Cisco SIP IP Phone Administrator's Manual page 168

Call Flow Scenarios for Failed Calls
Step Action
4. INVITE—Cisco SIP IP phone
(User A) to primary proxy
(fourth try)
5. INVITE—Cisco SIP IP phone
(User A) to primary proxy (fifth
try)
6. INVITE—Cisco SIP IP phone
(User A) to primary proxy (sixth
try)
7. INVITE—Cisco SIP IP phone
(User A) to primary proxy
(seventh try)
INVITE—Cisco SIP IP phone
8.
(User A) to backup proxy
100 Trying—Backup proxy to
9.
Cisco SIP IP phone (User A)
INVITE—Backup proxy to
10.
Cisco SIP IP phone (User B)
100 Trying—Cisco SIP IP phone
11.
(User B) to backup proxy
180 Ringing—Cisco SIP IP
12.
phone (User B) to backup proxy
13. 180 Ringing—Backup proxy to
Cisco SIP IP phone (User A)
14. 200 OK—Cisco SIP IP phone
(User B) to backup proxy
15. 200 OK—Backup proxy to
Cisco SIP IP phone (User A)
16. ACK—Cisco SIP IP phone (User
A) to backup proxy
17. ACK—Backup proxy to
Cisco SIP IP phone (User B)
18. BYE—Cisco SIP IP phone
(User A) to backup proxy
19. BYE—Backup proxy to
Cisco SIP IP phone (User B)
20. 200 OK—Cisco SIP IP phone
(User B) to backup proxy
200 OK—Backup proxy to
21.
Cisco SIP IP phone (User A)
Cisco SIP IP Phone Administrator Guide
B-58
Description
Cisco SIP IP phone retries a fourth time to connect to the primary proxy by
sending out the INVITE message.
Cisco SIP IP phone retries a fifth time to connect to the primary proxy by sending
out the INVITE message.
Cisco SIP IP phone retries a sixth time to connect to the primary proxy by
sending out the INVITE message.
Cisco SIP IP phone retries a seventh time to connect to the primary proxy. If the
connection is not successful after this trial, the "Network Delay, Trying Backup"
message displays on the Phone.
Cisco SIP IP phone tries to connect to the backup proxy by sending out the
INVITE message.
Backup proxy sends a SIP 100 Trying response to Cisco SIP IP phone. The
100 Trying response indicates that the INVITE request has been received by the
backup proxy.
Backup proxy tries to connect to User B by sending out the INVITE message.
User B sends a SIP 100 Trying response to backup proxy. The 100 Trying
response indicates that the INVITE request has been received by User B.
User B sends a SIP 180 Ringing response to the backup proxy. The 180 Ringing
response indicates that User B is being alerted.
The backup proxy sends a SIP 180 Ringing response to User A. The 180 Ringing
response indicates that the backup proxy is being alerted.
User B sends a SIP 200 OK response to the backup proxy. The 200 OK response
notifies the backup proxy that the connection has been made.
Backup proxy sends a SIP 200 OK response to User A. The 200 OK response
notifies User A that the connection has been made.
User A acknowledges backup proxy's Connect message.
Backup proxy acknowledges User B's Connect message.
User A terminates the call session and sends a SIP BYE request to backup proxy.
The BYE request indicates that User A wants to release the call.
Backup proxy terminates the call session and sends a SIP BYE request to User B.
The BYE request indicates that the backup proxy wants to release the call.
User B sends a SIP 200 OK response to the backup proxy. The 200 OK response
notifies the backup proxy that User B has received the BYE request.
Backup proxy sends a SIP 200 OK response to User A. The 200 OK response
notifies User A that the backup proxy has received the BYE request.
Appendix B SIP Call Flows