Re: [reSIProcate] Forking of INVITE request - regarding
On Nov 28, 2006, at 11:25 AM, Raj wrote:
Consider the following situation.
Adam wants to call Bob, let’s say that Bob is
registered at three locations, that is, at home, at
head office and at his branch office. Hence, when Adam
makes a call, INVITE request is forked by the proxy
and it reaches all the three destinations. Hence,
three 200 OK SIP response will be sent back to Adam.
This will only happen when (as you say below) the three phones answer
at the same time, where
"same time" is the window (measured in milliseconds) between the
first 200 arriving at the proxy
and the CANCELs it sends to the other legs making it to the other two
phones. So, realize when
choosing how to deal with this that it is an edge condition.
Unfortunately, studies in the traditional
PSTN suggest that it's not that unusual to stimulate this particular
edge.
Note also that early media (ringback or IVR media) can come from all
three branches. In this case,
there is no nice short window to save you from this edge condition,
you'll have to figure out what to do
for the duration of the "ringing" time.
Consider the situation, when Bob’s friends answer the
call at all the three locations at the same time, what
will happen? Either three media channel will be
established between them or which two will be
discarded.
Can anyone please clear this?
So, the bad news is that the specs don't tell you what to do with
this, and there is no current
frontrunner for an "industry best practice". A lot of implementations
will play media from whatever
source got a packet to them first, discarding the other streams.
Others have considered making
each leg appear on individual lines, or mixing them into a local ad-
hoc conference.
Finding a good solution is made more difficult by the lack of
information that allows you to associate a leg
with a branch. RTCP can eventually give you that, but there are a lot
of phones out there now that aren't
implementing RTCP yet. A lot of the work going into securing the
media streams will make this problem
easier to solve.
It's a non-trivial problem and the more folks we have looking for
good solutions, the better.
Check out the SIP/SIPPING mailing lists for the ongoing conversations.
RjS
With regards
Raj.
______________________________________________________________________
______________
Do you Yahoo!?
Everyone is raving about the all-new Yahoo! Mail beta.
http://new.mail.yahoo.com
_______________________________________________
resiprocate-devel mailing list
resiprocate-devel@xxxxxxxxxxxxxxxxxxxx
https://list.resiprocate.org/mailman/listinfo/resiprocate-devel