Link layer acknowledgement and retransmission for cellular telecommunications

Abstract

A mobile telecommunications system comprises a mobile user equipment unit and at least one node through which a packet switched data session is established between the user equipment unit and a data network. One of the node and the user equipment unit serves as a transmitter of segments of data packets and the other of the node and the user equipment unit serves as a receiver of the segments of data packets. If the first lost segment is not received within a timed interval, and if a second lost segment is also lost during the timed interval, at expiration of the timed interval the receiver sends a selective acknowledgment message to the transmitter which requests retransmission of both the first lost segment and the second lost segment. The acknowledgment messages of the system have a unique format including start sequence number and a variable size bitmap field. The start sequence number (ssn) is mapped to a first non-received segment in a receive buffer; the first bit in the bitmap maps to a segment with a sequence number equal to the start sequence number. In differing embodiments, the bitmaps of the acknowledgment messages may have or may not have a stop bit. The transmitter has a poll timer that is started/restarted and canceled in accordance with novel timer operational rules.