information is received for all of the one or more data units of said second communication ARQ-functional protocol that carry all of the data symbols of said data symbol stream that are contained in a given data unit of said first communication Relay-ARQ protocol, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said first type (RACK) of receipt information had been received for said given data unit of said first communication Relay-ARQ protocol. 20. The method according to claim 18 , further comprising: operating said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol such that if said specific receipt information is received for all of the one or more data units of said second communication ARQ-functional protocol that carry all of the data symbols of said data symbol stream that are contained in a given data unit of said first communication Relay-ARQ protocol, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said second type (ACK) of receipt information had been received for said given data unit of said first communication Relay-ARQ protocol. 21. The method according to claim 18 , wherein said second communication ARQ-functional protocol is a communication protocol suitable for transmitting data units from a sending peer of said second communication ARQ-functional protocol to a receiving peer of said second communication ARQ-functional protocol over one or more relay peers of said second communication ARQ-functional protocol, and said second communication ARQ-functional protocol providing for at least said first type of receipt information and said second type of receipt information, the method further comprising: operating said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol such that if said second type of receipt information is received for all of the one or more data units of said second communication ARQ-functional protocol that carry all of the data symbols of said data symbol stream that are contained in a given data unit of said first communication Relay-ARQ protocol, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said second type (ACK) of receipt information had been received for said given data unit of said first communication Relay-ARQ protocol. 22. The method according to claim 18 , wherein said first communication Relay-ARQ protocol and said second communication ARQ-functional protocol provide for a third type (NACK) of receipt information that is indicative of an incorrect receipt, the method further comprising: operating said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol such that if said third type (NACK) of receipt information is received for one of the one or more data units of said second communication ARQ-functional protocol that carry all of the data symbols of said data symbol stream that are contained in a given data unit of said first communication Relay-ARQ protocol, then said control procedure for controlling a transmission of said data units of said first communication Relay-ARQ protocol acts as if said third type (NACK) of receipt information had been received for said given data unit of said first communication Relay-ARQ protocol.
FIELD OF THE APPLICATION The present application relates to a communication device for transmitting data units. The application also relates to corresponding control methods for the communication device. BACKGROUND OF THE INVENTION The present invention basically relates to the general field of data unit communication. In data unit communication, an amount of data is divided into individual units, and said units are transmitted to a desired receiver over an appropriate communication path. This form of data communication is very well known and in wide use. Such data units carry a variety of names in the context of different communication systems and communication protocols, such as packets, frames, segments, protocol data units, etc. The term “data unit” as used in the present specification and claims generically refers to any such division of a data amount. In order to ensure the complete transmission of data units from a sender to a receiver, a mechanism referred to as ARQ (Automatic Retransmission reQuest) is known. When using an ARQ mechanism, the receiver of data units sends feedback messages to the sender, such that the sender can determine whether sent data units were properly received, and if not, to appropriately perform retransmissions of data units. It can also occur that the communication of data units from a given sender to a given receiver occurs via one or more relay points. One example of such a situation is if a desk top computer communicates with a portable computer that has a WLAN module, where the communication is handled via a WLAN router. Another example of such a situation is if a link layer (layer 2 ) communication between a sender and receiver occurs over several relay points. Such connections are also referred to as multi-hop connections. The basic problem encountered with such multi-hop connections is how to provide a reliable transmission of data units from the sender (i.e. the sending end-point) to the receiver (i.e. the receiving end-point). The paper “A comparison of Mechanisms for Improving TCP Performance over Wireless Links” by H. Balakrishnan et al, Proc. ACM SIGCOMM'96, Stanford, Calif., August 1996, gives an overview of techniques for dealing with multi-hop connections that involve wireless links. One known solution to the multi-hop problem is the provision of split connections. An example of this principle is shown in FIG. 1 . In the example of FIG. 1 , a link layer (layer 2 ) communication between a sender 10 and receiver 12 via a relay device 11 is considered. In order to provide reliable transmission of layer 2 data units, a sending peer 10 _ 2 in sender 10 and a receiving peer 11 _ 2 b in the relay device 11 implement an ARQ mechanism, and furthermore a sending peer 11 _ 2 a of relay device 11 and a receiving peer 12 _ 2 of receiver 12 implement another ARQ mechanism. In this way, the first ARQ mechanism provides for reliability from sender 10 to relay device 11 , and the second ARQ mechanism provides for reliability in the communication from relay device 11 to receiver 12 . Naturally, this split connection concept is applicable to any layer, not just the link layer. Nonetheless, it suffers from the disadvantage that if any problems occur in the relay device 11 , or a handover from the shown relay device 11 to another relay device becomes necessary, then the entire end-to-end communication is in jeopardy. More specifically, it can occur that the sender 10 has completed its communication with the relay device 11 , as the correct receipt of data units at relay 11 has been acknowledged to sender 10 , and thereafter a problem occurs in relay device 11 , such that some of these data units are lost. In such an event, these data units will be irrevocably lost at the given protocol level (L 2 in the example), as the sender has already completed its communication and consequently deleted the data units from its send buffer. In order to avoid such problems, it is known to introduce sub-layering. This is shown in an example in FIG. 2 . The example again relates to a link layer communication between a sender 20 and a receiver 22 . In order to provide end-to-end reliability, the link layer L 2 is divided into two sub-layers, where the upper sub-layer has two peers 20 _ 2 ′ and 22 _ 2 ′ located at the sender 20 and receiver 22 , respectively. These two peers implement their own ARQ mechanism, in order to provide for retransmission if data units of this upper sub-layer are lost on the end-to-end connection. Additionally, a lower sub-layer is provided, having respective peers 20 _ 2 and 21 _ 2 b between sender 20 and relay device 21 , and 21 _ 2 a and 22 _ 2 between relay device 21 and receiver 22 . The data units of the upper sub-layer are encapsulated or segmented into data units of the lower sub-layer, and each lower sub-layer peer pair has its own ARQ mechanism. Modifications of this sub-layering concept are known, e.g. U.S. Pat. No. 5,699,367 describes a situation, where the lower sub-layer is only provided on one hop, e.g. only between sender 20 and relay device 21 . Due to the end-to-end ARQ mechanism of peers 20 _ 2 ′ and 22 _ 2 ′, problems in the relay device 21 do not lead to irrevocable data unit loss. On the other hand, the ARQ mechanisms on the hops from sender to relay device and relay device to receiver ensure resource efficient and fast error recovery over each hop, e.g. by avoiding unnecessary end-to-end retransmissions. Nonetheless, the concept of sub-layering has the disadvantage of requiring complicated adjustment of the ARQ control in the upper sub-layer and lower sub-layer, in order to avoid ARQ conflicts, which can e.g. lead to unnecessary redundant data transmission, which in turn degrades the end-to-end performance. In order to provide an improved concept for reliable data unit transmission from a sender to a receiver via a relay device, the applicant/assignee of the present application has filed a patent application PCT/EP2004/009967, which is herewith fully incorporated by reference. In PCT/EP2004/009967, a novel concept and protocol is disclosed, according to which data units are sent from a sending peer to a receiving peer via one or more relay peers, where said protocol provides for a first and a second type of receipt information, said first type indicating the correct receipt at a relay peer, and the second type indicating the correct receipt at the receiving peer. This concept will be referred to as Relay-ARQ or RARQ in the following. This basic concept of Relay-ARQ is shown in FIG. 3 . A data unit communication between a sender 30 and a receiver 32 via a relay device 31 is handled in one layer, where the sender 30 comprises a sending peer 30 _ 2 and the receiver 32 a receiving peer 32 _ 2 , and the relay device 31 carries a relay peer 31 _ 2 . The communication occurs in accordance with a communication protocol for the sending peer, relay peer and receiving peer, where this communication protocol has a feed-back mechanism, and the feed-back messages are such that they carry information on the receipt of data units. The communication protocol provides for at least a first type and a second type of receipt information, where the first type of receipt information is indicative of a correct receipt of a data unit at the relay peer ( 31 _ 2 in the example of FIG. 3 ) and the second type of receipt information is indicative of a correct receipt of a data unit at the final destination peer ( 32 _ 2 in the example of FIG. 3 ) of the protocol. The sending peer ( 30 _ 2 in the example of FIG. 3 ) performs a first retransmission control procedure for a sent data unit for which no first type receipt information has been received, and a second receipt retransmission control procedure for a sent data unit if the first type receipt information has been received. Namely, looking at the example of FIG. 3 , not having received first type receipt information means that the relay peer 31 _ 2 has not acknowledged correct receipt. On the other hand, receiving the first receipt information means that the relay peer 31 _ 2 has acknowledged correct receipt. Nonetheless, the sender holds a data unit in its buffer at least until having received the second type of receipt information, namely information that indicates that the data unit in question has been received at the final destination (receiving peer 32 _ 2 in the example of FIG. 3 ). The relay peer is arranged to on the one hand send sender-side feedback messages to the sending peer ( 30 in the example of FIG. 3 ), which feedback messages provide the first type of receipt information when a data unit was correctly received from the sending peer 30 _ 2 . On the other hand, the relay peer generates send data units based on the receive data units, and transmits these send data units to the receiving peer. The receive data units (i.e. the data units received from the sending peer) and the send data units (i.e. the data units transmitted to the receiving peer) use the same sequence position identifiers. When the relay peer receives a feedback message on the receiver-side (from the receiving peer 32 _ 2 in the example of FIG. 3 ), then it generates a sender-side feedback message directed towards the sender-side peer (the sending peer 30 _ 2 in the example of FIG. 3 ) carrying the second type of receipt information for the given sequence position identifier that was already associated with the second type of receipt information in the receiver-side feedback message. Expressed in other words, when the relay peer receives an acknowledgement that a data unit has been correctly received at the final destination peer, then such an acknowledgement is passed on towards the sender. Based on the use of two different kinds of receipt information, one for indicating correct receipt at a relay device and another for indicating correct receipt at the final destination, the sender and the relay device (or several relay devices, if more than one relay device is involved) can appropriately manage their own retransmission function and buffer management, while both end-to-end-reliability and reliability on individual hops is ensured. This is achieved without the necessity of sub-layering, and consequently without the complexities or problems that occur due to ARQ conflicts between different sub-layers. This provides a highly reliable mechanism for multi-hop data unit communication that is very simple at the same time. Despite the above described advantages, it can occur that a transition from one data unit format to another becomes necessary, e.g. when one or more hops are over a wire-line network and one or more other hops are over a wire-less network that uses a different protocol and different format. OBJECT OF THE INVENTION The object of the present invention is to provide a communication device that can advantageously combine the concept of Relay-ARQ with a situation in which a transition from a Relay-ARQ protocol to another protocol takes place. SUMMARY OF THE INVENTION This object is achieved by the communication device of claim 1 and the method of controlling a communication device described in claim 12 . Advantageous embodiments are described in the dependent claims. The invention proposes a communication device, that comprises a first data unit buffer for holding data units of a first communication protocol. The first communication protocol is a communication protocol suitable for transmitting data units from a sending peer of said first communication protocol to a receiving peer of said first communication protocol over one or more relay peers of said first communication protocol, which provides for feedback messages sent in a direction of said sending peer of said first communication protocol, where said feedback messages carry information on a receipt of said data units of said first communication protocol, said first communication protocol providing for at least a first type and a second type of receipt information, said first type (RACK) of receipt information being indicative of a correct receipt at a relay peer and said second type (ACK) of receipt information being indicative of a correct receipt at said receiving peer, and where said first communication protocol provides that said sending peer of said first communication protocol uses a sending peer control procedure for controlling a transmission based on said feedback messages of said first communication protocol, and each relay peer of said first communication protocol uses a relay peer control procedure for controlling a transmission based on said feedback messages of said first communication protocol. In other words, the first communication protocol is a Relay-ARQ protocol. A second data unit buffer for holding data units of a second communication protocol is also provided. The second communication protocol is a communication protocol suitable for transmitting data units from a sending peer of said second communication protocol to a receiving peer of said second communication protocol, which provides for feedback messages sent in a direction of said sending peer of said second communication protocol, where said feedback messages of said second communication protocol carry information on a receipt of said data units of said second communication protocol, said second communication protocol providing for a specific type of receipt information that is indicative of a correct receipt at said receiving peer of said second communication protocol, and where said second communication protocol provides that said sending peer of said second communication protocol uses a control procedure for controlling a transmission based on said feedback messages of said second communication protocol and the receipt information contained therein. The second protocol can be a conventional ARQ protocol or also a Relay-ARQ protocol. In accordance with the invention, a control system is arranged to control a generation of said data units of said second communication protocol such that a data symbol stream carried in said data units of said first communication protocol is also carried in said data units of said second communication protocol, said control system being arranged to implement the control procedure for controlling a transmission of said data units of said first communication protocol in such a way that if all the data symbols of said data symbol stream contained in a given data unit of said first communication protocol are successfully transferred into said second data unit buffer, then said control procedure for controlling a transmission of said data units of said first communication protocol acts as if said first type (RACK) of receipt information had been received for said given data unit. This in other words means that the present invention proposes to expand the functionality of a controller that implements a control procedure according to the Relay-ARQ communication protocol using RACKs and ACKs by letting the controller couple the logic of the Relay-ARQ communication protocol to another communication protocol that at least has an ARQ functionality. Naturally, the second protocol can itself also have the novel features of using RACKs and ACKs, but this is not necessary. In accordance with the invention, the controller for the novel communication protocol CP 1 treats the passing of data symbols of a given data unit to a peer of a different protocol that at least has an ARQ functionality, like the reception of a RACK, which means that the controller has temporarily passed the responsibility for further forwarding the corresponding data to said peer of the different protocol CP 2 . In this way, the ARQ functionality of the second communication protocol CP 2 is exploited, to thereby simplify the handling of data units of the first communication protocol CP 1 . BRIEF DESCRIPTION OF FIGURES The present invention will be explained in more detail in the following by making reference to specific embodiments that are described with respect to the figures, where FIG. 1 shows a basic protocol architecture of the known split connection concept; FIG. 2 shows the basic protocol architecture of the known sub-layering concept; FIG. 3 shows a link layer example of the basic protocol architecture of Relay-ARQ; FIG. 4 schematically shows an example of a communication in accordance with an embodiment of Relay-ARQ; FIG. 5 schematically shows a specific data unit and message exchange in an embodiment of Relay-ARQ; FIG. 6 shows a further example of an embodiment Relay-ARQ; FIG. 7 shows an embodiment of Relay-ARQ, in which two relay devices operate in parallel; FIG. 8 shows an embodiment of Relay-ARQ, in which two relay devices are connected sequentially; FIG. 9 is an explanatory, schematic diagram for explaining an embodiment of Relay-ARQ, in which flow control is adjusted based on feedback information; FIG. 10 shows a schematic diagram of an embodiment of Relay-ARQ; FIG. 11 shows a schematic diagram of a data unit relay device; FIG. 12 shows a flowchart of an embodiment of a method for controlling a data unit sender; FIG. 13 shows a flowchart of another embodiment of a method for controlling a data unit sender; FIG. 14 a - c show flowcharts describing parts of a method embodiment for controlling a data unit relay device. FIG. 15 a - f show embodiments of the present invention and configurations between two different protocols in which the present invention can be applied, where layered configurations are shown; FIG. 16 a - d show embodiments of the present invention and configurations between two different protocols in which the present invention can be applied, where configurations in one protocol layer are shown; FIG. 17 shows a schematic block diagram of an embodiment of a communication device of the present application; FIG. 18 shows a flow chart of a method embodiment of the present invention; and FIG. 19 shows a flow chart of another method embodiment of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS FIG. 10 shows a schematic arrangement of a data unit sender 100 arranged in accordance with an embodiment of Relay-ARQ. The data unit sender 100 comprises a data unit buffer 1002 for holding data units 1003 of a communication protocol. A control unit 1001 is arranged to control a transmission of the data units 1003 to a peer of the communication protocol, a processing of feedback messages 1004 received from that peer, a re-transmission of the data units 1003 based on the feedback messages 1004 , and a management of the buffer. The control unit 1001 is arranged to let the data unit sender 100 act as a sending peer of the mentioned communication protocol. The term “buffer management” means the controlled placing of data units into the buffer and the controlled removal of data units from the buffer. The buffer can be any type of memory suitable for holding data units, and the control unit can equally be any device suitable for performing the control functions, e.g. the control unit can be a programmable processor. The communication protocol is such that the data units 1003 are arranged in a sequence, and each sent data unit is identifiable by a sequence position identifier. The feedback messages 1004 use the sequence position identifiers and carry information on the receipt of the data units 1003 . In accordance with Relay-ARQ, the communication protocol provides for at least a first type and a second type of receipt information. The first type of receipt information is indicative of a correct receipt of a data unit 1003 at a relay peer of the communication protocol, and the second type of receipt information is indicative of a correct receipt at a final destination peer of the communication protocol. The control unit 1001 is arranged to perform a first re-transmission control procedure for a given data unit that has been sent but for which no first type receipt information has been received, and to perform a second re-transmission control procedure for the given data unit if the first type receipt information has been received. Furthermore, the control unit 1001 is arranged to hold the given data unit in the buffer 1002 at least until having received the second type of receipt information for the given data unit. In accordance with the Relay-ARQ, the data unit sender is capable of distinguishing whether a sent data unit of the given communication protocol was correctly received at a relay peer of the given communication protocol, or whether it was received at the final destination peer of the protocol. The sending peer can accordingly adjust its re-transmission procedure. Namely, if no first type receipt information is received for a given data unit, this means that the sender has no acknowledgement that it was received at a relay peer. In this case the first re-transmission procedure is used, which is arranged to ensure reliable delivery to the next peer, typically a relay peer. On the other hand, if the first receipt information has been received for a given data unit, this means that delivery to a relay peer was successful, and the second re-transmission control procedure can be used, which is different from the first in that the sender can at least temporarily delegate the responsibility for the further delivery of the data unit to the relay device that sent the first type receipt information. Nonetheless, the second re-transmission control procedure has a retransmission function, in order to be able to safeguard reliable transmission to the final destination peer in the event that problems occur at the one or more relay peers involved in the communication. As an example, the first re-transmission control procedure can be based on a time-out function having a first time-out value, such that if no first type receipt information is received within the time span of said first time-out value, a re-transmission is performed. The second re-transmission control procedure can be based on a second time-out value, such that if no second type receipt information is received within the second time-out period, then a re-transmission is performed. The second time-out period is longer than the first time-out period. Another example is if the protocol additionally provides for third type receipt information, which indicates an incorrect receipt (an incorrect receipt means not received at all or received with an incorrectable error), then the second re-transmission control procedure may be chosen such that there is no time-out function, but that a data unit is re-transmitted in the event that the above-mentioned third type of receipt information is received, even if previously the first type receipt information was received for the same data unit. Different possibilities for the first and second re-transmission control procedures will be explained in more detail with reference to FIGS. 12 and 13 later. It is noted that the sequence position identifiers, which are shown as n, n+1, n+2, . . . , m, m+1, . . . in FIG. 10 b , can be chosen in any suitable or desirable way. Namely, they can be chosen as shown in the example of FIG. 10 , i.e. as integer values that directly correspond to the sequence position (1, 2, 3, . . . ). However, they can e.g. also be chosen as bit or byte count values, which indicate a certain bit or byte position in a data symbol stream that is being transported in the data units. Such a concept is e.g. known from TCP/IP. In the example of FIG. 10 , each data unit 1003 carries a sequence position identifier, and the shown feedback message 1004 also each carry a sequence position identifier. In the shown example, the first feedback message 1004 carries an “A”, which stands for ACK, which in turn will be used in the present specification as an example for the second type receipt information. The second feedback message 1004 contains an R, which stands for RACK, which will be used in the present specification as an example of the first type receipt information. RACK stands for relay acknowledgement. Naturally, this is only one possibility of many for associating the sequence position identifiers with the data units and feedback messages. For example, it is possible to place several data units into one message, where the message e.g. only contains the first sequence position identifier, and a peer receiving said message can then identify the sequence position identifier for each data unit by using the first sequence position identifier and counting the number of data units in the message. Equally, the feedback messages can relate to a plurality of data units, where it can again be sufficient to only indicate the first and/or last sequence position identifier for a sub-sequence of data units to which the feedback message relates. Now two examples of control methods for controlling the data unit sender 100 shown in FIG. 10 will be described with reference to FIGS. 12 and 13 . FIG. 12 shows a flowchart of a first example of a control method for the data unit sender 100 , e.g. implemented in the form of software in control unit 1001 . In a first step S 121 a given data unit is generated and stored in a buffer 1002 . In subsequent step S 122 this data unit is transmitted. A specific procedure according to which individual data units are released from the buffer 1002 , i.e. the specifics of flow control, can be chosen in any suitable or desirable way. For example, the flow control can be window-based or rate-based. Relay-ARQ is independent of the type of flow control used. In step S 123 a re-transmission timer is started to a first time-out period TO_ 1 . Then step S 124 determines whether an ACK (second type of receipt information) or a RACK (first type of receipt information) has been received for a sent data unit. If not, step S 125 determines whether TO_ 1 has expired yet. If not, the procedure loops back to step S 124 , and if the period TO_ 1 has expired, then the procedure goes to step S 126 , in which the given data unit is re-transmitted. After step S 126 , the procedure loops back to step S 123 . Steps S 123 -S 126 constitute an example of a first re-transmission control procedure for the given data unit in buffer 1002 that has been sent but for which no RACK has been received. If step S 124 determines that an ACK or RACK has been received for the given data unit, the procedure goes to step S 127 , in which it is determined whether the received feedback was a RACK. If yes, then a re-transmission timer is started with a second time-out period value TO_ 2 . Then step S 129 determines whether subsequently an ACK has been received for the given data unit, i.e. the second type receipt information which indicates that the given data unit was received at the final destination peer. If not, then step S 130 determines whether TO_ 2 has expired, and if not the procedure loops back to step S 129 . If TO_ 2 has expired, the procedure goes to step S 132 , in which the given data unit is re-transmitted. The procedure then loops back to step S 123 , i.e. treats the re-transmitted data unit as a data unit for which no RACK has yet been received. Steps S 128 , S 129 , S 130 and S 132 constitute an example of a second re-transmission control procedure for a given data unit if first type receipt information (RACK) has been received for the given data unit. Finally, if the outcome of step S 127 indicates that an ACK has been received in step S 124 , or if an ACK was received in step S 129 , then the procedure goes to step S 131 , in which the given data unit for which the ACK was received is removed from buffer 1002 . It is noted that this is only an example, and the overall control procedure can comprise further mechanisms that let a given data unit be held even after an ACK was received. Such mechanisms are outside of the scope of Relay-ARQ and shall not be discussed further here. However, in accordance with the Relay-ARQ, a given data unit is held in the buffer at least until the ACK (second type of receipt information) that acknowledges receipt at the final destination peer has been received. In this way, despite being able to delegate responsibility to one or more relay peers, the sending peer keeps final control over the end-to-end delivery to the final destination, because data units in the sending peer are not removed until receipt at the final destination has been confirmed. Due to this, the sending peer can always take back responsibility for delivery of data units, such that problems at one or more relay peers do not lead to an irrevocable loss of data units at the level of the communication protocol being described. In the example of FIG. 12 , the first time-out period TO_ 1 is shorter than the second time-out period TO_ 2 . This is due to the consideration that the first timeout period TO_ 1 serves to appropriately re-transmit data units on the first hop from the sending peer to the immediately adjacent relay peer. On the other hand, the second time-out period TO_ 2 serves to enable re-transmission if an end-to-end problem occurs, e.g. in one or more of the relay peers. As the expected end-to-end delivery time is longer than the expected delivery time on the first hop, the second time-out period TO_ 2 is chosen larger than the first time-out period TO_ 1 . However, it is also possible to select TO_ 1 and TO_ 2 as equal. For example, in situations in which a relay peer sends feedback messages at regular time intervals, TO_ 1 and TO_ 2 can be set to the same value. Optionally, the control unit 1001 and the corresponding control method are arranged such that the first time-out period TO_ 1 is adapted dynamically based on measurements of a time that passes between a transmission of at least some of the data units 1003 and the receipt of a RACK, and the second time-out period TO_ 2 is dynamically adapted based on a measurement of a time that passes between a transmission of at least some of the data units 1003 and a receipt of an ACK. For example, the data unit sender can keep an average value of the time between sending a data unit and receiving a corresponding RACK, and an average of the time that passes between the sending of a data unit and the receipt of an ACK, and then dynamically adjust TO_ 1 on the basis of the average value for receiving a RACK, and TO_ 2 on the basis of the average value for receiving an ACK. Any known technique for measuring round trip times (RTT) can be used for such measurements. FIG. 13 is a flowchart of another embodiment of a control method for controlling the data unit sender 100 . In the example of FIG. 13 , the communication protocol governing the communication provides for a third type of receipt information that is indicative of an incorrect receipt of a data unit at a peer of the communication protocol. This third type of receipt information will also be referred to as a NACK or negative acknowledgement. An incorrect receipt means that a data unit is not received at all or received with incorrectable errors. In FIG. 13 , the method is the same as that of FIG. 12 with respect to steps S 121 to S 125 , such that a repeated description is not necessary. However, if the outcome of step S 125 is negative, i.e. TO_ 1 has not expired, then the procedure goes to an additional step S 133 , in which it is determined whether a NACK has been received for the given data unit. If this is the case, the procedure goes to step S 126 , to re-transmit the given data unit. If no NACK has been received, the procedure loops back to step S 124 . Steps S 123 - 126 and S 133 constitute another example of a first re-transmission control procedure for a given data unit that has been sent but for which no RACK has been received. If the outcome of step S 124 in FIG. 13 indicates that an ACK or RACK has been received, then the procedure goes to step S 127 , in which it is determined whether a RACK has been received, just like in the method of FIG. 12 . If a RACK has been received, then the procedure directly passes to step S 129 , in order to determine whether a subsequent ACK has been received or not. If not, then it is asked whether a subsequent NACK has been received for the given data unit, see step S 134 . If no NACK has been received, the procedure loops back to step S 129 . If a NACK has been received, then the given data unit is re-transmitted in step S 132 , where after the procedure loops back to step S 123 , similar to the procedure in the example of FIG. 12 . Steps S 129 , S 134 and S 132 constitute another example of a second re-transmission control procedure for a given data unit for which the first type receipt information (RACK) has been received. Finally, just as in the example of FIG. 12 , if the outcomes of steps S 127 and S 129 indicate that an ACK has been received, then the corresponding data unit may be removed from the buffer in step S 131 . In FIG. 13 , steps S 126 and S 132 indicate the optional use of a retransmission prohibit timer. A retransmission prohibit timer can be triggered by a selected event, such as the transmission of a data unit and/or the retransmission of a data unit. Within the retransmission prohibit time period, a retransmission is prohibited. If the peers of Relay-ARQ are operated such that feedback messages are sent at regular intervals, then it is preferable to employ a retransmission prohibit timer, in order to avoid unnecessary retransmissions, e.g. to avoid unnecessary retransmissions each time that a NACK is received. When combining a retransmission prohibit timer feature with a retransmission time-out feature, the retransmission time-out period (such as TO_ 1 or TO_ 2 ) is set longer than the retransmission prohibit period. In other words, steps S 126 and S 132 can be implemented in such a way that a retransmission is in any case conducted if the procedure progresses to these steps, or a retransmission is only conducted if the retransmission prohibit time period has additionally expired. If the steps S 126 or S 132 are reached because of a time-out of a retransmission time-out period, then the retransmission prohibit time period will have expired, but if these steps are reached on account of a NACK, then the retransmission prohibit time period may not yet have expired. The effects of the example of FIG. 13 are the same as in FIG. 12 . Namely, a first and a second re-transmission control procedure for a data unit are provided, the first dealing with reliable delivery of the first hop to a relay peer, and the second dealing with end-to-end delivery, where the triggering of the respective different re-transmission control procedures is based upon having received the first type receipt information (RACK) for a given data unit or not. Also, the given data unit is held in the buffer at least until the second type receipt information (ACK) has been received. Thereby, the data unit sender is capable of always taking back responsibility for a delivery of a data unit, even if this responsibility had previously been temporarily passed to a relay peer. It is noted that in the above discussion it was generally assumed that the adjacent peer to the sending peer is a relay peer. However, it is important to note that the next peer can also already be the final destination peer. In this case, the data unit sender and corresponding control method of Relay-ARQ will automatically fall back into a standard ARQ procedure, because the final destination peer will directly send ACKs to the sending peer. Such operation requires absolutely no adjustment in the sending peer of Relay-ARQ. This is an important advantage of Relay-ARQ. Regarding the examples of FIGS. 12 and 13 , it is noted that variations are naturally possible. For example, it is also possible to combine the feature of the second time-out period TO_ 2 (as shown in FIG. 12 ) with the concept of re-transmission upon receiving a NACK (step S 134 in FIG. 13 ). Now a schematic representation of an embodiment of a data unit relay device of Relay-ARQ will be described with reference to FIG. 11 . The data unit relay device 110 comprises a data unit buffer 1102 for holding receive data units 1102 of a communication protocol received from a sender-side peer of that protocol, and for holding send data units 1103 of the communication protocol to be sent to a receiver-side peer. The sender-side peer can be an original sending peer (as e.g. described in FIG. 10 ) or another relay device placed between the original sender and the relay device 110 of FIG. 11 . Equally, the receiver-side peer can be the final destination peer, or another relay peer provided between data unit relay device 110 and the final destination peer. Data relay device 110 has a control unit 1101 , which is arranged to control a receiving of the receive data units 1102 , a transmission of the send data units 1103 , a processing of receiver-side feedback messages 1104 received from the receiver-side peer, a re-transmission of the send data units 1103 to the receiver-side peer based on the receiver-side feedback messages 1104 , a transmission of sender-side feedback messages 1105 to the sender-side peer, and the overall management of the buffer, as a relay peer of the given communication protocol. The “management of the buffer” means the placing of data units in the buffer and the removing of data units from the buffer. The buffer can be any type of memory suitable for holding data units, and the control unit can equally be any device suitable for performing the control functions, e.g. the control unit can be a programmable processor. As already described in connection with the sender in FIG. 10 , the communication protocol is such that the receive data units 1102 are arranged in a sequence, and each receive data unit 1102 is identified by a sequence position identifier, indicated as n, n+1, n+2 in FIG. 11 . The send data units 1103 are arranged in the same sequence, such that for each receive data unit 1102 there is a corresponding send data unit 1103 having at least a same payload section and the same sequence position identifier. Preferably, the receive data units and send data units not only have the same payload section and the same sequence position identifier, but are in fact identical. This simplifies buffer management, as the buffer 1102 then only holds the received data units and appropriately forwards them, without the action of copying parts of data units, which may lead to errors. The sender-side feedback messages 1105 and the receiver-side feedback messages 1104 use the sequence position identifier and carry information as already described in connection with the sender of FIG. 10 . Namely, the communication protocol provides for at least a first type and second type of receipt information, where the first type (RACK) is indicative of a correct receipt at a data unit relay device, and the second type is indicative of a correct receipt at the final destination peer. The control unit 1101 is arranged to send a sender-side feedback message carrying the first type of receipt information (RACK) for a given receive data unit 1102 that was correctly received. This is e.g. shown by the sender-side feedback message 1105 carrying an R for sequence position identifier n+2. The control unit 1101 is furthermore arranged to perform a re-transmission control process for a given send data unit 1103 in the buffer 1102 that has been sent, based on the receiver-side feedback messages 1104 . The control unit 1101 is furthermore arranged to hold a given send data unit 1103 in the buffer 1102 until a predetermined deletion condition is fulfilled. One such possible deletion condition is the receipt of a receiver-side feedback message 1104 providing the second type of receipt information (ACK) for the given data unit. The control unit 1101 is furthermore arranged such that after having received the second type of receipt information (ACK) for a given sequence position identifier in a receiver-side feedback message 1104 , a corresponding sender-side feedback message 1105 is sent to the sender-side peer, carrying the second type of receipt information (ACK) for the given sequence position identifier. This is shown in FIG. 11 in terms of the receiver-side feedback message 1104 carrying an A (for ACK) for sequence position identifier m, such that the data unit relay device 110 then sends the sender-side feedback message 1105 that equally carries an A (for ACK) for said sequence position identifier m. Examples of parts of the control method for controlling the data unit relay device 110 , e.g. executed as software in control unit 1101 , will now be explained with reference to FIGS. 14 a - 14 c. FIG. 14 a shows a procedure, where if a sender-side data unit 1102 is correctly received, step S 140 branches to step S 141 , in which a corresponding RACK is sent for the given data unit, i.e. for the sequence position identifier of said data unit. FIG. 14 b shows a flowchart of a process for generating a sender-side feedback message with an ACK, if a receiver-side feedback with an ACK is received. Namely, step S 142 determines whether a receiver-side feedback message with an ACK for a particular sequence position identifier has been received, and if this is the case, step S 143 sends a sender-side feedback message with an ACK for the same sequence position identifier. FIG. 14 c shows an example of a procedure for performing a re-transmission control process for transmitted send data units. In a first step S 144 , a send data unit 1103 is transmitted. Thereafter, in step S 145 , a re-transmission timer is set to a time-out period TO_ 1 . The procedure then determines whether an ACK (second type receipt information) has been received, see step S 146 . If not, it is determined in step S 147 whether TO_ 1 has expired. If not, the procedure loops back to step S 146 . If yes, then a re-transmission of the given send data unit is performed in step S 148 , and the procedure loops back to step S 145 . If step S 146 indicates that an ACK has been received, then the send data unit for which the ACK has been received is removed from the buffer 1102 in step S 149 . Receiving an ACK is an example of a deletion condition for a data unit. However, other deletion conditions can also be chosen. For example, it is also possible that, upon placing a given data unit into the buffer 1102 , a purge timer is set to a predetermined purge time period, and if said purge time period expires, the corresponding data unit is simply removed from the buffer. This has the purpose of avoiding the indefinite buffering of data units for which no second type receipt information has been received. Another deletion condition is the receiving of an indication that the sending peer has actually received the feedback message that forwards the ACK. Furthermore, it is noted that FIG. 14 c is an example of a re-transmission control process that does not involve RACKs. Namely, the re-transmission procedure for send data units 1103 can be chosen in any way suitable for the given situation. If the data unit relay device 110 is arranged such that the send data units 1103 are directly sent to the final destination peer, then the re-transmission control procedure only needs to take ACKs into account. On the other hand, in the more general case that the data unit relay device 110 transmits send data units 1103 to another data unit relay device, then it is preferable that the re-transmission control process executed at the data unit relay device 110 of FIG. 11 also processes the first type receipt information, i.e. RACKs. The basic arrangement of the control unit 1101 with respect to send data units 1103 can then be the same as that of control unit 1101 of sender 100 with respect to the data units 1003 sent by data unit sender 100 . As a consequence, the control unit 1101 of data unit relay device 110 can e.g. implement the control procedures described in FIGS. 12 and 13 with respect to the send data units 1103 . A renewed description of these procedures is therefore not necessary. If the underlying communication protocol provides for the above described third type of receipt information, i.e. a NACK that is indicative of an incorrect receipt of a data unit at a peer of the communication protocol, then the control unit 1101 of data unit relay device 110 is preferably arranged in such a way that if a receiver-side feedback message 1104 is received that carries this third type of receipt information for a sequence position identifier for which no data unit 1103 or 1102 is stored in said buffer, a sender-side feedback message 1105 is sent that carries this third type of receipt information for that sequence position identifier. In other words, the data unit relay device and the corresponding control method are arranged such that if a NACK is received for a data unit that is not present in the relay devices buffer, then this NACK is forwarded to the next peer in the overall direction of the end-to-end sender. Furthermore, the data unit relay device and corresponding control method are also preferably such that if in response to such a forwarded NACK, a corresponding sender-side data unit 1102 is received (i.e. the previous peer has retransmitted the NACKed data unit), then the send control on the receiver-side should be such that a corresponding send data unit 1103 is transmitted. When using the above-mentioned feature of forwarding NACKs, the following benefit can be achieved. If for whatever reason a data unit relay device does not have certain data units in its buffer (one reason could be that the data unit relay device has just been introduced into the communication by a handover process and is therefore just beginning to receive sender-side data units 1102 , but is nonetheless also already receiving receiver-side feedback messages 1104 ), then the overall ARQ mechanism still functions without any problems. Namely, if the data unit relay device does not have a particular data unit present for which a NACK has arrived, such that it cannot itself perform a re-transmission for this data unit, it simply forwards the NACK towards the next possible sender. If no data unit relay device along a given path is capable of re-transmission, because the data unit is lacking in each respective buffer, then the NACK will finally arrive at the original sending peer. If the original sending peer has not yet received an ACK for that data unit, then it can simply be re-transmitted. This is an example of the sending peer taking back the responsibility for reliable transmission if problems occur in one or more data unit relay devices. Naturally, if the sending peer has previously received an ACK for the given data unit, then the forwarded NACK can simply be ignored. Regarding the processing of RACKs received in receiver-side feedback messages, the data unit relay device can be arranged in any suitable or desirable way. For example, it is possible that received RACKs are never forwarded, in order to avoid unnecessary data traffic. On the other hand, it is equally well possible to always forward RACK information towards the sender-side. This can e.g. be useful to provide the sending peer with more information on the progress in moving a data unit over a series of relay peers (each RACK message is an indication that the data unit has moved one hop forward), or it can also be useful if the feedback messages are collective feedback messages that relate to a plurality of data units. In this case, the feedback messages constitute a type of status report on a number of data units, and for each data unit identified the feedback messages preferably indicate one of the first to third receipt information, i.e. either a RACK, an ACK or a NACK. Such collective feedback messages will be discussed in more detail further on. It is also possible to perform a forwarding of RACKs in such a way that if a receiver-side feedback message carrying a RACK for a given sequence position identifier is received, a corresponding sender-side feedback message with a RACK for said given sequence position identifier is only then sent, if there is no corresponding data unit having said given sequence position identifier stored in the buffer 1102 . The usefulness of this feature lies in the fact that if a given data unit is present in the buffer 1102 of the data unit relay device 110 , then this means that a RACK for said data unit has already been sent previously. A repeated RACK is avoided. However, if there is no corresponding data unit in the buffer 1102 of data unit relay device 110 , then it is possible that the source of the data unit has not yet been informed of the correct receipt at a relay peer such that the forwarding of the RACK is useful. Now a plurality of examples will be described in somewhat more detail. FIG. 4 shows a system comprising a sender 40 , a relay 41 and a receiver 42 . Each of the devices implements a peer of the inventive communication protocol. The sender 40 is an example of the data unit sender described in connection with FIG. 10 , and relay 41 is an example of the data unit relay device 110 described in connection with FIG. 11 . On the left-hand side of FIG. 4 , the sequence of data units 44 is shown, each represented together with an integer that stands for the sequence position identifier. The arrows at the top of FIG. 4 indicate the flow of data units from the sender to the relay and from the relay to the receiver, without providing further detail. The sender 40 , relay 41 and receiver 42 each keep a respective transmission and/or reception status with respect to the sequence of data units 44 . The receiver 42 sends feedback messages 45 to the relay 41 , and the relay 41 sends feedback messages 46 to the sender 40 . These feedback messages 45 , 46 are collective status reports for a group of data units. For example, feedback message 45 associates data unit 1 with an ACK, data unit 2 with a NACK, and data units 3 and 4 with an ACK, respectively. This corresponds to the receiver status of receiver 42 , namely where “ok” indicates correct receipt, and “err” indicates incorrect receipt. Based on status message 45 , the relay device 41 keeps a corresponding transmission status, i.e. the status on the successful or unsuccessful transmission of send data units (see 1103 in FIG. 11 ). The symbol “ns” stands for not sent. Relay device 41 furthermore keeps a receiver status, in which data units 1 - 4 are correctly received (“ok”), just like data units 6 and 7 , whereas data unit 5 was not correctly received. Accordingly, the feedback message 46 contains ACKs for data units 1 , 3 and 4 , because these were already successfully acknowledged by the receiver 42 . In other words, the sender-side feedback message 46 forwards the acknowledgements for data units with sequence position identifiers 1 , 3 and 4 . On the other hand, the feedback message 46 contains RACKs for data units 2 , 6 and 7 , because these data units were successfully received by the relay 41 , but not acknowledged by the receiver 42 , i.e. the final destination peer. Finally, the feedback message 46 carries a NACK for data unit no. 5 , because this data unit was not successfully received at the relay 41 . The sender 40 maintains a transmission status that is based upon the information received in the feedback message 46 . Namely, data units for which an ACK was received or marked as “ok”, those for which a RACK was received are marked as “rok”, and those for which a NACK was received or for which no feedback was received within the corresponding time-out period are marked as “err”. In the example of FIG. 4 , the sender 40 could at the shown state of transmission remove data units no. 1 , 3 and 4 , as these are known to have been successfully received at the final destination peer in receiver 42 . The first, second and third type receipt information can be coded in any suitable or desirable way. For example, two bits are sufficient to code the three different types. The feedback messages can therefore combine an appropriate receipt type bit value with the sequence position identifier for a given data unit. The coding used by the sender, relay and receiver for keeping a transmission and/or receive status can equally be chosen in any suitable or desirable way. For example, the four states ok, rok, err and ns can be coded by two bits. In the example of FIG. 4 , the relay peer in device 41 is operated such that if a receiver-side feedback message with a NACK is received, and the corresponding data unit has a receive status at 41 of err, then the NACK is forwarded to the sending peer in sender 40 , and as soon as the data unit retransmitted by the sending peer has been received locally at device 41 , it is transmitted to the peer in receiver 42 . If a receiver-side feedback message with a NACK is received, and the corresponding data unit has a receive status at 41 of ok, then the relay peer in device 41 performs the corresponding retransmission. If a receiver-side feedback message with a RACK is received, and the corresponding data unit has a receive status at 41 of ok, then the relay peer in device 41 forwards the RACK to the sending peer in 40 in the next status report. Finally, if a receiver-side feedback message with an ACK is received, then the relay peer in device 41 forwards the ACK to the receiving peer in the next status report. The relay device 41 can perform in-order delivery with respect to the sequence of data unit 44 , or out-of-order delivery. Preferably, the relay device performs out-of-order delivery, i.e. relays receiver-side data units 1103 (see FIG. 11 ) as they are available, irrespective of the order of the sequence. Correspondingly, the receiver 42 preferably has a re-sequencing functionality. FIG. 5 shows an example of a data unit transmission at the link layer between a user terminal UT and a network access point AP, via a relay node RN. At 51 ) the UT sends one data unit to the RN and starts a time-out timer. At 52 ) the data unit is lost on its way to the RN. At 53 ) no RACK or ACK arrives at the ARQ transmitter in time, such that the timer times-out and the data unit is re-transmitted. At 54 ) the data unit arrives at the RN and triggers the sending of a RACK. At 55 the data unit is delivered to the AP and another timer is started locally in the RN, in order to provide a re-transmission over the link from RN to AP in case of a data unit loss there. At 56 ) the UT receives the RACK and therefore knows that the responsibility for further delivery of the data unit is at least temporarily delegated to the RN. At 57 ) the AP successfully receives the data unit and replies with an ACK, i.e. the second type of receive information. At 58 ) the ACK received at RN is forwarded to the UT. At 59 ) the UT receives the ACK and consequently is informed that the data unit has been correctly delivered to the destination point. 60 ) indicates an option according to which the UT (generally the sending peer) sends an indication to RN (in general the next peer in direction of the receiver) that the ACK has successfully reached the sender. This is sometimes also called an ACK-ACK. The usefulness of such ACK-ACKs is to let the data unit relay device finally release data units from its buffer. Therefore the receipt of such an ACK-ACK from the sender-side is another example of a deletion condition as explained in connection with FIG. 11 . Preferably, each relay device is arranged to forward such an ACK-ACK in receiver direction, i.e. to the next receiver-side peer. In this way each peer of a chain is informed of the fact that the sending peer has been informed of the successful end-to-end transmission, such that the corresponding data unit can now certainly be removed from the respective local buffer. FIG. 6 shows another example, in which four data units carrying identifiers 1 , 2 , 3 and 4 are sent from a sender 61 to a receiver 63 via a relay 62 . The relay node 62 in-between forwards the data units as soon as it receives them, i.e. performs out-of-order delivery. Both the relay 62 and the receiver 63 send feedback messages to the respective peer in sender direction, to inform the peer about successfully or unsuccessfully received data units. In this example, a status message is sent whenever the respective peer receives a correct data unit. Although this is a preferable embodiment, it is by no means a necessity. For example, feedback messages can be sent at regular intervals or at both regular intervals and whenever a correct data unit is received. In the example of FIG. 6 , the first re-transmission control procedure (re-transmission control procedure for a given data unit that has been sent but for which no RACK has been received) and the re-transmission control process at the relay use a time-out value in the order of one round trip time RTT for the respective hop from sender 61 to relay 62 , or relay 62 to receiver 63 . In the shown example, sender 61 sends data units 1 , 2 , 3 , 4 one after the other. Data units 2 and 3 are lost on their way to relay 62 . When relay 62 receives data unit no. 1 , it sends a RACK to sender 61 and forwards data unit 1 to receiver 63 . When data unit 1 arrives at receiver 63 , an ACK (see message (A 1 )) is sent by receiver 63 to relay 62 . In the example of FIG. 6 , relay 62 does not immediately forward the ACK for data unit no. 1 , but much rather waits until another data unit arrives from the sender, to then send a collective feedback message. Naturally, the data unit relay device of Relay-ARQ could also be implemented in such a way that receiver-side acknowledgements are immediately forwarded to the sender-side. In the example of FIG. 6 the numbers attached to arrows simply identify a corresponding data unit. These numbers are sequence numbers, i.e. an example of a sequence position identifier. The indications in parentheses attached to feedback messages are to be read in the following way: an A followed by a number indicates an ACK for the data unit of said number, an N followed by a number indicates a NACK for said number and an R followed by a number is a RACK for said number. The transmission status confirmation written on the left-hand side for sender 61 is such that R followed by a number indicates a rok for the data unit of said number, N followed by a number indicates an err for the data unit of said number (i.e. that a NACK was received for said data unit or no feedback was received within the applicable time-out period), and A followed by a number indicates an ok for the data unit of that number. The same nomenclature will be used in the examples of FIGS. 7 and 8 as well. Returning to the example of FIG. 6 , the sender 61 updates its transmission status at first to (R 1 ), due to receiving a RACK for data unit number 1 . Thereafter, due to not receiving any feedback for sent data units 2 and 3 , the status is updated to err for data units number 2 and 3 . Due to the time-out, data units 2 and 3 are retransmitted by sender 61 . Relay 62 receives data units 2 and 3 , and forwards them. In the example of FIG. 6 , data unit 2 is lost on the hop from relay 62 to receiver 63 , but data unit 3 is correctly delivered. Accordingly, the receiver acknowledges the receipt of data unit number 3 (see feedback message (A 1 , N 2 , A 3 , A 4 )). Relay 62 retransmits data unit number 2 due to a time-out. After data unit 2 is correctly received at receiver 63 , an appropriate feedback message is sent that finally acknowledges all four data units. It can also be seen in the example of FIG. 6 how the relay 62 appropriately forwards the ACKs from receiver 63 to sender 61 , and sends RACKs for the data units that it locally receives. In accordance with Relay-ARQ, a system and method are provided for a reliable transport for data units over a multi-hop connection, which system and method are very simple, but at the same time provide full reliability. These are not the only advantages of Relay-ARQ. In accordance with Relay-ARQ, it is very simple to perform a transition from one relay device to another, e.g. in a handover. Due to the fact that the sending peer retains the overall responsibility for end-to-end delivery, it is not necessary that the old relay device performs a transfer of state information to the new relay device. In other words, data units that were already received by the old relay but not yet successfully forwarded to the receiving peer can be assumed to be lost, without this affecting the end-to-end reliability. Namely, the sending peer of Relay-ARQ can take back the responsibility for these data units and ensure end-to-end delivery. The process of switching from one relay device to another can be done in any suitable or desirable way, and can e.g. be performed in accordance with any known handover procedure such that a further description is not necessary here. As soon as the new relay device receives the first data units from the sender-side, it can begin to build up an appropriate receive state, and equally when it begins to receive feedback messages from the receiver-side, it can accordingly begin to build up a transmission state. Furthermore, the relay device generates its own feedback messages to be sent towards the sender-side, to report on the state of the receiver-side of the relay device (namely by appropriately forwarding ACKs and/or NACKs), and on its own receive status. By appropriately forwarding receiver-side feedback information to the sender-side, for data units that the new relay device itself has never received, the peer(s) on the relay device's sender-side (e.g. in the simple two-hop case of sending peer, one relay peer and receiving peer, there is only one sender-side peer for the relay, namely the sending peer itself) are appropriately informed of the correct receipt of data units at the receiver, namely through forwarded ACKs, or of data units not having been correctly received, namely by NACKs. In the event of forwarding a NACK, the new relay device expects to receive a retransmission for the corresponding data unit, and will forward the thus transmitted data unit once is arrives. On the other hand, if the new relay device forwards an ACK, it does not expect to receive any further communications with respect to that data unit, except possibly for ACK-ACKs as described in connection with the example of FIG. 5 . As discussed in connection with FIG. 5 , the use of ACK-ACKs is an option. As a result, the concept of Relay-ARQ can ensure a seamless transition from an old relay device to a new relay device without requiring any complicated transfers of state information between the old relay and the new relay. Much rather, the use of first type and second type receipt information, and preferably also third type receipt information as described above, together with the appropriate relaying of this receipt information in feedback messages, provides for reliable transmission. Effectively, each peer that transmits data units can delegate the responsibility for retransmissions to the next peer in the chain from sender to receiver as soon as this next peer has sent a RACK for a given data unit. If the next peer becomes obsolete for any reason, the peer can take back the responsibility. The ultimate responsibility can be taken back by the sending peer, i.e. the first peer in the chain. Preferably, each peer that transmits data units (i.e. the sending peer, and each relay peer) implements a mechanism to check whether the next peer in the chain is still valid or acting. This can be done in any suitable or desirable way. For example, peers connected over one hop can exchange polling messages on an event basis or in predetermined time intervals. Or each peer that receives data units can regularly send alive signals to the preceding peer in the chain. As another possibility, each peer that transmits data units can treat a hop to a next peer as dead if no feedback at all is received within a given time period, e.g. a predetermined number of retransmission time-out periods for the given hop. Upon determining that the hop to the next peer is dead, the peer in question can initiate a procedure for switching to a new next peer, or can alternatively inform a preceding peer in the chain that it should switch to a new next peer. As can be seen from the above explanation, the concept of Relay-ARQ allows the simple replacement of one relay device by another. Equally, Relay-ARQ allows the adding or removing of a relay device to an ongoing end-to-end communication. In other words, if necessary, a two-hop connection as shown in FIGS. 4-6 can be augmented to three-hop connection, or a k-hop (k is an integer greater than 1) can simply be switched to a (k−1) hop connection. The addition or removal of a relay device is very similar to the above-described change from an old relay device to a new relay device. When adding a new relay device, the added relay device starts to build up a receive state and a transmission state exactly in the same way as the above-described new relay device does this after a handover. Consequently, a repeated description is not necessary. In accordance with an embodiment of Relay-ARQ, in a data unit relay device that is arranged to operate in an environment in which relay devices can be exchanged, added and/or dropped from an ongoing end-to-end peer connection, the following relay actions for feedback information can be provided. If the relay peer in the relay device receives a receiver-side feedback message with a NACK, and the corresponding data unit has a receipt status of err, then the NACK is forwarded to the next peer on the sender-side, and as soon as the data unit in question is received, it is transmitted to the next peer on the receiver-side. If a receiver-side feedback message with a NACK is received, and the corresponding data unit has a receive status of ok, then the relay peer performs the appropriate retransmission. If a receiver-side feedback message with a RACK is received, and the corresponding data unit has a receive status of ok, then the relay peer forwards the RACK to the next peer on the sender-side in the next feedback message. If a receiver-side feedback message with a RACK is received, and the corresponding data unit has a receive status of err (i.e. the data unit has never been received at said relay device) then the relay peer forwards the RACK to the next peer on the sender-side in the next feedback message. Due to having forwarded a RACK, the relay peer does not wait or expect to receive the corresponding data unit in future. If a receiver-side feedback message with an ACK is received, then the relay peer forwards the ACK to the next peer on the sender-side in the next feedback message, and can possibly remove the corresponding data unit from its buffer, if the relay peer has the receipt of an ACK as a deletion condition. It is noted that the forwarding of an ACK is naturally also done if the corresponding data unit is not present in the buffer of the relay device. FIG. 8 shows an example of a data unit transmission from a sender 81 via two relay devices 82 , 83 to a receiver 84 . The nomenclature is the same as used in FIG. 6 . In this serial three-hop example, the sender 81 sends four data units being identified by their sequence position identifiers 1 , 2 , 3 and 4 to the first relay 82 . Data units 2 and 3 are lost on the way. As can be seen, the first relay device 82 sends RACKs for the received data units 1 and 4 . On the other hand, the sender 81 considers data units 2 and 3 as lost, due to a time-out of a first time-out period TO 1 set in the order of the roundtrip time for the peer-to-peer connection between sender 81 and the first relay 82 . Consequently, the sender 81 retransmits data units 2 and 3 . In response to these retransmissions, the first relay device 82 sends RACK feedback messages. As can furthermore be seen, the first relay 82 forwards each received data unit upon arrival. As can be seen, data unit 2 is lost on its way from the first relay 82 to the second relay 83 . The first relay performs a retransmission on account of a time-out. Otherwise, the second relay 83 sends RACK feedback messages for each correctly received data unit. The second relay 83 forwards the received data units to the receiver 84 . As can be seen in the example, data unit 3 is lost on its way from the second relay 83 to receiver 84 , and the second relay 83 accordingly performs a retransmission on account of a time-out. In the example of FIG. 8 , it is furthermore shown that the ACK sent by receiver 84 to the second relay 82 is lost. As a consequence, the second relay device 83 also performs a retransmission of data unit number 4 on account of a time-out. As can also be seen in the example of FIG. 8 , feedback messages to the next peer on the sender-side are only sent if appropriate. For example, the first relay 82 does not instantly report the successful delivery of data units to the second relay 83 , i.e. the receipt of RACKS. The sending of a feedback message is only triggered in the event of having correctly received a data unit from the adjacent sender-side peer, in which case a RACK is sent, or when forwarding an ACK received from the receiver-side. However, as already mentioned previously, this is only option, and it would equally be possible to immediately forward all RACK messages coming from the receiver-side, to thereby inform the adjacent peer on the sender-side, and ultimately the sender, on the progress of data units from one hop to the next. The case of removing a relay device from an ongoing end-to-end connection can also be described by looking at the example of FIG. 8 . If one assumes that the second relay device 83 is removed, then the first relay device 82 would take over the responsibility. Namely, it would begin to directly send data units to the receiver 84 , and to receive feedback messages directly from the receiver 814 . If for example the removing of the second relay device 83 would have led to the loss of data units for which the second relay 83 had previously sent RACK messages to the first relay 82 , but which had not yet been correctly forwarded to receiver 84 , then receiver 84 would eventually send NACK messages to the first relay 82 , on the basis of which a retransmission could be performed by the first relay 82 , despite the fact that the first relay 82 had previously received a RACK for the same data unit. Now an example of Relay-ARQ will be described in connection with FIG. 7 , in which two hops are operated in parallel. In the example, a sender 71 can in parallel send data units to a relay device 72 and a relay device 73 . Both relays 72 and 73 communicate with a receiver 74 . Such a parallel-hop situation can occur during a handover (i.e. simultaneous communication with an old relay device and a new relay device), or when different access techniques can be used at the same time, i.e. one hop is provided by a WLAN connection and the other by different wireless access technique, e.g. a UMTS connection. In the example of FIG. 7 , different delays on the hops are taken into account. For simplicity, as in the examples of FIGS. 6 and 8 , the delays are assumed as being constant over time. In the examples of FIGS. 6 and 8 , only one data unit was sent at a time, or more precisely during one transmission time interval (TTI). Relay-ARQ is by no means restricted thereto, and can also be applied if several data units are sent per TTI, where FIG. 7 gives an example. Both data unit relay devices 72 and 73 send their feedback messages back to the sender 71 . The receiver 74 sends feedback messages to both the data unit relay device 72 and the data unit relay device 73 . In FIG. 7 , the data units 1 , 2 and 3 are sent to relay 72 , and nearly at the same time the data units 4 and 5 are sent to relay device 73 . The roundtrip time or delay between the sender 71 and the relay device 72 is more than twice as long as that between the sender 71 and the relay device 73 . In the example of FIG. 7 , data units 1 and 2 are lost, and only the data unit 3 is successfully received at the relay device 72 . The data units 4 and 5 are received successfully at the relay device 73 before said time. In the example of FIG. 7 , it is assumed that the relay device 72 and relay device 73 implement a missing data unit detection function. Such a function indicates that a data unit is missing, if a data unit with a sequence position identifier is received, where a gap occurs with respect to the sequence. As a consequence, the relay device 73 detects data units 1 , 2 and 3 as missing, because it received a data unit with a sequence position identifier 4 . As a consequence, relay device 73 sends a feedback message in which data units 1 , 2 and 3 are negatively acknowledged (NACK). In circumstances in which there are no parallel hops, the sending device 71 would retransmit these three data units immediately to the relay device 73 . However, when the situation of parallel hops can occur, it is preferable to implement a retransmit prohibit timer, which prohibits a retransmission within a given time period. In the example of FIG. 7 , the retransmit prohibit timer was set on the basis of the roundtrip time of the hop between sender 71 and relay device 72 . This retransmit prohibit timer expires just when the feedback message from relay 72 arrives, in which data unit number 3 is indicated with a RACK, and data units 1 and 2 with a NACK. At this point in time, the sending device 71 could choose to retransmit the data units 1 and 2 to either relay device 72 or relay device 73 . In the example, the data units are retransmitted to relay device 72 . In situations, where a peer of the inventive protocol receives data units from more than one peer in parallel, it is preferable that feedback messages are sent to all peers from which data units can be received. This increases the probability that the feedback information will arrive where it can be put to use. Nonetheless, it is naturally also possible to operate a peer in such a way that it only sends feedback messages to the peer from which it has just received a data unit, or that the peer has a decision procedure for deciding which peer to send a feedback message to. In the example of FIG. 7 , a retransmission prohibit timer was used. It is noted that a retransmission prohibit timer can be used in any retransmission context, i.e. also in systems that only have individual serial hops. The retransmission prohibit timer can be triggered by a selected event, such as the transmission of a data unit and/or the retransmission of a data unit. Within the retransmission prohibit time period, a retransmission is prohibited. If the peers of Relay-ARQ are operated such that feedback messages are sent at regular intervals, then it is preferable to employ a retransmission prohibit timer, in order to avoid unnecessary retransmissions, e.g. to avoid unnecessary retransmissions each time that a NACK is received. When combining a retransmission prohibit timer feature with a retransmission time-out feature, the retransmission time-out period (such as TO_ 1 or TO_ 2 ) is set longer than the retransmission prohibit period. If a peer of the inventive protocol is able to transmit data units to at least two different peers in parallel, then there exists a first value indicative of a roundtrip time between the transmitting peer and the first peer, and a second value indicative of the roundtrip time between the transmitting peer and the second parallel peer. These values could be fixed values, or the control unit could implement procedures for determining one or both of the values. The peer is arranged to employ a retransmission prohibit timer for retransmissions to said peer of the two parallel peers which is associated with the smaller round trip time vale. The retransmission prohibit timer is set based on the larger of the round trip time values. Now, a further embodiment of Relay-ARQ will be described with reference to FIG. 9 . FIG. 9 shows an example similar to the one discussed in connection with FIG. 4 . In accordance with an example of Relay-ARQ, it is possible to use the transmission state, which can also be referred to as the send window of a peer that transmits data units as an indication for the buffer fill state in the next peer to which data units are being sent. The send window comprises the sent data units, for which no feedback for a RACK has been received. As can be seen in FIG. 9 , the send window at the transmitter provides information for a flow/congestion control decision. The active send window starts above the highest accumulatively acknowledged (i.e. for which an ACK was received) data unit (i.e. the data unit with the highest sequence position), and typically comprises in the lower part data units for which a RACK has been received, or already an ACK from the receiver. Above there is typically a window region in which data units can be found for which the sender has received a RACK or a NACK. The amount of data in the send window can therefore be viewed in three parts: Data units with NACK, not yet received at the next peer, transmitter has retransmission responsibility; Data units with RACK: received at the next peer, next peer has retransmission responsibility; and Data units with ACK: received at the receiver, i.e. at the end-point, no more retransmission. If the window is much larger than the pipe capacity and the amount of data units with RACK is larger than the amount of data units with NACK, then the hop following the next peer is congested, because the buffer at the next peer has filled up. Under this condition, the peer that is transmitting should slow down its transmission rate or stop until the ratio of RACKs and NACKS in feedback messages indicate that the situation has changed. In the above discussion it was assumed that the data units have equal size. If the sizes differ, then the data unit size needs to be taken into account. As a consequence, in the general case, any peer of the inventive protocol that is arranged to transmit data units is preferably arranged to keep a record of the data units which were sent and for which first type receipt information (RACK) has been received, and of the data units that were sent and for which third type receipt information (NACK) has been received. Then the transmission rate is preferably controlled based on the relationship between an amount of data in the data units for which the first type receipt information has been received and an amount of data in data units for which the third type receipt information has been received. In the examples of Relay-ARQ described in connection with FIGS. 1-14 , communication devices and control methods were described that related to a communication protocol for transmitting data units from a sending peer to a receiving peer over one or more relay peers. The communication protocol uses feedback messages sent in a direction of the sending peer, and the feedback messages are designed to carry information on a receipt of data units that were sent. The described communication protocol provides for at least a first type and a second type of receipt information, where the first type of receipt information (RACK) is indicative of a correct receipt of a data unit at a relay peer, and the second type of receipt information (ACK) is indicative of a correct receipt at the receiving peer. The described communication protocol is such that each of the relay peers forwards the second type of receipt information in direction of the sending peer and the sending peer is arranged to hold each data unit until having received the second type of receipt information for said data unit. In this way, the described communication protocol is suitable for the reliable transmission of data units over relay peers, where each peer that transmits data units (i.e. the sending peer and the relay peers) can delegate the responsibility for correct transmission to a next peer in the direction of the receiving peer after having received the first type of receipt information (RACK), but the sending peer retains the overall responsibility by holding each data unit until having received the second type of receipt information (ACK), whereby problems occurring in the relay peers or the receiving peer do not lead to a non-recoverable loss of data and the level of the described communication protocol. In connection with the use of such a Relay-ARQ communication protocol, it can occur that a transition from the described protocol and its format to another communication protocol and its respective format becomes necessary. One example of such a transition from the format of the above-described novel Relay-ARQ communication protocol to a different format of a different communication protocol is when layering occurs, as can e.g. be seen from the example of FIG. 15 a . FIG. 15 a shows a sending peer 1500 of a first communication protocol (CP 1 ) that has the above-described features of using a first and second type of receipt information for distinguishing between the correct receipt at a relay peer and the correct receipt at the receiving peer. In FIG. 15 a , the sending peer 1500 communicates with a relay peer 1501 in accordance with the first communication protocol CP 1 , which is also indicated as format A. CP 1 is a Relay-ARQ protocol. The relay peer 1501 of CP 1 is in a communication device 150 that also comprises a peer 1502 of a second communication CP 2 . CP 2 is provided at a lower layer than CP 1 in the example of FIG. 15 a . The peer 1502 acts as a sending peer of CP 2 , and a corresponding peer 1503 acts as a receiving peer of CP 2 . The receiving peer 1503 is co-located with a relay peer 1504 of CP 1 , which in turn communicates with the receiving peer 1505 of CP 1 . FIG. 16 a shows another example, in which a format change occurs, where a sending peer of a first protocol CP 1 is indicated as 1600 , in communication with a relay peer 1601 of CP 1 . CP 1 is again a Relay-ARQ protocol. The relay peer 1601 of the Relay-ARQ communication protocol is part of a communication device 160 in which a transition is performed to a different format B of a second communication protocol CP 2 . As a consequence, the communication device 160 comprises a peer 1602 of CP 2 . In the example of FIG. 16 a , the first communication protocol CP 1 and the second communication protocol CP 2 are provided in the same protocol layer. The peer 1602 of CP 2 communicates with peer 1603 of CP 2 , which in turn is co-located with peer 1604 of CP 1 . Peer 1604 communicates with receiving peer 1605 of CP 1 . The reasons for a change in format and communication protocol along a connection can be various, e.g. when making a transition from a fixed line network to a wireless network. The present invention proposes an improvement to such communication devices that on the one hand hold data units of the novel Relay-ARQ communication protocol that uses RACKs and ACKs (CP 1 in the example of FIG. 15 a and FIG. 16 a ) and at the same time performs a transition to a second communication protocol (CP 2 in the examples of FIGS. 15 a and 16 a ) that is suitable to transmit data units from a sending peer to a receiving peer and which uses feedback messages sent in the direction of the sending peer, where the feedback messages carry information on the receipt of the data units. The second communication protocol provides for a specific type of receipt information that is indicative of a correct receipt at the receiving peer, e.g. the protocol can be a known ARQ protocol that uses acknowledgment messages ACKs for acknowledging the correct receipt at the receiving peer. Both the first communication protocol and the second communication protocol provide for a control procedure according to which the transmission of the respective data units is controlled in accordance with the respective feedback messages and the receipt information contained therein. FIG. 17 shows a schematic representation of a communication device according to the present invention. The communication device 170 comprises a first data unit buffer 1702 for holding the data units of the first communication protocol CP 1 and a second data unit buffer 1703 for holding data units of the second communication protocol CP 2 . A control system 1701 is provided, which controls the transfer of data symbols from the first buffer 1702 to the second buffer 1703 , and controls the transmission of the data units 1704 of CP 2 and the processing of corresponding feedback messages 1705 of CP 2 . In accordance with the present invention, the control system 1701 is arranged to control the generation of the data units of the second communication control CP 2 such that a data symbol stream carried in the data units of the first communication protocol CP 1 is also carried in the data units of the second communication protocol CP 2 . The stream of data symbols can e.g. be a stream of bits or bytes. The transfer of parts of the data symbol stream from data units of CP 1 to data units of CP 2 can e.g. be performed by removing the payload section of data units of CP 1 , (which payload sections carry the desired data symbol stream) and placing the payload section in one or more corresponding data units of CP 2 . The transition can also occur by simply embedding the complete data units of CP 1 in data units of CP 2 , not only the payload section, but also other sections such as a header section that may or may not carry the desired data symbol stream. In accordance with the present invention, the control system 1701 is arranged to implement the control procedure for controlling a transmission of the data units of CP 1 in such a way that if all of the data symbols of the data symbol stream contained in a given data unit of CP 1 are successfully transferred into the second data buffer 1703 , then the control procedure acts as if the first type of receipt information (RACK) had been received for said given data unit. Buffer 1703 is a send buffer for sending CP 2 data units to a following peer of CP 2 . This in other words means that the present invention proposes to expand the functionality of a controller that implements a control procedure according to the Relay-ARQ communication protocol using RACKs and ACKs by letting the controller couple the logic of the Relay-ARQ communication protocol to another communication protocol that at least has an ARQ functionality. Naturally, the second protocol can itself also have the novel features of using RACKs and ACKs, but this is not necessary. In accordance with the invention, the controller for the novel communication protocol CP 1 treats the passing of data symbols of a given data unit to a peer of a different protocol that at least has an ARQ functionality, like the reception of a RACK, which means that the controller has temporarily passed the responsibility for further forwarding the corresponding data to said peer of the different protocol CP 2 . In this way, the ARQ functionality of the second communication protocol CP 2 is exploited, to thereby simplify the handling of data units of the first communication protocol CP 1 . The specific reaction of the control procedure to the successful transfer from the first buffer to the second buffer will depend on whether the communication device is a sender (sending peer of CP 1 ) or a relay device (relay peer of CP 1 ), because the control procedure is generally somewhat different for a sending peer for CP 1 than for a relay peer of CP 1 . Also, the individual implementation can be different with respect to the Relay-ARQ communication protocol. As was e.g. explained in connection with the example of FIG. 4 , the control procedure may comprise the keeping of an appropriate status record, e.g. using the status values described as “ok”, “rok”, “err” and “ns”. If the control procedure is arranged to keep such a record, then in accordance with the present invention, the successful transfer of data symbols into the second buffer 1703 of FIG. 17 leads the control procedure to set a “rok” for the corresponding data unit of CP 1 for which the data symbols were successfully transferred. The present invention can be applied together with any of the control procedures described in connection with FIGS. 1 to 14 . For example, the present invention can be applied as shown in FIG. 18 , which uses a part that is similar to a part of the control procedure described in connection with FIG. 12 for a sending peer of the first communication protocol. More specifically, step S 180 of FIG. 18 relates to the transfer of data symbols of a data unit of CP 1 to the second buffer for CP 2 data units. Step S 181 determines whether the transfer was successful. If the transfer was successful, then the procedure passes to steps S 181 -S 184 , which are similar and analogous to steps S 128 -S 131 , which were already explained in connection with FIG. 12 subsequent to the receipt of a RACK. More specifically, a retransmission timer TO_ 2 is set in step S 1281 , and thereafter the procedure checks whether or not an ACK was received for the CP 1 data unit in question (step S 182 ) or TO_ 2 has expired (step S 183 ). If an ACK is received for the CP 1 data unit (or information is received that the control procedure likes the receipt of an ACK), then the procedure goes to step S 184 , in which the data unit is removed from the buffer for CP 1 data units ( 1702 in FIG. 17 ). If TO_ 2 expires before an ACK is received, a “retransmission” is performed, i.e. the data symbols of the data unit in question are again transferred to the buffer for CP 2 data units ( 1703 in FIG. 17 ). Equally, FIG. 19 shows an example, in which step S 181 is followed by steps S 182 , S 184 and S 185 , like in the example of FIG. 13 subsequent to receiving a RACK (see step S 127 in FIG. 13 ). In the example of FIG. 19 , CP 1 also uses NACKS, instead of a timer as used in FIG. 18 . The embodiments of FIGS. 18 and 19 can also be combined by using both a retransmission timer and NACKs. As mentioned previously, the present invention can be applied in connection with a control system that is arranged to implement a sending peer control procedure or in connection with a control system implementing a relay peer control procedure. In the case of the control system 1701 implementing a sending peer control procedure, the data units of CP 1 in the first buffer 1702 will be generated from data received from a higher protocol layer, e.g. from an application layer. If the communication device 170 implements a relay peer control procedure for CP 1 , then the data units of CP 1 in the first buffer 1702 may be received from a corresponding peer of CP 1 , which is not shown in FIG. 17 for simplicity. If the control system 1701 is arranged to implement a sending peer control procedure of the first communication protocol, then it can e.g. comprise performing a first retransmission control procedure for a data unit that has been sent but for which no first type receipt information (RACK) has been received, performing a second retransmission control procedure if the first type of receipt information (RACK) has been received, and holding the data unit that has been sent at least until having the second type of receive information (ACK), as has been previously described in connection with FIGS. 1 to 14 for a sending peer. Equally, if the control system 1701 is arranged to implement a relay peer control procedure of the first communication protocol, then it can e.g. comprise performing a first retransmission control procedure for a data unit that has been sent but for which no first type of receipt information (RACK) has been received, performing a second retransmission control procedure if the first type (RACK) receipt information has been received, holding the data unit until a predetermined deletion condition is fulfilled, and after having received the second type of receipt information (ACK), sending to a sender-side peer of the first communication CP 1 a feedback message carrying the second type of receipt information. Again, this has already been explained in connection with FIGS. 1 to 14 for relay peers. In connection with the example shown in FIG. 17 , it is noted that the control system 1701 can be provided in any suitable or desirable way. For example, the control system can consist of a programmable processor suitably connected to a memory that comprises the buffers 1702 and 1703 . The control system 1701 can also consist of a plurality of processors that may or may not be interconnected. Equally, the buffers 1702 and 1703 can be provided in any suitable or desirable way. For example, they can be provided as logically separate address spaces in one memory device, or as two or more different memory devices. The concept of the present invention can be used in an arrangement as discussed previously in connection with FIG. 15 a . More specifically, the communication device 150 of FIG. 15 a can be realised as an embodiment of the present invention, in order to couple the transmission control logic used for peer 1501 of CP 1 with the ARQ functionality of peer 1502 of CP 2 . Naturally, the present invention can also be applied if the second protocol CP 2 is capable of providing the novel relay functionality of Relay-ARQ using RACKs and ACKs, as shown in FIG. 15 b . Namely, in FIG. 15 b the sending peer 1502 of CP 2 and receiving peer 1503 of CP 2 are separated by relay peers 1506 and 1507 of CP 2 . FIG. 15 c shows an example of an inventive communication device acting as a sender 151 . In this case the sending peer 1510 of CP 1 is coupled with the sending peer 1511 of CP 2 . 1511 communicates with a receiving peer 1512 of CP 2 , which is co-located with a relay peer 1513 of CP 1 , which in turn communicates with a receiving peer 1514 of CP 1 . Similar to the example of FIG. 15 b , FIG. 15 d shows a modification of the example of FIG. 15 c , where CP 2 is not only an ARQ protocol as in the example of FIG. 15 c , but has relay capability and uses additional relay peers 1515 and 1516 of CP 2 . Feedback messages of the first communication protocol CP 1 , if they occur, can be communicated to peers of the first communication protocol CP 1 via embedding in data units of CP 2 . Considering the example of FIG. 15 a , e.g. the relay peer 1504 of CP 1 can simply embed (encapsulate or segment) feedback messages in data units of CP 2 through peer 1503 of CP 2 . These embedded feedback messages are then sent to peer 1502 of CP 2 , and relay peer 1501 of CP 1 then extracts the feedback messages of CP 1 from the received data units of CP 2 . The same concept of “tunnelling” the feedback messages of CP 1 over the peer-to-peer connection provided by CP 2 can be used in the example of FIG. 16 a. However, this is not the only possibility. In accordance with another embodiment of the present invention, it is possible to not only couple the logic in the transmission direction, but it is also possible to couple the logic in the feedback direction. In other words, the control system 1701 of the present invention is preferably also arranged to identify receipt information associated with data units of the first communication CP 1 on the basis of receipt information associated with data units of the second communication protocol CP 2 contained in feedback messages of CP 2 . In other words, the control system can analyse receipt information (such as ACKS, RACKs and/or NACKS) related to data units of the second communication protocol CP 2 , and then process this information in order to infer information that can be used as receipt information for data units of CP 1 . Different examples of the coupling of the control logic for handling data units of the first communication protocol CP 1 with receive information contained in data units of the second communication protocol CP 2 will be described in the following. As a first example, the control system can be arranged to implement the control procedure for controlling a transmission or handling of the data unit of the first communication protocol CP 1 such that if the specific receipt information associated with the data units of the second communication protocol CP 2 (in other words CP 2 is a simple ARQ protocol in this case, in which the specific information is an ACK sent from the receiving peer CP 2 to the sending peer of CP 2 ) is received for all of the one or more data units of CP 2 that carry all of the data symbols of the data symbol stream that are contained in a given data unit of CP 1 , then the control procedure for handling data units of CP 1 acts as if the first type of receipt information (RACK) had been received for said given data unit of CP 1 . Examples for such a feedback coupling are shown in FIGS. 15 a and 16 a . Namely, the control system in communication device 150 of FIG. 15 a may interpret ACKs sent by receiving peer 1503 of CP 2 in terms of a RACK for data units of CP 1 , because receiving peer 1503 of CP 2 is co-located with relay peer 1504 of CP 1 . The same situation can be seen in FIG. 16 a. In the event that the receiving peer of CP 2 is co-located with the receiving peer of CP 1 , as e.g. shown in FIG. 15 e , where CP 2 receiving peer 1508 is co-located with CP 1 receiving peer 1509 or in FIG. 16 d , where CP 2 receiving peer 1606 is co-located with CP 1 receiving peer 1607 , a different feedback coupling can be chosen. Namely, the control system can then be arranged to implement the control procedure for controlling the transmission of data units of the first communication protocol CP 1 such that if the specific receipt information (ACK for CP 2 ) is received for all of the one or more data units of CP 2 that carry all of the data symbols of the data symbol stream that are contained in a given data unit of CP 1 , then the control procedure acts as if the second type (ACK) of receipt information had been received for the given data unit of CP 1 . In the case that the second communication protocol CP 2 is itself a Relay-ARQ protocol, i.e. uses the first and second kind of receipt information and is suitable for sending data units from a sending peer via relay peers to a receiving peer, the control system can be arranged to implement the control procedure for controlling the transmission of data units of CP 1 , such that if the second type of receipt information (ACK) is received for all of the one or more data units of the second communication protocol that carry all of the data symbols of the data symbol stream that are contained in a given data unit of CP 1 , then the control procedure acts as if the second type of receipt information (ACK) had been received for said given data unit of CP 1 . Such an embodiment of the control system can e.g. be used in the situation as shown in FIG. 15 f , i.e. where the second communication protocol CP 2 has a sending peer 1502 , a relay peer 1506 and a receiving peer 1508 , and the receiving peer 1508 of CP 2 is co-located with the receiving peer 1509 of the first communication protocol CP 1 . However, it is noted that the just described control system and control procedure is also applicable in the case that the peer of the second communication protocol CP 2 is not co-located with the receiving peer of the first communication protocol CP 1 . Namely, taking the example of FIG. 15 b , it is possible to implement the peer 1503 of CP 2 in such a way that it does not act like a receiving peer of CP 2 , but like a relay peer. Furthermore, a feedback coupling between peer 1503 of CP 2 and relay peer 1504 of the first communication protocol CP 1 is provided, such that the control procedure for controlling the transmission and handling of data units of the second communication protocol CP 2 is implemented such that if the second type of receipt information (ACK) is received for all of the one or more data units of the first communication protocol CP 1 in which the data symbols of a given data unit of the second communication protocol are contained, then the control procedure for controlling the transmission of the data units of CP 2 sends a feedback message carrying the second type of receipt information (ACK) for the given data unit of the second communication protocol CP 2 towards the sender-side. In this way, the ACKs of the first communication protocol CP 1 are passed on through the peers of CP 2 , such that effectively the peers of CP 2 act like relay peers of CP 1 . Now a further embodiment will be described in the case that both the first and the second communication protocol provide for the third type of receipt information (NACK) that is indicative of an incorrect receipt. In this case, the control system can be arranged to implement the control procedure for controlling the transmission of data units of CP 1 in such a way that if the third type of receipt information (NACK) is received for a single one of the one or more data units of the second communication protocol that carry all of the data symbols of the data symbols of the data symbol stream that are contained in a given data unit of CP 1 , then the control procedure acts as if the third type of receipt information (NACK) had been received for the given data unit of CP 1 . Regarding the various embodiments of the present invention described up to now, one important thing should be noted. Namely, although data units of the first communication protocol are handled and the first communication protocol has the suitability for transmitting data units from a sending peer to a receiving peer over one or more relay peers and specifically provides for the novel concept of a first type of receipt information that indicates a correct receipt at a relay peer and a second type of receipt information that indicates a correct receipt at the receiving peer, it is by no means necessary that feedback messages of the first communication protocol are ever in fact received. Namely, the present invention relates to the concept of implementing a control procedure that is able to operate in accordance with the described first communication protocol (i.e. a Relay-ARQ protocol) in such a way that it couples its control logic to the handling of data units of the second communication protocol CP 2 . This can e.g. be seen in the example of FIG. 16 b . In FIG. 16 b , the communication device 161 operates as described in one or more of the previous embodiments for letting the control procedure operate in such a way that the successful transfer of data symbols from data units of CP 1 into a buffer for data units of CP 2 lets the control procedure react as if a RACK had been received for the corresponding data units. It is noted that the communication between entity 1610 and 1615 uses the first communication protocol CP 1 of format A for the first half, and the second communication protocol CP 2 with its format B for the second half. Due to the terminating entity 1615 not operating in accordance with CP 1 , the relay peer 1612 of CP 1 in communication device 161 does not receive any feedback messages relating to CP 1 . However, in accordance with the present invention, it can treat the successful transfer of data into the buffer for data units of CP 2 as the receipt of a RACK associated to data units of CP 1 . Furthermore, the control procedure for handling data units of CP 1 in relay peer 1612 can be implemented and operated in such a way so as to identify receipt information associated with CP 1 data units on the basis of receipt information associated with CP 2 data units, i.e. also use feedback coupling. Naturally, in some instances it might also be desired to provide a terminating peer of CP 1 at the end of the overall multi-hop connection, as can be seen in FIG. 16 c . More specifically, in the example of FIG. 16 c , a communication device 162 is provided between a multi-hop path established by peers 1620 , 1621 and 1622 of CP 1 , and a second multi-hop path established by peers 1623 , 1624 and 1625 of CP 2 . Despite the fact that the peer 1625 of CP 2 is at the end point, the example of FIG. 16 c furthermore includes peer 1626 of CP 1 , despite there not being any further peer of communication protocol CP 1 with which peer 1626 would communicate. The addition of such a peer 1626 can e.g. be due to the use of encryption for CP 1 , such that the peers of CP 2 cannot decrypt the data. As mentioned above, the present invention proposes a coupling of control logic when transferring data from a buffer that holds data units of the first communication protocol to a buffer that holds data units of a second communication protocol. The transfer of the data can be done in any suitable or desirable way. In general, the data units of the first communication CP 1 held in the first buffer will form a first sequence, such that each data unit of CP 1 is identifiable by a corresponding sequence position identifier of said first sequence, and the data units of the second communication protocol CP 2 will form a second sequence such that each data unit of CP 2 is identifiable by a corresponding sequence position identifier of said second sequence. Preferably, the control system keeps a record of the data symbols transferred from the first buffer to the second buffer in terms of respective sequence identifiers of the first and second sequence, but this is by no means a necessity. Namely, it is also possible that the control system keeps an internal record that does not make use of the sequence position identifiers used by the respective protocols. However, as already mentioned, it is preferable that the transfer be recorded in terms of the respective sequence position identifiers. This can e.g. take the form of “CP 1 data unit n corresponds to CP 2 data unit k”, if there is a one-to-one correspondence between the CP 1 data units and the CP 2 units in terms of their payload, where n represents a sequence position identifier of CP 1 and k represents a sequence position identifier of CP 2 . Therefore, if there is a one-to-one correspondence in payload size (i.e. the number of data symbols in a data unit of CP 1 that are to be transferred fits into exactly one data unit of CP 2 ), then the keeping of a record can e.g. be simplified in the form SPI(CP 1 )=SPI(CP 2 )+Δ, were SPI(CP 1 ) represents a sequence position identifier of CP 1 and SPI(CP 2 ) represents a sequence position identifier of CP 2 , and A represents an offset that may be due to a different reference point in the sequence numbering of CP 1 and CP 2 . If there is not a one-to-one correspondence between the payload sizes of CP 1 and CP 2 , then the above-mentioned record will generally have the form “CP 1 data unit n corresponds to CP 2 data units k, k+1, k+2, . . . ”. It is noted that it can occur that the identified number of CP 2 data units that carry data symbols from a given CP 1 data unit additionally carry a part of the data symbols from neighbouring CP 1 data units. For example, if CP 1 data unit n corresponds to CP 2 data units k, k+1 and k+2, then it is possible that CP 2 data unit k also carries some data symbols from CP 1 data unit n−1 and that CP 2 data unit k+2 carries some data symbols from CP 1 data unit n+1. The above-described record of associating CP 1 data units and CP 2 data units can especially be used for performing the previously described feedback coupling for identifying receipt information related to CP 1 on the basis of receipt information contained in feedback messages relating to CP 2 . For example, when using the above-mentioned example of CP 1 data unit n corresponding to CP 2 data units k, k+1, k+2, the translation of receipt information relating to data units of CP 2 into receipt information relating to data units of CP 1 can be accomplished in the following way. If e.g. the control system is arranged such that ACKs are forwarded over the transition from CP 2 to CP 1 , then the control procedure will treat the reception of an ACK for CP 2 data units k, k+1 and k+2 as an ACK for CP 1 data unit n. As another example, if both CP 1 and CP 2 use NACKs, then the control procedure can treat the receipt of a NACK for any one of CP 2 data units k, k+1, k+2 as a NACK for CP 1 data unit n. The present invention has been described in terms of a communication device and in terms of specific methods for controlling such a communication device. The present invention can therefore also be embodied in the form of a computer program product that comprises a computer program for executing method embodiments of the present invention on the suitably arranged communication device, e.g. a communication device having one or more programmable processors. Although the present invention has been described by making reference to specific embodiments, these are not intended to limit the scope of the invention, which scope is defined by the appended claims. Reference numerals and reference signs in the claims serve to make these easier to read, but also have no limiting effect.

Description

Topics

Download Full PDF Version (Non-Commercial Use)

Patent Citations (5)

    Publication numberPublication dateAssigneeTitle
    US-2002041400-A1April 11, 2002Klaus HunlichMethod for transporting facsimile information in IP-based networks
    US-2003050051-A1March 13, 2003Vilander Harri TapaniIP communication in a cellular telecommunications system
    US-2006159079-A1July 20, 2006Joachim Sachs, Michael MeyerTransmission control method in an arq system
    US-5699367-ADecember 16, 1997Telefonaktiebolaget Lm EricssonConcatenated error detection coding and packet numbering for hierarchical ARQ schemes
    WO-2006024320-A1March 09, 2006Telefonaktiebolaget Lm Ericsson (Publ)Dispositif d'envoi d'unites de donnees et dispositif relais d'unites de donnees

NO-Patent Citations (4)

    Title
    Hari Balakrishnan et al, "A Comparison of Mechanisms for Improving TCP Performance over Wireless Links", Aug. 1996, Stanford, CA.
    James Won-Ki Hong: "Communication Abstractions for Distributed Systems" Thesis, 1991, XP002338178 University of Waterloo, Ontario, Canada Retrieved from the Internet: URL:http://www.cs.uwaterloo.ca/cs-archive/CS-1991/43/cs-9143.pdf> p. 22-p. 27 p. 92-p. 96.
    Komatsu, Masaharu, Simple Go-Back-N ARQ Scheme for Satellite Channels with Double Acknowledgements, Electronics and Communications in Japa, Part 1, vol. 74, No. 5. XP 000274084, May 1, 1991.
    Rosenberg et al., IETF RFC 3262 "Reliability of Provisional Responses in SIP", Jun. 2002.

Cited By (9)

    Publication numberPublication dateAssigneeTitle
    US-2006239229-A1October 26, 2006Nokia CorporationCombined handover of the circuit-switched (CS) and packet-switched (PS) resources
    US-2010115363-A1May 06, 2010Electronics And Telecommunications Research Institute, Industry Academic Cooperation Foundation Of Kyunghee UniversityCooperative h-arq supporting method
    US-2010180172-A1July 15, 2010Henning Weimann, Niclas Wiberg, Joachim Sachs, Reiner Ludwig, Michael MeyerCommunication control method
    US-2011038376-A1February 17, 2011Henning Wiemann, Reiner Ludwig, Michael MeyerData Unit Sender and Data Unit Relay Device
    US-2011167326-A1July 07, 2011Panasonic CorporationRelay apparatus and wireless communication system
    US-2011173519-A1July 14, 2011Panasonic CorporationWireless communication apparatus and error detection result feedback method
    US-8072933-B2December 06, 2011Nokia CorporationCombined handover of the circuit-switched (CS) and packet-switched (PS) resources
    US-8392780-B2March 05, 2013Telefonaktiebolaget L M Ericsson (Publ)Communication control method
    US-8553698-B2October 08, 2013Telefonaktiebolaget Lm Ericsson (Publ)Data unit sender and data unit relay device