DTMF Decode

• DTMF program monitors COS and DTMF

• Once detected DTMF sequence passed to the decode script

• Decode script checks custom_decode for matches

• Assuming a call is decoded, call script is started with the node number as the argument

Call Script

• Best server is determined by using find_best_server script

• Best server is asked for latest IP of node being called

• If IP received is different from IP in hosts file, a new hosts file is d/l from best server

• Irlp_call is started, and a TCP connection is made to the called node on port 15425

IRLP_CALL / IRLP_ANSWER

• Remote node starts irlp_answer in response to TCP call on port 15425

• PGP security performs a dual challenge to ensure calling node is an IRLP node

• Codec (GSM/ADPCM) is determined

• Irlp_call and irlp_answer start speak freely software on UDP ports 2074 and 2075

During the Call

• Irlp_call and irlp_answer send keepalives in the background. If keepalive fails, the connection drops (every 15 sec)

• Irlp_call and irlp_answer keep open info channel to pass dtmf regeneration info, disconnect/timeout message

Disconnects

• Disconnecting node uses TCP info channel to send disconnect message. Both nodes run the off script

• Unexpected drop in the TCP connection prompts reset of IRLP node

• If the timeout elapses, disconnect is sent