Make fax work with SPA112 with asterisk over a VPN

[jorgebastos]

Hi,

I have a SPA112, for FXS for fax machine, that work's well, if it's on the local LAN, have a few setup's like this and no problems at all, just using g.711a, perfect.

Now I have a new scenario:

(VPN connection)

Side A (192.168.2.0) and Side B (192.168.1.0)

Asterisk server (with ISDN connection) on Side A with: 192.168.2.239

SPA112 on side B with: 192.168.1.12

Since this is VPN, sip extension in asterisk is configured with nat=route, so that the audio works onm both directions 'cause of the RTP ports (same for normal sip extensions).

But when I call the fax using the outside number (234377377 for example, it's routed from asterisk on 192.168.2.239 to SPA112 on 192.168.1.12, and, with echo canceller enabled on the SPA112, i hear echo, for example when i talk.

When trying to send a fax from the side B, in the fax machine that will use SPA112 (192.168.1.12=>192.168.2.239 via VPN), fax's never work!

Is there a different or sensitive configuration for this VPN configuration?

the VPN connection has high priority for SIP and RTP ports, and about 512kb reserved, so i don't thing it's a bandwidth problem.

Thanks in advanced,

Jorge Bastos,

[chrebert]

Hello Jorge,

There is a section in the admin guide called Optimizing Fax Completion Rates that goes over a few settings to change to make VOIP work a bit better with faxing.

The guide is available here:

http://www.cisco.com/en/US/docs/voice_ip_comm/csbpvga/spa100-200/admin_guide/SPA100_AG_OL-25117.pdf

And the section is called Optimizing Fax Completion Rates under Configuring Voice on page 40.

For echo cancelation it is recommended you disable it for faxing, as well as a few other tweaks.

Give those settings a try and see if you can get a fax over your VPN.

Christopher Ebert

Network Support Engineer - Cisco Small Business Support Center

*Please rate helpful answers*

[jorgebastos]

Hi Chris,

Going to give it a try.

Tell me, other thing that happens is this, and I don't know if this is making any difference, at least on local LAN doesn't.

[2013-02-17 11:51:40] NOTICE[15506]: res_rtp_asterisk.c:2358 ast_rtp_read: Unknown RTP codec 100 received from '192.168.1.12:16438'

This "100" corresponds to which codec?

[Tom Watts]

Just to add to Chris' post a bit. Codec 100 is usually related to T.38 error with an incorrect mapping to the Asterisk. So are you using T.38 fax or trying to use g7.11?

On the rtp.c file is a codec list. You can clone over whatever setting you want to 100 to void that error.

If you're using T.38 you need to make sure you have the t.38 passthrough configuration set on sip.confg and also the udptl.conf.

T.38 in general does not work with Asterisk unless you are running 1.2.4.

-Tom
Please mark answered for helpful posts

[jorgebastos]

Tom,

No T.38 either on SPA112 or asterisk.

My asterisk version is 10.10.0, are you saying rtp.c from asterisk sources or SPA112 firmware?

SPA112 has latest firmware, 1.3.1

[jorgebastos]

Howdy,

The recomendations on:

http://www.cisco.com/en/US/docs/voice_ip_comm/csbpvga/spa100-200/admin_guide/SPA100_AG_OL-25117.pdf

Didn't worked

Any more ideias?

Since this is behind a VPN, There's no need to special configuration for the SPA112 due to the RTP ports?

The SIP extension in asterisk is configured with nat=route, just like other SIP extensions that are on this VPN side, to make audio work on both sides.

One extra info is, I answered the call to see the quality of the audio, and there's alot of noise in the connection, is there something to to tune to solve this noise problem? This is strange 'cause on local LAN I don't have noise, may be this that is causing fax transmission to fail.

Please help me, I'm about 3 weeks to make this work, and havent got it working.

Please answer ASAP, i have two more places to configure with this SPA112,

[jorgebastos]

Hi Chris/Tom,

I'm sorry, but I do really need to get this working.

Since this is a Cisco device, I need to have own Cisco support to solve this!

[jorgebastos]

Hi,

Chris,

You as Cisco support, you'd like to have this working, since I buyed this hardware.

Please make it ASAP.

Jorge,