Yealink SIP-T2 SERIES Administrator's Manual page 1000

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones
3. User B hangs up.
User A
Step
INVITE—User A to Proxy
F1
Server
978
Proxy Server
F1. INVITE B
F4. 100 Trying
F6. 180 Ringing
F8. 200 OK
F9. ACK
2-way RTP channel established
F12. BYE
F13. 200 OK
Action
F2. INVITE B
F3. 100 Trying
F5. 180 Ringing
F7. 200 OK
F10. ACK
F11. BYE
F14. 200 OK
Description
User A sends a SIP 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

session initiator in the From field.
A unique numeric identifier is

assigned to the call and is inserted
in the Call-ID field.
The transaction number within a

single call leg is identified in the
CSeq field.
User B