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Cell Relay Retreat>List Archive>month:1999-May> msg00045



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Re: CBR always 47 byte payload?

  • From: James Carlson <carlson@ironbridgenetworks.com>
  • Date: 16 May 1999 12:56:14 -0400
  • Organization: UltraNet Communications , an RCN Company http://www.ultranet.com/
  • X-Complaints-To: abuse@ultra.net
  • X-Ultra-Time: 16 May 1999 16:56:15 GMT


michael_silver@my-dejanews.com writes:
> Is the payload (data) of CBR cells always 47 bytes?

No.  The payload of CES is 47 octets (or fewer; if you're sending DS0s
over CES and you're trying to minimize delay, as mentioned in the ATMF
spec for CES).

CBR is just how you schedule your cells.  Running CES with CBR is just
one option.  You can also run AAL-5 with CBR scheduling if you wanted.

>  I know that it is
> for CES since you need that extra byte for a timestamp, but what if I
> just have data that I want to be prioritized higher than other data.

It's not *quite* priority that you're getting with CBR.  It's
determinism.  If you're not actually doing circuit emulation, you may
want GFR instead ...

-- 
James Carlson, Software Architect                   <carlson@ibnets.com>
IronBridge Networks / 55 Hayden Avenue   71.246W   Vox:  +1 781 372 8132
Lexington MA  02421-7996 / USA           42.423N   Fax:  +1 781 372 8090
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp