[asterisk-users] Inefficient Codec Translation

[Steve Totaro]

On Tue, Aug 19, 2008 at 7:10 AM, Jim Boykin <boykinjim at gmail.com> wrote:
> We run asterisk to handle incoming DIDs and we have observed
> inefficient Codec Translation.
>
> Here is the scenario
>
> [DID Vendor] ---------------------------> [Asterisk ]
> ------------------------> External GW [G729]
>                                                                      |
>
> |-------------------> External GW [iLBC]
>
> Our DID vendor and asterisk box supports both ilbc & g729. However,
> our external gateway termination supports either ilbc or g729 (and not
> both) and depending on users location, we terminate it on either
> gateway.
>
> Since DID and asterisk box supports both the codecs, we assumed that
> asterisk will appropriately select codecs depending on where we
> terminate the call so that no codec translation happens. However, this
> seems to be an incorrect assumption and we see that different codecs
> get selected on two legs which leads to quality drop and extra CPU
> cycles.
>
> May be we are doing something wrong. Pls suggest what we are doing
> wrong. Below is asterisk configuration.
>
> [did]
> type=friend
> host=xxx
> canreinvite=yes
> disallow=all
> allow=g729
> allow=ilbc
>
> [gw1]
> type=friend
> host=xxx
> canreinvite=yes
> disallow=all
> allow=g729
>
> [gw2]
> type=friend
> host=xxx
> canreinvite=yes
> disallow=all
> allow=ilbc
>
> Thanks
> Jim
>

To be more clear, when a call comes in on [did] the codec should match
on the order that they are listed and supported, so you should always
get g729 and transcode to ilbc on gw2.

Asterisk handles one leg at a time, so it does not look ahead to see
what the second leg of the call will be using for it's codec.

Thanks,
Steve T