A type of distributed signaling that allows computers, handheld gadgets, and telephones to establish active links (sessions) with each other, over broadband, but without requiring much intelligence or help from the broadband network. SIP is the behind-the-scenes underpinnings of voice-over-IP services such as Vonage, AT&T’s CallVantage, and Verizon’s Broadwing. It started being built into the Microsoft operating system starting with Windows XP.
The nuts and bolts of SIP are significantly different than the nuts and bolts of the VoIP technology first fielded by cable providers, known as “NCS,” or “Network-based signaling.” In essence, SIP assumes a “dumb” broadband network. It asks nothing of broadband, really, except for a ride. Instead, SIP anchors its smarts in the end points.
SIP isn’t something consumers see. What they do see, in SIP-based offers, is an adapter box, usually tied to a low-cost voice service. The phone plugs into the box, the box plugs into the cable or DSL modem.
Because broadband doesn’t heed normal geographies, a big selling feature is the ability to call, say, your niece, who is interning abroad, using your local area code.
Another big feature of SIP-based offers is the notion of “presence” (see definition), which is one of those terms that doesn’t work well in spoken conversations. (Network provider: “We have presence.” Consumer: “Give them to me!”) Presence tracks where a person is, using what devices (cell phone, instant messaging client, office phone, home phone). It lets people control how “available” they are for conversations. Maybe you want your spouse to reach you on all possible numbers. Or, maybe you set yourself in “do not disturb” mode on all devices. Sometimes people call this “find me/follow me” (or don’t.)
The existence of SIP-based services gave rise to another new term, which began circulating in early 2005: “Over the top.” As in, SIP services ride “over the top” of ordinary broadband connections. Generally, if one guy is providing the broadband bandwidth for a second guy, who’s offering “over the top” services of a competitive nature, the first guy is the unhappiest.
That said, cable providers are outfitting their technical specifications to accommodate SIP techniques, and especially presence services, into their plans.