Feb-March 2003

Wireless radio data networks are the Cinderella of the mobile communications sector. Cellular telephone networks grab all the attention, but data networks are proven technology. Sharon Clancy hears the arguments for and against

Always-on connectivity is currently one of the buzz-phrases in the mobile communications sector ­ the implication often being that this is completely new technology.

In fact, something that may be a new concept for the cellular telephone network has long been one of the chief attractions of the dedicated radio data networks operated by companies such as Cognito, Siemens Datatrak and Transcomm. These are popular with companies with large groups of mobile workers and with emergency services, where an always-on connection to the mobile worker or vehicle is often mission-critical.

Nowadays, GPRS (General Packet Radio Service) presents a challenge to them, and is being heralded as a technology that can deliver data communications to a wider audience. And if you look at the many new mobile data applications coming on to the market, you can't deny the fact that GRPS is the communications method chosen by a lot of them.

 

Indeed, such has been force of the challenge that one of the traditional data network providers, Cognito, has taken an "if you can't beat them, join them" approach. At the end of January it closed its 100-strong network of proprietary radio base stations and moved its network on to GRPS.

Transcomm, on the other hand, believes its dedicated data network still has a lot to offer in terms of efficiency and security benefits. And the huge Siemens corporation has a foot in both camps. Through Siemens Datatrak, it has its own UHF radio communications network, integrated with vehicle tracking. Meanwhile, though, another division, Siemens Communications, is developing mobile units designed to work on GPRS and, later, 3G networks.

Transcomm's wireless data network was established in the UK in 1991 under the name RAM Mobile Data. It uses Ericsson's Mobitex wireless packet switching technology. This is called packet switching, by the way, because the data streams are broken up into small packets before being sent around the network. The packets can travel using various paths over the network, and are assembled automatically into the complete message on arrival. There are no call set-up times: users are always connected and pay for the amount of data sent, not the time connected. The system is designed to handle just the sort of short, frequent, data exchanges that characterise many communications with mobile units.

Packet switching also helps network operators optimise traffic. Transcomm, for example, delivers 8 kbits of data a second over a single 12.5 kHz channel. Up to 400 users can share a Mobitex channel without loss of spectrum efficiency, and there can be as many as 2,500 users. Transcomm says this ability to handle a large number of users without degradation of the service is one of the key advantages of the Mobitex network. It admits that at 40 to 50kbps, theoretical GPRS data transfer speeds are faster, but points out that these can drop dramatically as soon as there is more than one user on a particular channel.

GRPS is also packet-switched technology, but overlaid on a GSM circuit-switched mobile phone network. Circuit switching requires an end-to-end connection for each call, and a dedicated line while the transfer is taking place. GPRS speeds up the process by using Internet Protocol to set up a session from the mobile unit to a gateway service before transmitting the data.

Transcomm argues that this method is less efficient. Users actually go online only after the terminal has requested a session and received acknowledgement from the network, so the "always-on" moniker only applies if you interpret the term liberally. Transcomm accepts the process is much faster than with GSM, but emphasises that it still has to happen, and it must be initiated by the mobile terminal. "On a cellular network, voice traffic will get priority, so at busy times there can be a delay in data messages getting through," a spokesman says. "Nor can you use voice and data at the same time."

Battery life of handheld units is also better on a proprietary data network, Transcomm claims. Its Grapevine PDA units can give three to four days' continual usage between recharges, thanks to the use of the latest RPM3 credit-card size wireless modems that are used to connect to the network. These have 2 watts of power to boost coverage and power-saving features.

The Mobitex network is intelligent: it includes positive acknowledgement that messages have been delivered or returned for whatever reason. A mailbox facility stores packets addressed to devices temporarily out of coverage, and forwards them later. Each mobile unit has a permanent IP address; with many GPRS-based networks, by contrast, IP addresses are assigned dynamically at the time the session begins. There is no public access into the system so the host system is less vulnerable to attack and data is more secure.

Steve Alderson, managing director at Cognito, agrees that data traffic speeds are dictated by the switching capability of the particular GPRS network. However, he says experience to date has been that only a "very small" percentage of data packets sent via GPRS go to Cognito's Network store for later forwarding, indicating that the majority of messages go through virtually immediately. "It's partly because GPRS has given us increased geographic coverage in the UK, and partly because we have private 'pipes' into all of the networks from both our communications centres at Newbury and Heathrow. The two are interconnected, and if the mobile unit cannot connect through one, it tries the other."

When the mobile unit is on, the G21 software establishes and maintains a GPRS connection to the Cognito Network. Store and Forward service removes the need for complex back-end communication servers, says Alderson, and overcomes any transient breaks in communication, such as poor radio coverage, of which the mobile user is unaware. The network store is triggered when the mobile device next contacts the Cognito Network.

Alderson also points out although Cognito has switched from radio base-stations to cellular communications, G21 is still a managed, secure network. "The G21 service retains many of the benefits of a dedicated radio network, including 'push and pull' data capability, audit trails and structured responses."

Data transactions are time- and date- stamped at specific points and the information is returned to the sender. The Store and Forward service removes the need for complex back-end communication servers.

Once stored, messages will be delivered to users in one of two ways ­ "store retry", and "user appearance". The store retry mechanism is a scheme whereby the "network store" will reattempt delivery of data to the destination over a period of hours. User appearance covers situations where the mobile device is either switched off or completely without radio coverage. The network store is triggered when the mobile device next contacts Cognito. An audit trail keeps the sender informed of message status.

"The key security issue is authentication of the mobile device. Does it belong on the network? That's why we only allow integrated handsets on the network. The G21 network automatically checks user name and password, together with the user address, hardware and SIM ID, each time the mobile unit logs on. The password changes weekly."

When GPRS uses Internet Protocol to connect, there is a risk that data travelling over the public Internet can either be accessed or used as an illegal entry point into a corporate network. That's why some companies don't permit GPRS-enabled devices access to their corporate LAN. The dedicated Internet access pipe overcomes this.

Voice services are also available. The operator can set limits for voice usage, including restricted phone number lists, maximum call duration and time of day.

Siemens Datatrak is unique in offering a radio network that incorporates not only data transfer, but also navigation capabilities. To achieve this, the Datatrak network uses two technologies in parallel ­ land-based low-frequency radio transmitters for tracking, and a UHF communication network for transmitting real-time data.

Base stations positioned at 40- to 50-kilometre intervals provide radio data coverage, and Siemens says a vehicle will usually be within range of more than one base station. Datatrak services include TWD (Two Way Data), EATS (Event Activated Tracking System), and AVL (Automatic Vehicle Location). Each vehicle has a locator unit with an RS232 port for connecting to mobile devices, and there are integrated roaming facilities with other networks including GSM. TWD gives two-way data transmission with messages and confirmation of receipt messages in both directions

These networks, while firmly entrenched in the dedicated mobile data market, are not on their own. Other contenders are also emerging, including Symbol, whose SymbolAir system is typical of the new generation of products now on offer. Managing director Neil Bonner says customers using Symbol handhelds are typically transferring only small amounts of data such as barcodes or POD signatures. "The user is unaware if network congestion means that data takes a few minutes to arrive. It's rarely that time-critical." SymbolAir also has a private access pipe to the Internet. "Data does not travel across the publicly-accessible Web."

It is clearly a mistake to write off dedicated wireless networks as belonging to the dark ages. They are evolving to meet the demands of today's corporate networks, offering services such as push-pull email. They're certainly a solution if you are concerned about security. However, neither can GPRS solutions be dismissed as lacking necessary security for corporate data networks. Make sure you identify your priorities, and ensure that the service provider can meet them.

The tetra alternative

TETRA offers a further option for keeping in touch with field workers. Dolphin has licence to operate the TETRA (Terrestrial Trunked Radio) network for commercial uses in the UK, the world's largest network.

TETRA combines mobile telephony, fast data communications and the workgroup capabilities of mobile radio. A low operating frequency allows Dolphin to achieve national coverage with far fewer base stations than other mobile networks. TETRA is digital, and offers more functionality than the old analogue networks, including Short Data Service text and numeric messaging.

Dolphin has been revitalised since it was acquired in June last year by wireless network developer and operator Inquam Telecom. Inquam has been focusing on restructuring the business, and has also been developing a new generation of handsets (which the previous owners had postponed through lack of funds).

The new Nokia THR850 handset aims to broaden the appeal of the TETRA service to workers more familiar with lightweight GSM phones. At 196 grams, it is a third of the weight of earlier models and easier to use, and has more functionality. Battery life has also been improved; fitting an li-ion battery is said to have increased standby time threefold to between 20 and 30 hours. Talk time is now between three and four and a half hours.

Dolphin's service also offers Express Text, a point-to-point and multi-point messaging service called SDS. This is similar to SMS services on GSM networks, except that there is instant acknowledgement that the message has arrived (or not).

The THR850 also supports some of the more advanced TETRA functions such as "group scanning", which allows simultaneous membership of more than one work group.