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Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02
Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
10
200 OK—Cisco SIP IP phone C
to Cisco SIP IP phone B
Cisco SIP IP phone C sends a SIP 200 OK response to
Cisco SIP IP phone B. The 200 OK response notifies Cisco
SIP IP phone B that the connection has been made.
If Cisco SIP IP phone C supports the media capability
advertised in the INVITE message sent by Cisco SIP IP
phone B, it advertises the intersection of its own and Cisco
SIP IP phone B’s media capability in the 200 OK response.
If Cisco SIP IP phone C does not support the media
capability advertised by Cisco SIP IP phone B, it sends
back a 400 Bad Request response with a 304 Warning
header field.
11
ACK—Cisco SIP IP phone B to
Cisco SIP IP phone C
Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP
phone C. The ACK confirms that Cisco SIP IP phone B has
received the 200 OK response from Cisco SIP IP phone C.
The ACK might contain a message body with the final
session description to be used by Cisco SIP IP phone C. If
the message body of the ACK is empty, Cisco SIP IP phone
C uses the session description in the INVITE request.
A two-way RTP channel is established between SIP IP phone B and SIP IP phone C.
12
INVITE—Cisco SIP IP phone B
to Cisco SIP IP phone A
Cisco SIP IP phone B sends a mid-call INVITE to Cisco
SIP IP phone A with the same call ID as the previous
INVITE and new SDP session parameters (IP address),
which are used to reestablish the call.
Call_ID=1
SDP: c=IN IP4 181.23.250.2
To reestablish the call between phone A and phone B, the
IP address of phone B is inserted into the c= SDP field.
13
200 OK—Cisco SIP IP phone A
to Cisco SIP IP phone B
Cisco SIP IP phone A sends a SIP 200 OK response to
Cisco SIP IP phone B.
14
ACK—Cisco SIP IP phone B to
Cisco SIP IP phone A
Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP
phone A. The ACK confirms that Cisco SIP IP phone B has
received the 200 OK response from Cisco SIP IP phone A.
SIP IP phone B acts as a bridge mixing the RTP channel between User A and User B with the channel
between User B and User C; establishing a conference bridge between User A and User C.
Step Action Description