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Beginner

transcoding question

Hello,

Can someone explain to me how the transcoder is chosen.from different option:

DP of the Device, MRGL  of the device DP of the gateway 

 

For exemple I have Two site (A and B), all device are registred with the same CUCM Cluster, and each site have it's own gateway, G729 is configured for interregion and G711 is configured for intraregion .

 

If device From A site make PSTN call with LCR (Least cost routing)  configured and go through the WAN to use B Site Gateway, wich transcoder will be used ? (transcoder from A site or B site).

 

The call should go in G729 to the B site gateway and be transcoded to G711 from there.

 

Please help.

 

Thank you

 

1 ACCEPTED SOLUTION

Accepted Solutions
Highlighted
VIP Mentor

Transcoding is only used when

Transcoding is only used when two devices involved in a call cannot agree upon a codec to use, and then CUCM will use the MRGL of the device trying to negotiate the higher bit rate codec, to locate a Transcoding resource.

 

This idea of using the higher bit rate codec relies upon a design fundimental that Transcoders are always local to the device.  This way, the higher bit rate codec is used on the high speed LAN, and the lower bit rate codec is used on the low speed WAN.

 

In Figure 17-10, Unified CM knows that a transcoder is required and allocates one based on the MRGL and/or MRG of the device that is using the higher-bandwidth codec. In this case it is the VM/UM server that determines which transcoder device is used. This behavior of Unified CM is based on the assumption that the transcoder resources are actually located close to the higher-bandwidth device. If this system was designed so that the transcoder for the VM/UM server was located at the remote site, then G.711 would be sent across the WAN, which would defeat the intended design. As a result, if there are multiple sites with G.711-only devices, then each of these sites would need transcoder resources when an LBR is run on the WAN.

Source: http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/uc8x/media.html#wpmkr1247719

 

Again, codecs have to be negotiated and agreed upon by both endpoints in the call.  Many endpoints support more than one codec, to include IP Phones, Gateways (if configured correctly), Voicemail, etc.  Therefore, even with region settings of 64kbps and/or 16kbps, a common codec can be found and used without the need for a transcoder.

 

Some devices do not support more than one codec, to include UCCX, CUCM Software Conference Bridge, CER CTI Ports for alerts, and Meeting Place Express 2.0 and lower.  So, either you put these devices in a region which can do 64kbps everywhere, or give them an MRGL with a Transcoder.  Which you choose is an exercise in cost, beause 64kbps over the WAN means bandwidth costs and Transcoding means DSP costs.

 

Some helpful reading would be the Media Resource section of the CUCM SRND:

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/uc8x/media.html

View solution in original post

4 REPLIES 4
Highlighted
Cisco Employee

Hello Salim, Here the media

Hello Salim,

 

Here the media resource allocation would be done on basis of MRGL & region settings of two devices in question. Say IP phone & PSTN Gateway.

 

Assuming you have PSTN gateway , so DSPs are able to do conversion from PCM ( to any codec like g.729 ) as well. So ideally no need to have transcoder here, as DSPs are pre reserved m while configuring voice-ports.

 

Transcoders will come in to force, basically for ip to ip leg. When you use an CUBE or PSTN is accessed over sip or h.323. So party which is not able to support offered capabilities should allocate an transcoder from its MRGL.

 

Hope that makes sense.

 

Thanks,

Amit

Highlighted
Beginner

Thank you for your answer,But

Thank you for your answer,

But if you go through AN in G729 until the  site B and from site B you have gateway with E1 link, then you have to use Transcoding to go from G711 (E1 link) to G729 in site A?  

Highlighted
Participant

Hi,You will use transcodings

Hi,

You will use transcodings resources only when you have to stablish a call from codec A to codec B, for example if you have 2 sites with its own region so site A would communicate to site A with G711 or G722 and site A to site B with G729, you only use transcoding when a user on site A call a user on site B and visceversa.

Regards.

Highlighted
VIP Mentor

Transcoding is only used when

Transcoding is only used when two devices involved in a call cannot agree upon a codec to use, and then CUCM will use the MRGL of the device trying to negotiate the higher bit rate codec, to locate a Transcoding resource.

 

This idea of using the higher bit rate codec relies upon a design fundimental that Transcoders are always local to the device.  This way, the higher bit rate codec is used on the high speed LAN, and the lower bit rate codec is used on the low speed WAN.

 

In Figure 17-10, Unified CM knows that a transcoder is required and allocates one based on the MRGL and/or MRG of the device that is using the higher-bandwidth codec. In this case it is the VM/UM server that determines which transcoder device is used. This behavior of Unified CM is based on the assumption that the transcoder resources are actually located close to the higher-bandwidth device. If this system was designed so that the transcoder for the VM/UM server was located at the remote site, then G.711 would be sent across the WAN, which would defeat the intended design. As a result, if there are multiple sites with G.711-only devices, then each of these sites would need transcoder resources when an LBR is run on the WAN.

Source: http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/uc8x/media.html#wpmkr1247719

 

Again, codecs have to be negotiated and agreed upon by both endpoints in the call.  Many endpoints support more than one codec, to include IP Phones, Gateways (if configured correctly), Voicemail, etc.  Therefore, even with region settings of 64kbps and/or 16kbps, a common codec can be found and used without the need for a transcoder.

 

Some devices do not support more than one codec, to include UCCX, CUCM Software Conference Bridge, CER CTI Ports for alerts, and Meeting Place Express 2.0 and lower.  So, either you put these devices in a region which can do 64kbps everywhere, or give them an MRGL with a Transcoder.  Which you choose is an exercise in cost, beause 64kbps over the WAN means bandwidth costs and Transcoding means DSP costs.

 

Some helpful reading would be the Media Resource section of the CUCM SRND:

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/uc8x/media.html

View solution in original post