B-18
Cisco Unified IP Phone 7960G and 7940G Administration Guide for Release 8.0 (SIP)
OL-7890-01
Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Call Transfer Without Consultation
Figure B-7
illustrates a successful call between Cisco SIP IP phones in which two parties are in a call
and then one of the participants transfers the call to a third party without first contacting the third party.
This is called a blind or unattended transfer. In this call flow scenario, the end users are User A, User B,
and User C. They are all using Cisco SIP IP phones, which are connected via an IP network.
The call flow scenario is as follows:
1.
User A calls User B.
2.
User B answers the call.
3.
User B transfers the call to User C.
Figure B-7
Call Transfer Without Consultation
IP Network
SIP IP
Phone User B
IP
IP
IP
2. 100 TRYING
3. 180 RINGING
4. 200 OK
12. BYE
13. 200 OK
14. INVITE (Referred-By: B)
15. 100 TRYING
16. 180 RINGING
17. 200 OK
18. ACK
19. NOTIFY (Event:Refer; Subscription-State:Terminated)
20. 200 OK
2-way voice path
5. ACK
2-way voice path
User B presses blind transfer.
6. INVITE (a=sendonly)
7. 200 OK
8. ACK
9. REFER (Refer-To: C,Referred-By: B)
10. 202 ACCEPTED
11. NOTIFY (Event:Refer; Subscription-State: Active)
1. INVITE
SIP IP
Phone User A
SIP IP
Phone User C
137204
User B dials user C.