A method to operate a radio link protocol receiver when receiving datablocks from a transmitter, comprising: receiving a data block; and determining in the receiver whether a size of a receive window is less than or equal to a bitmap size, wherein the bitmap size is a maximum size, expressed in a number of bits, of the bitmap to be reported in an acknowledgment message, and wherein determining in the receiver whether the size of the receive window is less than or equal to a bitmap size is based on a condition [V -V] mod SNS≤bitmap size; then if the determination is positive, the reported bitmap covers the entire receive window which is provided by setting SSN=V; where: V is a send state variable that denotes a sequence number of a next in-sequence data block to be transmitted; SNS is a sequence number space that denotes a range [0; SNS-1] in which a block sequence number, BSN, takes its value, where each transmitted data block is assigned a BSN equal to V at the time of transmission; V is a receive window state variable that denotes a lowest BSN not yet received, modulo SNS, and represents the start of a receive window; V is a receive state variable that denotes the BSN which has a value one higher than the highest BSN yet received, modulo SNS; and SSN is a starting sequence number; and based on the determination, if the size of the receive window is greater than the bitmap size, the reported bitmap comprises a partial bitmap covering one of an initial portion of the receive window and a portion other than the initial portion of the receive window, further determining, in the receiver, which portion of the receive window is reported, wherein the further determining, in the receiver, which portion of the receive window is reported comprises: determining if [PBSN-V] mod SNS<WS and if [V -(PBSN+PBSN_Threshold)] mod SNS<WS and, if the further determination is positive, sending the partial bitmap covering a portion other than the initial portion of the receive window, otherwise sending the partial bitmap covering the initial portion of the receive window, where PBSN is a partial block sequence number denoting the highest BSN that was included in the bitmap when previous acknowledgement message was transmitted, and where PBSN_Threshold is a threshold value that identifies a limit for the difference between PBSN and V, beyond which a partial bitmap covering a portion other than the initial portion of the receive window is generated, and WS denotes window size. receiving a data block; and determining in the receiver whether a size of a receive window is less than or equal to a bitmap size, wherein the bitmap size is a maximum size, expressed in a number of bits, of the bitmap to be reported in an acknowledgment message, and wherein determining in the receiver whether the size of the receive window is less than or equal to a bitmap size is based on a condition [V -V] mod SNS≤bitmap size; then if the determination is positive, the reported bitmap covers the entire receive window which is provided by setting SSN=V; where: V is a send state variable that denotes a sequence number of a next in-sequence data block to be transmitted; SNS is a sequence number space that denotes a range [0; SNS-1] in which a block sequence number, BSN, takes its value, where each transmitted data block is assigned a BSN equal to V at the time of transmission; V is a receive window state variable that denotes a lowest BSN not yet received, modulo SNS, and represents the start of a receive window; V is a receive state variable that denotes the BSN which has a value one higher than the highest BSN yet received, modulo SNS; and SSN is a starting sequence number; and based on the determination, if the size of the receive window is greater than the bitmap size, the reported bitmap comprises a partial bitmap covering one of an initial portion of the receive window and a portion other than the initial portion of the receive window, further determining, in the receiver, which portion of the receive window is reported, wherein the further determining, in the receiver, which portion of the receive window is reported comprises: determining if [PBSN-V] mod SNS<WS and if [V -(PBSN+PBSN_Threshold)] mod SNS<WS and, if the further determination is positive, sending the partial bitmap covering a portion other than the initial portion of the receive window, otherwise sending the partial bitmap covering the initial portion of the receive window, where PBSN is a partial block sequence number denoting the highest BSN that was included in the bitmap when previous acknowledgement message was transmitted, and where PBSN_Threshold is a threshold value that identifies a limit for the difference between PBSN and V, beyond which a partial bitmap covering a portion other than the initial portion of the receive window is generated, and WS denotes window size. determining if [PBSN-V] mod SNS<WS and if [V -(PBSN+PBSN_Threshold)] mod SNS<WS and, if the further determination is positive, sending the partial bitmap covering a portion other than the initial portion of the receive window, otherwise sending the partial bitmap covering the initial portion of the receive window, where PBSN is a partial block sequence number denoting the highest BSN that was included in the bitmap when previous acknowledgement message was transmitted, and where PBSN_Threshold is a threshold value that identifies a limit for the difference between PBSN and V, beyond which a partial bitmap covering a portion other than the initial portion of the receive window is generated, and WS denotes window size.