Thursday, September 16, 2010

Packet Dynamics

I just read a paper on End-to-End Internet Packet Dynamics, which was kind of interesting as it showed data about changes in packet flow from December 1994 - December 1995. The paper details an experiment the authors performed that measured TCP bulk transfers between 35 sites running special measurement daemons. One of the interesting data points shared was that during the first experiment, out-of-order packet delivery was quite prevalent. It is interesting because reordering in TCP can cause of lot of packet retransmission, which would have been an expensive thing to do considering the internet was very small back then with considerably lower bandwidth capabilities than we have today. There are times, however, where a packet is honestly lost and retransmission is necessary. The authors found that during the first experiment, the ratio of good retransmissions to bad one was 22. In the second experiment (a year later), they increased the window size and the ratio increased to 300 which is much better.

One of the other parts in this paper that I found interesting was that of packet loss. One of the initial data points that they gave was that between the first and second experiments that packet loss increased. One of the measurements they took was rates of ack loss. The data shows that at one point, ack's flowing into the US were like likely to be lost than those flowing into the Europe. Those roles switched in the subsequent experiment. 

I think the current internet infrastructure is fairly stable today and packet loss is generally low on a good connection. One of the interesting complaints I hear from a lot of people is that the internet is so much faster in other companies compared to what is available in the US. Obviously other countries don't have the infrastructure in place on the scale the US does, but it would be interesting to study the dynamics of those smaller systems to learn something from how those countries decided to build their networks. I think one of the great advantages that countries who are relatively new in building up internet connectivity is that they can learn from the mistakes of countries like the US. This would enable their networks to be faster, in a sense, than the US because they wouldn't have to build and work around their mistakes. 

No comments:

Post a Comment