Cisco 7960G Administrator's Manual page 133

Appendix B SIP Call Flows
Step Action
INVITE—Phone A to SIP proxy
1.
server
INVITE—SIP proxy server to
2.
SIP redirect server
300 Multiple Choices—SIP
3.
redirect server to SIP proxy
server
ACK—SIP proxy server to
4.
redirect server
INVITE—SIP proxy server to
5.
Phone B
180 Ringing—Phone B to SIP
6.
proxy server
180 Ringing—SIP proxy server
7.
to Phone A
The timeout expires before the phone is answered.
CANCEL (Ring Timeout)—SIP
8.
proxy server to Phone B
9. 200 OK—Phone B to SIP proxy
server
10. INVITE—SIP proxy server to
Phone C
180 Ringing—Phone C to SIP
11.
proxy server
200 OK—Phone C to SIP proxy
12.
server
200 OK—SIP proxy server to
13.
Phone A
Description
Phone A sends a SIP INVITE request to the SIP proxy server. The request is an
invitation to User B to participate in a call session. In the INVITE request:
The phone number of User B is inserted in the Request-URI field in the form
•
of a SIP URL. The SIP URL identifies the address of User B and takes a form
similar to an e-mail address (user@host, where user is the telephone number
and host is either a domain name or a numeric network address). For example,
the Request-URI field in the INVITE request to User B appears as "INVITE
sip:555-0199@companyb.com; user=phone." The "user=phone" parameter
distinquishes that the Request-URI address is a telephone number rather than
a username.
Phone A is identified as the call session initiator in the From field.
•
A unique numeric identifier is assigned to the call and is inserted in the
•
Call-ID field.
• The transaction number within a single call leg is identified in the CSeq field.
The media capability User A is ready to receive is specified.
•
The SIP proxy server sends the SIP INVITE request to the SIP redirect server.
The SIP redirect server sends a SIP 300 Multiple choices message to the SIP proxy
server. The message indicates that User B can be reached either at Phone B or
Phone C.
The SIP proxy server sends the SIP ACK to the SIP redirect server.
The SIP proxy server sends a SIP INVITE request to Phone B. The request is an
invitation to User B to participate in a call session.
Phone B sends a SIP 180 Ringing response to the SIP proxy server.
The SIP proxy server sends a SIP 180 Ringing response to Phone A.
The SIP proxy server sends a CANCEL request to Phone B to cancel the
invitation.
Phone B sends a SIP 200 OK response to the SIP proxy server. The response
confirms receipt of the cancellation request.
The SIP proxy server sends a SIP INVITE request to Phone C. The request is an
invitation to User C to participate in a call session.
Phone C sends a SIP 180 Ringing response to the SIP proxy server.
Phone C sends a SIP 200 OK response to the SIP proxy server.
The SIP proxy server forwards the SIP 200 OK response to Phone A.
Cisco SIP IP Phone Administrator Guide, Release 6.x and 7.x
Call Flow Scenarios for Successful Calls
B-37