Which codec will CUBE transcode to ?

[RITT]

Hi,
I am trying to understand the call flow for transcoding SIP calls.
here is the setup

CUCM---CUBE---SIP Gateway

CUBE has local transcoding interface (LTI) setup
to transcode the following codecs
g711ulaw
g711alaw
g729ar8
g729abr8
g729r8

An incoming call from the gateway declares its codec as g729ar8. This is in the list
so CUBE will trancode. My question is how does CUBE decide what to transcode to?

If CUBE has a prefered codec list for the CUCM dial peer, will it use that list to make the decision.
If there is no prefence list set for the CUCM dial peer, will it negotiate with CUCM, who has its own prefence list?

Many thanks

[M02@rt37 · Accepted solution]

Hello @RITT 

In a CUBE setup, when transcoding is required, the decision on which codec to transcode to is typically based on a negotiation between the CUBE and the CuCM

If there is a preferred codec list configured on the CUBE dial peer facing the SIP gateway, CUBE will attempt to use the codec from this list during negotiation.

If there is no preferred codec list set on the CUBE dial peer or if the declared codec from the SIP gateway is not in the CUBE's preferred list, CUBE will engage in negotiation with CUCM. CUCM has its own codec preference list. The negotiation involves CUBE and CUCM exchanging capabilities and selecting a common codec from their respective preference lists that is supported by both sides.

Once a common codec is agreed upon through negotiation, CUBE will transcode the call to the selected codec if needed. The decision may take into account the resources available on the CUBE, the capabilities of the devices involved, and the configured preferences.

[RITT]

Thanks M02@rt37. That's a really clear explanation

[M02@rt37]

You're very welcome @RITT 

[Carlo Poggiarelli]

Just to add my 2 cents, codec negotiations between CUBE and CUCM depends on which phone the call will land and which Device Pool adn consequent REGION it relies on.

Eg. TSP negotiatiates G729 and the CUBE and the Phone are in a Region that has G711 as defined Codec a Transcoding resource is requested by CUCM.

HTH

Regards

Carlo

[RITT]

M02@rt37 / @Carlo Poggiarelli 

Thanks for both your reply's. Could I ask a follow up question please? I have read the documentation for configuring a Transcoder media resource in CUCM where the DSPs are physically installed in CUBE.

The CUBE configuration for registering the DSPs with CUCM seems to exclusively use SCCP. If the call to be transcoded uses SIP as its session protocol will CUCM be able to use the CUBE transcoding media resource? Many thanks again for your help.

[Carlo Poggiarelli · Accepted solution]

Hi @RITT 

Sure. CUCM uses sccp to manage Transcoding resources configured on a VG/CUBE no matter what signaling protocol is used for original call. MTP/TRANSCODING are separated Media  services from Call Control

HTH

Regards

Carlo

[RITT]

@Carlo Poggiarelli , that's good to know, thanks for your reply.  I have not seen anything in the documentation that states that. For beginners, like myself, clarification of that would help. Thanks again. 

[Carlo Poggiarelli]

Hi

Look into this guide. on section SCCP TRANSCODING.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/configuration/cube-book/cube-book_chapter_0111111.pdf

HTH

Regards

Carlo