Re: Dialup congestion and winter weather (fwd)

[Jeff Mcadams <jeffm () iglou com>]

Also sprach Mark Milhollan
> Jeff Mcadams writes:
> > its been our experience that once all of the channels on all of the
> > available PRI to the ISP are in use, the telco will generate an all
> > circuits busy type of response as the PRI are trunk-side, so the
> > switches typically treat them as inter-switch trunks being filled, not
> > end lines to the ISP being full.

> As always YMMV.  The result is affected to a great extent by
> provisioning.  Which is obvious and yet hasn't been mentioned.

I'll buy "YMMV", but I've never run into this situation, and I'm a bit
skeptical.

> One way causes a call setup request to be sent even though the switch
> knows that there are no available B channels, which permits the
> terminal to make it's own decision as to the disposition of the call,
> e.g., refuse it with cause code 17 which _should_ cause some switch in
> the call path (the originating one usually) to generate a normal busy
> tone.

OK...so...if I have 20 PRI spread across 10 pieces of RAS equipment, and
thus, consequently at least 10 D channels (more likely 20 since NFAS is
a pain to manage IMO), which D channel is the setup request sent to?

My understanding is that the switch will typically find a B channel
that's unused, and send the setup request down the corresponding D
channel.  If no B channels are unused, then the switch would have no way
of knowing which D channel to pick to send the setup request.

I certainly won't say that there aren't provisioning setups that would
do this correctly, but it would be beyond my knowledge as to how that
would be set up, that's for sure.

Now, if you're using SS7, or SIP or something like that...all bets are
off, I've never worked with them, so have no knowledge of how they work.
-- 
Jeff McAdams                            Email: jeffm () iglou com
Head Network Administrator              Voice: (502) 966-3848
IgLou Internet Services                        (800) 436-4456