Section: New Results

Algorithms: Internet without Congestion Control Algorithms

Participant : Mathieu Feuillet.

It is commonly accepted that the observed robustness of the Internet in the last two decades, despite an exponential growth in traffic, is largely due to the use of congestion control algorithms. Since the introduction of congestion control mechanisms in TCP in the late 1980s, no congestion collapse has been observed. Unfortunately, it is not clear if the IETF will be able to enforce the use of TCP in the future. More and more applications do not comply with the “TCP-friendliness” principle. With the generalization of broadband access through optical fiber (FTTH), the impact of such applications cannot be neglected.

In this project we analyze Internet behavior at flow level in the absence of any control congestion. We assume all sources send at their maximum access rate and recover from packet loss by the use of some source coding or retransmissions independent of the congestion control. The bandwidth allocation is then fully determined by the buffer management policy implemented in routers. We study two possible policies: Fair Dropping and Tail Dropping . In both cases, we study the efficiency of resource utilization in terms of the maximum load the network can sustain. For Fair Dropping , utilization is optimal. This is not the case for Tail Dropping although efficiency is shown to be very high in most topologies of practical use. For the latter, the order of magnitude difference between the maximum access rates and link capacity plays a crucial role. The complete model and first results are presented in [15] .