T38 issue with MTP enabled on H323 Gw CUCM6.0.1

Unanswered Question
Sep 12th, 2008

On CUCM6.0.1 we use mobileconnect with access to midcall features like transfer.To do that we have to validate the "MTP Required" option on the gateway. This is our H323 PRI PSTN gateway (3825) through which outgoing calls to mobiles go and through which we access mobileconnect DID number. But this gateway support also incomming and ougoing fax calls to and from a H323 VG224. When MTP is not validate, all fax calls are T38 (14400) and work very well, when MTP is validate all fax calls fall back to Cisco Fax-relay mode and fail very often. Why is t38 imcompatible with MTP?

I have this problem too.
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Michael Owuor Fri, 09/12/2008 - 07:19

Hi Guy,

If the MTP being invoked here is a software MTP, that might explain why the T.38 calls are failing. Software MTP does not support T.38 fax. Try invoking a hardware based MTP resource such as the SVC-CMM-ACT module in Cat6K or the 6608.

Hope this helps.

Regards,

Michael.

guy.richard Fri, 09/12/2008 - 09:04

Hi Michael

Thanks a lot for your answer. I thought about software MTP and T38 but could not find any reading on it. Do you think a Hardware MTP on my 3825 (PVDM2) will fix the issue ?

Regards

Guy

Michael Owuor Fri, 09/12/2008 - 09:55

Hi Guy,

I believe it will. Here's the output of the capabilities on of the MTP/Transcoders on my 2821 using the PVDM2's. Notice it includes support for passthrough.

BR2(config)#dspfarm profile 800 mtp

BR2(config-dspfarm-profile)#codec ?

g711alaw G.711 A Law 64000 bps

g711ulaw G.711 u Law 64000 bps

g722-64 G722r64

g729abr8 G.729ab 8000 bps

g729ar8 G.729a 8000 bps

g729br8 G.729b 8000 bps

g729r8 G.729 8000 bps

ilbc ILBC codec

pass-through Stream Pass Through

!

BR2(config)#dspfarm profile 801 transc

BR2(config-dspfarm-profile)#codec ?

g711alaw G.711 A Law 64000 bps

g711ulaw G.711 u Law 64000 bps

g722-64 G722r64

g723r53 G.723.1 5300 bps

g723r63 G.723.1 6300 bps

g729abr8 G.729ab 8000 bps

g729ar8 G.729a 8000 bps

g729br8 G.729b 8000 bps

g729r8 G.729 8000 bps

gsmamr-nb GSMAMR codec

ilbc ILBC codec

pass-through Stream Pass Through

Hope this helps.

Regards,

Michael.

guy.richard Fri, 09/12/2008 - 22:53

Thanks a lot,

I'll try this next monday and write you back the result. Have a good week-end

Kind Regards

Guy

guy.richard Wed, 09/17/2008 - 05:19

Hi Michael

This night I've upgraded my 3825 to ipvoice 12.4-20T to have "sccp ccm 172.17.1.1 identifier 1 version 6.0+" availiable in the gateway config.

I tried software and hardware in the dspfarm profile. This the only one MTP the gateway can require through its MRGL / MRG.

As soon as I validate "MTP require" in the CUCM gateway config, I have no more fax.

Why can I put only one codec in the profile ? I tried G711Alaw and G711uLaw

Regards

Guy

sccp local BVI100

sccp ccm 172.17.1.1 identifier 1 version 6.0

!

sccp ccm group 1

associate ccm 1 priority 1

!

associate profile 10 register XCOD_3825-1_NY

associate profile 20 register CFB_3825-1_NY

associate profile 30 register MTP_3825-1_NY

!

dspfarm profile 30 mtp

codec g711ulaw

maximum sessions software 100

associate application SCCP

Michael Owuor Wed, 09/17/2008 - 06:45

Hi Guy,

On the dspfarm profile, add codec passthrough, so that the configuration looks as follows:

!

dspfarm profile 30 mtp

codec g711ulaw

codec pass-through

maximum sessions software 100

associate application SCCP

!

Reset the MTP with 'no sccp' followed by 'sccp', then verify that it is registered with CallManager by looking at the output of 'show sccp' and the configuration page in CallManager.

In CallManager verify that the MRGL, and MRG configuration provides access to this MTP resource.

When testing, please gather the output of 'debug h225 asn1' and 'debug h245 asn1'.

Regards,

Michael.

guy.richard Wed, 09/17/2008 - 09:44

Hi Michael,

I think you are right. I am not at my customer but I have tested it on my lab with an AudioCodes MP112 -> CUCM6 -> Gw2811 in H323

Without codec passthrought in MTP profile, fax goes on Cisco mode and then G711 because MP112 does not support Cisco mode.

With passthrought, fax goes on t38 14400bps.

In fact I am developping a small IVR in Tcl to accomodate with mobileConnect transfert.

When the call is on the mobile, the user dials *1 to put on hold then dials a shortcut to the FeatureAccess DID number the the script answers collect the digits the user dials, he can press bad digits, no matter, he just has to have the good 4 last then he press #

The script collects the last 4 digits, setup a leg to the CUCM then send 1234# (same PIN for every mobile users) then sends *2 (transfer) then sends the last 4 digits and # so the transfer can be achieved. The probleme was no error correction on digits and too many digits to dials.

I am looking for mobile able to send a few digits after connection (the user could configure his PIN after the DID)

Kind Regards and Thank you so much

Guy

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