Delivery of transport layer packets

An apparatus for communication with another apparatus over a packet-switched network, wherein the apparatus comprises a transport protocol portion arranged to cause the apparatus to carry out at least the following:

• transmit, to the other apparatus, user data in a sequence of data blocks having respective sequence numbers assigned thereto,
• receive, from the other apparatus, acknowledgements blocks acknowledging reception of at least some of said data blocks,
• retransmit, to the other apparatus, those ones of said data blocks that are not acknowledged by the other apparatus,
• enter a congestion avoidance state in response to a predefined amount of said data blocks not being acknowledged by the other apparatus,
• wherein the apparatus comprises a complementary transport protocol portion arranged to:
• provide the transport protocol portion with information that indicates acknowledgement of all data blocks up to one having a first reference sequence number assigned thereto via modifying the acknowledgement blocks received from the other apparatus before passing the acknowledgement blocks to the transport protocol portion such that the respective acknowledgement blocks indicate reception of all data blocks up to one having the first reference sequence number assigned thereto, and
• selectively cause the apparatus to transmit, to the other apparatus, a control block instructing the other apparatus to ignore any unreceived data blocks having assigned thereto a sequence number that is smaller than a second reference sequence number.