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SIP AG Call Flow
Figure 3-5 shows the SIP AG call flow.
- The calling party POTS1 picks up a phone. When the SIP AG detects that the calling party picks up a phone, it allocates DSP resources to the calling party and plays a dial tone.
- When detecting that the calling party dials the first digit of a dialing number, SIP AG1 stops the dial tone and matches the digit with a digitmap.
- When detecting that the calling party dials the last digit of the dialing number, the SIP AG matches the dialing number with digitmaps. When the dialing number matches a digitmap, the SIP AG constructs an Invite message and sends it to the IMS proxy server.
- The IMS proxy server receives the Invite message from the calling party, analyzes the called number, finds SIP AG2 to which the called party belongs, sends an Invite message to the called party, and returns a 100 Trying message to SIP AG1.
- The called party receives the Invite message and responds with a 100 Trying message, indicating that it is receiving the called number.
- SIP AG2 receives a complete called number, requests the called party POTS2 to ring, and sends a 180 Ringing message to SIP AG1. The calling party then hears the ringback tone.
- The called party POTS2 picks up a phone. When SIP AG2 detects that the called party picks up a phone, it sends a 200 OK message to the calling party POTS1.
- The calling party stops playing the ringback tone, and SIP AG1 sends an ACK message to the called party.
- A call is established.
- The calling party hangs up.
- When detecting that the calling party hangs up the phone, the IMS proxy server sends a BYE message to the called party.
- SIP AG2 receives the BYE message, plays the busy tone to the called party, and sends a 200 OK message to the calling party.
- The called party hangs up the phone.
