2007 Exchange UM fax doesn't work after applying Service pack updates

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To troubleshoot 2007 Exchange UM fax issues,

  1. always check with the Exchange/Voice administrator on the fax tone detection method they use.
  2. collect a netmon/wireshark trace and filter it for SIP protocol. Verify the SIP INVITEs, Re-INVITES, 200OK, ACK as appropriate for the call flow
  3. Filter on rfc2833 if the UM is expected to receive out-of-band RFC2833 packets. Of note, RFC2833 is used for sending the DTMF as well
  4. Filter on t.38 and verify the direction of t.38 packets.

 As per https://technet.microsoft.com/en-us/library/bb691398(EXCHG.80).aspx 

Inband fax tone detection Fax tone detection enables an IP gateway, an IP PBX, or Exchange Unified Messaging to determine the type of incoming call that is being received. Fax tone detection can work in the following three ways:

  • The IP PBX or IP gateway detects the fax tone and sends a reinvite request by using T.38 Session Description Protocol (SDP). -- > This method should continue to work after the Service Pack upgrade

  • Fax tone detection can be performed by using both an IP PBX or IP gateway and Unified Messaging. In this method, when the IP gateway or IP PBX detects the fax tone, it does not send a re-invite but instead sends CNG tones (out of band) as named telephony events as defined in RFC 2833. As soon as the IP PBX or IP gateway has sent the CNG tones, the Unified Messaging server performs out-of-band fax tone detection and sends a reinvite by using T.38 SDP. -- > This method should continue to work as well after the Service Pack upgrade

  • If the IP PBX or IP gateway does not use either of these methods, Unified Messaging inband fax tone detection should be turned on. This will enable the Unified Messaging server to detect incoming inband fax tones. By default, this feature is turned off. However, it can be enabled in environments that use IP PBXs or IP gateways that cannot detect fax tones. You enable inband fax tone detection by changing the EnableInbandFaxDetection setting to True in the globcfg.xml file. The globcfg.xml file is located in the \Program Files\Microsoft\Exchange\bin folder on a computer that is running the Unified Messaging server role.

In scenarios, where fax stops working after upgrading to a newer Service Pack the issue may be with the globcfg.xml file getting overwritten. This is applicable when customer has the fax detection through EnableInbandFaxDetection flag.

Change EnableInbandFaxDetection flag to true. Save the file without changing any other file content or file properties. UM and speech services needs a restart to get the EnableInbandFaxDetection flag into effect.

There is no other special configuration on UM for fax.