1. User Bob, who works at Acme Inc., requests a session with user Sue, who works at King Corp. 2. Bob's user agent client sends a query to Acme's SIP proxy server on how to reach Sue. 3. Acme's SIP proxy server retrieves Sue's network address from Acme's SIP registrar server. 4. Acme's SIP proxy server sends an invitation to Sue's laptop over the WAN that links the companies and through the King SIP servers. 5. Sue informs King's proxy server that she will accept the message. 6. King's proxy server relays acceptance to Bob via the WAN and Acme's SIP servers and establishes a session. 7. Real-Time Transfer Protocol or'media path provides a point-to-point connection.

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Microsoft's Exchange 12 should boost UM

Along with the boost unified messaging is enjoying from SIP, the technology is expected to get another shot in the arm later this year or in early 2007, when Microsoft Corp. releases Exchange 12, which will include a UM component.