3.1.5 Message Processing Events and Sequencing Rules

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 When the Session Initiation Protocol (SIP) proxy routes an INVITE to voice mail based on rules as specified in [MS-SIPRE] or when an INVITE with a voice-mail-gruu (as specified in [MS-SIPRE] section 2.2.3) arrives, and the user is enabled for Exchange Unified Messaging (UM), the proxy MUST process the request as follows:

  1. If the INVITE already contains any Diversion headers, as specified in [IETFDRAFT-DIISIP-08], these headers MUST be removed before forwarding the request to Exchange UM.

  2. If the user and host portions of the Request-URI field are not the same as those of the From header field, the proxy MUST add a Diversion header with name-addr equal to the SIP URI in the Request-URI field value without any uri-parameters or headers, as specified in [RFC3261].

  3. The UM server can request the provisioning information from the SIP proxy to detect the Globally Routable User Agent URI (GRUU) of the Audio/Video Edge Server (A/V Edge Server).<4> The QoE Monitoring Server protocol and the message format for in-band provisioning requests to obtain provisioning information are specified in [MS-SIPREGE] section 3.3.

  4. If an A/V Edge Server is configured, the proxy MUST add an Ms-Mras-Address header with the value of the A/V Edge Server GRUU, as specified in [MS-SIPRE]. The Ms-Mras-address header in the incoming INVITE can be the secondary source to detect the A/V Edge Server GRUU in the absence of provisioning information.<5>

  5. The proxy SHOULD<6> include the Ms-Fe option tag in the Supported header field of the request if one is not already present.

  6. The proxy MUST decide on an ordering of the UM servers in the user's dial plan and route the INVITE to the first UM server. The Request-URI MUST be constructed as specified in section 2.2.2.

  7. If there are multiple UM servers in the users dial plan with different versions, the proxy must restrict the ordering to UM servers with the highest version. Similarly, if at least one UM server in the user’s dial plan is a front end or front end array, then the proxy SHOULD use only the front ends or arrays when determining the ordering<7>.

  8. The proxy MUST start the Unified Messaging server timer.

  9. Outgoing messages from Exchange UM can include an Ms-fe header parameter containing its specific fully qualified domain name (FQDN) value. The proxy MUST be able to handle the contact header with the Ms-fe parameter. The syntax and handling for the Ms-Fe parameter is specified in [MS-SIPRE].