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User receives no-way audio with a hairpinned call on TDM bus

Core Issue

It is sometimes not obvious when the network-clock-participate command is required, as shown in these two examples:

  • The gateways with Time-Division Multiplexing (TDM) bus capability include platforms with a Multiservice Interchange (MIX) capability running a Cisco IOS  Software version that supports the network-clock-participate command.    

    These are platforms and Cisco IOS Software versions for cases with TDM bus capability:

           
    • The 3660 platform with the MIX-3660-64 card installed and running Cisco IOS Software version 12.1(5)XM, 12.2T, 12.3 mainline or later        

    • The 3725, 3745 and 2691 platforms running Cisco IOS Software version 12.2(13)T or later

    The Cisco IOS Software automatically assumes that you want to use local-bypass (no Digital Signal Processor (DSP) resources) for the hairpin calls, and it cannot be switched off.

    Therefore, to obtain two-way audio, the network-clock-participate commands referred to in Cisco bug ID CSCeb77249 are mandatory.

           
  • The gateways with no TDM bus capability include platforms with no MIX capability, or platforms with MIX capability but running a Cisco IOS Software version that does not support the network-clock-participate command.       

    These are platforms and Cisco IOS Software versions for cases without TDM bus capability:

       
    • The 3660 platform without the MIX-3660-64 card installed and running any Cisco IOS Software version        

    • The 3725, 3745 and 2691 platforms running Cisco IOS Software versions earlier than 12.2(13)T, which is the first version to recognize the network-clock-participate command
         

    When the hairpin call between the different High Density Voice Network Modules (NM-HDVs) is made, the Cisco IOS Software automatically uses DSPs on each NM-HDV to complete the call, thereby allowing two-way audio.

          

    Therefore, the network-clock-participate commands are not required.

     

To check whether DSPs are in use on a particular platform, issue the show voice call summary command on the completed call.

This is a sample output of the show voice call summary command on a 3745 platform running a Cisco IOS Software release (in this case 12.2(11)T10) in which the network-clock-participate command is not available. It shows that the DSPs are in use and the hairpinned call is successful:

W1MS-11.7-3745-A#sh voice call sum
PORT         CODEC    VAD VTSP STATE            VPM STATE
============ ======== === ==================== ======================
1/0:15.1      g711ulaw  y  S_CONNECT             S_TSP_CONNECT
1/0:15.2      -         -  -
2/0:15.1      g711ulaw  y  S_CONNECT             S_TSP_CONNECT
2/0:15.2      -         -  -

This is a sample output of the show voice call summary command on the same 3745 platform running a Cisco IOS Software release (in this case 12.2(15)T10) where the network-clock-participate command is available. This output allows you to verify that there are no DSPs in use for the hairpin call. Although the call is established, no audio is available until the network-clock-participate commands are issued for the appropriate slots on the gateway:

W1MS-11.7-3745-A#sh voice call sum
PORT         CODEC    VAD VTSP STATE            VPM STATE
============ ======== === ==================== ======================
1/0:15.1      None      y  S_CONNECT             S_TSP_CONNECT
1/0:15.2      -         -  -
2/0:15.1      None      y  S_CONNECT             S_TSP_CONNECT
2/0:15.2      -         -  -

Resolution

In general, hairpin calls automatically use DSPs if you do not have a MIX-capable chassis. If you have a MIX-capable chassis, local-bypass (no DSP resources) is used, and you need to set the proper clock participation. This is important, as the new c2691, c3725 and c3745 platforms are all MIX capable. Therefore, for hairpin calls between different NM-HDVs to work, you must issue the network-clock-participate commands in global configuration mode.

This is an example of the required configuration for a gateway with NM-HDV in slots 2 and 4, respectively:

Router#conf t            
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#network-clock-participate slot 2
Router(config)#network-clock-participate slot 4   
Router(config)#^Z

For more information on TDM bus platforms, refer to Multiservice Interchange for Cisco 2600 & 3600 Series Platforms.

For further background information on clocking configurations, refer to Clocking Configurations On Voice-Capable IOS-Based Platforms.

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Last update:
‎06-22-2009 05:30 PM
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