Hi All,
The 3pcc RFC 3725 depicts call flows that are best current practices for
B2BUAs...
In all the Call Flows the signalling initiates from the B2BUA i.e the INVITE
is sent from the B2BUA that then puts the 2 UAs into a Call.
But in the real life scenario like Call Transfer, the Call originates from
an End Point A that then reaches a IP-PBX (B2BUA) that then tranfers the
Call to End Point B. Pl. find below the flows equivalent to those given in
the RFC 3725 where the Call originates from an End Point.
Equivalent to Flow 1
A B2BUA B
INV (Sdp A)
------------>
100 Trying INV (Sdp A)
<------------ ------------>
200 (Sdp B)
<--------------
ACK
200 (Sdp B) ----------->
<-------------
ACK
------------>
RTP
<----------------------------------->
Equivalent to Flow 2
A B2BUA B
INV (Sdp A)
-------------->
200 ( blackhole Sdp)
<--------------
INV (Sdp A)
ACK ------------->
<---------------
200 (Sdp B)
<-------------
ACK
-------------->
ReINV (Sdp B)
<--------------
200
-------------->
ACK
<--------------
RTP
<-------------------------------->
Equivalent to Flow 3
A B2BUA B
INV (Sdp A)
-------------->
200 (black hole Sdp)
<--------------
ACK
---------------> INV (No Sdp)
--------------->
200 (Sdp B)
<--------------
ReINV (Sdp B)
<---------------
200 (Sdp C)
---------------> ACK (Sdp C)
---------------->
ACK
<---------------
RTP
<--------------------------------->
Flow 4 in RFC 3725 sends out an INVITE from the B2BUA without any media line
in the Sdp.
This flow is not possible for an INVITE that comes from an external enppoint
that will always have an SDP with some media line.
I am in the process of coming up with a test Suite for B2BUA. I am assumuing
that a B2BUA that implements Call Transfer functionality will use any one of
the above flows to achieve Call transfer. Am I correct in assuming this.
Also in general in any B2BUA call flow, in a real life situation the Call
originates from an Endpoint and reaches the B2BUA that then ends & initiates
the Call and controls it. Is that correct..?
Thanks,
Badri
Badri Srinivasan S
Networking Technology Labs,
HCL Technologies,
Plot No:66 South Phase
Ambattur Industrial Estate
Chennai-58
Phone:91 44 26521077, 26521270 Xtn: 2243
Fax 52060485
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