Cisco SIP IP Phone Administrator's Manual page 134

Call Flow Scenarios for Successful Calls
Step Action
6. INVITE—Cisco SIP IP phone B
to Cisco SIP IP phone A
200 OK—Cisco SIP IP phone A
7.
to Cisco SIP IP phone B
ACK—Cisco SIP IP phone B to
8.
Cisco SIP IP phone A
User B dials User C.
REFER—Cisco SIP IP phone B
9.
to Cisco SIP IP phone A
10. 501 Not Implemented—
Cisco SIP IP Phone A to Cisco
SIP IP phone B
BYE—Cisco SIP IP phone B to
11.
Cisco SIP IP phone A
200 OK—Cisco SIP IP phone A
12.
to Cisco SIP IP phone B
INVITE—Cisco SIP IP phone A
13.
to Cisco SIP IP phone C
100 Trying—Cisco SIP IP phone
14.
C to Cisco SIP IP phone A
180 Ringing—Cisco SIP IP
15.
phone C to Cisco SIP IP phone A
200 OK—Cisco SIP IP phone C
16.
to Cisco SIP IP phone A
Cisco SIP IP Phone Administrator Guide
B-24
Description
Cisco SIP IP phone B sends a mid-call INVITE to Cisco SIP IP phone A with
new SDP session parameters (IP address), which are used to place the call on
hold.
Call_ID=1
SDP: c=IN IP4 0.0.0.0
The c= SDP field of the SIP INVITE contains an 0.0.0.0. This places the call in
hold.
Cisco SIP IP phone A sends a SIP 200 OK response to Cisco SIP IP phone B.
Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP phone A. The ACK
confirms that Cisco SIP IP phone B has received the 200 OK response from
Cisco SIP IP phone A.
Cisco SIP IP phone B sends a REFER message to Cisco SIP IP phone A. The
REFER message contains the following information:
Refer-To: C
•
Referred-By: B
•
The REFER message indicates that Cisco SIP IP phone A should send an
INVITE request to Cisco SIP IP phone C.
Cisco SIP IP phone A sends a 501 Not Implemented message to
Cisco SIP IP phone B. This message indicates that the REFER message is not
supported and that Cisco SIP IP phone B should failover to Bye/Also.
Cisco SIP IP phone B sends a BYE message to Cisco SIP IP phone A. The BYE
message includes the following information:
Also: C
•
This message indicates that the 501 Not Implemented message was received in
response to a REFER message.
Cisco SIP IP phone A sends a SIP 200 OK response to Cisco SIP IP phone B. The
200 OK response notifies Cisco SIP IP phone B that the BYE message was
received.
Cisco SIP IP phone A sends a SIP INVITE request to Cisco SIP IP phone C. The
INVITE request is an invitation to User C to participate in a call session. The
INVITE request contains the following information:
• Requested-By: B
This message indicates that the INVITE was requested by Cisco SIP IP phone B.
The Cisco SIP IP phone C sends a SIP 100 Trying response to
Cisco SIP IP phone A. The 100 Trying response indicates that the INVITE
request has been received by Cisco SIP IP phone C.
Cisco SIP IP phone C sends a SIP 180 Ringing response to Cisco SIP IP phone A.
Cisco SIP IP phone C sends a SIP 200 OK response to Cisco SIP IP phone A. The
200 OK response notifies Cisco SIP IP phone A that the connection has been
made.
Appendix B SIP Call Flows