NexGen City has used embedded Linux to build what it claims to be the first VoIP (voice over internet protocol) push-to-talk (PTT) handset for emergency workers and “first responders.” Designed for use with NexGen's NexLink wireless broadband mobile network, the handset will reach general availability in Q4, 2004.

NexGen's NexPaq PTT VoIP handset
(Click to enlarge)

The NexPaq is currently undergoing testing in the first NexLink network, which is nearing completion in Garland, Texas. The Garland network covers 57 square miles, and is the first deployment of mobile mesh networking technology for use by a public safety organization, according to NexGen.

NexGen's NexLink wireless broadband mobile network

NexLink is a mesh-based broadband network that can carry data, VoIP calls, and streaming video at broadband connection speeds of up to 1.5 Mbps, while traveling at multi-lane highway velocities, according to NexGen. It is based on 2.4GHz wireless networking, but is not 802.11 compliant. Instead, NexCity implemented a proprietary networking protocol, for greater security and privacy.

Linux is used in the central network operations center (NOC), and on all devices throughout the NexLink network, including fixed intelligent wireless routers and gateways.

The NexLink system includes NexCard wireless cards for laptops that repurpose the driver of a commonly available wireless NIC, easing installation for users, according to Embedded Software Director Kevin Farley.

Both mobile and fixed infrastructure devices in the NexLink network can act as repeaters and routers. This capability allows each unit to extend the network with self-forming and self-healing networks based on ad hoc, peer-to-peer networking. In the event of a major emergency that disables local fixed devices, first responders arriving on the scene can form a network “automatically and seamlessly,” Farley says, using mobile NexLink devices.

More typically, mobile NexLink users are aggregated into “virtual talk groups” that are assembled at a central command and control center. This enables different first responder organizations arriving at an emergency scene to communicate immediately on the same channel.

The NexPaq

The rugged, lightweight NexPaq communicator runs embedded Linux on an Intel PXA255 microprocessor clocked at 400MHz. The device currently includes a backlit text display, with a more sophisticated graphical display planned. The device includes a keypad, cursor controls, and programmable multi-function keys. Each PTT unit has an emergency call button, a channel selection switch, and volume control.

The NexPaq communicator includes a 10-bit analog-to-digital converter (ADC) that can be used to process biometric data. For example, in conjunction with a “smart shirt” or other analog sensors, the device could monitor firefighters' heart rates, respiration rates, or oxygen tank levels, communicating biometric data to a battalion chief outside a burning structure, NexGen says.

The device uses the BLOB bootloader from the Lart project, according to Farley. It boots from 32MB of StratoFlash, into 64MB of system RAM.

A USB device interface supports camera attachments, enabling law enforcement officers to send real-time video to fellow officers in the vicinity, or back to a command and control center.

The NexPaq also includes a PCMCIA slot for the NexCard wireless card, a serial port, and external connections for speaker/microphone headsets.

The NexPaq communicator is cased in a magnesium-based package, and meets environmental, shock, and vibration requirements compliant with MIL STD 810F, according to NexGen. Available accessories include a variety of speaker and microphone attachments.

NexPaq software

The NexPaq runs a Linux kernel 2.4.20 from MontaVista Linux Pro 3.1. In addition to support from MontaVista, NexGen outsourced a Linux board support package from an unnamed contractor. The company rounded out its Linux implementation with packages from a Red Hat Pro development environment, according to Farley.

The device uses busybox and a “fairly standard SBC Linux environment with sound drivers and what-not,” according to Farley. It also includes a VoIP stack developed in-house. “We use H.323 and SIP (session initiation protocol), but really, we have a fairly custom app at this time,” notes Farley.

“Users can make ad hoc calls to other systems on the network by IP address, or they can go through a gateway/gatekeeper combination to call any phone number on the planet,” according to Farley. “They use it most in radio talkgroup mode, through a central server. But, they just need to make one button push to make a phone call.”

Additional in-house software includes an addressbook and other basic PDA applications. Farley plans to deploy a J2ME Java runtime environment in future revisions of the NexPaq, opening the door to additonal user applications.

Why Linux?

Farley says NexGen chose Linux because of “the enormous amount of existing software to give us a fast entry into the market. We didn't want to have to reinvent things. [Linux lets us] do what we do best. I've used various RTOSes in the past, and other embedded Linux products. We're basing every one of our product designs on Linux, including our NOC.”

Asked about any particularly difficult parts of the project, or any challenges that had to be overcome in using embedded Linux, Farley insists, “There weren't any tough parts! Everything went smoothly. We pulled this together in a few short months. It's been an enjoyable, smooth project.”

Farley credits the project's success so far to extensive planning. “We spent months in planning before we ever started. We spent two to three months going over the technical requirements and specifications and researching parts. Proper planning is essential for any embedded Linux project.”

Farley adds that the entire NexPaq project, including custom hardware design and the outsourcing of manufacturing, took less than a year.

Asked for predictions about the future of embedded Linux, Farley replied, “The market's going to have some challenges from Microsoft, which is pushing into phones. Traditional RTOSes are feeling the pressure, more than Microsoft. VxWorks, and Nucleus and ThreadX are going to fight back. It's gonna get really gnarly and nasty.

“But one of the best things I've seen so far in predicting the market is how, with Linux, you can get a lot of stuff up, fast,” Farley continues. “Linux can reduce the total development time because of its large supporting software base. We have a lot of confidence in embedded Linux being able to withstand the barrage.”

---

 
This article was originally published on LinuxDevices.com and has been donated to the open source community by QuinStreet Inc. Please visit LinuxToday.com for up-to-date news and articles about Linux and open source.