Monthly Archives: June 2012

From SIP to RTP (Part 5) – Trunks & surroundings

Definition of Trunks Trunk lines are the phone lines coming into the PBX from the telephone provider. Trunking saves cost, because there are usually fewer trunk lines than extension lines, since it is unusual in most offices to have all … Continue reading

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From Sip to RTP (Part 4) – Invite & Register friendship

INVITE Session Call Establishment Call Flow The UAC (Alice) sends an INVITE message to Bob (UAS). The UAS receives the request and responds with a 100 Trying. The UAS sends a 180 Ringing response to the UAC when the phone … Continue reading

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From Sip to RTP (Part 3) – B2BUA… What ?!

Def. of Back-to-Back User Agent (B2BUA). A B2BUA essentially bolts two user agents together in a back-to-back fashion, similar to two people standing back to back. A B2BAU establishes a two-legged call, keeping the SIP server in the middle of … Continue reading

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