In an increasingly digital world, the distinction between voice and data has grown thin. On networks using Internet-style technology, the pipeline simply doesn't know — or doesn't care — whether it's carrying an alphanumeric string or a spoken command.

And in this increasingly digital world, Internet-style technology — transmission control protocol/Internet protocol (TCP/IP) — has emerged as the standard for transmitting information across the room or around the world. That's why this standard — informally called IP — is likely to become a major force in wireless voice and data communications for first responders.

“I think we're moving to IP networks, both commercial and private,” said Dan Bart, senior vice president, standards and special projects, at the Telecommunications Industry Association. “Some of that will be taken advantage of by the public-safety community.”

“Circuit-based links and proprietary-based communications links are on the way out,” said Chuck Jackson, vice president and director, system operations, at Motorola. In contrast, IP technology “is getting to be the norm,” according to Jackson.

First responders are starting to use IP technology in two kinds of wireless systems. The first are land mobile radio (LMR) networks for transmitting voice and data on privately licensed frequencies. The second are wireless broadband networks that use unlicensed spectrum.

In the LMR world, for example, Motorola's Astro 25 system uses the Project 25 (P25) protocol, a public-safety industry standard, to transmit data and digitized voice over the air, but the rest of the system is IP-based. EFJohnson's Netelligent system also uses IP on the network backbone. M/A-COM's P25^IP system offers IP on the backbone and P25 over the air. Its OpenSky product uses IP throughout, including a modified version of that protocol on the wireless link; its NetworkFirst product allows radios of many types to interoperate over an IP backbone; and its recently announced VIDA platform provides voice, interoperability, data and access over an IP infrastructure.

At the same time, some public-safety agencies are experimenting with communications over wireless data networks that operate in the 2.4 GHz band. The Pratt, Kan., police department, for example, supplements its 450 MHz radio system with voice-over-IP (VoIP) telephones on a 2.4 GHz network provided by Alvarion of Carlsbad, Calif.

One major advantage IP offers is interoperability. IP on an LMR network's backbone serves as a kind of lingua franca, allowing communications among radios that employ different frequencies, as well as different digital and analog technologies, over the air. If an agency using M/A-COM's NetworkFirst system wanted to communicate with first responders using an analog radio network from another vendor, for instance, M/A-COM could connect the two systems via a gateway, “a box with a couple of cards in it,” Facella said. “NetworkFirst would talk IP to the box, and then the box would talk analog audio to the other vendor's system.”

With IP on the backbone, “all the analog systems can co-exist with the more digital systems of the future, which are P25 based,” said Amalesh Sanku, vice president of marketing at EFJohnson.

There's a limit, however, to how many disparate radio systems can interoperate over an IP backbone, Bart cautions. “Some of these network-based things can handle the ordinary traffic, but capacitywise they weren't designed to solve a large-scale, multi-jurisdictional kind of thing.”

A second advantage IP offers is lower cost. An IP-based backbone for a radio network uses the same kinds of off-the-shelf components as a local or wide area data network, and those tend to be less expensive than the hardware designed specifically for LMR, Sanku said. “The cost is spread over several industries, so it's much lower.”

Also, agencies have a simpler time hiring personnel to manage IP-based networks than traditional LMR networks. “For administering a radio system that sort of looks like a [local area network], it's pretty easy to find those people, and it's pretty easy to train them,” Facella said. Agencies with IP-based communications systems “still need their RF people, but they don't need a lot more of them.”

IP-based systems allow agencies to easily prioritize communications, Sanku said. On a network shared by several government organizations, for example, messages from public-safety officers can take precedence over messages from dogcatchers and garbage collectors, and emergency messages can take precedence over routine communications.

Because it's a standard technology for transmitting data, IP also makes it easier for first responders to deploy mobile computing applications along with voice, Jackson said. “It's really bringing the desktop out to the car,” although graphics-heavy applications, such as transmitting building plans to fire vehicles, won't see widespread use until more agencies gain access to more radio spectrum, he said.

With voice and data integrated on an IP-based network, vendors could someday incorporate card-swiping devices into radios, so police can swipe drivers' licenses and quickly retrieve data from motor vehicle databases, Sanku said. The Pratt, Kan., police use their IP-based broadband network to view images from wireless security cameras, installed downtown, on their mobile computers. “You can also record it to the server just by right clicking and hitting ‘Record,’” said Steve Holmes, the department's acting chief.

Although they are not yet widely deployed, and they're not all that widely understood, IP-based communications networks are starting to draw interest from first responders. G. Thomas Steele, chief of the IT and Communications Bureau at the Maryland State Police, said he discussed IP with several colleagues at a meeting in May of the International Association of Chiefs of Police Law Enforcement Information Managers, and “it appears that it will be a hot topic next year.”

As public-safety agencies investigate IP-based communications, their big worry is security, Steele said. Marshall Gage, chief of the Boynton Beach, Fla., Police Department, agreed. “What does it open up the organization to, as far as hackers being out there, trying to get into your system?” he asked.

Agencies' technology experts know that vendors build safeguards into IP-based communications systems, but politicians and voters don't necessarily trust that these systems are safe, Steele said.

Vincent Stile, director of police radio communications with the Suffolk County (N.Y.) Police and president of the Association of Public-Safety Communications Officials, voiced concerns about reliability as well as security. “Can the performance of these types of systems be up to the speed of being mission-critical? Can we utilize this system and not worry about somebody else being able to jump on and capture our transmission?” he asked.

Much apprehension about IP-based communications springs from the term “Internet protocol.” When many people — both public-safety professionals and ordinary citizens — hear the term applied to emergency networks, they fear that police, fire and emergency medical communications will be asked to share data pathways with music downloads and ads for Viagra.

“The Internet is based on IP, but the Internet is not all IP,” and not all IP communications travel over the Internet, Bart said. “It's just a technical means to do things. You could have private networks, AT&T networks, MCI networks, local carrier networks, based on IP protocol, but they're not the Internet.”

In fact, IP-based communications systems for first responders rarely employ the public data highway. “We make them put in a dedicated network. It doesn't go over the Internet,” said Jackson.

First responders also worry that if they integrate voice and data on an IP system, congestion might cause unacceptable delays, Sanku said. But public-safety agencies can configure and control their networks to reduce latency, he said. “Congestion can be removed through privatization as well as over-committing the bandwidth.”

As they contemplate any new technology, public-safety agencies inevitably wonder if they can embrace the new without throwing away their investments in existing systems. Because an IP-backbone can connect radio systems based on different technologies, vendors say it allows for a gradual migration. “If you have an existing analog system and you deploy a digital system that is IP based, you put in the [IP-based] gateway that connects the analog system to the digital system,” Sanku said. Thus, the agency can phase out old radios and buy more of the new ones as money allows.

Subscriber units built to the P25 standard can be programmed to work in either analog or digital mode, said Jackson. Consequently, agencies can phase in IP technology gradually, introducing new infrastructure and subscriber equipment according to their normal replacement cycles, and reprogramming their radios as needed.

“We believe strongly there's a migration plan that will allow customers to gracefully adopt future technology that is modest in cost, that does not require what we call a ‘forklift upgrade,’ where you have to throw all the software and hardware away and start all over again,” Facella said.

Even with plans for gradual migration, public-safety agencies that want to implement IP networks and other up-and-coming technologies will have to pay for new equipment. That means developing a sense of urgency among the people who control the funds.

“You've got to do it because it's a matter of policy and because you want to do it — you want your first responders to have the same communications that my daughter uses on her cell phone,” Bart. “If you want first responders to be able to talk, then you need the money to buy the equipment. You need to support the standards processes that will yield to that, as well as keeping up with the emerging technology.”

That little piece IP never thought of

While numerous vendors of land mobile radio equipment have started offering networks that employ IP technology on the system backbone, they disagree about using IP over the air.

“IP was designed for the wired world, where you don't have to worry about driving behind signs and getting the signal going up and down,” said Chuck Jackson, vice president and director of system operations at Motorola. P25, the public-safety standard for digital wireless communications, is much better suited to handling “that little piece over the air that IP never thought of,” he said.

But M/A-COM, for one, has modified IP to accommodate irregular signal strength and other quirks of wireless communications, so it can offer end-to-end IP in its Open Sky system, said John Facella, the company's director of public safety markets.

“We do things like ensure that every packet is received. If not, we attempt to resend it or error-correct it.”

End-to-end IP offers one important advantage: it gives every subscriber unit on the system an IP address, Facella said.

This allows a system administrator to manage the radios exactly as if they were computers on a local area network. The administrator can easily download software modifications, change the talk groups in which a radio participates, define the data applications a mobile computer can access, revise security parameters and otherwise control the unit.

In networks that use a protocol other than IP over the air, “you lose control in a sense, or you have to exert a different kind of control for the subscriber radio,” he said.

“It's essentially another protocol that has to be invoked, and it complicates the system.”
— Merrill Douglas

How good is VoIP?

In an emergency, clear communication can mean the difference between life or death. Can mobile voice-over-IP systems relay mission-critical information reliably and clearly enough to support first responders?

Steve Holmes, acting chief of the Pratt (Kan.) Police Department, said his department's nine mobile VoIP phones perform very well. “It's hard to tell the difference” between calls on these phones and calls on desktop extensions in the office, he said.

Pratt uses a 2.4 GHz system from Alvarion of Carlsbad, Calif., to provide voice and data communications to police officers in the field. Using computers in their cars, police can submit or print reports and send and receive text messages, Holmes said. For an officer in the field, the VoIP phone serves as “an extension to our in-office telephone system, which allows the dispatcher to transfer telephone calls to their car. They can make local and long-distance calls, or you can just dial their intercom number and talk car-to-car or car-to-office.” As a supplement to the department's UHF radio system, the IP network offers a secure voice channel for sensitive communications involving bomb threats, bank alarms or other emergencies, he said.

Unlike many public-safety organizations, the Pratt police use the Internet as the backbone for their IP-based system, but they use a firewall, a virtual private network (VPN) and 168-bit encryption to secure their communications, Holmes said. The wireless portion of the network consists of a central tower and four “cell extenders.” Together, these antennas provide coverage over 12 square miles with no dead spots, he said.

The system provides data rates of 500 to 600 kb/s, and officers can use it while in motion as well as when parked, Holmes said.

Although he has no first-hand experience with IP-based radio systems, Marshall Gage, chief of the Boynton Beach (Fla.) Police Department, said he was impressed with a VoIP system he saw last December, during an interoperability demonstration that Cisco Systems and Science Applications International Corp. hosted at a U.S. Coast Guard Station in Miami.

“They had UHF frequencies, 800 MHz and IP-based telephones. And you could communicate as if you were just talking on a regular radio. All you had to do was get the software to plug you in, to allow you access, and then you could talk as if you were next door,” Gage said. He termed the sound on the system “excellent.”

Steve Litschauer, captain at the Manatee County (Fla.) Sheriff's Office, recalled the voice quality on the earliest encrypted digital radio systems, which hit the market about a dozen years ago. “It sounded like Donald Duck talking on the radio,” but the distortion was acceptable when weighed against the security these systems provided. A similar tradeoff might apply to emerging VoIP systems, he said.

For about three years, the sheriff's office has been migrating its mobile data applications from an 800 MHz digital network, which it shares with 43 other agencies, to a 450 MHz IP-based system, provided by IPMobileNet of Irvine, Calif. The department plans to test plug-in VoIP units on that network, for possible use as a backup to its voice radio system, Litschauer said. One factor he will evaluate is whether speech transmitted on the VoIP system suffers any delay, and whether that delay is acceptable.

Having seen a demonstration of the VoIP technology, Litschauer said he heard a difference between its sound and the sound on an analog radio system. But the discrepancy was insignificant, he added. And whatever the state of the art right now, VoIP systems, like early digital radio systems, will “do nothing but improve,” he said. “That's the wave of the future.”
— Merrill Douglas

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