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Call path replacement in OCS

One of OCS 2007's most useful new features has a variety of names. You can call it "simultaneous ring" or "call forking"; the idea is that an incoming call can cause all of your defined phones to ring at the same time. For example, your desk phone, logged-in Communicator session, and cell phone can all ring at once, so you can answer the call from wherever you happen to be. However, this leads to a question: doesn't this tie up more phone lines?

The answer (as with so many other telephony issues) is "it depends". (In fact, I should start a new blog category called "It Depends" just for this kind of question!) Consider two scenarios:

• Alice is using Communicator and calls Bob, who's logged in to Communicator and has a Tanjay phone on his desk. In this case, Alice's call can ring Bob's two devices without tying up any lines through the gateway-- because there are no PSTN or PBX components involved, there's no need to take any lines from the gateway.
• Carol is an outside PSTN caller; she calls Dave, who has a TDM PBX phone, Communicator, and a cell phone. In this scenario, Carol's already occupying one line (from her phone to the OCS gateway). When OCS rings his cell phone, that will use a PSTN line. Ringing Dave's PBX phone may or may not require an additional line, depending on the connection between OCS and the PBX.

However, thanks to call path replacement, under many circumstances OCS can provide simultaneous ring without taking up additional lines. However, whether or not this works depends on the PBX (if any) in use, because not all PBX systems support this feature.

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