emot
e-access LAN servers, the Internet, and other on-line service providers. And the functionality of different mobile devices is becoming increasingly blurred.
The Right Standard at the Right Time
Setting the demanding GSM standard was a long, tedious process, but it was worth the wait. It arrived when the market need for better mobile communications was emerging, and being digital meant that the need for wireless data was foreseen -- all the way to ISDN rates. However, no data was sent over GSM until March 1994, when Nokia demonstrated a notebook PC linked to a GSM phone via a PC Card. Today, several vendors such as Ericsson and Motorola offer similar PC Cards that provide a 9600-bps interface to the GSM network. All the current notebook-GSM phone interfaces are proprietary, but vendors are working their way toward a standard.
The PC Cards provide a communication link to the GSM network, but the modulation/demodulation facility is part of the network infrastructu
re. The Mobile Switching Center (MSC) of the network interfaces the Public Switched Telephone Network (PSTN), and the modem pool of the GSM network operator pumps the data over the phone network. However, a communications application on the notebook sees the card as if it were a regular data/fax modem, enabling E-mail, file transfer, and faxing to be done with regular Windows programs.
ISDN Link
Last summer, the German company AVM Computersysteme demonstrated an all-digital link from a GSM notebook client to a corporate LAN or Web server over ISDN. AVM's PC Card ISDN controller M1 works with Siemens S4 and compatible phones. This device, which complies with the Common ISDN API (CAPI), compresses the data to allow for effective data-transfer rates of up to 40 Kbps. It uses the standard ISDN rate adapter of the MSC to connect to the ISDN network (see the figure
"How the GSM Network Connects to a LAN"
).
The advantages of having an all-digital mobile ISDN lin
k are significant, particularly for short communications. Modems take 30 to 40 seconds to set up a connection over GSM. The modems need time to negotiate with each other (i.e., find the highest common speed as well as the compression and error-correction capabilities). The setup times are pretty high overhead if you're sending just a few E-mail messages.
A mobile ISDN connection, however, takes only 5 to 7 seconds, according to AVM's Stephan Reuter. Together with the high data throughput, this solution makes a number of heavy-duty applications more cost-effective.
This mobile technology is a significant development, but in the next decade, the majority of traffic will continue to be handled by the PSTN for some considerable time. Mobile data communications over this medium are currently conveyed by the GSM radio link protocol (RLP) that handles traffic from the data card to the MSC, and V.42-compliant communication takes over for the modem-to-modem part over the PSTN. What is needed, and will come
this year, is a standard that implements V.42bis on GSM networks. It has been approved by the European Telecommunications Standards Institute (ETSI) but not yet implemented by the network operators.
Mobile Access to the Internet
Higher data throughput via V.42bis compression, coupled with the fast setup times of all-digital connections, will boost applications such as mobile access to the Internet, particularly when this data network is used to access a corporate LAN or host. By the year 2000, half the information over GSM could be data, says Nokia's Olli-Pekka Lintula. "The Internet and ISDN are currently driving this development," he says, "and there is no technology reason why multislot GSM should not go all the way to 64-Kbps ISDN speeds." The only limitation will be the price subscribers will pay for the extra bandwidth.
The difference between ISDN-enabled applications and systems that employ the PSTN is usage of the transport layers of the communication protocol. Regular
AT commands send data to the PSTN modem facility in the GSM infrastructure. In an all-digital scenario, a wireless AT command extension directs the call over ISDN.
A more elegant solution would use CAPI and so-called service indicators. ETSI is currently in the process of extending CAPI to include GSM specifications. The service indicators are control instructions, which are sent over a separate channel. In this case, data and instructions are independent and can be sent simultaneously. Service indicators also enable much quicker setup times. Thus, when a CAPI-compliant application is loaded, file transfer can start almost immediately. If the instruction is to use ISDN but the called party has an analog connection, then the modem pool in the digital network is used. The setup time will still be quicker, but the end-to-end transfer rate will be determined by the weakest link in the chain -- the modem. The separate control channel enables GSM to send a fax and receive, for example, a short message via GSM
's Short Message Service (SMS) at the same time.
GSM Short Message Service
The GSM SMS was originally used to let people know that voice mail was waiting, but it can also be used as an indicator of E-mail and faxes. Short messages can contain 160 characters. This service functions similarly to two-way paging, but it is rapidly evolving into an electronic messaging system.
With the appropriate software, SMS messages can be managed like E-mail.
Nokia's CellularWare Windows utility
lets users send, receive, and forward messages from the PC to single users or groups. Additionally, it provides phone-management facilities such as maintaining a large phone book on a notebook computer and letting the user drag and drop relevant names and numbers to the two memories of the Nokia 2110 cellular phone.
Forté Communications developed a value-added applications gateway that facilitates message transfer between corporate information platforms (e.g., LANs) and th
e network operator's SMS center (SMSC). The gateway acts as an intelligent two-way multiplexing system between regular messaging protocols and the SMSC. Comprehensive communications functionality is provided for notebook PCs and the Apple Message Pad over a Nokia GSM phone.
Even more interesting is Forté's concept of opening up the world of short messaging to the LAN. This is done by providing an API that enables companies to customize their messaging requirements; for example, in-house programmers could customize data-entry worksheets for use by staff in the field. A typical application might extract data from the client (field) worksheet and send it as short messages into a duplicate worksheet that resides on the server. This eliminates having to download unnecessary data.
Swiss Telecom PTT wants to set a new standard based on GSM that will allow interactive communication applications and value-added services to be built on top of Short Message Service. Swiss Telecom, together with the Ge
rman software company LHS, has conceived a universal development platform known as NATELsicap.
NATEL
is an established messaging service in Switzerland;
sicap
stands for SIM card application platform. A SIM card is the subscriber identity module that goes in a mobile phone.
SIM cards are fully functional embedded computer systems that are currently being used only to store data but could perform more intelligent tasks. The level of intelligence and memory is determined by the network operator and the value-added services that are available. "Turbocharged" SIM cards can function as clients in a client-server architecture. The basic idea is that these cards talk to a central server using SMS as the communication medium. The server enables access to external databases and interfaces to the SMSC for sending and receiving short messages. Thus, the NATELsicap platform provides transparency between the SMS center and almost any kind of third-party application or service.
Swiss Telecom w
ill begin delivering its first applications this year, but the objective is to establish NATELsicap as a global standard. Clearly, the current size of GSM phone displays will limit the implementation of this concept. But proponents aim to demonstrate its practicality and to establish a development platform that the industry can carry forward. Applications such as downloading a list of free parking lots or available hotel rooms make sense even with small phone displays.
Next-generation phones may well have a second, fold-out display, and touch-screens will certainly be shown at CeBIT '96. Longer term, the phone will assume more of the functionality of a personal digital assistant, PDAs will get GSM-enabled PC Cards (see
"Mobile Communications Options,"
December '95 BYTE, international edition), and data-centric users will be able to talk to their multimedia notebook PCs. There are no technological barriers to this latter development.
Higher Speeds, Better Services
Higher
data rates will come as a result of compression, including compression at the application level. But multislot services can take it all the way to 64 Kbps and thereby facilitate internetworking with ISDN. These services are some way off in the future since demand is chasing capacity at the moment, but by 1997 the baseline standard will be 19.2 Kbps (two slots), the targeted service being fax and file transfer at 14.4 Kbps.
By then we might also have General Packet Radio Service (GPRS), a technology that is intrinsically superior for bursty data applications like E-mail. And multislot services will probably be marketed as a bandwidth-on-demand facility, making it ideal for high-speed file transfers and mobile video communications.
We can look forward to a best-of-both-worlds scenario, where the applications will decide which service to use. We can also foresee intelligent agents and other technologies being used to automate, simplify, and otherwise enhance the mobile communications process. Exciti
ng times are ahead, indeed.
WHERE TO FIND
AVM Computersysteme
Berlin, Germany
Phone: +49 30 399 76-0
Fax: + 49 30 399 76-244
Forté Communications
Auckland, New Zealand
Phone: + 64 9 358 5703
Fax: + 64 9 358 5704
E-Mail:
sales@forte.co.nz
LHS
Dietzenbach, Germany
Phone: +49 6074 831 102
Fax: + 49 6074 831 170
Nokia Mobile Phones
Tampere, Finland
Phone: + 358 10 5051
Fax: + 358 10 505 5768
Internet: htpp://www.nokia.com/
Swiss Telecom PTT
Berne, Switzerland
Phone: + 41 31 338 02 80
Fax: + 41 31 338 02 79
HotBYTEs
- information on products covered or advertised in BYTE
illustration_link (28 Kbytes)
The GSM infrastructure is evolving rapidly to meet the data communications requirements of mobile professionals. The mobile switching center (MSC) of the network connects to the Public Switch Telephone Network (PSTN), and the modem pool of the GSM network pumps the data over the phone network. This solution is ubiquitous but includes modulation/demodulation at both ends of the communications link. To bypass modulation, all-digital solutions such as the AVM Computersysteme M1 controller use the GSM/ISDN interface. In the near future, Internet service providers partnering with GSM operators will offer direct Internet access at ISDN rates.
The General Packet Radio Service (GPRS) data packet techn
ology, which will be suitable to handle the bursty nature of wireless data traffic, is still two years off. Meanwhile, when GSM phones with PDA-like functionality show up, Short Message Service (SMS) will take off as a platform for communication applications with low data-transfer requirements.
screen_link (34 Kbytes)
Nokia's CellularWare provides phone management facilities and enables GSM Short Message Service messages to be managed like E-mail. It complies with the Open Database Connectivity (ODBC) extensions and works on Nokia phones like the model 2110.
Bob Emmerson is a telecommunications journalist
based in The Netherlands. David Greetham is a consultant with Greetham Associates (Turnhout, Belgium). You can reach them at
73252.1364@compuserve.com
.
GSM's Extraordinary Growth
