Configuring SRS Telephony and MGCP Fallback

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Updated:February 12, 2008
Document ID:29960

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Introduction

If you have both Survival Remote Site Telephony (SRST) version 2.0 or later and Media Gateway Control Protocol (MGCP) fallback configured on the gateway, use this document in order to solve either of these MGCP failover problems:

  • A telephone on a Foreign Exchange Station (FXS) port does not get a dial tone, or you cannot make incoming calls through a Foreign Exchange Office (FXO) port or through the ISDN link.

  • You cannot make incoming calls with direct inward dial (DID) to an MGCP gateway, configured for MGCP fallback, in a failover situation.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on this software version:

  • Cisco IOS® Software Release 12.2(11)T and later

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

No Dial Tone on an FXS Port, or Cannot Make Incoming Calls through FXO Ports or ISDN Links

This problem is explained in detail in this section.

You are presented with a telephone on an FXS port that does not get a dial tone, or you cannot make incoming calls through an FXO port or ISDN link. In such situations, this is configured under the relevant plain old telephone service (POTS) dial peer:

dial-peer voice X pots
     application mgcpapp

Note: For Cisco IOS Software Release 12.3(7)T or later, the application mgcpapp command must not be applied to the POTS dial peer that supports PRI Backhaul.

In this situation, an error message similar to this appears on the console of the Cisco IOS gateway: 

*Mar  1 20:41:58.571: %CALL_CONTROL-6-APP_NOT_FOUND: 
Application mgcp in dial-peer 10 not found.  
Handing callid 13 to the alternate app.

Note: For Cisco IOS Software Release 12.4(8c) or later, when the application mgcpapp command is applied:

In this situation, a Warning message similar to this appears on the console of the Cisco IOS gateway: 

Warning: This command has been deprecated and will be automatically
converted to the following:
     service mgcp

For Cisco IOS Software Release 12.3(7)T or later, the application mgcpapp command should not be applied to the POTS dial peer.

Solutions

Figure 1: Branch Office Cisco IP Phones Connected to a Remote Central Cisco CallManager

configsrst_mgcpfallback1.gif

If the Cisco CallManager becomes inaccessible, phones can use a Cisco voice router for call processing. Phones go into SRST mode when either of these occurs:

  • The WAN link to the Cisco CallManager at the central site goes down.

  • The connection to the Cisco CallManager is lost.

SRST allows phones in branch offices to continue to function until the WAN link comes up or until the phones can register with a Cisco CallManager again.

Use one of the solutions described in this section to resolve this problem.

Solution 1

For the router to fallback to the default application, configure this command in global configuration mode:

For Cisco IOS Software Release 12.3(13)T or earlier:

R(config)#call application alternate default

For Cisco IOS Software Release 12.3(14)T or later:

R(config)#application
R(config-app)#global
R(config-app-global)#service alternate Default

If the MGCP application is not available, the default application takes over.

Solution 2

You must create a different POTS dial-peer (default application H323) to use in the fallback mode.

No Incoming Calls with DID to an MGCP Gateway in Failover

This problem is explained in detail in this section.

You cannot make incoming calls, with DID, to an MGCP gateway configured for MGCP failover in a failover situation—even though there is a connection, the phone does not ring. This is an example of the debug isdn q931 command used on the Cisco IOS gateway, when you verify this problem:

Problem Verification Example 
*Mar  1 20:53:33.511: ISDN Se1/0:15 Q931: RX <- SETUP pd = 8  callref = 0x000A 
        Bearer Capability i = 0x8090A3 
                Standard = CCITT 
                Transer Capability = Speech 
                Transfer Mode = Circuit 
                Transfer Rate = 64 kbit/s 
        Channel ID i = 0xA98381 
                Exclusive, Channel 1 
        Calling Party Number i = 0x00, 0xA2, '5000' 
                Plan:Unknown, Type:Unknown 
        Called Party Number i = 0xC1, '5002' 
                Plan:ISDN, Type:Subscriber(local) 
*Mar  1 20:53:33.543: ISDN Se1/0:15 Q931: TX -> CALL_PROC pd = 8  callref = 0x800A 
        Channel ID i = 0xA98381 
                Exclusive, Channel 1 
*Mar  1 20:53:33.543: ISDN Se1/0:15 Q931: TX -> CONNECT pd = 8  callref = 0x800A 
*Mar  1 20:53:33.595: ISDN Se1/0:15 Q931: RX <- CONNECT_ACK pd = 8  callref = 0x000A 
*Mar  1 20:53:40.045: ISDN Se1/0:15 Q931: RX <- DISCONNECT pd = 8  callref = 0x000A 
        Cause i = 0x8090 - Normal call clearing 
*Mar  1 20:53:40.057: ISDN Se1/0:15 Q931: TX -> RELEASE pd = 8  callref = 0x800A 
*Mar  1 20:53:40.073: ISDN Se1/0:15 Q931: RX <- RELEASE_COMP pd = 8  callref = 0x000A

Solution

The solution to this problem is explained in detail in this section.

You must verify that you have made these configurations on the relevant POTS dial peer:

dial-peer voice X pots
     application mgcpapp
     incoming called-number .
     direct-inward-dial
     port 1/0:15

Note: For Cisco IOS Software Release 12.3(7)T or later, the application mgcpapp command must not be applied to the POTS dial peer that supports PRI Backhaul.

This is an example of a proper configuration:

Configuration Example 
isdn switch-type primary-net5 
! 
! 
ccm-manager fallback-mgcp 
ccm-manager mgcp 
ccm-manager config 
mta receive maximum-recipients 0 
! 
controller E1 1/0 . pri-group timeslots 1-12,16 service mgcp 
! 
controller E1 1/1 
! 

! 
! 
interface Ethernet0/0 
 ip address 10.48.80.9 255.255.255.0 
 duplex auto
speed auto
! 
interface Serial1/0:15 
 no ip address 
 no logging event link-status 
 isdn switch-type primary-net5 
 isdn incoming-voice voice 
 isdn bind-l3 ccm-manager 
 no cdp enable 
! 

! 
! 
call rsvp-sync 
! 
call application alternate DEFAULT 

!--- For Cisco IOS® Software Release 12.3(14)T or later, this command was replaced by the service command in global application configuration mode. application global service alternate Default Refer to Solution 1 for the command syntax.

! 
voice-port 1/0:15 
! 
mgcp 
mgcp dtmf-relay voip codec all mode cisco 
mgcp package-capability rtp-package 
mgcp sdp simple 
! 
mgcp profile default 
! 
! 
! 
dial-peer cor custom 
! 
! 
! 
dial-peer voice 10 pots 
application mgcpapp 
incoming called-number .
destination-pattern 9T 
direct-inward-dial 
port 1/0:15 

! 
! 
call-manager-fallback 
 limit-dn 7960 2 
 ip source-address 10.48.80.9 port 2000 
 max-ephones 10 
 max-dn 32 
 dialplan-pattern 1 704.... extension-length 4 
 keepalive 20 
 default-destination 5002 
 alias 1 5003 to 5002 
 call-forward busy 5002 
 call-forward noan 5002 timeout 12 
 time-format 24 
! 
! 
line con 0 
 exec-timeout 0 0 
line aux

Note: For outgoing calls, you must configure the destination-pattern .

Here is a link to a video on the Cisco Support Community leavingcisco.com that describes the procedure to setup basic SRST: Configuring Basic SRST leavingcisco.com

configsrst_mgcpfallback2.gif

Verify

This section provides information you can use to confirm your configuration is working properly.

Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.

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