North American Network Operators Group|
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Re: MTU of the Internet?
At 09:11 PM 2/7/98 -0800, Sean M. Doran wrote: >Tli was just pointing out n messages ago that no matter >how well you do in terms of aggregating data traffic into >bigger chunks, you still will see an enormous number of >small packets around (ACKs). You have to be prepared to >switch those at line rate; engineering for some >statistical mix of big and small packets is asking for a >disaster when someone suddenly goes simplex. some of the histograms i've seen show close to 50% of the packets being 40 bytes long. the 'desired' tcp behavior is to have no more than 2 data packets for every ack (since congestion control uses ack-reception to pace the transmission of data and try to quickly detect losses). >There is, however, the spectre of there being so many SYNs >flying around that they alone might cause congestion >collapse. I dunno if I should be frightened of that or >not you should be. not because of the packet-load it causes (as tony pointed out, you have to be able to move 40-byte packets at 'fiber speed') but because it's a symptom of lots of short-lived tcp connections. these connections never get out of slowstart. when there is only a small number of them, it's not important. when there is a large number of them, you have large, non-congestion-controlled, data flows. it's called being nibbled to death by mice.