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Re: [RRG] Why delaying initial packets matters
On 2008-2-11, at 9:36, ext Stig Venaas wrote:
I can see at least 3 possible theoretical effects of delaying the
1. First packet is delayed, packets are kept in order
2. First packet is delayed, subsequent packets may arrive first
3. All initial packets dropped
Well, this is still more or less speculation. I suppose what
should be done, is to study some common applications or
protocols and see what the effects would be. An obvious first
candidate would be DNS I think.
Exactly right. I've said this a few times in the past; data on how
these different behaviors affect applications and transport protocols
are essential before we can determine what's acceptable.
Although UDP-based apps (e.g., RTP) are important, what will happen
depends a lot on the individual application. Initially, it would be
easier to investigate how TCP/SCTP/DCCP react when 1, 2 or 3 happens,
because their behavior is more tightly specified.
For example, for TCP, I'd expect that in case 1, the initially sampled
RTT would be too high, causing a slower slow-start, in case 2, there'd
be a few 500msec timeouts during the first few roundtrips due to the
reorderings appearing as losses, and for 3, a 3-second timeout will
kick in before the SYN will be retransmitted. But that's just a guess
- I haven't measured/simulated anything, either.
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