[Asterisk-Users] A question on codec translation.

Tom Lowe
Mon, 12 Jan 2004 06:45:21 -0000

If the incoming and outgoing Codecs are the same, there is no
"conversion" done.  It basically becomes a packet relay, what goes in,
comes out.

I'm not sure of the answer to your second question.  However, your
question actually begs a question I've been wondering about in the last
couple of days:

I'm doing H.323 in, H.323 out....simple relay.  (This is my customer's
requirement...not my preference).  What I want to do is ALWAYS use the
same codec for the outgoing leg as for the incoming leg.  In other
words, if the call comes in as G.729, the outgoing call uses G.729 ONLY.
If the incoming call is G.711, I want the outgoing to be G.711.   I want
to avoid any sort of transcoding.

Is it possible?

Thanks.

Tom Lowe

(FYI, Dual Xeon 3.06, 120 channels (60 calls) of above scenario, G.729
using less than 10% CPU!)  (Remember, no transcoding is being performed)


-----Original Message-----
From: WipeOut [mailto:wipe_out@users.sourceforge.net]
Sent: Monday, January 12, 2004 6:54 AM
To: asterisk-users@lists.digium.com
Subject: [Asterisk-Users] A question on codec translation.


Here is the scenario...

SIP UA's can use either GSM or G.711 ( in that order of preference in
the sip.conf )..
Asterisk Server1 is linked to Asterisk Server2 via IAX2 and also
supports GSM and G.711 ( also in that order of preference)..

1. If a call comes in from the UA using GSM and then goes out over the
IAX2 leg, Will Asterisk simply move the GSM encoded data from the SIP
channel to the IAX2 channel and so have very little performance overhead

since it will not be decoding and re-encoding the GSM data? or will it
decode and re-encode the voice data?

2. Assuming that the answer to question1 is that Asterisk will simply
move the encoded data from the SIP channel to the IAX2 channel without
decoding and re-encoding (otherwise the question is irrelevant), would a

call coming in in SIP using G.711 be converted to GSM on the IAX2
channel since it is higher in the order of preference or will it
identify that G.711 is also available on the IAX2 leg and so switch the
call using G.711 to save the performance overhead so that the data does
not have to be decoded and re-encoded?

Thanks..

Later..

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