Ascend Archive
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: (ASCEND) ATM MTU 64 KB ?

Matt Holdrege wrote:
> 
> At 12:50 PM 12/23/97 +0100, Tassilo Erlewein wrote:
> >Hi there,
> >
> >I heared about Cray bus-based ATM OC3 boards that allow
> >ATM MTU's up to 64 KB...
> >now I would like to ask you:
> >
> >Did you ever hear of plans, did you ever see a manual page
> >in NetStar/Ascend GigaRouter/GRF documentation which could be
> >interpreted in the direction of a non-standard big ATM MTU size
> >- say 64K Bytes - in order to make ATM-to-HIPPI transitions
> >in a Cray environment a happier affair?
> >(I know there is now a hint in the GRF manual saying only
> >ATM MTU's up to 9180 bytes are supported)
> 
> I believe the max size for a SONET frame is 9188 bytes. Are you sure you
> want to go higher?

Matt,
thanks for your answer

No I'm not. I had a discussion with a colleage about wether or not
64 KB ATM IP MTU is a common feature. In his opinion some Netstar 
people made him believe the GigaRouters could do such a thing -
two years ago or so. It even seems to be possible if you consider SDH. 
And RF1626 only recommends the 9180 bytes default ATM MTU.
But I never heard anything about ATM boards/routers supporting 
ATM MTU's higher than 9180 bytes. 
In fact we tried to set the GigaRouter's ATM OC3 to 64 KB MTU.
(this was some playing around with the SNMP vars...) 
We then saw up to 16 KB IP packets travelling unfragmented through
the GigaRouter (HiPPI to ATM), just before the GR's crashed ;-)
Now there is this hint in the manual saying ATM MTU over 
9180 bytes is not supported.

But this Cray ATM OC3 board can obviously do this thing. 
And it would be a nice option in a partially HiPPI-based environment 
in order to avoid HiPPI to ATM fragmentation. 
But again, I'm not sure I want to rely on a 64KB-option in 
the AAL5 standard if nobody (except Cray of course...) ever 
goes higher than 9180 bytes.

Tassilo Erlewein


-- 
Tassilo Erlewein
Computing Center University of Stuttgart
Communication Systems & BelWue Development          
Allmandring 30, D-70550 Stuttgart

tel ++49 711 685 5871
fax ++49 711 678 7626
e-mail: erlewein@rus.uni-stuttgart.de
++ Ascend Users Mailing List ++
To unsubscribe:	send unsubscribe to ascend-users-request@bungi.com
To get FAQ'd:	<http://www.nealis.net/ascend/faq>
Follow-Ups: References: