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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: T1 Circuit actual throughput 1290Kbp
> >(!) 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 <[email protected]> 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
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