[Asterisk-Users] Amazing, great protocol IAX

[steve at daviesfam.org]

On Sun, 3 Oct 2004, Thomas Hutton wrote:

> 1) IAX transfer - I'm running Asterisk boxes A, B, and C.  B is in the
> middle and has a dialplan that points to extensions on C.  When a client
> on A in the proper context on B tries dialling a client of C, B is smart
> enough to release itself somehow from playing telephone in the middle,
> letting A and C network directly with each other.  This totally rocks. 
> Who cares if it takes an extra 2 - 3 seconds to complete dialling.  This
> is called Native Transfer Mode, no?  I don't see why anyone would want
> to disable it unless they were worried about missing CDR's - or hadn't
> figured out how to connect to a remote DB from A, C, or both.  

It rocks even more than you think.  Before and whilst the transfer is
taking place, audio is still passed via the B system.

> A) Which is better sound quality in this situation?
> On a local net (100 megabit) my SIP phone talks to Asterisk running on
> my firewall.  I only have 128K upload (sometimes) on my fricken
> Third-World DSL connection so I want to use GSM or ILBC going out over
> IAX2.  Should I let the DSP in the phone talk to asterisk in ULAW or
> ALAW, having Asterisk translate to GSM or should I force the phone to do
> it in the lower bandwidth codec?  I honestly can't tell a difference in
> quality or latency.  I'm not real impressed with the Grandstream
> Handytone 286 because it doesn't have GSM - so I'm stuck trying to
> compare straight through ILBC to translated GSM.  Any fine tuning codec
> advice would be appreciated.

If all your calls go through to the DSL line, you'd probably do best using
iLBC on your phone.  Asterisk doesn't have to transcode, and your phone
has probably got iLBC's lost packet concealment, which isn't implemente on
Asterisk right now.

G711 does sound better - so if you will have calls to other LAN places or 
use Asterisk IVR, Voicemail etc a lot, then maybe its worth using G711.

Regards,
Steve

PS: Where in the 3rd world?