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B-15
Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02
Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
13
INVITE—Gateway 1 to
Gateway 2
Gateway 1 sends a SIP INVITE request to Gateway 2. In
the INVITE request, a unique Call-ID is generated and the
Requested-By field indicates that User B requested the call.
14
Setup—Gateway 2 to PBX B Gateway 2 receives the INVITE request from Gateway 1
and initiates a Call Setup with User C via PBX B.
15
100 Trying—Gateway 2 to
Gateway 1
Gateway 2 sends a SIP 100 Trying response to the INVITE
request sent by Gateway 1. The 100 Trying response
indicates that Gateway 2 has received the INVITE request
but that User C has not yet been located.
16
Call Proceeding—PBX B to
Gateway 2
PBX B sends a Call Proceeding message to Gateway 2.
User C’s phone begins to ring.
17
Alerting—PBX B to Gateway 2 PBX B sends an Alert message to Gateway 2.
18
180 Ringing—Gateway 2 to
Gateway 1
Gateway 2 sends a SIP 180 Ringing response to Gateway 1.
The 180 Ringing response indicates that Gateway 2 has
located, and is trying to alert, User C.
19
Connect—PBX B to Gateway 2 User C answers the phone. PBX B sends a Connect
message to Gateway 2. The Connect message notifies
Gateway 2 that the connection has been made.
20
200 OK—Gateway 2 to
Gateway 1
Gateway 2 sends a SIP 200 OK response to Gateway 1. The
200 OK response notifies Gateway 1 that the connection
has been made.
If User C supports the media capability advertised in the
INVITE message sent by User A, it advertises the
intersection of its own and User A’s media capability in the
200 OK response. If User C does not support the media
capability advertised by User A, it sends back a 400 Bad
Request response with a 304 Warning header field.
21
Connect ACK—Gateway 2 to
PBX B
Gateway 2 acknowledges PBX B’s Connect message.
22
ACK—Gateway 1 to Gateway 2 Gateway 1 sends a SIP ACK to Gateway 2. The ACK
confirms that Gateway 1 has received the 200 OK message
from Gateway 2.
Step Action Description