issue with fax machine in H323 gateway.

[ciscoroyzhang]

                   Hi there,   recently we have deployed voice system in our Korea office, user experience problem to receiving fax in some fax machine. 

on H323 gateway, there are 4 fxs ports connected to 2 faxe machines. fax01 is working fine but fax02 can't send/receive fax. From deb ISDN q931, I can see both inboun call arrived to the gateway successfully, but when call forward to the fxs port, one fax receiving the call, another not.

I have compared the "deb isdn q931" resoult,  only diffference is that inbound fax to fax01 Bearer Cap is set to 9090A3 (3.1kHzAudio), while the inbound fax to fax02 Bearer Cap is set to 8090A3 (sech). under the voice port 0/0/0:15, bear-cap is set to speech.   my believe is this might cause the issue.

I tried to change bear-cap to 3.1audio and default bear-cap in voice port 0/0/0:15,  as well as FXS ports, not change. (correct me if I am wrong, but my understanding is these configuration mailnly affects the outbond call, rather than inbound call)   

Now my question is why the inbound fax to FAX01 is with bearer-cap SPEECH,  while to FAX02 is 3.1kHzAudio. is this controlled by TEL or I can manipulate via some command in gateway.

Router: cisco 2901

fxs card: VIC3-4FXS/DID

CUCM: 8.6, but no relevent here. 

DEB to FAX01 - working one:

Bearer Capability i = 0x9090A3

                Standard = CCITT

                Transfer Capability = 3.1kHz Audio

                Transfer Mode = Circuit

                Transfer Rate = 64 kbit/s

        Channel ID i = 0xA98387

dial-peer voice 100002 pots

description Sales Department FAX 7825759

huntstop

destination-pattern 7825759

clid network-number 7825759

port 0/1/2

Bearer Capability i = 0x9090A3
                Standard = CCITT
                Transfer Capability = 3.1kHz Audio
                Transfer Mode = Circuit
                Transfer Rate = 64 kbit/s
        Channel ID i = 0xA98387

DEB to FAX02 - not working one:

Bearer Capability i = 0x8090A3

                Standard = CCITT

                Transfer Capability = Speech

                Transfer Mode = Circuit

                Transfer Rate = 64 kbit/s

        Channel ID i = 0xA98386

                Exclusive, Channel 6 Bearer Capability i = 0x8090A3
                Standard = CCITT
                Transfer Capability = Speech 
                Transfer Mode = Circuit
                Transfer Rate = 64 kbit/s
        Channel ID i = 0xA98386
                Exclusive, Channel 6

Sample configuration for dial-peer to fxs port:

dial-peer voice 6715001 pots
description Sales Department FAX 6715001
huntstop
destination-pattern 6715001

clid network-number 6715001
port 0/1/2

Above same configuration used in Australia and other countries, no such issue so far.

many thanks Roy

[Jorge Armijo]

roy zhang

So, let me see if I'm getting all this clear:

PSTN---PRI---GW---FXS---FAX

Is the above flow correct? If so, we have a POTS-TO-POTS call, there won't be any FoIP, instead, a local hairpin from PRI to FXS with no VoIP signaling. 

There is a known issue with PVDM3 and POTS faxing:

voice service pots

fax rate disable

What happens is: PVDM3 does not support legacy cisco fax relay, and for certain POTS "fax calls" the router will try to use cisco fax relay and the DSP will drop the connection.

In addition, you can disable the local-bypass on POTS-TO-POTS calls on gateway:

voice-card x

no local-bypass

This will force the gateway to use a DSP resource and might help if the fax tones are getting distorted or something.

HTH

--
Jorge Armijo

Please remember to rate helpful responses and identify helpful or correct answers.

[ciscoroyzhang]

Hi Jorge,  thanks for the suggestion, I was aware of the issue with hairpin and tried the diable fax rate and problem persists. I have also tried the no local-bypass command today, still not work.  

But the interesting thing is I can make fax between two fax machines, which connected to the port 1 and 2 on same FXS card.  next thing I try to do is upgrade the IOS version. it was 150-1.M7 try to upgrade to the 151. what do you think? Roy

[Jean-Christophe Majchrzak]

Hello,

What is your IOS version ?

I'm currently working on a TAC case for 6 months regarding fax tones that are not processed well by PVDM3 DSP.

With the debug fax relay t30 all-level-1 you can see when the failure happens.

My problem is on CFR and MCF messages never transmitted / received, then leading to a No Good sending. It happens only with a few remote fax. Using an old legacy PBX, always successful.

All the IOS versions have this bug except 151-2.T4 which is the better. Still problems anyway, even with latest 15.3.2T(ED).

For example with 151-3.T4 you always have a CRC error, and not with 151-2.T4

000235: Jun 15 11:19:29.297 mest: 0/0/0:15 (12)  893002 fr-entered=10(ms)

    timestamp=893172 FR_BAD_CRC_LS_DATA 0x0 bytes

    timestamp=902622 fr-msg-det DIS

    timestamp=905112 fr-msg-tx DCS

    timestamp=910442 fr-msg-det CFR

    timestamp=923902 fr-msg-tx EOP

    timestamp=928132 fr-msg-tx EOP

    timestamp=932632 fr-msg-tx EOP

    timestamp=937132 fr-msg-tx DCN

000236: Jun 15 11:20:13.634 mest: 0/0/0:15 (12)  937342 fr-end-dcn

I know it's an old version but I've downgraded to make my faxes and T.38 fax server work better.

A bug is currently under investigation at development team but I don't have the reference.

JC,