Path Tail Emulation: An Approach to Enable End-to-End Congestion Control for Split Connections and Performance Enhancing Proxies

Wide area mobile networks facilitate TCP/IP with radio link protocols (RLP) in order to achieve acceptable throughput. Varying channel properties, roaming etc. which interfere with the TCP retransmission and congestion control mechanisms can be alleviated by split connection techniques and performance enhancing proxies (PEP). However, current split connection techniques and PEP do not sufficiently maintain end–to–end congestion control and rate control. Flow control and window clamping techniques, which are often used for this purpose, do not solve but work around the problem and undermine TCP’s sliding window mechanism. In this paper we propose the concept of Path Tail Emulation to overcome this weakness. A TCP flow is split at the gateway from the Internet into the mobile network. The mobile network is then hidden behind an emulated loss free link, the bandwidth and capacity of which correspond to the mobile network’s properties. Using Path Tail Emulation, congestion control and acknowledgement pacing is done exactly the same way as in pure wirebound networks, thus TCP can fully exploit the available network capacity without suffering from any adverse interaction with lower layers. The behaviour of a mobile network behind a PEP using Path Tail Emulation is reduced to a network which is compliant to the network model used for TCP in wirebound networks and therefore can be handled with well known and well proven techniques.