[cisco-voip] Audio Codec

[Andre Beck]

Hi,

On Wed, Mar 28, 2007 at 06:41:04PM +0200, Ahmed Elnagar wrote:
>
> No it is not I searched alot but I didnot find any parameter for this

Neither did I. AFAIK you cannot force CCM to use A-Law only or even
to prefer A-Law over µ-Law. It will always prefer µ-Law if the gateway
can provide it, resulting in unnecessary conversions (e.g. coming in on
from the ISDN PSTN as A-Law, converted by the gateway to µ-Law and sent
to the phone when the phone would actually be able to playout A-Law).

I was able to force CCM to use A-Law by enforcing it on the gateway:

voice class codec 1
 codec preference 1 g711alaw

dial-peer voice 10 voip
 tone ringback alert-no-PI
 destination-pattern [1-7].
 progress_ind setup enable 3
 voice-class codec 1
 session target ipv4:192.168.123.1
 dtmf-relay h245-alphanumeric
 no vad

As soon as I allow µ-Law, even when giving it lower preference in the
voice class codec statement, CCM will pick it instead, uselessly
requesting conversion. I'm also somewhat convinced that unnecessary
A-Law to µ-Law conversion will reduce quality and further fax problems,
but this is just a guess.

BTW, when I read about newer phones like the 7941/61 class, I tripped
about a statement that they *only* speak G.711u, *not* G.711a. Now
that's clever...

Andre.
-- 
                  The _S_anta _C_laus _O_peration
  or "how to turn a complete illusion into a neverending money source"

-> Andre Beck    +++ ABP-RIPE +++    IBH Prof. Dr. Horn GmbH, Dresden <-