Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

Exchange 2007 T.38 Fax over CUCM


has anyone ever succeeded running CUCM 7.x and Exchange 2007 with Fax over T.38?

I tried and failed due to a lack of documentation and knowledge.

Even with hardware MTP,T.38 mline and Fax Inline Detection set I got only voicemail running. When it comes to fax it doees not detect CNF tones.

Can someone supply me with gateway config (voice service voip & dial-peer) as well as any non-standard cucm and exchange server configuration?

Regards & Thanks



Re: Exchange 2007 T.38 Fax over CUCM

Hi Sebastian I have worked with 2,3 customers for this deployment in CUCM 7.x

Normal error is check region to be G711 and MTP config in IOS router.

dspfarm profile 3 mtp

codec g711ulaw

maximum sessions hardware 34

associate application SCCP

Normallly you need to add

"codec pass-through" command to detect tones.

Let us know which type of MTP and VGW you are using.

New Member

Re: Exchange 2007 T.38 Fax over CUCM


thanks for the reply

VGW is a 2821 Router + NM-HDV + 3x PVDM-12 + VWIC-1MFT-E1

IOS: 12.4.22T1

MTP is 2811 Router + PVDM2-32

IOS: 12.4.15T9

Is a hardware MTP mandatory? I've seen that only in some posts not in any official documentation.

We're using G711alaw from end to end. Is there a restriction that requires G711ulaw here?


New Member

Re: Exchange 2007 T.38 Fax over CUCM

Back in our lab i did some testing:

symptom remains unchanged:

Exchange 2007 answers a voice call, does not detect a fax but mentions invalid input by the fax machine on the other side and finally hung up.

VGW Config:

voice service voip

allow-connections h323 to h323

allow-connections h323 to sip

allow-connections sip to h323

allow-connections sip to sip


h225 signal overlap

modem passthrough nse codec g711alaw


registrar server

transport switch udp tcp

asymmetric payload dynamic-codecs

dial-peer voice 1000 voip

destination-pattern XXXX

modem passthrough nse codec g711ulaw

session target ipv4:

codec g711ulaw

fax-relay ecm disable

fax-relay sg3-to-g3

fax rate 14400

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

no vad

MTP config:

dspfarm profile 2 mtp

codec g711ulaw

maximum sessions hardware 16

associate application SCCP

The new MRGL is assigned to the H323 GW and to the Exchange SIP Trunk

Changing (end to end) to g711alaw does not change anything


CreatePlease to create content