How The Peer-To-Peer Sip Connection Works - ZyXEL Communications X6004 User Manual

6.11.1 How the Peer-to-Peer SIP Connection Works

The following is a basic explanation of how the X6004 creates a peer-to-peer SIP
connection between two IP phones within the same host range.
The first phone (A) sends an invite for the other phone to the X6004. This invite
1
includes its IP address and which codecs it can use.
Next, the X6004 accepts the invite on behalf of the second phone (B) and sends
2
an acknowledgement back to A.
The X6004 sends an new invite to B. This invite includes the X6004's IP address
3
and the codecs it has in common in with A.
For example, if A says it can use the G.723, Speex, and GSM codecs but the
X6004 is set to G.723, then the X6004 lets B know that only the G.723 codec is
available for the telephone call.
When B accepts the invite from the X6004, it sends back an acknowledgement.
4
The X6004 has now received confirmation from both phones of their IP addresses
and an mutually agreed upon codec.
The X6004 sends out a re-invite to both A and B that includes both IP addresses
5
and the codec to be used. This allows the two phones to create a bridge directly
with one another. The X6004 then removes itself from the communication chain.
Note: If either phone A or B requests to use a feature specific to the X6004, such as
call parking or music on hold, the X6004 interrupts the direct communication
bridge and re-establishes control of the two SIP connections.
Figure 66 A Peer-to-Peer Example
A
X6004 User's Guide
Bridge
X6004
Chapter 6 Server
B
147