We have many users dialing into a TNT running TAOS 9.1.8.  Some of these
are 2-channel ISDN users, often using Cisco 802s/SOHO71/SOHO91 routers to
access our network.  Lately, we've been experiencing an issue where users
may experience roughly 50% packet loss after one of their B channels
drops.

What I've noticed is that in cases where the remote router shows that one
of the B channels has dropped, the TNT still reports a call up at 112k or
128k, if the user uses 56 or 64k B channels respectively.  If I kick user
session where I see the packet loss, the user normally immediately
re-establishes the connection and runs fine (no packet loss) for a
seemingly random length of time before the same thing happens again.  I
understand why users would be having 50% packet loss in these cases, but
not why the second B channel isn't dropping.

We're not doing any dial-out or callback so each call must be initiated by
the customer premise gear.

It seems like it is some type of low-level signaling compatibility or call
setup/teardown issue between the TNT and the Ciscos in the field.

I see a continual handful of failed/suspect modems on the box, but they
are all in an ENABLE state, so I'm guessing the TNT was able to reset
those modems successfully.  The modems are not in one specific card, and I
don't have any modem cards in a fault state.

All of our PRIs are ISDN-NFAS, using NI2 signaling, which matches what the
telco provisioned.  We had a similar problem a few weeks ago, but founf
that some of the T1s were not set for the correct switch type on our side.

We've made no major configuration changes on our TNT, or the customer's
endpoint routers in the past several weeks.

Has anyone run into this issue?  Is there any debugging or further
troubleshooting I can do from the TNT that may help pinpoint this issue?

jms

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