Wednesday, November 12, 2008

End-to-End Internet Packet Dynamics

This paper sets out to model and explore measurements that reflect packet dynamics over a network. The author approaches the Internet as a mysterious quantity that needs to be probed to discover "pathologies" in the network. Specifically, out-of-order delivery, packet replication and packet corruption are examined using TCP-based measurement techniques. Of course, there is an emphasis on the need to account for TCP protocol-related symptoms to attain accurate measurements. Statistical analysis reveals several interesting trends, such as the occurrence of spikes (indicating a minimum time related to common 56 kbps links) in time-plots for out-of-order delivery . Moreover, measurements are explained in the context of TCP congestion control and acknowledgment mechanisms and reveal valuable insight into why, for example, TCP uses triple duplicate acknowledgments to trigger fast retransmission (and why it should but can't make a change to only two duplicate acknowledgments).

One thing that I appreciated here was the clear acknowledgment of possible improvements in measurement techniques and the drawbacks of some techniques employed in this study. This paper definitely gives an idea of just how complex and unpredictable Internet packet dynamics can be and provides approaches to measuring them; such measurements may be more difficult in today's significantly more evolved Internet, but several notions discussed here still hold value. For its time, Paxson's paper dispels several crucial assumptions about the Internet.

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