[VoiceOps] using a T1 to extend PRI service and involuntary fax over sip

[Peter R.]

You added two more points of interference - each side of the T1. That 
may have something to do with it.

It is likely that the SIP back-haul changed and it's not running G.729

On 1/24/2011 1:24 PM, Mark Kent wrote:
> I stumbled across a situation where a fax-to-email service gets
> inbound calls, from Carrier X, over a PRI into a cisco 5350 which then
> relays the calls, via an x-conn PRI, to a directly-attached linux box.
> This has worked for years.
>
> About a year ago, it was revealed that the above-mentioned PRI
> connects to the edge of Carrier X's SIP infrastructure.  That is,
> calls start from some PSTN-connected fax machine, somewhere in the
> USA, go through a PSTN-to-SIP gateway, travel as SIP to the building
> where this cisco 5350 is, and then go through Carrier X's SIP-to-TDM
> equipment for delivery over the PRI to the cisco 5350.
>
> This led to some concern, since we all know that fax over SIP can be
> problematic.   But everything was working, hundreds of faxes a day
> were pulsing through the system.
>
> Up until September the cisco 5350 was in the same building as Carrier
> X's TDM equipment.  In late September, a point-to-point, B8ZS/ESF T1
> was used to extend the in-building cross-connect between Carrier X
> and the cisco 5350.  The cisco 5350, and related servers, are now
> eight miles away (both endpoints in Manhattan, using VerizonBusiness
> for the T1, both endpoints "on-net", no ILEC involved).
>
> Since November, maybe half a percent of the faxes fail to work.
> They get a communication error at the start, at the modem negotiation.
> The T1 circuit is clean.
>
> Some people think that failures may not have been reported/noticed in
> October, but they occured nevertheless.  This would suggest that the
> previous set-up was a very delicately balanced system and the moving
> of the cisco5350 eight miles away, necessitating the use of a T1 to
> carry the PRI to the new location, may be the root cause of the
> failures.  Occam's razor reasoning supports this.
>
> The grassy knoll people believe that, in November, Carrier X started
> an effort to wring more out of their SIP network. Perhaps they started
> using different peers in various parts of the country.  Maybe their
> PSTN-to-SIP gateways were tuned to use less bandwidth.  When asked,
> Carrier X answered a different question, in a fashion similar to a
> politician.
>
> I'm wondering whether any experts here have an opinion to offer?
>
> Thanks,
> -mark
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