Switching to VoIP

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Key Issues: Replacing Call Signaling with VoIP

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and more enterprise-savvy way to build a phone system is using CallManager,

Cisco’s full-fledged softPBX.

CallManager supports one endpoint-signaling protocol: SCCP. On the server, capa-

bilities negotiation and other setup functions are handled by H.323, but it’s SCCP

that signals call progress events to the phones themselves. So, it’s fair to say that

Cisco’s endpoint signaling is mainframe-like, because some big pieces of the signal-

ing process occur on the server rather than “over the wire” between the server and

the phone.

In order to use analog, SIP, or H.323 phones with a CallManager PBX, those phones

must be connected to a media gateway, where their signals are trunked back to the

CallManager, preferably using SCCP. In Cisco’s environment, it’s the media gate-

way that is multiprotocol aware—not the PBX.

Asterisk

A softPBX built with Asterisk is probably more like an Avaya or Nortel softPBX than

like a Cisco one. Asterisk has all the signaling capabilities it needs on one PC server.

Whereas a Cisco setup requires trunks to media gateways in order to support non-

SCCP endpoints, Avaya’s MultiVantage and Nortel’s Meridian IP-enabled softPBX

systems, like Asterisk, support all the necessary signaling standards in one machine.

Key ...