[asterisk-dev] IAX2 OSP support - issue 8531

[Tilghman Lesher]

On Thursday 12 April 2007, Kevin P. Fleming wrote:
> My two cents:
>
> I agree with Tim's assertion that there will be no standardization of
> variable names passed across IAX sessions; those are for the users to
> decide what they want.
>
> However, I think that would be a poor decision for OSP, since if we add
> this support it would become a 'standard' part of the IAX2 protocol and
> all IAX2 implementations would be expected to consider implementing it.
> Given that, it should have a consistent representation within the IAX2
> signaling, and that is why I felt that dedicated IEs for the OSP token
> were the right thing to do.

I think, though, that as OSP is properly a CDR mechanism, appropriate
for post-call billing, placing it within the IAX2 protocol specifically is the
wrong place for it.  As it is protocol agnostic, we shouldn't make it IAX2
specific.  Even if we did, I would prefer to see the information encoded
within OSP compressed in some way.  While SIP is a text protocol and
additional text is no threat, IAX2 is a binary protocol, meant to be as
compact as possible.  If we want to encode billing information in IAX2,
we should adopt this same design and encode that billing information as
compactly as possible.

My concern is that at some point, we're going to run into a wall of the
standard IAX2 NEW packet becoming too big, consistently fragmented by
IP to pass the MTU, with a net effect that with a certain amount of packet 
loss, IAX2 will become unusable.  As much as possible, I'd like to avoid that
threat.

-- 
Tilghman