Merit Network
Can't find what you're looking for? Search the Mail Archives.
  About Merit   Services   Network   Resources & Support   Network Research   News   Events   Home

Discussion Communities: Merit Network Email List Archives

North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: T1 Circuit actual throughput 1290Kbp

  • From: James Carlson
  • Date: Mon Jul 13 13:13:12 1998

> >(!)  The cell tax is about 10% -- the SAR expands user data from 48
> >bytes to 53 bytes, plus an additional amount of overhead for internal
> >fragmentation on the final cell (AAL-5), plus overhead for whatever
> >encapsulation mode is being used.
> 
> The cell tax is actually about 20%, based on the traces of the backbone IP
> traffic. Reason for this is the additional overhead imposed of partially =
> filled cells.

That's what I meant about internal fragmentation.  Depending on frame
size, it can be a non-trivial part of the overhead.  If we assume
null-VC encapsulation and 256 byte packets, this is 1 cell partially
filled (20 bytes average ((48-8)/2)) for every 5 full cells, or an
additional 9.7% overhead.  (Which matches up nicely with your
measurements.  ;-))

-- 
James Carlson, Consulting S/W Engineer  <carlson@ironbridgenetworks.com>
IronBridge Networks / 55 Hayden Avenue  71.246W    Vox:  +1 781 402 8032
Lexington MA  02421-7996 / USA          42.423N    Fax:  +1 781 402 8092
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp




Discussion Communities


About Merit | Services | Network | Resources & Support | Network Research
News | Events | Contact | Site Map | Merit Network Home


Merit Network, Inc.