B-32
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
Figure B-11 Network Call Forwarding (Unconditional)
Step
Action
Description
1.
INVITE—Phone A to SIP proxy
server
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:[email protected]; 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.
2.
INVITE—SIP proxy server to
SIP redirect server
The SIP proxy server sends the SIP INVITE request to the SIP redirect server.
IP
IP
8. 200 OK
5. INVITE C
7. 200 OK
10. ACK
6. 180 Ringing
1. INVITE B
9. ACK
3. 302 Moved Temporarily
2. INVITE B
4. ACK
IP Network
SIP IP
Phone
User A
SIP IP
Phone
User B
SIP IP
Phone
User C
Proxy
Server
Redirect
Server
IP
41471
2-way RTP channel
