Cell Relay Archive

[Paul Koning <pkoning@xedia.com>]

Walt Weber wrote:
> 
> I think you are asking:  If a connection uses 1.40 at an endpoint's transmit
> direction, will it always use 1.40 at the same endpoint's receive?
>...
> For SVC's I am pretty sure that the switch will allocate a VPI/VCI based on
> some algorithm like least-used, so it doesn't necessarily allocate the same
> in both directions.

That's incorrect.  Yes, the switch allocates the VPI/VCI (based on
whatever
algorithm it likes; LRU is fine but anything else is fine too, subject
only
to the VPI/VCI supported bit counts communicated in ILMI).  But the SAME
value is ALWAYS used for both directions -- for the simple reason that
the protocol only has a single field to communicate the chosen value...

Derek Becker wrote:
> ...
> Sorry for the verbosity, but in response to your question, no the forward
> and back VCs are not required to take the same path (VPI/VCI), although they
> may, depending on how UNI is implemented for your switch.

Again, incorrect.  The question was about PNNI, and in that case, the
call setup mechanism establishes both directions on the same route.
It is certainly possible to imagine a different NNI protocol that
wouldn't have that property, but such a protocol would not be PNNI...

	paul

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