[asterisk-dev] New codec support in Asterisk 10

[Kevin P. Fleming]

On 10/14/2011 01:10 PM, Tilghman Lesher wrote:
> On Fri, Oct 14, 2011 at 12:28 PM, Simon Perreault
> <simon.perreault at viagenie.ca>  wrote:
>> On 2011-10-14 13:15, Tilghman Lesher wrote:
>>> On Fri, Oct 14, 2011 at 11:53 AM, Jason Parker<jparker at digium.com>  wrote:
>>>> In Asterisk 10, we've changed the way codecs are defined, to expand the number
>>>> of codecs that we can support.  However, due to protocol limitations, many
>>>> channel drivers (pretty much everything but chan_sip) can only support a limited
>>>> number of codecs.  As an example, chan_iax2 uses a 32-bit bitfield on the wire,
>>>> which means the codec list on each side can never change.
>>>
>>> One small correction:  chan_iax2 uses a 64-bit bitfield on the wire,
>>> with approximately
>>> 30 of those bits unallocated.  (Testlaw can be removed; it's just a
>>> duplicate of ulaw.)
>>
>> (just trolling a little bit)
>>
>> So chan_iax2 doesn't follow the RFC?
>>
>>    While IAX is very effective, addressing many of today's
>>    communications needs, it does have a few limitations.  For instance,
>>    IAX uses a point-to-point codec negotiation mechanism that limits
>>    extensibility because every IAX node in a call path must support
>>    every used codec to some degree.  In addition, the codec definition
>>    is controlled by an internally defined 32-bit mask, so the codecs
>>    must be defined in the protocol, and the maximum number of
>>    simultaneous codecs is, therefore, limited.
>>
>> http://tools.ietf.org/html/rfc5456#section-1.2
>
> For interoperability reasons, chan_iax2 actually sends both a 32-bit
> codec mask AND a 64-bit codec mask.  So in answer to your question,
> yes, it's backwards-compatible.

... but no document has been produced to document this information 
element (nor for the other information elements we've already added 
since the RFC was published).

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
Jabber: kfleming at digium.com | SIP: kpfleming at digium.com | Skype: kpfleming
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
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