Remote access to a centralized voice mail server for the mailbox owner typically is not a problem during WAN failure, because most users know how to check their mailboxes from payphones, cell phones, or home. When reaching any outside line, they know the proper sequence of digits to enter to walk through the menus and retrieve their messages. Within those menus in voice mail systems is the ability to leave voice mail for a particular extension. SRST can use these same menus to redirect calls that have reached a busy or no answer directory number destination to a centralized voice mail system. SRST can dial the voice mail system pilot number, send DTMF tones to emulate the button presses to navigate the mail system menu structure, and then connect the redirected call to the appropriate mailbox.
NOTE Message waiting indicator (MWI) is not supported in a centralized deployment via SRST voice mail integration. MWI on each phone potentially might not indicate the mailbox’s current status after a WAN failure. The failure to indicate current status is because of lack of reachability immediately following message storage or retrieval.
Calls originating at the central site that attempt to reach an extension being supported by SRST immediately divert to voice mail if the voice mail number is configured as the call forward no answer setting. Callers at the central site attempting to reach the remote location need to add the appropriate digits to dial around the failure by using the PSTN.
Figure 2-18 illustrates the call flows of an inside and outside caller being redirected to a voice mail system over the PSTN because the target phone is unavailable, busy, or is retrieving messages.
Three variables are used to hold state information:
•
Calling number information (CGN)•
Called number information (CDN)•
Forwarding number (FDN)TIP Calling Line ID (CLID) is also needed for this mechanism to operate as described. CLID is not always available, especially internationally. Outside call interaction varies depending on CLID information availability.
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Figure 2-18 SRST Voice Mail Integration over the PSTN
Three events can cause call routing to a voice mail server in SRST:
•
The user presses the messages button on the phone.•
The call is not answered before being routed to voice mail as a result of the call forward no answer setting.•
The called destination is busy, and the call is routed to voice mail as a result of the call forward busy setting.Figure 2-19 shows an example of a complex call redirection flow and resulting variables being filled.
The voice mail setting is the dial string that reaches the voice mail system via the messages button. Call forward busy and no answer settings are likely to be the same voice mail server, but they can differ if sent to a general mailbox. With the CGN, CDN, and FDN strings, it becomes a task of getting the pattern command to match the voice mail system menu structure. V CallManager Cluster Location A Central Site Target Phone Inside Caller Outside Caller SRST Gateway Voice Mail Voice Gateway
Call Forward Busy Message Retrieval Call Forward No Answer
1 2 3 1 2 3 PSTN
Figure 2-19 SRST Voice Mail Variables
All pattern commands follow a similar format: first, a keyword to identify what the command is to be used for, followed by a digit to navigate the menu structure of the voice mail server, then one of the strings (CGN, CDN, or FDN) to identify the original target or mailbox, and finally an * to end this set of digit instructions. Multiple digit instructions are supported for one pattern command in order to navigate complex menu structures, and would continue to be appended to the command in the order just described. For a voice mail system that prompts at the main menu for a 2 as the subscriber login, the corresponding command is displayed in Figure 2-20.
Example 2-4 shows a sample configuration for redirecting calls over the PSTN via plain old telephone service (POTS). The call-manager-fallback commands establish the voice mail, call forward busy, and call forward no answer redirection numbers. Next, the
vm-integration pattern commands send the appropriate DTMF digits along with the CGN,
CDN, and FDN strings to reach the correct mailbox for extension and trunk calling combinations.
TIP Redirecting calls over the PSTN is recommended only for ISDN because of the inherent capability of Q.931 and other trunks that can provide quick call setup times. Foreign Exchange Office (FXO) connectivity can be challenging because of the variable timing involved in call setup, which in turn affects the pattern command and is not recommended. Use the timing digit and timing inter-digit commands on POTS dial peers to slow dual- tone multifrequency (DTMF) tone sending.
Calls to x1002 Forward to x1005 Busy to VM Originator x1001 User x1002 User x1005 Voice Mail Calling Number CGN = 1001 Forwarding Number FDN = 1002 Called Number CDN = 1005 CGN = 1001 FDN = 1002 CDN = 1005
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Figure 2-20 Sample pattern Command
Example 2-4 POTS Voice Mail Routing Sample Configuration
ISDN lines can carry redirect within the call Q.931 setup information and require no special SRST DTMF sequence configuration. Redirected dial number ID service (RDNIS), the outgoing option in the settings of the central site gateway, must be enabled.
TIP RDNIS information is not always supported by the carrier, especially internationally. Check to ensure that RDNIS information is indeed transported by your carrier if you’re attempting to use this functionality.
all-manager-fallback voicemail 9999
call-forward busy 9999
call-forward noan 9999 timeout 3 !
vm-integration
pattern direct 2 CGN *
pattern ext-to-ext no-answer 5 FDN * CGN * pattern ext-to-ext busy 7 FDN * CGN * pattern trunk-to-ext no-answer 4 FDN * CGN * pattern trunk-to-ext busy 6 FDN * CGN *
SRST Gateway Voice Mail
Pattern Command for Message Retrieval:
Pattern Keyword Identifier Keyword for Direct Voice Mail Access Send Digit 2 for Message Retrieval Calling Number Mailbox Delimiter to End Digit Sequence pattern direct 2 CGN *
Voice Mail Menu:
2 to Retrieve Your Messages 5 to Leave a New Message …
Example 2-5 shows a sample configuration for redirecting calls over ISDN via RDNIS.
Example 2-5 ISDN RDNIS Voice Mail Routing Sample Configuration