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Standard User youngtaff
(newbie) Tue 06-Mar-12 11:18:25
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Optimal MTU for 21CN


[link to this post]
 
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
Standard User XRaySpeX
(eat-sleep-adslguide) Tue 06-Mar-12 11:43:32
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Re: Optimal MTU for 21CN


[re: youngtaff] [link to this post]
 
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).

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC
Standard User camieabz
(sensei) Tue 06-Mar-12 12:36:02
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Re: Optimal MTU for 21CN


[re: XRaySpeX] [link to this post]
 
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...confused

~~~~~~~~~~


© Camieabz 2002-2012

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Scottish Labour politician: “The SNP are on a very dangerous tack. What they are doing is trying to build up a situation in Scotland where the services are manifestly better than south of the border in a number of areas.”

Interviewer: ”Is that a bad thing?”

Scottish Labour politician: “No, but they are doing it deliberately.”


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Standard User Seansmit17
(eat-sleep-adslguide) Tue 06-Mar-12 12:54:21
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Re: Optimal MTU for 21CN


[re: youngtaff] [link to this post]
 
Can i ask what exchange your on?

1492 is usually a good number to use

BT 8MB
Standard User ionic
(fountain of knowledge) Tue 06-Mar-12 13:07:37
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Re: Optimal MTU for 21CN


[re: camieabz] [link to this post]
 
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
Standard User XRaySpeX
(eat-sleep-adslguide) Tue 06-Mar-12 13:33:02
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Re: Optimal MTU for 21CN


[re: camieabz] [link to this post]
 
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.

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC
Standard User camieabz
(sensei) Tue 06-Mar-12 13:52:50
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Re: Optimal MTU for 21CN


[re: XRaySpeX] [link to this post]
 
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.

~~~~~~~~~~


© Camieabz 2002-2012

All Connection Data ~ plusnet

Scottish Labour politician: “The SNP are on a very dangerous tack. What they are doing is trying to build up a situation in Scotland where the services are manifestly better than south of the border in a number of areas.”

Interviewer: ”Is that a bad thing?”

Scottish Labour politician: “No, but they are doing it deliberately.”
Standard User youngtaff
(newbie) Tue 06-Mar-12 15:50:27
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Re: Optimal MTU for 21CN


[re: Seansmit17] [link to this post]
 
Our exchange is Stonehouse (SSSHE)
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