VG224 Analog Voice Gateway - Fax issue g711a

[cisco.xenpak3]

Hello,

we do have Cisco VG224 Analog Voice Gateway where there are some FAX machines connected.

Now there is the issue, that with the old analog line, the Fax transmission to frequently use numbers seem to be more unstable.

It looks that with the old analog system the Fax transmission where much more stable than now with the Cisco AVG.

Maybe there are some settings, that allow to use a higher current or a stronger signal from the AVG to the FAX or other means to get a stable transmission.

We already have set all the Faxes to the recomended speed 9600, NO ECM, NO Compression.

This was only helping a little bit.

Regards

Chris

[Steven Griffin]

Chris,

I am not sure I completely understand your issue.  The gist of it seems to be unreliable fax transmission.  In that case, would recommend utilizing T.38 fax relay instead of G.711 pass-through.  You'll get much better results.

-Steven

[cisco.xenpak3]

Hi Steven,

yes, we where looking into that direction. But T.38 also need to be supported by the provider.

So that option is not possible to go that way.

Just wonder why some fax transmissions are better than others.

There are some numbers that work better than others.

Regards

Chris

[tonyperla]

In addition to what Steven stated,  Depending on you gateway setup (I.E. H.323),  I would also make sure that your network clocking is setup correctly as well.  This will cause multiple issues.

[cisco.xenpak3]

Hi Tony,

how to check that ? where can I verify that ?

Regards

Chris

[Les Pruden]

Hi Chris -

To follow up on Tony's comments.  I would agree with setting these VG-224's for T.38 is your best bet.  Unless you are using SIP from your service provider the T.38 configuration would affect how your fax traffic passes over PRI or POTS circuits. 

Set your IOS to use T.38 with the VG-224 configured as MGCP.  We have a couple hundred VG-224's deployed across our hospital network with this configuration (for fax machines and patient roon phones) and we do not have any faxing issues.  you can also set the voice port in IOS to support long lines which might help you if your VG-224 is a fair distance from the fax machine.  Below is a configuration that works for us as many VG's are in the basement of a multi-story hospital and we had long cable line issues

For Example:

------- Sample T.38 configuration for VG-224 and Ingress / Egress gateway

voice service voip

fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback none

modem passthrough nse codec g711ulaw

------ MGCP Config for VG-224

mgcp

mgcp call-agent 10.X.X.X 2427 service-type mgcp version 0.1

mgcp dtmf-relay voip codec all mode out-of-band

mgcp rtp unreachable timeout 1000 action notify

mgcp modem passthrough voip mode nse

mgcp package-capability rtp-package

mgcp package-capability sst-package

mgcp default-package mt-package

no mgcp package-capability res-package

no mgcp timer receive-rtcp

mgcp sdp simple

no mgcp fax-relay sg3-to-g3

mgcp rtp payload-type g726r16 static

mgcp bind control source-interface FastEthernet0/0

mgcp bind media source-interface FastEthernet0/0

!

mgcp profile default

----  VG-224 port config:

voice-port 2/19

input gain -3

output attenuation 3

timeouts interdigit 18

timeouts ringing infinity

Configure the VG-224 as MGCP in CUCM including T.38 and MT package enabled.

When configured and running verify the MCGP configuration in IOS.  Also, when testing a fax between the VG-224 and your ingress / egress gateway you should see the port switch to T.38 when running a show voice call status  or show voice port summary.  If you do not see the call swtiching to T.38 you have missed something in your design.

Regards,

Les