I just had a long conversation with our Austrian PTT folks here on how the
switches they use (Nortel, Siemens) handle the sitution. The answer is short:
There seems to be no obvious way (for them..) to redirect a call to the
next PRI in a hunt group if a PRI isnt fully busy but all modems 'behind'
it are.
This is the problem (*they* say):
If a call reaches *the telco switch*, the switch *first* negotiates a
B-channel with the PM3 to allocate. If the PRI is full, fine - switch rolls
over to next PRI in hunt group since allocation fails, no problem here.
If the PRI is *not full*, the B-channel allocation succeeds. Only *after
the allocation*, the call setup message is presented on the D-Channel, with
the bearer capability (voice or 64k). And only now the Pm3 can tell wether
she can handle it (depending on all modems busy or not). Our PTT folk says
if the get a reject at this point that was it for the call - there's no way
to rollover to the next PRI - they say after b-channel allocation the call
is 'committed' to this PRI (in transactional speak). Not good.
I am not fully up to speed on q.931, allocation of channels and that, so I
might be wrong here. I looked through the portmaster-users archive at
dataman (great search engine!); the issue has come up several times, but I
did not see a decisive answer.
We would very much appreciate details on provisioning the hunt group in
such a case, and details on the D-channel messages so we can tell the telco
what will happen. Switch type, software level, all that helps.
So what do you guys recommend?
Having all boxes fully loaded if there are several boxes in a series?
-Michael Haberler
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====== ====== Michael Haberler MH182
=== ____ === EUnet Austria, Ltd.
=== / / / ___ ___ _/_ === Diefenbachg. 35
=== /---- / / / / /___/ / === 1150 Vienna, AUSTRIA
=== /____ /___/ / / /___ / === E-mail: M.Haberler@Austria.EU.net
===== ===== Phone: +43 (1) 89933 610
===== Connecting Europe since 1982 ===== Fax: +43 (1) 89933 533
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