Hi All,
I have some questions about the message flow with respect to SUBSCRIBE
and NOTIFY when there is a proxy/registrar involved. Maybe someone could
clear it up for me. In particular, I need to know how the
proxy/registrar should deal with subscribe and notify, assuming it is
functioning in the PA role. I have 3 scenarios in mind, maybe someone
could tell me which is the right one:
(time to turn on the fixed-width font)
The first example, I am assuming that the registrar fully functions as a
PA and does not forward requests to the peer UA (UA2 in this diagram).
It is assumed that UA1 is SUBSCRIBEing to UA2:
+------------+ +--------------+ +-------------+
| | | proxy/ | | |
| UA1 | | registrar | | UA2 |
+-----+------+ +-------+------+ +------+------+
| | |
| SUBSCRIBE | |
+-------------------------> |
| OK | |
<-------------------------+ |
| NOTIFY | |
<-------------------------+ |
| OK | |
+-------------------------> |
| | REGISTER |
| <------------------------+
| | OK |
| +------------------------>
| NOTIFY | |
<-------------------------+ |
| OK | |
+-------------------------> |
The second example, the proxy/registrar functions more like a proxy and
less like a PA in that it simply forwards the request to the peer UA2:
+-----------+ +--------------+ +--------------+
| | | proxy/ | | |
| UA1 | | registrar | | UA2 |
+-----+-----+ +-------+------+ +-------+------+
| SUBSCRIBE | |
+----------------------> |
| PENDING | |
<----------------------| SUBSCRIBE |
| ------------------------->
| | OK |
| OK <------------------------+
<----------------------| |
| | |
| | |
| NOTIFY |
<-----------------------------------------------+
| OK |
+----------------------------------------------->
| | |
Finally, the third is basically a mixture of the first two.. probably
wrong but this is closer to some behavior I've seen before, where the
proxy/registrar both responds to the SUBSCRIBE request and forwards it
to the peer UA:
+------------+ +--------------+ +---------------+
| | | proxy/ | | |
| UA1 | | registrar | | UA2 |
+-----+------+ +-------+------+ +-------+-------+
| SUBSCRIBE | |
+----------------------> |
| PENDING | |
<----------------------+ SUBSCRIBE |
| ---------------------->
| | OK |
| OK <---------------------+
<----------------------+ |
| NOTIFY | |
<----------------------+ |
| OK | |
+----------------------> |
| NOTIFY |
<--------------------------------------------+
| OK |
+-------------------------------------------->
| | |
| | |
If someone could please let me know which of these is closest to the
truth, it would go a long way for me. Also I may have made mistakes
above so feel free to correct me.. :)
--
David Stuart, SIPQuest
phone: 254-8886 x234 web: http://www.sipquest.com/
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