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Re: Network latency


On 2009-10-26, andrew bell <allenheath1@googlemail.com> wrote:

> I?ve gone back to the nc_master / slave tests and monitored
> the throughput when connecting a PC to one of the boxes
> running eCos. Initially everything looked fine until I insert
> a switch between the PC and eCos box.
>
> With any switch between the PC / eCos box, there is poor
> performance when doing an RX test (PC -> eCos box), which
> shows lots of out of order delivery / delayed ACK / fast
> rexmit, and the throughout graph looks like a saw tooth.

In my experience that's usually a sign of half/full duplex
mismatch between one of the PHYs and the Ethernet controller to
which it is attached.  It could also be due to a mismatch
between a PHY and the switch, but you've got to try pretty hard
to make that happen.  Can you try setting the switch ports to
various different duplicities?  Or try a half-duplex hub/switch
instead of a full-duplex switch?

> But hey, the PC?s running faster than the eCos box, so maybe
> this is to be expected.

Nope.

-- 
Grant



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