[SIP] On SIP-H323 Interworking
"rafi" <rafi@sasi.com> Thu, 13 July 2000 11:52 UTC
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From: rafi <rafi@sasi.com>
To: sip@lists.bell-labs.com
Date: Thu, 13 Jul 2000 17:19:05 +0530
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Subject: [SIP] On SIP-H323 Interworking
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Hi,
Following are my understanding when a call is established
from H.323 terminal to a SIP terminal ( draft-singh-sip-h323-01.txt).
Following could be the call flow diagram for such a call setup.
(Assuming no faststart in the SetUp message)
SIP IWF GK H323Terminal
Terminal
GRQ
<---------------
GCF
---------------->
RRQ
<----------------
RCF
----------------->
ARQ
<----------------
ACF
----------------->
SETUP
<------------------------------
ARQ
----------->
ACF
<-----------
INVITE(SDP=C)
<----------------
200 OK (SDP=C1)
------------------->
ACK
<------------------
TCS ( Cap=C1)
-------------------------------->
TCS ACK
<-------------------------------
TCS (Cap = C2)
<-------------------------------
TCS ACK
------------------------------->
/* MSD is not shown */
OLC
-------------------------------->
OLC ACK
<--------------------------------
OLC
<--------------------------------
OLC ACK
--------------------------------->
INVITE ( Cap = C3)
<---------------------
183
---------------------->
Alerting
---------------------------------->
200 OK
---------------------> CONNECT
-------------------------------->
ACK
<-----------------------
Following are the difficulties with the above type of call set up.
(i) IWF must know default capability set of H323 terminal. There
is no way to know actual capabilities in H323 without establishing
the call.
(ii) The capability final agreed upon by the Terminals (C3) is always
a subset of C ( default capability), thus making selection of C
a critical one.
(iiI) When a call is established initially at SIP Terminal ( first
ACK), H323 terminal MAY miss the media info.
In RFC2543bis sending empty SDP is allowed in INVITE message.
Thus instead of above call scenario can we have call flow something
like this
SIP IWF GK H323Terminal
GRQ
<--------------------
GCF
------------------------>
RRQ
<-----------------------
RCF
------------------------>
ARQ
<------------------------
ACF
------------------------>
SETUP
<-----------------------------------
ARQ
----------->
ACF
<-----------
INVITE(SDP=0)
<----------------
200 OK (SDP=C)
------------------->
TCS ( Cap=C)
------------------------------->
TCS ACK
<-------------------------------
TCS (Cap = C1)
<-------------------------------
TCS ACK
------------------------------->
/* MSD is not shown */
OLC
-------------------------------->
OLC ACK
<--------------------------------
OLC
<--------------------------------
OLC ACK
--------------------------------->
CONNECT
-------------------------------->
ACK ( SDP = C2) C2 is the maximal subset of C and C1
<-----------------------
Any comments?
Regards
Rafi Assadi H.M.