Cisco 7960G Administration Manual page 135

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
486 Busy Here—Phone B to SIP
6.
proxy server
ACK—SIP proxy server to
7.
Phone B
INVITE—SIP proxy server to
8.
Phone C
9. 180 Ringing—Phone C to SIP
proxy server
200 OK—Phone C to SIP proxy
10.
server
200 OK—SIP proxy server to
11.
Phone A
ACK—Phone A to SIP proxy
12.
server
ACK—SIP proxy server to
13.
Phone C
OL-7890-01
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 486 Busy here message to the SIP proxy server. The message
indicates that Phone B is in use and the user is not willing or able to take
additional calls.
The SIP proxy server forwards the SIP ACK to the Phone B. The ACK confirms
that the SIP proxy server has received the 486 Busy here response from Phone B.
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.
Phone A sends a SIP ACK to the SIP proxy server. The ACK confirms that
Phone A has received the 200 OK response from Phone C.
The SIP proxy server forwards the SIP ACK to the Phone C. The ACK confirms
that Phone A has received the 200 OK response from Phone C.
Cisco Unified IP Phone 7960G and 7940G Administration Guide for Release 8.0 (SIP)
Call Flow Scenarios for Successful Calls
B-35