Cell Relay Archive

[James Carlson <carlson@ironbridgenetworks.com>]

Rohit Gupta <rogupta@hss.hns.com> writes:
> In that case why does the ATM Forum or ITU-T put this line in first para of the
> AAL1 specs
> 
> "transfer of service data units with a constant source bit rate and the delivery of them
> with the same bit rate"

Because that's what the retiming information in the one octet header
of AAL-1 gives you.  You need that to forward the clocking information
from one end of the pipe to the other.  (The assumption here being
that if you're doing AAL-1, then you're doing it in order to carry
PDH-like circuits over ATM.)

CES assumes a CBR-like service underneath in order to limit the delay
variance enough that a single octet timestamp is sufficient to handle
jitter values.  That doesn't mean you can't use CBR cell scheduling
for other things.

(Theoretically, at least, you could also transfer CES data over a
non-CBR service, as long as the ordering properties and buffering were
sufficient to cover any latency variance.)

-- 
James Carlson, Software Architect                   <carlson@ibnets.com>
IronBridge Networks / 55 Hayden Avenue   71.246W   Vox:  +1 781 372 8132
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