[Gllug] Bank Holiday Monday type question

[Chris Bell]

On Mon 30 May, Ian Norton wrote:
> 

> 
> atm cells are 53 bytes, 48 payload, 5 header ( gfc, vpi, vci, pt, clp, hec ).
> 
> some ISPs recomend dropping the MTU of your ppp connection a little so that its
> a multiple of 48 so as to not have wasted cells
> 
> afaik most adsl lines are setup with a 1500 byte mtu, for a max size datagram
> this means you will waste the last 36 bytes of every 32nd atm cell.
> 
> which can add up, it also adds to the overhead of re-assembly of your packet.
> 
> dont forget tho, that your ppp actually runs over AAL5 of the atm connection so
> you loose a few more bytes there ( 5 or so i think )
> 
> soo.
> 
> if my brain is working, you will get better efficiancy by setting your mtu to
> be about 1483 bytes (or maybe 1531).
> 
> See:-
> http://support.metronet.co.uk/adsl/general-opt.xhtml1
>  
   The advice from Demon/Thus is that BT upgraded their system some time
ago, so that is no longer relevant, just use 1500.

-- 
Chris Bell

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