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

[Beth Johnson]

All "Chuckles" aside, it doesn't matter if you wield the razor or the magic
bullet on this one.  Open tickets with everybody, blame everything in sight,
and one of those efforts will pay off.



-B



On Mon, Jan 24, 2011 at 1:46 PM, Beth Johnson <bethjohnson5060 at gmail.com>wrote:

> "A year ago", "September", "November"... looks like there is no solid time
> domain event correlation to be had.
>
>  What would Chuck Norris do?  Bash in everyone's head at the same time,
> knowing that one of them must be the bad guy.
>
> -B
>
>
>
>
>
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> On Mon, Jan 24, 2011 at 10:24 AM, Mark Kent <mark at noc.mainstreet.net>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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>
>
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