Modeling Wireless Links for Transport Protocols

Andrei Gurtov, Sally Floyd, "Modeling Wireless Links for Transport Protocols," ACM SIGCOMM Computer Communications Review, Volume 34, Number 2, (April 2004).

One line summary: This paper discusses modeling wireless links, including problems with current models and how the assumptions of a model can affect the evaluation of transport protocols using that model.

Summary

This paper discusses modeling wireless links especially for the purpose of evaluating transport protocols. The paper first briefly describes the three main types of wireless links: cellular, wireless LANs, and satellite links. It then discusses common topologies found with wireless links, as well as the typical kinds of traffic that run over them. It states that common performance metrics for wireless links include throughput, delay, fairness, dynamics, and goodput. The paper goes on to give four reasons why better models are needed, along with support examples for each reason: (1) some current models are not realistic, (2) some current models are realistic but explore only a small fraction of the parameter search space, (3) some current models are overly realistic, and (4) many models are not reproducible. The paper then describes specific characteristics of wireless links: error losses and corruption, delay variation, packet reordering, on-demand resource allocation, bandwidth variation, and asymmetry in bandwidth and latency. It also discusses the effect of queue management and node mobility on transport protocols. The paper then argues that it is not necessarily the case that transport protocols must adapt to wireless links or that wireless link layer protocols must accommodate all transport protocols but rather that designers of each should take into account the characteristics of the other and their interplay. The paper discusses three particular areas where it is not clear how link layer and transport layer protocols should interact: bit error detection and correction, packet reordering, delay variation, and cross-communication between layers.

Critique

I didn’t really like this paper. It’s not that I would disagree with anything the authors said. Many of the things they pointed out are well known and they say so. It is useful that they aggregated all this information and presented it in a nicely organized and logical way. It was somewhat informative. I guess I’m just surprised that it was published at a conference when they didn’t really implement anything or prove anything or even have that many results. I would more expect to find this in a textbook or something.