Cisco VM Integration with SRST

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In this blog entry I will only discuss how VM-integration’s call routing works. In a nutshell, VM-integration is another technique used to access (send and receive) voicemail system in a centralized setup usually deployed at the headquarters or Data Center when the IP WAN is down. During the IP WAN outage, the branch router engages its Survivable Remote Site Telephony (SRST) feature either using Call-Manager-Fallback or CME-SRST. VM-integration supports access to user’s voice mailbox on these situations – direct voicemail access (by pressing the message button on an IP phone), busy (all lines are engaged) and no-answer (ring timeout exceeded).

As an example, let say you have the following configuration below.

ephone-dn 1 dual-line
number 4000
!
ephone 1
mac-address xxxx.yyyy.zzzz
type 7945
button 1:1
!
! Note: Ephone and Ephone-dn are SRST learned configuration. I put it here just to show completeness in my example.
!
call-manager-fallback
ip source-address 1.1.1.1 port 2000
max-dn 10
max-ephone 10
secondary dial-tone 0
voicemail 014082022220
call-forward busy 014082022220
call-forward no-answer 014082022220 timeout 20
!
vm-integration
pattern direct * CGN
pattern trunk-to-ext busy # FDN
pattern trunk-to-ext no-answer # FDN
pattern ext-to-ext busy # FDN
pattern ext-to-ext no-answer # FDN
!
dial-peer voice 1000 pots
description ** Used for VM-integration **
destination-pattern 014082022220T
forward-digit 0
prefix 14082022220
port 0/0/0:15

Scenario 1: The user of extension 4000 presses the Message button.
1. The IP phone dials the central voicemail pilot number 014082022220 (0 is used to get an outside line and 14082022220 is the ISDN DID number of the voicemail pilot number).
2. The router forwards 14082022220 to the PSTN. Then router login onto the voicemail system by entering * and 4000. 3. Finally, voicemail system plays the user’s personal greeting and will ask to enter the PIN.

Above scenario is accomplished by this vm-integration commands – pattern direct * CGN.

Scenario 2: External callers call user’s direct-inward PSTN number (e.g. 19723034000). Either the called party is busy or doesn’t answer the call.
1. The IP phone forwards the call to the central voicemail pilot number 014082022220.
2. The router forwards 14082022220 to the PSTN. Then router login onto the voicemail system by entering # and 4000 (FDN. 3. Finally, voicemail system plays the user’s personal greeting and asking to enter the PIN.

Above scenario is accomplished by this vm-integration commands –
pattern trunk-to-ext busy # FDN
pattern trunk-to-ext no-answer # FDN

Scenario 3: Internal callers call user’s internal extension number (e.g. 4000). Either the called party is busy or doesn’t answer the call.
1. The IP phone forwards the call to the central voicemail pilot number 014082022220.
2. The router forwards 14082022220 to the PSTN. Then router login onto the voicemail system by entering # and 4000 (FDN stands for
3. Finally, voicemail system plays the user’s personal greeting and asking to enter the PIN.

Above scenario is accomplished by this vm-integration commands –
pattern ext-to-ext busy # FDN
pattern ext-to-ext no-answer # FDN

DTMF digit pattern forwarding:
CGN: Calling number (CGN) information is sent to the voice-mail system.
CDN: Called number (CDN) information is sent to the voice-mail system.
FDN: Forwarding number (FDN) information is sent to the voice-mail system.

For more information kindly refer to this link.

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