Making Push-to-Talk Look Easy

Messaging — not the instant kind most teenagers are familiar with, but the kind that ping-pongs across a network carrying all the necessary information about a call that can tell a brainless network who you are, who you want to talk to and whether or not they want to talk to you — can be an insufferably tedious but indispensable tool for troubleshooting a network. For non-Nextel networks — those not built from the ground up to do push-to-talk and that carry their signaling and session control across separate paths from their traffic — messaging can be 100 times as insufferable and just as indispensable.

That's how many more control messages are required to maintain a typical push-to-talk (P2T) call in emerging networks. And when conferencing or broadcast calling are involved — well, you can either break out the Tylenol or break out the Agilent.

Brian Moody, software engineer for VoIP analysis applications at Agilent Technologies, took on the task of building an analysis system capable of corralling, correlating and analyzing the enormous number of messages in this seemingly pregnant P2T technology. Last month, the company introduced the fruits of his labor: a system the company says is the first to monitor and manage wireless SIP-based push-to-talk services. It is an extension of Agilent's NgN Analysis System, which is a distributed, remote-controllable network monitoring system for next-generation networks.

Moody came over from the insurance biz, having developed systems for that data intensive industry as well as for imaging systems. “The real-time aspect [of voice] is a fun challenge,” he said.

It also is critical — not just for Agilent itself to get out in front of this market, but for the wireless industry overall, which will be squabbling ad infinitum about what constitutes a quality P2T service. Will it be the speed of the initial connection, or only subsequent connections? Will it be ubiquity or consistency? Will SIP trump IDEN? Ultimately the consumer will decide, but without a proper analysis system to help operators build the best service possible, operators may find themselves supporting a push-to-walk service.

Moody said operators recognize that to ensure the service level they are communicating to their customers, they have to have a system in place.

“We believe we are the only ones who can give a networkwide view of the signaling traffic from all the softswitches in a network,” he said. “Your only other option is a standard protocol analyzer, but that is not a coordinated effort and doesn't correlate messages from across the network.”

Agilent already has its VoIP analysis tools in many Tier 1 networks. The P2T extension is currently under trial with three operators, two of which are in the U.S.

The NgN Analysis System is both a testing and analysis tool as well as an OSS component. It correlates the SIP signaling messages from every leg of a call into a single call record and applies performance metrics to determine the service level of each call. It also stores historical records on which it can do trend analysis to identify service degradation and assist in troubleshooting, using Agilent's NetExpert network management system.

So far, Agilent has been able to identify erroneous connectivity statuses between servers and handsets when determining presence and availability of the handset. And more often than not, it has been able to point to the mundane issues of improper provisioning. But Agilent also has been able to help equipment makers fix bugs in their software logic.

“They sometimes make certain assumptions that just aren't accurate and have not been factored into certain scenarios,” Moody said. One area Agilent may have trouble with is the SIP protocol itself. While SIP has been accepted by the 3GPP as the call control standard, implementations tend to be anything but standard. Moody cited the core voice-call feature, “intent-to-transfer,” as one example.

“That they haven't gotten around to standardizing that means vendors all over the place have been implementing that however they see fit,” Moody said. “That opens the door for all kinds of coroner case problems and connectivity issues.”

Analysts agree. “People forget that while they may be using SIP, with all the proprietary extensions, it is by no means standard. And I would put push-to-talk in that same category,” said David Fraley, principal analyst at Gartner Dataquest.

Fraley added that because of Agilent's size, it could add any P2T SIP stack it needed in short order.

At the heart of SIP is the ability to communicate presence and availability not only to the network but also to other users. Dynamicsoft, the company whose chief scientist, Jonathan Rosenberg, is largely responsible for developing the SIP protocol, said that the “buddy list” concept (inherent to P2T) increases the call completion rate by 40%.

However, at the heart of presence and availability is the abundance of messaging required to communicate them. And initial call completion is just the beginning.

“To work properly in push-to-talk, you need to know if the other person is available. There is no reason for you to push the button if they are not,” Moody said.

The challenge for Agilent and its customers is keeping track of presence status and communicating that status in real time to the network and those within the users' circles of friends. If presence information is wrong or a handset doesn't respond when the network thinks it should, both the user and the network complicate the problem by adding unnecessary retransmissions.

“It creates a very complex call flow and if just one person isn't able to talk when they think they should, that goes into the call center as a complaint,” said Paul Capozzoli, [director] of marketing for Agilent.

November being the month that wireless number portability goes into effect, mobile customers are likely to call into their carriers' call centers less often than they used to. They'll simply jump ship — and maybe take all their buddies with them.