receiver ropenwin receiver 39 s open window is the amount of data the receiver can accept in the temporary buffers before they are sent to the user process it usually would be the transmission window minus the sum of all the missing and received spans fig4 a is an illustration of how the fields can be laid out in an acknowledgement report for the data received in accordance with the present invention the first mandatory field of the acknowledgement report 400 is the rlowseq 402 that reports the last sequence number up to which the data 140 has been received without any gap if the protocol does not have a way of determining the number of span lengths being reported the count is specified in the field nspanpairs 404 the first mspanlen1 406 which follows the nspanpairs 404 reports the length of the first missing span of data following that is rspanlen1 408 the length of the next span of data received by the receiver 120 similarly the next missing span and received spans are reported by mspanlen2 412 and rspanlen2 414 respectively this is done till the last span of data received is being reported by rspanlenn 416 which follows the last missing span mspanlenn 414 the acknowledgement report 400 can optionally include a field ropenwin 418 to report the additional length of data 140 the receiver 120 can accommodate in its temporary buffers the implementation specific decision to send any of the optional fields.