Proxy caching in split TCP: dynamics, stability and tail asymptotics

The split of a multihop, point-to-point TCP connection consists in
replacing a plain, end-to-end TCP connection by a cascade of TCP
connections.In such a cascade, connection
n feeds connection n+1 through some proxy node n.
This technique is used in a variety of contexts.
In overlay networks, proxies are often peers of the underlying
peer-to-peer network.split TCP is also already proposed and largely
adopted in wireless networks at the wired/wireless interface to separate
links with vastly different characteristics.In order to avoid losses in the
proxies, a backpressure mechanism is often used in this context.
In this paper we develop a model for such a split TCP connection
aimed at the analysis of throughput dynamics on both links as well as
of buffer occupancy in the proxy.The two main variants of split TCP
are considered: that with backpressure and that without.The study
consists of two parts: the first part is purely experimental and is based on
ns2 simulations.It allows us to identify complex interaction phenomena
between TCP flow rates and proxy buffer occupancy, which seem to have
been ignored by previous work on split TCP.The second part of the
paper is of a mathematical nature.We establish the basic equations that
govern the evolution of such a cascade and prove some of the experi-
mental observations made in the first part.In particular, we give the
conditions for system stability and we show the possibility of heavy tail
asymptotics for proxy buffer occupancy and delays in the stationary
regime.