Push-to-Talk Boosts SIP App Development

Jonathan Rosenberg, co-author of the Session Initiation Protocol, sees its spread into handsets as the launching pad for a wealth of more SIP application development.

Push-to-talk technology is a prime area for expansion of the Session Initiation Protocol in 2004, one of its authors said Tuesday at the SIP Summit.

The summit, a conference-within-a-conference produced by Jeff Pulver of Vonage fame, kicked off Tuesday at Supercomm in Chicagos McCormick Center.

Frequent industry speaker Jonathan Rosenberg, who coauthored the text-based VOIP protocol, counted Vonages adoption of it among its most prominent gains. Rosenberg, who is chief technology officer at Parsippany, N.J.-based dynamicsoft Inc., went on to pinpoint areas for SIPs growth in 2004, with push-to-talk technology chief among them.

Push-to-talk, the walkie-talkie mode of radio communication between preset speakers, has been the almost exclusive terrain—and gravy train—of Reston, Va.-based Nextel Communications Inc., Rosenberg said. Nextels service runs on its own nationwide, Motorola-built IDEN (Integrated Digital Enhanced Network).

Push-to-talk is a natural application for IP data networks and for SIP, he said. Its also been made practical this year by the arrival of credible SIP phones that cost less than $100. Wireless carriers, jealous of Nextels ARPU (average revenue per user) and eager to exploit the radio frequencies they have licensed at great cost, are jumping aboard.

/zimages/4/28571.gifSIP also underpins Sprints PCS push-to-talk service. Click here to read more.

Verizon Wireless Inc. was the first to launch such a service, using proprietary extensions to SIP and Motorola Inc. phones. Overland Park, Kan.-based Sprint PCS launched its PTT service last November using SIP phones from Tokyo-based Sanyo Electric Co. Both services feature Web-based contact list setup and one-to-many reach.

From the end-user device side, Motorola, Ericsson and Siemens have created a push-to-talk standard they call POC (push-to-talk over cellular), with an eye toward selling POC-compliant devices to cellular carriers. They have taken it to the Open Mobile Alliance, which has revised it and put together a more interoperable, SIP-compliant push-to-talk solution.

Rosenberg sees the spread of SIP into handsets as the launching pad for a wealth of more SIP application development. "You can have the best service in the universe, but you must have a base of clients first." In the virtuous circle he envisions, a critical mass of SIP-speaking handsets will create demand for solving some of VOIPs other issues, such as intercarrier transport.

VOIP services today, such as Vonage, Voice Pulse and Packet8, exist as isolated islands, forced to route traffic out to the PSTN (Public Switched Telephone Network) to reach subscribers on a second VOIP service. E-mail, by contrast, works on a completely open-connectivity, full-mesh model.

"Who would deploy an e-mail service that doesnt talk to other e-mail services?" Rosenberg said. The industry agrees that for the long term, VOIP networks must decide on means of interoperating.

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