Freeze-TCP: a true end-to-end TCP enhancement mechanism for mobile environments

Optimizing TCP (transport layer) for mobility has been researched extensively. We present a brief summary of existing results which indicates that most schemes require intermediaries (such as base stations) to monitor the TCP traffic and actively participate in flow control in order to enhance performance. Although these methods simulate end-to-end semantics, they do not comprise true end-to-end signaling. As a result, these techniques are not applicable when the IP payload is encrypted. For instance IPSEC, which is expected to be standard under IPv6, encrypts the entire IP payload making it impossible for intermediaries to monitor TCP traffic unless those entities are part of the security association. In addition, these schemes require changes (in the TCP/IP code) at intermediate nodes making it difficult for the mobile clients to inter-operate with the existing infrastructure. In this paper we explore the "freeze-TCP" mechanism which is a true end-to-end scheme and does not require the involvement of any intermediaries (such as base stations) for flow control. Furthermore, this scheme does not require any changes on the "sender side" or intermediate routers; changes in TCP code are restricted to the mobile client side, making it possible to fully inter-operate with the existing infrastructure. We then outline a method which integrates the best attributes of freeze-TCP and some existing solutions. Performance results highlight the importance of pro-active action/signaling by the mobile-host. The data indicate that in most cases, simply reacting to disconnections tends to yield lower performance than pro-active mechanisms such as freeze-TCP.