CISCO 2811 VoIP CODEC Byte Conversion

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Aug 16th, 2010
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Hello.

Could anybody give me example how to convert VoIP calls CODEC bytes? Like,


Incoming CODEC g729 (any byte size)       --->    Outgoing CODEC g729 120bytes


Incoming CODEC g723r63 (any byte size)   --->   Outgoing CODEC g723r63 120byte


No transcoding required.

Thanks in advance. Expecting your reply soon.


Regards.

Sakibnaz.

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Steven Holl Tue, 08/17/2010 - 08:09
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The IOS HW MTP is designed for this--to transrate between the same codec.  It still requires a physical DSP.


Sample config:
sccp local FastEthernet0/0
sccp ccm identifier 12 ver
sccp
!



!
dspfarm profile 12 mtp
codec
codec pass-through
maximum sessions hardware
associate application SCCP
no sh


sccp ccm group 1
associate ccm 12 priority 1
associate profile 12 register



-Steve

md.sakibnaz Tue, 08/17/2010 - 15:39
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Dear Steve.

Thanks for your reply. But the 2811 Router dont have any PVDMs (DSPs).

Is it possible to achieve the CODEC byte conversion without PVDMs (DSPs)?


Regards.

Sakibnaz.

Steven Holl Wed, 08/18/2010 - 05:47
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Nope.  Anytime a RTP packet's payload needs to be reformed, you need to invoke a DSP.  Hence, any time you repacketize, you need to invoke a DSP via HW MTP.

md.sakibnaz Thu, 08/19/2010 - 04:55
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Thanks Steven.

Actually I dont need transcoding.

Is possible like, after sencing the source codedc the dial-peer will be selected on a router.

Here all the incomming packets are of g723 & g729 with any byte size.

Is it possible, dial-peer 100 will be selected for the incoming packet with g723 & similarly dial-peer 200 will be selected for g729?

So that I can define the outgoing CODEC with specific byte size under the dial-peers.

Expecting reply soon. Thanks.


Regards.

Md. Nazmus Sakib.

Steven Holl Thu, 08/19/2010 - 06:35
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I know you don't need transcoding.  You need transrating.  That still requires a DSP.


There is no way to do this below scenario which you mentioned without a DSP:

Incoming CODEC g729 (any byte size)       --->    Outgoing CODEC g729 120bytes


Incoming CODEC g723r63 (any byte size)   --->   Outgoing CODEC g723r63 120byte



If you want CUBE to change packetization rates between legs, DSPs will be required.


The only other option is to use the packetization that is offered on the inbound leg on the outbound leg (i.e. it would behave functionally as if the two endpoints on each side of CUBE were talking media negotiation directly with each other).  If you are doing h323-to-h323 CUBE you can use codec transparent on both legs as an easy way to do this.  Otherwise, you need to know the criteria for each incoming leg and craft an incoming and outgoing dial-peer specifically for those flows.  That can get tricky unless you understand inbound and outbound dial-peer matching and translation rules very well.


In summary, you need to buy DSPs or don't have packetization mismatches between endpoints.


-Steve

md.sakibnaz Thu, 08/19/2010 - 12:20
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Dear Steve,


So will the command "codec g723r63 bytes 120" wont work under a dial-peer winthout a DSP?


thanks.

Sakibnaz.

Steven Holl Thu, 08/19/2010 - 12:26
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That command will work, but in order for the codec to negotiate without a DSP, you need to use that same codec and same packetization on each leg of the CUBE, so that needs to be configured under both the inbound and the outbound dial-peer.  You cannot use a different packetization on one side.

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