Optimal MTU for 21CN

Our exchange has just been upgraded to 21CN and we've moved onto ADSL2+

We're on a long line (3KM+) and I'm looking to squeeze every last drop out of it, current MTU is set to 1492 (router default)

Is this OK, or is there a more optimal setting?

Thanks

Andy

Usually 1500 but measure it yourself by following "Working out your maximum MTU" on http://www.kitz.co.uk/adsl/MTU2.htm , but 1st set router to MTU=1500 (to allow it full range).

Interesting. I created a batchfile to ping all mtus from 1472 to 576 and output to file. At the 1472 end it was 60ms / 59ms and it gradually decreased to 39ms at the 576 range. However, I'm getting 26ms with a standard ping...

Can i ask what exchange your on?

1492 is usually a good number to use

A standard ping packet is usually much smaller than 576 bytes - IIRC either 40 or 54 bytes on windows.

Assuming an upstream speed of approx 400kbit/s it takes (40*8)/400000 = 0.0008s (0.8ms) to transmit a 40 byte packet up your DSL line. At 576 bytes this will take 11.5ms . Lather, rince, repeat. Hence seeing your pings take longer the bigger they are

On mine the sized PINGs takes from 24 ms at top end to 15 ms at bottom.

That's the diff between our Interleaved/Fastpath I pointed out elsewhere.

Standard ping is far faster, 11 ms, cuz it only sends 32 bytes.

In reply to a post by XRaySpeX:

On mine the sized PINGs takes from 24 ms at top end to 15 ms at bottom.

That's the diff between our Interleaved/Fastpath I pointed out elsewhere.

Standard ping is far faster, 11 ms, cuz it only sends 32 bytes.

See the reply in the other thread. Fastpath.

Our exchange is Stonehouse (SSSHE)