nanog mailing list archives
Re: TCP congestion control and large router buffers
From: Carsten Bormann <cabo () tzi org>
Date: Thu, 23 Dec 2010 19:00:52 +0100
Some more historical pointers: If you want to look at the early history of the latency discussion, look at Stuart Cheshire's famous rant "It's the Latency, Stupid" (http://rescomp.stanford.edu/~cheshire/rants/Latency.html). Then look at Matt Mathis's 1997 TCP equation (and the 1998 Padhye-Firoiu version of that): The throughput is proportional to the inverse square root of the packet loss and the inverse RTT -- so as the RTT starts growing due to increasing buffers, the packet loss must grow to keep equilibrium! We started to understand that you have to drop packets in order to limit queueing pretty well in the late 1990s. E.g., RFC 3819 contains an explicit warning against keeping packets for too long (section 13). But, as you notice, for faster networks, the bufferbloat effect can be limited in effect by intelligent window size management, but the dominating Windows XP was not intelligent, just limited in its widely used default configuration. So the first ones to fully see the effect were the ones with many TCP connections, i.e. Bittorrent. The modern window size "tuning" schemes in Windows 7 and Linux break a lot of things -- you are just describing the tip of the iceberg here. The IETF working group LEDBAT (motivated by the Bittorrent observations) has been working on a scheme to run large transfers without triggering humungous buffer growth. Gruesse, Carsten
Current thread:
- RE: TCP congestion control and large router buffers, (continued)
- RE: TCP congestion control and large router buffers George Bonser (Dec 14)
- RE: TCP congestion control and large router buffers Mikael Abrahamsson (Dec 14)
- Re: TCP congestion control and large router buffers Joel Jaeggli (Dec 19)
- Re: TCP congestion control and large router buffers Jim Gettys (Dec 20)
- Re: TCP congestion control and large router buffers Mikael Abrahamsson (Dec 20)
- Re: TCP congestion control and large router buffers Sam Stickland (Dec 21)
- Re: TCP congestion control and large router buffers Fred Baker (Dec 21)
- Re: TCP congestion control and large router buffers Jim Gettys (Dec 22)
- Re: TCP congestion control and large router buffers Fred Baker (Dec 22)
- RE: TCP congestion control and large router buffers George Bonser (Dec 22)
- Re: TCP congestion control and large router buffers Carsten Bormann (Dec 23)