[e2e] Reacting to corruption based loss
perfgeek at mac.com
Wed Jun 29 20:03:14 PDT 2005
On Jun 28, 2005, at 11:35 PM, Cannara wrote:
> Now, if you were a network manager for a major corporation, would you
> rush to
> fix a physical problem that generated less than 1% errors, if your
> boss &
> users were complaining about mysterious slowdowns many times larger?
> wasn't even enough to trigger an alert on their management consoles.
> certainly be looking for bigger fish. Well, TCP's algorithms create a
> fish -- talk about Henny Penny. :]
> The files were transferred in many 34kB SMB blocks, which required
> like 23 server pkts per. The NT servers had a send window of about 6
> (uSoft later increased that to about 12). All interfaces were
> 100Mb/s, except
> the T3 and a couple of T1s, depending on path. RTT was about 70mS for
> Thankfully, the Sniffer traces also showed exactly what the TCPs at
> both ends
> were doing, despite Fast Retransmit, SACK, etc.: a) the typical,
> timeouts were knocking the heck out of throughput;
with a send window of only 6 packets, and a synchronous
request/response protocol like SMB (IIRC) it would seem that fast rtx
wouldn't have had much of a chance anyway
> b) the fact that transfers
> required many blocks of odd numbers of pkts meant the the Ack Timer at
> receiver was expiring on every block, waiting (~100mS) for the magical
> even-numbered last pkt in the block, which never came.
Why on earth should that have mattered unless perhaps the sending TCP
had a broken implementation of Nagle that was going segment by segment
rather than send by send?
Wisdom teeth are impacted, people are affected by the effects of events
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