Dear PJSIP-users,
This is my first time posting to this list and I'm very beginner to the subjects about STUN, ICE and PJSIP.
Currently I'm working in a project with a SIP proxy and softphones. When a softphone 'A' calls another softphone 'B', 'A' will provide early media to 'B' as depicted in the diagram below.
The diagram below doesn't represent what we have implemented already. It just represents what we think we can do with PJSIP, in a overview. That is, this diagram is the representation of what could be our final solution, if the answers for the following questions will be yes.
Softphone A (UAC) Softphone B (UAC)
|-------------------------------------- | |---------------------------------|
| | | - Is behind NAT |
| | | - Run PJSIP + ICE |
| - Has public IP:port | | |
| - Run PJSIP in a softphone| |--------------------------------|
| - PJSIP + ICE | |
| | |
|---------------------------------------| |
| |
| ----------------------------------------ICE message ------------------------------------>|
| |
| |
|<----------------------------------------ICE message -------------------------------------|
| |
| |
| ----------------------------------------SIP INVETE ------------------------------------->|
| |
| |
|<----------------------------------------SIP 183 --------------------------------------------|
| |
| . |
| . |
| . |
| . |
|-----------------------------------Early media--------------------------------------------->|
| |
In our solution, one softphone will always has a public IP : PORT. Such softphone 'A' will always be the provider of early media. The softphone 'B' behind NAT will always be the consumer of the early media. I this scenario I ask:
1 - Is it necessary to use a STUN server, to the SIP 183 message carries the correct IP address and port, where 'A' should send its media?
2 - By doing a test of this scenario and using WireShark, we can see some ICE messages being exchanged between 'A' and 'B'. Why the peers send and receive ICE messages? Is it automatically and transparently controlled by PJSIP?
We run this test without a STUN server.
3 - If the peers really exchange ICE messages, is it possible to trigger such protocol whenever our softphone needs?
4 - I guess that for this specific scenario a STUN server/client will not be necessary, because I guess the peers using PJSIP are exchanging information about IP address, via ICE, what in some way is substituting a STUN work. Am I correct?
Any hint will be very helpful!
Best regards.
RODRIGO PIMENTA CARVALHO
Inatel Competence Center
Software
Ph: +55 35 3471 9200 RAMAL 979
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