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3G/HSPA

Winphoria Talks Back

Earlier this week, Unstrung reported on the challenges that some U.S. carriers were facing in rolling out so-called push-to-talk (PTT) services, which enable mobile phones to work like walkie-talkies. The challenges centered around time delays when rolling out these services over CDMA 1xRTT networks. And some sources suggested that this had been a particular problem for Winphoria Networks (see Walking, Not Running, to PTT).

Today, Winphoria responded to these comments, saying that the majority of these call-setup and latency problems are a function of the CDMA 1xRTT network technology itself, rather than the hardware and software platforms that would be used to implement PTT systems.

The Tewksbury, Mass.-based wireless switching equipment startup also claims to have come up with some cunning techniques to get around the delays inherent in setting up PTT calls on a CDMA 1xRTT network.

As we reported on Monday, PTT is a technology priority for CDMA and GPRS carriers in the U.S, but not one they are keen to talk about. These carriers look upon Nextel Communications Inc. (Nasdaq: NXTL), which has its own push-to-talk system and average revenue per user (ARPU) of around $70 a month, with envious eyes.

Analysts say carriers such as Sprint PCS (NYSE: PCS) are working on systems that use a wireless switching architecture -- to detect and route the voice-over-IP PTT calls from one person to another or multiple people on a network -- combined with server-based software that brings the different users on the network for group calls.

Winphoria is rumored to be one of the suppliers whose technology Sprint is testing as a possible PTT system for its CDMA 1xRTT network. But neither carrier nor startup will comment on suggestions that they are working together.

However, Winphoria's business is about supplying PTT switching systems to CDMA carriers, so the company wanted to talk about the call-setup times and voice-latency issues that we raised in our last story. The call-setup delays we mentioned for CDMA aren't the fault of the Winphoria technology, according to Steve Kish, director of product marketing at the company, but because CDMA 1xRTT handsets and networks have a "wake-up period" before they start sending and receiving data packets.

"You hear CDMA carriers talk about 'always-on' networks… but they aren't really," says Kish. Rather, when the user tries to make a data connection, the handset has to request a session and be assigned a resource in the network before packet transmission can begin. This takes around four seconds, according to Kish. "We don't introduce more than 200 milliseconds delay," he insists.

However, a four-second delay is a long time in a PTT system. So Winphoria has been working on ways to get around this delay with some little tricks on its handset software. The client software fulfills three different roles: It translates a user's keystrokes into SIP (session initiation protocol) commands; interfaces between the handset and the network; and converts the user's voice so it can be routed over a VOIP transport.

However, that's not all the client software does. In order to try to get around the call-setup delay, the Winphoria client starts making the network wakeup call as soon as the user goes to look for a PTT contact in their address book. Kish also suggests that services could be configured so that the client might send a text message that will initiate the PTT session. Another technique considered would be voice buffering, allowing the user to start talking before the PTT session starts. Kish says Winphoria is working with handset manufacturers on its client software but has no plans to commercialize it.

Network latency -- the amount of time it takes for data packets to reach their destination on the network -- is also seen as another PTT issue. In VOIP situations, network latency leads to jittery sound and aggravating enforced pauses in the conversation. If you have streamed a conference call over the Web using a media player, you are probably familiar with the sound of network latency.

However, Kish says that the Winphoria system has a voice latency of around 800 milliseconds. That kind of delay, he says, is something you would notice if you were standing facing the person you were calling, but not if you were phoning them from the next room.

And CDMA 1xRTT systems are not just about delays. Because the network is a packet-based technology, Kish suggests that PTT could in the future be used for instant and picture messaging as well as voice calls. Indeed, a user could switch between voice calls and text- or picture-based messaging in the same session, he says.

— Dan Jones, Senior Editor, Unstrung www.unstrung.com
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