SIP Trunks and Fax Machines 2

[WhosYourDiffie]

Good day everyone,

So we just signed up a customer for SIP trunks which also includes their fax machine. After we crossed them over, the fax machine started to become "flakey" in which some times the faxes will go through and sometimes they won't. They seem to be intermittent when it comes to sending AND receiving faxes.

Does anyone have any experience with fax machines on SIP trunks?

Thank you all!!

 

[iProfessor]

Hi Diffie

Fax works best using T38 Fax Protocol if your provider supports it else G711 is what you will have to use

 

[tlpeter]

Faxing should be burned down straight away.
It is an old and unsafe way of communication.
It will only get worse.

BAZINGA!

I'm not insane, my mother had me tested!

 

[mkoker]

SIP and Fax are hit or miss, they either work or they don't. In my experience its better to keep a pots line for fax if the price is right.

NTSDirect

 

[WhosYourDiffie]

@iProfessor: Yes! We have it set to G711. At this point we are hoping for the best.

@tlpeter: I honestly couldn't agree more. I'd be more inclined to sell the customer carrier pigeons!

@mkoker: I had a feeling it was going to be this way. A shake of the dice if you will.

 

[joe2938]

lots of carries still do not support t38 so good luck

 

[rdoubrava]

If the fax machine has the options
turn the speed to the lowest settings
turn off ECM

 

[kyle555]

Depending on who your carrier is, even if they support t38, they may or may not convert t38 to G711 everywhere in their network.

So, if you call another one of their customers on their SIP service and your media offer includes t38 and the far end's does as well, the carrier might just have you 'direct' in their network and not be in the way and let t38 fly.

If the carrier has SS7 trunks to another carrier, their media gateway that you'd send your audio to may support T38, so you'd be T38 to the carrier and the carrier would handle going 711 across their links to certain other carriers.

If the carrier has SIP trunks to another carrier, and your media offer includes t38 and 711 and the far end only supports 711, your carrier may not sit in the middle and convert your t38 to g711 - so if your WAN is suspect, you might not have the benefit of using t38 to get into your carrier's network to go 711 our of their network.

Tracing out the media offers in the SDP would tell you whether t38 is offered or not.
Tracing the RTP stream would tell you what kind of media type it actually is.
Just because our offers include, say, 711 and 729, nothing in the SIP signaling tells you which codec I selected - you said you're able to receive either, so looking at RTP packets would be the only way to know what media type was used.

 

[mforrence]

If the fax machine has the options
turn the speed to the lowest settings
turn off ECM

This is the best path to success from our experience

Mike Forrence

http://www.goteamvox.com

 

[MINet-Jared]

We've actually started using Adtran Total Access 904 (4 FXS) or 908 (8 FXS) depending on the customer needs for faxing. You can set each user (fxs port)
Adtran has been fed from a SIP trunk. It has greatly improved our fax completion rate (and therefore many less angry customer phone calls).


[pre]voice user 101
connect fxs 0/1
no cos
first-name "First"
last-name "Last Name"
password "1234"
caller-id-override external-number 1111111111
modem-passthrough
t38
t38 redundancy high-speed 3
t38 redundancy low-speed 2
t38 fallback-mode g711
t38 max-rate 9600
no nls
no echo-cancellation
[/pre]

 

[stownsend]

We've had nothing but issues with Faxing over SIP. We have a Fire Alarm with Similar Issues when it does its Calling back to the mothership. We ended up getting a Couple of VoIP 'POTS' lines form a Cable Modem carrier and then Jacked those two lines into the IPOffice System and the Fire Alarm and the Faxes/Fire Alarm use those Lines for Outgoing Calls.

Our SIP Provider has a FAX Receiving Service, though Its maybe 75% Functional. Anyone with sub par sending faxes cant get through.

I Tell all of the people that complain to Scan and Email.