Total Acknowledgements: A Robust Feedback Mechanism for End-to-End Congestion Control

End-to-end data transport protocols have two main functions: error recovery and congestion control. The information required by the sender to perform these functions is provided by acknowledgements (ACKs) from the receiver. The Internet transport protocol, TCP/IP, uses cumulative acknowledgements (CACKs), which provide a robust but minimal mechanism for error recovery which is inadequate for heterogeneous networks with random loss. Furthermore, TCP's congestion control mechanism is based on counting ACKs, and is therefore vulnerable to loss of ACKs on the reverse path, particularly when the latter may be slower than the forward path, as in asymmetric networks. The contributions of this paper are as follows: (a) We show that a simple enhancement of CACK provides sufficient information for end-to-end congestion control. We term this ACK format total ACKs (TACKs). (b) We devise a novel ACK format that uses TACKs for congestion control, and negative ACKs (NACKs) for efficient error recover..