Yealink SIP-T21 E2

Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
1072
4. User B accepts the call from User C.
F9. INVITE A
F11. 180 Ringing
F20. 200 OK
F1. INVITE B
F3. 180 Ringing
F5. 200 OK
F7. ACK
User A User B
User CProxy Server
F2. INVITE B
F4. 180 Ringing
F6. 200 OK
F8. ACK
F10. INVITE A
F12. 180 Ringing
F13. INVITE B ( sendonly )
F15. 200 OK
F316 200 OK
F17. ACK
F18. ACK
F19. 200 OK
F21. ACK
F22. ACK
F14. INVITE B ( sendonly )
2-way RTP channel established
No RTP Packets being sent
2-way RTP channel established
Step
Action
Description
F1
INVITE—User A to Proxy Server
User A sends an INVITE message to a
proxy server. The INVITE request is an
invitation to User B to participate in a call
session.
In the INVITE request:
 The IP address of User B is inserted
in the Request-URI field.
 User A is identified as the call