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Appendix B
SIP Call Flows
Step
Action
INVITE—Cisco SIP IP phone A
1.
to SIP proxy server
2.
INVITE—SIP proxy server to
SIP redirect server
300 Multiple Choices—SIP
3.
redirect server to SIP proxy
server
4.
INVITE—SIP proxy server to
Cisco SIP IP phone B
180 Ringing—Cisco SIP IP
5.
phone B to SIP proxy server
180 Ringing—SIP proxy server
6.
to Cisco SIP IP phone A
The timeout expires before the phone is answered.
CANCEL (Ring Timeout)—SIP
7.
proxy server to Cisco SIP IP
phone B
200 OK—Cisco SIP IP phone B
8.
to SIP proxy server
INVITE—SIP proxy server to
9.
Cisco SIP IP phone C
180 Ringing—Cisco SIP IP
10.
phone C to SIP proxy server
200 OK—Cisco SIP IP phone C
11.
to SIP proxy server
12.
200 OK—SIP proxy server to
Cisco SIP IP phone A
Description
Cisco SIP IP phone A sends a SIP INVITE request to the SIP proxy server. The
INVITE 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:555-0002@companyb.com; user=phone." The "user=phone"
parameter distinquishes that the Request-URI address is a telephone number
rather than a username.
Cisco SIP IP 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.
SIP proxy server sends the SIP INVITE request to the SIP redirect server.
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 SIP phone B
or Cisco SIP IP phone C.
SIP proxy server sends a SIP INVITE request to Cisco SIP IP phone B. The
INVITE request is an invitation to User B to participate in a call session.
Cisco SIP IP phone B sends a SIP 180 Ringing response to the SIP proxy server.
SIP proxy server sends a SIP 180 Ringing response to Cisco SIP IP phone A.
SIP proxy server sends a CANCEL request to Cisco SIP IP phone B to cancel the
invitation.
Cisco SIP IP phone B sends a SIP 200 OK response to the SIP proxy server. The
response confirms receipt of the cancellation request.
SIP proxy server 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 the SIP proxy server.
Cisco SIP IP phone C sends a SIP 200 OK response to the SIP proxy server.
SIP proxy server forwards the SIP 200 OK response to Cisco SIP IP phone A.
Call Flow Scenarios for Successful Calls
Cisco SIP IP Phone Administrator Guide
B-41
- Quick Links:
- Using the Command-Line Interface
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