[Asterisk-Dev] Asterisk / OpenH323 Bearer-Capability

[Aaron S. Joyner]

Michael Procter wrote:

>>From: Aaron S. Joyner [mailto:asjoyner at intrex.net]
>>    
>>
>>Apparently the last octet in the Bearer-Capability actually 
>>defines the user information layer 1 protocol.  Strangely,
>>the setting A5 would seem to indicate synchronous (bit 7),
>>in-band negotiation (bit 6), 
>>recommending G.722 or G.725 7kHz audio (bits 5-1, neither of 
>>which are 
>>supported by Asterisk, OpenH323, or the remote Cisco end 
>>we're talking 
>>    
>>
>
>No - you have mis-decoded the final octet.  Sync and negotiation
>are only present in octet 5a - but there is no octet 5a in this
>element, only unextended octets 3, 4 and 5.
>
>You are right that you want 80 90 A3 or 80 90 A2 (A-Law and u-law
>respectively), although I would strongly favour A-law wherever
>possible to improve interoperability.
>
>Don't forget that you can download 3 ITU specs for free, by
>registering your email address...
>
Okay that took me a min of looking at the spec again to figure out what 
I missed, but you are correct.  I was accidentally reading beyond octet 
5 into 5a, but as luck would have it the first 3 bits of the binary for 
A (i.e. 101) is logical for the extended 5a octet that I was 
mis-reading, as well as the standard 5th octet.  We weren't attempting 
to change that particular aspect of the output, so it didn't directly 
affect our code, only the auxiliary understanding of it.  Thanks very 
much for pointing out the detail.  Since you have a far firmer grasp on 
the art of standard-reading than I do, perhaps you can shed some light 
on what that first (8th) bit in the 5th octet is supposed to indicate?  
The only reference to it I've seen is in the overall diagram, as "0/1 
ext".  Is that supposed to indicate an "extended" interpretation or 
something?

-- 
Aaron S. Joyner
System Administrator
Intrex.net Internet Services
(919) 573-5488 x102