[asterisk-users] Inefficient Codec Translation

[Jim Boykin]

Brent/Steve, Thanks for the answer. Point here is that asterisk
already knows about first leg and the codec so shouldn't it select the
best codec for second leg to match first leg. Instead asterisk is
selecting first codec in order.

To illustrate, if the first leg was ilbc and second leg supports both
g729/ilbc, I will assume that asterisk will select ilbc but that does
not seems to be the case.

Jim

On 8/23/08, Brent Davidson <brent at texascountrytitle.com> wrote:
>
> Steve Totaro wrote:
> 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

> Why don't you allow=g729 only on all entries. Maybe I have misread
your
> email but I interpret what you wrote to mean that all endpoints
support
> g729

>
> I may be wrong but I understood the situation as the DID supplier supports
> either g.729 or ilibc, but the user has 2 locations that calls are routed
> to.  One location supports iLibc only, the other supports g.729 only.  What
> they seem to be trying to accomplish is to get the DID <-> Asterisk leg to
> use the same codec as the Asterisk <-> Remote Location leg.  I think the
> problem is going to be that the call has to be established to the Asterisk
> box before a destination can be selected.  The DID and Asterisk Box are
> going to negotiate the first available common codec before doing anything
> else, including setting a destination.  Since you can't change a codec once
> a call has been established you're always going to end up with calls to one
> of the 2 remote locations being transcoded.
>
> The only solution I could think of would be if there was some way to
> identify which incoming calls were going to be routed to which location and
> set the codec accordingly.  To do that, you'd either have to have 2
> different DID's or some other massively more complicated mechanism.
>
> Forcing a reinvite (Is that even possible?) would be the only other
> long-shot I could think of.
>
> Good luck,
> Brent
>
>
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