B-58
Cisco SIP IP Phone Administrator Guide
Appendix B SIP Call Flows
Call Flow Scenarios for Failed Calls
4.
INVITE—Cisco SIP IP phone
(User A) to primary proxy
(fourth try)
Cisco SIP IP phone retries a fourth time to connect to the primary proxy by
sending out the INVITE message.
5.
INVITE—Cisco SIP IP phone
(User A) to primary proxy (fifth
try)
Cisco SIP IP phone retries a fifth time to connect to the primary proxy by sending
out the INVITE message.
6.
INVITE—Cisco SIP IP phone
(User A) to primary proxy (sixth
try)
Cisco SIP IP phone retries a sixth time to connect to the primary proxy by
sending out the INVITE message.
7.
INVITE—Cisco SIP IP phone
(User A) to primary proxy
(seventh try)
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.
8.
INVITE—Cisco SIP IP phone
(User A) to backup proxy
Cisco SIP IP phone tries to connect to the backup proxy by sending out the
INVITE message.
9.
100 Trying—Backup proxy to
Cisco SIP IP phone (User A)
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.
10.
INVITE—Backup proxy to
Cisco SIP IP phone (User B)
Backup proxy tries to connect to User B by sending out the INVITE message.
11.
100 Trying—Cisco SIP IP phone
(User B) to backup proxy
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.
12.
180 Ringing—Cisco SIP IP
phone (User B) to backup proxy
User B sends a SIP 180 Ringing response to the backup proxy. The 180 Ringing
response indicates that User B is being alerted.
13.
180 Ringing—Backup proxy to
Cisco SIP IP phone (User A)
The backup proxy sends a SIP 180 Ringing response to User A. The 180 Ringing
response indicates that the backup proxy is being alerted.
14.
200 OK—Cisco SIP IP phone
(User B) to backup proxy
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.
15.
200 OK—Backup proxy to
Cisco SIP IP phone (User A)
Backup proxy sends a SIP 200 OK response to User A. The 200 OK response
notifies User A that the connection has been made.
16.
ACK—Cisco SIP IP phone (User
A) to backup proxy
User A acknowledges backup proxy’s Connect message.
17.
ACK—Backup proxy to
Cisco SIP IP phone (User B)
Backup proxy acknowledges User B’s Connect message.
18.
BYE—Cisco SIP IP phone
(User A) to backup proxy
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.
19.
BYE—Backup proxy to
Cisco SIP IP phone (User B)
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.
20.
200 OK—Cisco SIP IP phone
(User B) to backup proxy
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.
21.
200 OK—Backup proxy to
Cisco SIP IP phone (User A)
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.
Step
Action
Description
