B-17
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
10.
200 OK—Phone B to Phone C
Phone B sends a SIP 200 OK response to Phone C. The response notifies
Phone C that the connection has been made.
11.
ACK—Phone C to Phone B
Phone C sends a SIP ACK to Phone B. The ACK confirms that Phone C has
received the 200 OK response from Phone B.
The ACK might contain a message body with the final session description to
be used by Phone B. If the message body of the ACK is empty, Phone B uses
the session description in the INVITE request.
A two-way RTP channel is established between Phone B and Phone C.
12.
INVITE—Phone B to Phone C
Phone B sends a midcall INVITE to Phone C with new Session Description
Protocol (SDP) attribute parameter.
SDP: a=sendonly
The a= SDP field of the SIP INVITE contains sendonly. This value places
the call on hold.
13.
200 OK—Phone C to Phone B
Phone C sends a SIP 200 OK response to Phone B.
14.
ACK—Phone B to Phone C
Phone B sends a SIP ACK to Phone C. The ACK confirms that Phone B has
received the 200 OK response from Phone C.
The RTP channel between Phone B and Phone C is torn down.
15.
INVITE—Phone B to Phone A
User B takes User A off hold. Phone B sends a SIP INVITE request to
Phone A with the same call ID as the previous INVITE and a new SDP
attribute parameter (sendrecv), which is used to reestablish the call.
16.
200 OK—Phone A to Phone B
Phone A sends a SIP 200 OK response to Phone B.
17.
ACK—Phone B to Phone A
Phone B sends a SIP ACK to Phone A. The ACK confirms that Phone B has
received the 200 OK response from Phone A.
A two-way RTP channel is reestablished between Phone A and Phone B.
18.
BYE—Phone B to Phone A
The call continues and then User B hangs up. Phone B sends a SIP BYE
request to Phone A. The request indicates that User B wants to release the
call.
19.
200 OK—Phone A to Phone B
Phone A sends a SIP 200 OK response to Phone B. The response notifies
Phone B that the BYE request has been received. The call session between
User A and User B terminates.
The RTP channel between Phone A and Phone B is torn down.
20.
INVITE—Phone B to Phone C
User B takes User C off hold. Phone B sends a SIP INVITE request to
Phone C with the same call ID as the previous INVITE (sent to Phone C) and
a new SDP attribute parameter (sendrecv), which is used to reestablish the
call.
21.
200 OK—Phone C to Phone B
Phone C sends a SIP 200 OK response to Phone B.
22.
ACK—Phone B to Phone C
Phone B sends a SIP ACK to Phone C. The ACK confirms that Phone B has
received the 200 OK response from Phone A.
A two-way RTP channel is reestablished between Phone B and Phone C.
Step
Action
Description
