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Call Flow Scenarios for Successful Calls
Step
Action
6.
200 OK—Cisco SIP IP phone A
to Cisco SIP IP phone B
7.
ACK—Cisco SIP IP phone B to
Cisco SIP IP phone A
The RTP channel between Cisco SIP IP phone A and Cisco SIP IP phone B is torn down.
INVITE—Cisco SIP IP phone B
8.
to Cisco SIP IP phone C
180 Ringing—Cisco SIP IP
9.
phone C to Cisco SIP IP phone B
200 OK—Cisco SIP IP phone C
10.
to Cisco SIP IP phone B
ACK—Cisco SIP IP phone B to
11.
Cisco SIP IP phone C
A two-way RTP channel is established between Cisco SIP IP phone B and Cisco SIP IP phone C.
BYE—Cisco SIP IP phone B to
12.
Cisco SIP IP phone C
13.
200 OK—Cisco SIP IP phone C
to Cisco SIP IP phone B
The RTP channel between Cisco SIP IP phone B and Cisco SIP IP phone C is torn down.
INVITE—Cisco SIP IP phone B
14.
to Cisco SIP IP phone A
200 OK—Cisco SIP IP phone A
15.
to Cisco SIP IP phone B
Cisco SIP IP Phone Administrator Guide
B-12
Description
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 SIP INVITE request to Cisco SIP IP phone C. The
INVITE request is an invitation to User C to participate in a call session.
Cisco SIP IP phone C sends a SIP 180 Ringing response to Cisco SIP IP phone B.
Cisco SIP IP phone C sends a SIP 200 OK response to Cisco SIP IP phone B. The
200 OK response notifies Cisco SIP IP phone B that the connection has been
made.
If Cisco SIP IP phone B supports the media capability advertised in the INVITE
message sent by Cisco SIP IP phone A, it advertises the intersection of its own
and Cisco SIP IP phone A's media capability in the 200 OK response. If
Cisco SIP IP phone B does not support the media capability advertised by
Cisco SIP IP phone A, it sends back a 400 Bad Request response with a 304
Warning header field.
Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP phone C. The ACK
confirms that Cisco SIP IP phone B has received the 200 OK response from
Cisco SIP IP phone C.
The ACK might contain a message body with the final session description to be
used by Cisco SIP IP phone C. If the message body of the ACK is empty,
Cisco SIP IP phone C uses the session description in the INVITE request.
The call continues and then User B hangs up. Cisco SIP IP phone B sends a SIP
BYE request to Cisco SIP IP phone C. The BYE request indicates that User B
wants to release the call.
Cisco SIP IP phone C sends a SIP 200 OK message to Cisco SIP IP phone B. The
200 OK response notifies Cisco SIP IP phone B that the BYE request has been
received. The call session between User A and User B is now terminated.
Cisco SIP IP phone B sends a mid-call INVITE to Cisco SIP IP phone A with the
same call ID as the previous INVITE and new SDP session parameters
(IP address), which are used to reestablish the call.
Call_ID=1
SDP: c=IN IP4 181.23.250.2
To reestablish the call between phone A and phone B, the IP address of phone B
is inserted into the c= SDP field.
Cisco SIP IP phone A sends a SIP 200 OK response to Cisco SIP IP phone B.
Appendix B
SIP Call Flows
- Quick Links:
- Using the Command-Line Interface
Hide quick links:
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