TCP Optimized for Wireless Access

Abstract: Transmission control protocol (TCP) is a connection-oriented, end-to-end reliable transport layer protocol. TCP is today used in ways that was not considered back when the protocol initially was designed. New use cases such as video streaming, instant messaging and online games are common today. The new use cases bring new challenges to the TCP protocol. For example when an instant messaging message is sent it consists of a small stream of TCP segments. If the last segment in a transaction like that is lost it can only be recovered through retransmission timeout which might increase the delay time for the client several times over. New enhancements to the protocol are necessary to keep up with the new use cases. This thesis investigates three experimental enhancements for TCP. The enhancements are New Congestion Window Validation (CWV), Tail Loss Probe (TLP) and TCP Instant Recovery (IR). The enhancements are tested in a Long-term Evolution (LTE) simulator. LTE is a mobile communication technology handling broadband data.
The simulations show that CWV keeps congestion window (cwnd) in a more relevant state but does not affect the performance greatly at the large scale simulations. TLP reduces the amount of retransmission timeouts through probe segments who trigger fast retransmit which leads to higher object bitrate. IR recovers lost packets without retransmission by sending encoded data segments. IR reduces the amount of retransmission timeouts and increase the object bitrate seen over all simulations. In simulations with heavy load on the networks IR causes longer delay time for many users because of the higher overhead.