Fax rate disable

[AT]

I am using a vg320 as an analog gateway to a SIP provider.  I am using fax pass-through.  Should I include fax rate disable command under dial-peer for best practices? I have seen it in some Cisco config examples, but read it will disable fax-passthrough.

AT

[Mohammed al Baqari]

Yes, to avoid any chance of triggering or negotiating T38 fax relay.

[AT]

This dial-peer is sending faxes to a SIP PSTN network.  Does "fax rate disable" disable the fax protocol pass-through in addition to fax relay?  Is fax-relay enabled by default on a vg320 even if you have pass-through configured globally?  You can enter both pass-through and fax rate disable under the same dial-peer.  So is pass-through invoked and fax relay disabled using the commands below?  

dial-peer voice 1999 voip
description  call to SIP provider
pattern 5712......
session protocol sipv2
session target ipv4:10.80.18.2:5060
early-offer forced
dtmf-relay rtp-nte
fax-relay ecm disable
fax rate disable
fax protocol pass-through g711ulaw
no vad

[Manish Gogna]

Hi AT,

As per the following link

http://www.cisco.com/c/en/us/support/docs/voice/fax-modem-over-ip/20227-faxrelay-tsguide.html#topic3-6

Disable Fax Relay and Change Codec for Passthrough

In the previous steps, you established that voice calls work, faxes work through PSTN, and all digital interfaces in the fax relay path are free from errors. This step determines whether faxes can go through with fax relay disabled. Under the VoIP/VoATM/VoFR dial-peers, enter this:

fax rate disable Command
vnt-3660-23(config)#voice-port 2/0:15 vnt-3660-23(config-voiceport)#no echo-cancel enable vnt-3660-23(config)#dial-p voice 3 vnt-3660-23(config-dial-peer)#fax rate disable vnt-3660-23(config-dial-peer)#codec g711ulaw vnt-3660-23(config-dial-peer)#no vad

Make sure these commands are entered on both gateways. These commands disable fax relay, disable echo cancellation, and force the call to use a high bandwidth codec without VAD. The router then samples the tones like a normal voice call, and, with the high bandwidth codec (G.711), the most precise sample possible is captured. The tone to be replayed on the other side will be as accurate as possible. The caveat to this step is that, since G.711 is a 64 kbps bandwidth codec, each call will consume up to 80 kbps (for VoIP) when additional transport protocol overhead is added.

If this test is positive, two things have been accomplished. First, if per call bandwidth consumption is not a major issue for the network, there is now a potential fax passthrough workaround for the fax relay problem. Second, and more significantly, if bandwidth consumption is an issue, the problem has been isolated to the fax relay software, and you should open a TAC case.

If this test fails, it is likely that whatever causes the fax calls to fail with fax relay also causes the failures with this test. What comes to mind first is that the network can have a large amount of jitter or packet loss.

HTH

Manish