1. A method of controlling the transmission of a sequence of data symbols over a connection provided by a predetermined communication layer (Lm) , said connection having a sending peer and a receiving peer, said predetermined sequence of data symbols being divided into a sequence of first data units on the basis of a first data unit generation scheme, said first data units being sent from said sending peer to said receiving peer, a feedback mechanism being implemented according to which the receiving peer sends feedback messages to the sending peer, said feedback messages comprising information on the receipt of data units sent by said sending peer, the sending peer keeping a first sender- side transmission record of data units in which each data unit is associated with sender-side transmission status information, the receiving peer keeping a first receiver-side transmission record of data units in which each data unit is associated with receiver-side transmission status information, the transmission control for transmission of data units over said connection being done on the basis of said sender-side transmission record, and reassembling said sequence of data symbols being done on the basis of said receiver- side transmission record, said method comprising modifying said transmission by', '- identifying a reference data symbol in the sequence of data symbols,', '- dividing the data symbols following said reference data symbol in the sequence of data symbols into a sequence of second data units on the basis of a second data unit generation scheme, - generating a second sender-side transmission record by mapping said sender-side transmission status information associated with data units in said first sender-side

transmission record onto said second data units in accordance with a predetermined mapping scheme for sender-side transmission records,', '- generating a second receiver-side transmission record by mapping said receiver-side transmission status information associated with data units in said first receiver-side transmission record onto said second data units in accordance with a predetermined mapping scheme for receiver-side transmission records, and - performing the transmission control of said second data units on the basis of said second sender-side transmission record and performing the reassembling of said sequence of data symbols on the basis of said second receiver-side transmission record.

2. The method of claim 1, wherein said sender-side transmission status information distinguishes between at least the statuses of', '- correct receipt confirmed, and - correct receipt not confirmed, said receiver-side transmission status information distinguishes between at least the statuses of', '- correctly received, and', '- not correctly received, said mapping scheme for sender-side transmission records comprises', '- mapping the status of correct receipt not confirmed onto each second data unit that contains at least one data symbol that belonged to a first data unit that was associated with the status of correct receipt not confirmed, and', '- mapping the status of correct receipt confirmed onto each second data unit that completely contains data symbols that all belonged to first data units that were associated with the status of correct receipt confirmed,

and said mapping scheme for receiver-side transmission records comprises', '- mapping the status of not correctly received onto each second data unit that contains at least one data symbol that belonged to a first data unit that was associated with the status of not correctly received, and', '- mapping the status of correctly received onto each second data unit that completely contains data symbols that all belonged to first data units that were associated with the status of correctly received.

3. The method of one of claims 3 to 12, wherein the number of data symbols in each first data unit is variable, and said communication device is arranged to receive information from the receiving-side of the connection on which first data units the receiver-side has not correctly received, and in response thereto transmits to the receiver-side of the connection information on how many data symbols are contained in each of the first data units that said receiver-side has not correctly received.', '14. A method of controlling a communication device to operate as a sending peer of a connection provided by a predetermined communication layer for transmitting a sequence of data symbols, a feedback mechanism being implemented for said connection, according to which a receiving peer of the connection sends feedback messages to a sending peer of the connection, said feedback messages comprising information on the receipt of data units sent over connection, said method comprising:', '- receiving from a previous sending peer of said connection a sequence of data symbols and a first sender-side transmission record of data units that were generated in accordance with a first data unit generation scheme, in which record each data unit is associated with sender-side transmission status information,', '- obtaining a reference data symbol in the sequence of data symbols,', '- dividing the data symbols following said reference data symbol in the sequence of data symbols into a sequence of second data units on the basis of a second data unit generation scheme, - generating a second sender-side transmission record by mapping said sender-side transmission status information associated with data units in said first sender-side

transmission record onto said second data units in accordance with a predetermined mapping scheme for sender-side transmission records, and', '- controlling the sending of said second data units over said connection on the basis of said second sender-side transmission record.', '15. The method of claim 14, wherein said sender-side transmission status information distinguishes between at least the statuses of', '- correct receipt confirmed, and', '- correct receipt not confirmed, and said mapping scheme for sender-side transmission records comprises - mapping the status of correct receipt not confirmed onto each second data unit that contains at least one data symbol that belonged to a first data unit that was associated with the status of correct receipt not confirmed, and - mapping the status of correct receipt confirmed onto each second data unit that completely contains data symbols that all belonged to first data units that were associated with the status of correct receipt confirmed.', '16. The method of claim 15, wherein said sender-side transmission status information further distinguishes the status of correct receipt not confirmed into - sent and correct receipt not confirmed, and', '- not sent, and said mapping scheme for sender-side transmission records comprises', '- mapping the status of not sent onto each second data unit that contains at least one data symbol that belonged to a first data unit that was associated with the status of not sent, and

- mapping the status of sent and correct receipt not confirmed onto each second data unit that contains at least one data symbol that belonged to a first data unit that was associated with the status of sent and correct receipt not confirmed and that contains no data symbols that belonged to a first data unit that was associated with the status of not sent .', '17. The method of one of claims 14 to 16, wherein said first data unit generation scheme comprises generating said first data units with a predetermined first size, and said second data unit generation scheme comprises generating said second data units with a predetermined second size, said second size being different from said first size.', '18. The method of one of claims 14 to 17, wherein said communication device obtains said reference data symbol by receiving a message sent from the receiving-side of said connection.', '19. The method of one of claims 14 to 18, wherein said communication device uses a sliding window technique for transmission control, and where the initial low end of the sliding window with respect to the sequence of data symbols, used for transmission control of said second data units on the basis of said second sender-side transmission record, is said reference data symbol.

3. A method of controlling a communication device to operate as a sending peer of a connection provided by a predetermined communication layer for transmitting a sequence of data symbols, a feedback mechanism being implemented for said connection, according to which a receiving peer of the connection sends feedback messages to a sending peer of the connection, said feedback messages comprising information on the receipt of data units sent over the connection, said method comprising: conducting said transmission by', '- dividing said sequence of data symbols into a sequence of first data units on the basis of a first data unit generation scheme,', '- controlling the sending of said first data units to a receiving peer of said connection on the basis of a first sender-side transmission record of data units in which each data unit is associated with sender-side transmission status information, characterized by modifying said transmission of data symbols by', '- obtaining a reference data symbol in the sequence of data symbols,', '- dividing the data symbols following said reference data symbol in the sequence of data symbols into a

sequence of second data units on the basis of a second data unit generation scheme,', '- generating a second sender-side transmission record by mapping said sender- side transmission status information associated with data units in said first sender-side transmission record onto said second data units in accordance with a predetermined mapping scheme for sender- side transmission records, and', '- controlling the sending of said second data units on the basis of said second sender-side transmission record.

4. The method of claim 3, wherein said sender-side transmission status information distinguishes between at least the statuses of', '- correct receipt confirmed, and', '- correct receipt not confirmed, and said mapping scheme for sender-side transmission records comprises - mapping the status of correct receipt not confirmed onto each second data unit that contains at least one data symbol that belonged to a first data unit that was associated with the status of correct receipt not confirmed, and - mapping the status of correct receipt confirmed onto each second data unit that completely contains data symbols that all belonged to first data units that were associated with the status of correct receipt confirmed.

5. The method of claim 4, wherein said sender-side transmission status information further distinguishes the status of correct receipt not confirmed into - sent and correct receipt not confirmed, and', '- not sent,

and said mapping scheme for sender-side transmission records comprises', '- mapping the status of not sent onto each second data unit that contains at least one data symbol that belonged to a first data unit that was associated with the status of not sent, and', '- mapping the status of sent and correct receipt not confirmed onto each second data unit that contains at least one data symbol that belonged to a first data unit that was associated with the status of sent and correct receipt not confirmed and that contains no data symbols that belonged to a first data unit that was associated with the status of not sent .

6. The method of one of claims 3 to 5, wherein said first data unit generation scheme comprises generating said first data units with a predetermined first size, and said second data unit generation scheme comprises generating said second data units with a predetermined second size, said second size being different from said first size.

7. The method of one of claims 3 to 6, wherein said modifying of said transmission is triggered by a reconfiguration of said connection or a handover of said connection to a new receiving peer, and said communication device continues to operate as said sending peer but performs the transmission control of said second data units on the basis of said second sender-side transmission record after said reconfiguration or handover.

8. The method of one of claims 3 to 7, wherein said modifying of said transmission is triggered by a handover of said connection to a second sending peer, said communication device also operating as said second

sending peer, where said second sending peer performs the transmission control of said second data units on the basis of said second sender-side transmission record after said handover.', 'The method of one of claims 3 to 8, wherein said communication device obtains said reference data symbol by receiving a message sent from the receiving-side of said connection.', '10. The method of one of claims 3 to 9, wherein said communication device uses a sliding window technique for transmission control, and where the initial low end of the sliding window with respect to the sequence of data symbols, used for transmission control of said second data units on the basis of said second send record and said second receive record, is said reference data symbol .', '11. The method of one of claims 3 to 10, wherein said sender-side transmission status information comprises information on one or more of', '- a time value associated with a data unit,', '- a number of retransmission attempts associated with a data unit,', '- reliability associated with a data unit, and', '- priority associated with a data unit.', '12. The method of one of claims 3 to 11, wherein said data symbols are provided to said communication layer (Lm) in the form of protocol data units of a higher layer (L(m+1)), and where said identifying of said reference symbol comprises determining the first data symbol of the higher layer protocol data unit that follows the last higher layer protocol data unit of which all data symbols were correctly received by said receiving peer as said reference data symbol.

20. The method of one of claims 14 to 19, wherein said sender-side transmission status information comprises information on one or more of', '- a time value associated with a data unit, - a number of retransmission attempts associated with a data unit,', '- reliability associated with a data unit, and

- priority associated with a data unit.

21. The method of one of claims 14 to 20, wherein said data symbols are provided to said communication layer (Lm) in the form of protocol data units of a higher layer', '(L(m+1)), and where said obtaining of said reference symbol comprises determining the first data symbol of the higher layer protocol data unit that follows the last higher layer protocol data unit of which all data symbols were correctly received by said receiving peer as said reference data symbol .

22. The method of one of claims 14 to 21, wherein the number of data symbols in each first data unit is variable, and said communication device is arranged to receive information from the receiving-side of the connection on which first data units the receiver-side has not correctly received, and in response thereto transmits to the receiver-side of the connection information on how many data symbols are contained in each of the first data units that said receiver-side has not correctly received.

23. A method of controlling a communication device to operate as a receiving peer of a connection provided by a predetermined communication layer for transmitting a sequence of data symbols, a feedback mechanism being implemented for said connection, according to which a receiving peer of the connection sends feedback messages to a sending peer of the connection, said feedback messages comprising information on the receipt of data units sent over connection, and where the sending peer divides said sequence of data symbols into a sequence of first data units on the basis of a first data unit generation scheme, and controls the sending of said first data units to a receiving peer of said connection on the basis of a first sender-side transmission record

of data units in which each data unit is associated with sender-side transmission status information, said method comprising: conducting said transmission by - keeping a first receiver-side transmission record of first data units in which each first data unit is associated with receiver-side transmission status information, and', '- reassembling said sequence of data symbols on the basis of said first receiver-side transmission record,', 'characterized by modifying said transmission of data symbols by', '- obtaining a reference data symbol in the sequence of data symbols,', '- dividing the data symbols following said reference data symbol in the sequence of data symbols into a sequence of second data units on the basis of a second data unit generation scheme, - generating a second receiver-side transmission record by mapping said receiver-side transmission status information associated with data units in said first receiver-side transmission record onto said second data units in accordance with a predetermined mapping scheme for receiver-side transmission records, and', '- reassembling said sequence of data symbols on the basis of said second receiver-side transmission record.

24. The method of claim 23, wherein said receiver-side transmission status information distinguishes between at least the statuses of', '- correctly received, and', '- not correctly received, and said mapping scheme for receiver-side transmission records comprises', '- mapping the status of not correctly received onto each second data unit that contains at least

one data symbol that belonged to a first data unit that was associated with the status of not correctly received, and', '- mapping the status of correctly received onto each second data unit that completely contains data symbols that all belonged to first data units that were associated with the status of correctly received.

25. The method of claim 23 or 24, wherein said first data unit generation scheme comprises generating said first data units with a predetermined first size, and said second data unit generation scheme comprises generating said second data units with a predetermined second size, said second size being different from said first size.

26. The method of one of claims 23 to 25, wherein said modifying of said transmission is triggered by a reconfiguration of said connection or a handover of said connection to a new sending peer, and said communication device continues to operate as said receiving peer but performs the reassembling of said sequence of data symbols on the basis of said second receiver-side transmission record after said reconfiguration or handover.

27. The method of one of claims 23 to 26, wherein said modifying of said transmission is triggered by a handover of said connection to a second receiving peer, said communication device also operating as said second receiving peer, where said second receiving peer performs the reassembling of said sequence of data symbols on the basis of said second receiver-side transmission record after said handover.

28. The method of one of claims 23 to 27, wherein said reference data symbol is obtained from a procedure conducted by said communication device.

29. The method of claim 28, wherein said data symbols are provided to said communication layer (Lm) in the form of protocol data units of a higher layer (L(m+1)), and where said procedure for obtaining of said reference symbol comprises determining as said reference data symbol the first data symbol of the higher layer protocol data unit that follows the last higher layer protocol data unit of which all data symbols were correctly received by said communication device.

30. The method of one of claims 23 to 29, wherein said receiver-side transmission status information comprises information on one or more of', '- a time value associated with a data unit,', '- a number of retransmission attempts associated with a data unit,', '- reliability associated with a data unit, and', '- priority associated with a data unit .

31. The method of one of claims 23 to 30, wherein the number of data symbols in each first data unit is variable, and where prior to said step of generating a second receiver-side transmission record, the communication device is arranged to receive from the sender-side of the connection information on how many data symbols are contained in each of the first data units that said communication device has not correctly received.

32. A method of controlling a communication device to operate as a receiving peer of a connection provided by a predetermined communication layer for transmitting a sequence of data symbols, a feedback mechanism being implemented for said connection, according to which a

receiving peer of the connection sends feedback messages to a sending peer of the connection, said feedback messages comprising information on the receipt of data units sent over connection, said method comprising: - receiving from a previous receiving peer of said connection a sequence of data symbols and a first receiver-side transmission record of data units that were generated in accordance with a first data unit generation scheme, in which record each data unit is associated with receiver-side transmission status information,', '- obtaining a reference data symbol in the sequence of data symbols,', '- dividing the data symbols following said reference data symbol in the sequence of data symbols into a sequence of second data units on the basis of a second data unit generation scheme,', '- generating a second receiver-side transmission record by mapping said receiver-side transmission status information associated with data units in said first receiver-side transmission record onto said second data units in accordance with a predetermined mapping scheme for receiver-side transmission records, and', '- reassembling said sequence of data symbols on the basis of said second receiver-side transmission record.

33. The method of claim 32, wherein said receiver- side transmission status information distinguishes between at least the statuses of - correctly received, and', '- not correctly received, and said mapping scheme for receiver-side transmission records comprises', '- mapping the status of not correctly received onto each second data unit that contains at least one data symbol that belonged to a first data unit

that was associated with the status of not - correctly received, and - mapping the status of correctly received onto each second data unit that completely contains data symbols that all belonged to first data units that were associated with the status of correctly received.

34. The method of claim 32 or 33, wherein said first data unit generation scheme comprises generating said first data units with a predetermined first size, and said second data unit generation scheme comprises generating said second data units with a predetermined second size, said second size being different from said first size.

35. The method of one of claims 32 to 34, wherein said reference data symbol is obtained from a procedure conducted by said communication device.

36. The method of claim 35, wherein said data symbols are provided to said communication layer (Lm) in the form of protocol data units of a higher layer (L(m+1)), and where said procedure for obtaining of said reference symbol comprises determining as said reference data symbol the first data symbol of the higher layer protocol data unit that follows the last higher layer protocol data unit of which all data symbols were correctly received by said communication device.

37. The method of one of claims 32 to 36, wherein said receiver-side transmission status information comprises information on one or more of', '- a time value associated with a data unit,', '- a number of retransmission attempts associated with a data unit,', '- reliability associated with a data unit, and', '- priority associated with a data unit.

38. The method of one of claims 32 to 37, wherein the number of data symbols in each first data unit is variable, and where prior to said step of generating a second receiver-side transmission record, the communication device is arranged to receive from the sender-side of the connection information on how many data symbols are contained in each of the first data units that said communication device has not correctly received.

39. A method of controlling a communication device to operate as a sending peer of a connection provided by a predetermined communication layer for transmitting a sequence of data symbols, a feedback mechanism being implemented for said connection, according to which a receiving peer of the connection sends feedback messages to a sending peer of the connection, said feedback messages comprising information on the receipt of data units sent over the connection, said method comprising: - receiving from a previous sending peer of said connection a sequence of data symbols and a sender-side transmission record of data units that were generated in accordance with a data unit generation scheme, in which record each data unit is associated with sender-side transmission status information,', '- dividing the data symbols into a sequence of data units on the basis of said data unit generation scheme, and', '- controlling the sending of said data units over said connection on the basis of said received sender-side transmission record.

40. A method of controlling a communication device to operate as a receiving peer of a connection provided by a predetermined communication layer for transmitting a sequence of data symbols, a feedback mechanism being implemented for said connection, according to which a

receiving peer of the connection sends feedback messages to a sending peer of the connection, said feedback messages comprising information on the receipt of data units sent over the connection, said method comprising: - receiving from a previous receiving peer of said connection a sequence of data symbols and a receiver- side transmission record of data units that were generated in accordance with a predetermined data unit generation scheme, in which record each data unit is associated with receiver-side transmission status information,', '- receiving from a sending peer of said connection data units generated according to said predetermined data unit generation scheme, and - reassembling said sequence of data symbols on the basis of said second receiver-side transmission record.

41. A method of controlling a communication device to operate as a sending peer of a connection provided by a predetermined communication layer for transmitting a sequence of data symbols, a feedback mechanism being implemented for said connection, according to which a receiving peer of the connection sends feedback messages to a sending peer of the connection, said feedback messages comprising information on the receipt of data units sent over the connection, said method comprising: conducting said transmission by', '- dividing said sequence of data symbols into a sequence of first data units on the basis of a first data unit generation scheme,', '- controlling the sending of said first data units to a receiving peer of said connection on the basis of a first sender-side transmission record of data units in which each data unit is associated with sender-side transmission status information, characterized by modifying said transmission of data symbols by transferring to another communication device

a sequence of data symbols and a sender-side transmission record.

42. The method of claim 41, wherein said sender-side transmission record transferred to said other communication device is said first sender-side transmission record.

43. The method of claim 41, wherein modifying said transmission further comprises:', '- obtaining a reference data symbol in the sequence of data symbols,', '- dividing the data symbols following said reference data symbol in the sequence of data symbols into a sequence of second data units on the basis of a second data unit generation scheme,', '- generating a second sender-side transmission record by mapping said sender-side transmission status information associated with data units in said first sender-side transmission record onto said second data units in accordance with a predetermined mapping scheme for sender-side transmission records, and', '- transferring to said other communication device said second sender-side transmission record.

44. A method of controlling a communication device to operate as a receiving peer of a connection provided by a predetermined communication layer for transmitting a sequence of data symbols, a feedback mechanism being implemented for said connection, according to which a receiving peer of the connection sends feedback messages to a sending peer of the connection, said feedback messages comprising information on the receipt of data units sent over the connection, said method comprising: conducting said transmission by

- receiving from a sending peer of said connection data units generated according to a predetermined data unit generation scheme, and', '- reassembling said sequence of data symbols on the basis of a first receiver-side transmission record,', 'characterized by modifying said transmission of data symbols by transferring to another communication device a sequence of data symbols and a receiver-side transmission record.

45. The method of claim 44, wherein said receiver-side transmission record transferred to said other communication device is said first receiver-side transmission record.

46. The method of claim 44, wherein modifying said transmission further comprises:', '- obtaining a reference data symbol in the sequence of data symbols,', '- dividing the data symbols following said reference data symbol in the sequence of data symbols into a sequence of second data units on the basis of a second data unit generation scheme, - generating a second receiver-side transmission record by mapping said receiver-side transmission status information associated with data units in said first receiver-side transmission record onto said second data units in accordance with a predetermined mapping scheme for receiver-side transmission records, and', '- transferring to said other communication device said second receiver-side transmission record.

47. A computer program product arranged to perform the method of one of claims 3 to 46 when executed on a communication device.

48. A data carrier storing the computer program product of claim 47.

49. A communication device arranged to perform the method of one of claims 3 to 46.

50. The communication device of claim 49, wherein said communication device is a mobile station or fixed station of a mobile communication network.']