Call Redirection into Voice Mail

As mentioned in the section "Message Leaving and Mailbox Login," Cisco UE uses the last Redirected Number field in the call information to select the mailbox greeting to play to a caller. This field can be seen in the Diversion header in the SIP INVITE message delivering the call to Cisco UE, as shown in Example 10-5. In this example, 6800 is the voice mail pilot number, extension 7010 originates a call to extension 5010, and the call is redirected to voice mail by CFNA.

Example 10-5. SIP INVITE for a Call Forwarded to Cisco UE

router#debug ccsip messages
INVITE sip:6800@1.3.6.179:5060 SIP/2.0
Via: SIP/2.0/UDP 1.3.6.4:5060
From: "7010" 7010@1.3.6.4>;tag=691AE6E4-223C
To: 6800@1.3.6.179>
Call-ID: E5D39E6A-8FC011D7-9025DAEC-459632B0@1.3.6.4
CSeq: 101 INVITE
Max-Forwards: 6
Remote-Party-ID: ;party=calling;screen=no;privacy=off
Timestamp: 1054070868
Contact: 
Diversion: ;reason=no-answer;counter=1 

Correct voice mailbox selection depends on the redirection information delivered with the call, which is extension 5010 in Example 10-5. A call can be redirected to voice mail in numerous ways, and these ways may populate the redirection information differently. The following sections explore some common ways for calls to be redirected to voice mail and their dependencies on voice mailbox selection and operation.

Call Forward into Voice Mail

CFNA, CFB, and CFA are the typical ways to divert a call to voice mail. If a call is redirected multiple times before reaching voice mail, the value in the last Redirected Number field always selects the voice mail greeting that Cisco UE plays to the caller. For example, if extension 3001 calls extension 3061, which CFAs to extension 5001, which in turn CFNAs to voice mail, the caller at extension 3001 hears the voice mail greeting of the subscriber associated with extension 5001.

Some voice mail systems use the original called Number Field for voice mailbox selection. In the call flow just described, that would be extension 3061. This field does not change, regardless of how many times the call is subsequently diverted before reaching voice mail. Some voice mail systems, including Cisco UE, use the last Redirected Number field. Other systems allow you to configure which field to use.

Transfer and Conference

Other possible ways for a call to enter a voice mail system are by using call modification features such as transfer and conference. Call transfer to voice mail is fairly common, but call conference is perhaps less so.

If your business has a receptionist or administrative assistant answering calls, a caller may choose to transfer to the employee's voice mail instead of waiting to speak to the person. This scenario is discussed in detail in Chapter 9 in the section "Transferred Calls That Forward to Voice Mail."

When a call is transferred to voice mail, the extension initiating the transfer is the last redirected number, and this extension's mailbox is selected. For example, suppose a PSTN caller calls the receptionist at extension 3001. The caller wants to speak to User5 at extension 3005. If the receptionist transfers the call to voice mail, extension 3001's mailbox is selected. Chapter 9 describes a workaround configuration that allows your receptionist to transfer a call without ringing the destination extension (3005) while having the caller hear extension 3005's voice mail greeting.

Conferencing with voice mail being one of the endpoints usually happens when you are talking to a caller and you want to add another employee to the call. You initiate a conference to the extension, but that person is unavailable, and your conference consultative call forwards to voice mail. You can choose to drop the consultative call at that point, and return to the original caller. Or you can complete the conference and have both of you leave a combined voice message for the unavailable person. If you decide to leave a combined message, you must hang up at the end of the voice mail session, because there is no manual way to disconnect the voice mail endpoint from your conference call while preserving the other conference participants.

Transcoding

Cisco UE voice mail supports only G.711 voice streams. If you have a multisite network with voice over IP (VoIP) calling between the sites, it is likely that you are using G.729 between the sites to conserve bandwidth on your IP network. Figure 10-17 shows a call from extension 2010 at a remote site calling to extension 3001 at your site. The call uses G.729 as it crosses your WAN backbone. If extension 3001 does not answer and the call forwards to Cisco UE voice mail, the call must use G.711 for the caller to hear the voice mail greetings and prompts correctly. For this you need a transcoder device, as shown in Figure 10-17. Transcoding with Cisco CME is covered in greater detail in Chapter 7, "Connecting Multiple Cisco CMEs with VoIP" in the section "DSP Resources for Transcoding."

Figure 10-17. Transcoding Calls into Voice Mail

Transcoding can be classified as a call modification in the sense that the call is split into two call legs, each using a different codec. Each leg is terminated by a digital signal processor (DSP) hardware device. Yet transcoding is not a call modification in the same sense as the call forward, transfer, and conference features discussed earlier in this section. Transcoding a call does not alter the dialplan in any way and does not cause the last Redirected Number field to be changed. Therefore, it does not affect voice mailbox selection.

Working with Users and Names