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Re: Split flows across Domains
From: "Matt Buford" <matt () overloaded net>
Date: Tue, 24 Jan 2006 14:17:04 -0500


On Tue, 24 Jan 2006, Christopher L. Morrow wrote:

that was my thought... and yes, it could get ugly for tcp services. Why
would you knowningly induce this complication?

When you want single flows to go faster than a single member link? (not that I am saying this is a good idea)

Actually, TCP handles out of order packets rather well as long as the reordering isn't too severe. You see a bunch of SACKs flying around, but as long as it doesn't get too out of hand it doesn't affect throughput.

It is the non-TCP protocols that often suffer. Many of them implement sequence numbers and simply drop out of order packets. From my own experience, RealPlayer UDP streams and PPTP are two examples that fail (or at least feel like 50% packetloss) under heavy reodering, where TCP continues to work reasonably well.

Years ago, I had ISDN and IDSL between home and the ISP I worked at, and out of curiosity I experimented with per-packet load balancing across these links. Reordering was rather severe, as these links had slow uneven speeds, and uneven latencies. TCP transfers got about 192kbit (75% total link capacity, 1.5 times single link capacity), but things like RealPlayer and PPTP VPNs were downright unusable.

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