General Fax over SIP inquiry 1

[avayastrongman79]

Hi all, we have a customer on newly installed Aura CM7, with R7 session managers and Avaya SBC-E. Inbound calls, voice quality all working well. Around 1400 endpoints, mixed environment of H.323 stations and analogs. As an Avaya BP, we've never deployed a non-fax server solution across SIP trunking. We typically retain a PRI and then partition those faxes/modems over the PRI.

My question is if there's anybody on this forum that has deployed fax over SIP in the range of 35-40 devices? I'm just looking for similar case and any experience or feedback. Its just basically sending fax over SIP trunks, and terminating it to tdm fax machine. This customer is adamant to get it working, and there seems to be a substantial failure rate over SIP vs PRI in my limited test environment thus far.

Utilizing g.711u, packet size 20ms and fax set to relay on the ip-codec form.

Thanks in advance for any input.

 

[kyle555]

Depending on the faxes, their modem speed and network stuff, it'd be a lot more sensitive than regular voice.

use t38 if you can, and then the dsps would do the heavy lifting for you and not rely on absolute screechy modem perfection across the whole network.
Still, if you run into carriers that don't do t38, it'll get touchy.

Maybe you could try something like t38 from your environment to your core, relay from your core to the sip trunks so it's only sensitive modem stuff as little as possible. The network regions seem to let you set it up, though I've never tried using G450 DSPs like that where say your core gateways are NR1, SIP trunks 222 and branch is 10 and everything's direct to NR1, but 10-->222 is thru intervening region 1 and the codec sets are setup for t.38 from 10-->1 but relay from 1-->222

Might work?

 

[avayastrongman79]

Thanks kyle555, I will change the ip codec set in my test NR to t.38, the carrier did say they supported t.38-g711 fallback. Customer also stated that they have very old fax machines, so t.38 may be the route needed. I follow you on the t.38 to core and then relay out after that. I may try and see if I can set that up in test scenario, not sure yet. I appreciate your feedback.

 

[kyle555]

hey, older faxes are better. Easier to get 9600baud than 56kbps!

Even if your carrier does t38, if your carrier gets to verizon over SIP trunks and verizon's media gateways don't do t38, you'll be old modem in the PSTN - which isn't necessarily an issue. If you can be certain you're t38 only into your core and only t38-g711fallback out the core to the carrier, at least you'll have nailed up your end as best you can.

 

[jimbojimbo]

Also significantly impacted by type of cabinet/gateway, DSP resource, and CM version. G4x0 with DSP 160 supports T.38 with Error Correction Mode (ECM). TN2302/TN2602 do not. Analog port on G4x0 gateway is your best bet.

 

[avayastrongman79]

We're utilizing g450s w/MP160s for DSP. I appreciate your responses, I'll post some feedback after we complete the testing with some of the suggested settings from the thread.

 

[kyle555]

Once upon a time before I got into telecom I answered customer service for fax machines. Got some funny stories about it. One thing I remember is going into the service menu of those faxes and turning off error correction mode. I don't know how it works, but it feels like something to do with reliable transport and restarting if something isn't perfect. It's easier to get a page with some blemishes of uncorrected errors than to get a picture perfect page that is made up only of data confirmed to have been reliably transported. UDP vs TCP for faxing I guess. All to say, ECM off has helped me at some point in my life

 

[rejackson]

Fax and modem are not the same thing. That is why there is field for each in the codec. Use T.38 fax (fallback to G3 using G711 is the default) and you must turn OFF modem on the codec. Basically you have to choose between faxing and using modems on the codec configuration. Having modem enabled makes the fallback to g711 and G3 faxing very iffy and causes the problems because it has trouble distinguishing between modem and fax during the fallback. It is very reliable for us since we turned off the modem support in the codec.

REJ