T38 Fax-Relay SIP to MGCP not working

Unanswered Question
Sep 25th, 2008

Dear All,

We have a setup like this:

CUCM6 --> SIP Trunk --> CUBE --> SIP Trunk --> SIP SP

We have a fax machine attached to an MGCP gateway that is trying to send/receive a T38 fax-relay fax across this infrastructure.

The call setup proceeds and connects but the fax is never transmitted/received. A debug of CCSIP messages reports "488 NOT ACCEPTABLE MEDIA".

Here are the configs:-

MGCP Gateway Config (fax machine attached here)

ccm-manager fallback-mgcp

ccm-manager redundant-host x.x.x.x

ccm-manager mgcp

ccm-manager music-on-hold

ccm-manager config server x.x.x.x

ccm-manager config

!

mgcp

mgcp call-agent x.x.x.x 2427 service-type mgcp version 0.1

mgcp dtmf-relay voip codec all mode nse

mgcp rtp unreachable timeout 1000 action notify

mgcp modem passthrough voip mode nse

mgcp package-capability rtp-package

mgcp package-capability sst-package

mgcp package-capability pre-package

no mgcp package-capability res-package

no mgcp package-capability fxr-package

no mgcp timer receive-rtcp

mgcp sdp simple

mgcp fax rate 9600

mgcp rtp payload-type g726r16 static

mgcp bind control source-interface Vlan2

mgcp bind media source-interface Vlan2

mgcp rtp payload-type nse 101

mgcp rtp payload-type nte 100

!

SIP Config on CUBE:

voice service voip

address-hiding

allow-connections sip to sip

redirect ip2ip

fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw

sip

bind control source-interface GigabitEthernet0/0

bind media source-interface GigabitEthernet0/0

early-offer forced

midcall-signaling passthru

g729 annexb-all

dial-peer voice 200 voip

description ** outgoing call to CUCM **

destination-pattern 44T

rtp payload-type cisco-fax-relay 101

rtp payload-type nse 99

rtp payload-type nte 100

modem passthrough nse codec g711ulaw

session protocol sipv2

session target ipv4:x.x.x.x

dtmf-relay rtp-nte

codec transparent

fax-relay sg3-to-g3

fax rate 9600

fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw

!

dial-peer voice 300 voip

description ** incoming dial peer **

rtp payload-type cisco-fax-relay 101

rtp payload-type nse 99

rtp payload-type nte 100

modem passthrough nse codec g711ulaw

session protocol sipv2

incoming called-number .

dtmf-relay rtp-nte

codec g711ulaw

fax-relay sg3-to-g3

fax rate 9600

fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw

!

dial-peer voice 400 voip

description ** outgoing call to SIP SP **

destination-pattern 9T

rtp payload-type cisco-fax-relay 101

rtp payload-type nse 99

rtp payload-type nte 100

modem passthrough nse codec g711ulaw

session protocol sipv2

session target ipv4:x.x.x.x

dtmf-relay rtp-nte

codec transparent

fax-relay sg3-to-g3

fax rate 9600

fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw

My SIP SP tells me that I am not sending a RE-INVITE to his messages and this is why its failing.

Can anyone provide some more help?

Thanks,

I have this problem too.
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hadbou Wed, 10/01/2008 - 05:47

Some MGCP call agents do not properly pass those portions of Session Description Protocol (SDP) messages that advertise T.38 and NSE capabilities. As a result, gateways that are controlled by these call agents are unable to use NSEs to signal T.38 fax relay to other gateways that use NSEs. As of Cisco IOS Release 12.2(13)T, you can configure gateways to use T.38 fax relay and NSEs even though those gateways may be unable to negotiate those attributes by themselves at the time of call setup.The mgcp fax t38 gateway force command provides a way to ensure gateway-controlled T.38 fax relay between an MGCP gateway and another gateway. The other gateway in the negotiation can be an H.323, Session Initiation Protocol (SIP), or MGCP gateway. Both gateways must be configured to use NSEs to signal T.38 fax relay mode switchover. On H.323 and SIP gateways, use the fax protocol t38 nse force command to specify the use of NSEs for T.38 fax relay. On MGCP gateways, use the mgcp fax t38 gateway force command.

csg-admin Fri, 10/03/2008 - 01:49

Thanks I had tried that but no joy.

My SIP SP says that he supports T38 according to RFC4612 and RFC3363. He does not support fax switchover using NSE.

Has anyone had any luck in getting T38 over SIP to work? Thanks.

csg-admin Tue, 11/11/2008 - 07:35

For those who may be interested I finally managed to get t38 fax from MGCP to SIP working.

Firstly, it seems that super g3 does not like operating at super g3 speeds across SIP, therefore I had to ensure that any super g3 fax machine operated at g3 speeds. In mgcp the command is mgcp fax-relay sg3-to-g3 and in sip it is fax-relay sg3-to-g3 under the dial peer or in global config.

Secondly my SIP SP does not support nse for the switchover from a voice call to a t38 fax call. NTE's are supported and a debug of ccsip messages shows that my provider uses a payload value of 101.

So, with this information I was able to add the following commands to my mgcp gateway:-

MGCP Gateway

============

no mgcp fax t38 inhibit

mgcp package-capability fxr-package

mgcp default-package fxr-package

mgcp fax rate 9600

mgcp rtp payload-type nte 101

and these commands to my SIP gateway:-

SIP Gateway

===========

voice service voip

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

fax-relay sg3-to-g3

Regards,

Nicholas Matthews Fri, 02/27/2009 - 21:20

Hi Vince,

This will be heavily dependent on your SIP provider's fax support. Many providers do not support T38, etc.

You can try this configuration on the VG224 and on the cube (providing that you remove all other configuration):

voice service voip

fax protocol pass-through g711ulaw

hth,

nick

gsidhu Sun, 11/13/2011 - 06:54

Hi Nicolas,

I understand that Cisco Fax passthrough solution support NSE (Cisco proprietary).

What are the options if the remote gateway is non-Cisco and G729 is used for voice calls?

Is there an industry standard for Fax passthrough that uses NTE for interoperability?

Thanks

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