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pradeep 5May2005 23:45

What's the buzz on GSM?
 
GSM, short for Global System for Mobile Communication, is the standard behind digital mobile phones. It has opened up a new era of digital communications, which extends beyond voice to include data. GSM was planned from the outsell to provide a full range of data and fax transmission on the move, providing the first true implementation of mobile phones.

GSM Technology

Before GSM, most countries have their own, incompatible analog mobile phone networks, working on different frequencies. This prevented phones being used across national boundaries. Analog phones are also not economical in their use of frequency brands, and with the explosive growth in mobile telephony in the late 80s, radio capacity was being threatened.

Work started in 1982 and the first GSM service appeared in 1991, and by the middle of 1996 over 110 services was available in 50 different countries.

The success of GSM has been staggering but its growth has brought its own set of problems. Although GSM digital transmission is more efficient than analog systems, typically allowing three times the number of calls for the same frequency spectrum, predicted demand suggested that GSM could clog up before the end of this century.

To solve this an additional frequency was specified at 1800 MHz. This is commonly known as PCN or Personal Communication Network. PCN and GSM phones aren't compatible, however in near future dual standard phones will become available, allowing roaming between different service providers.

Key Features of GSM

SIMs

Each GSM phone contains a small smart card called a SIM or Subscriber Identity Module. The SIM contains a microprocessor and memory, which personalizes the phone. As well as storing passwords and the phone's identity, It also contains details of the services enabled, store numbers and can store incoming messages.

Because the SIM stores the whole personality of the phone it can be moved to different handsets, allowing users to hire phones and inserts their Identity SIM.

SMS what's the entire Buzz About?

One of the most interesting features of GSM is SMS, the Short Messaging Service. SMS uses spare time in the control channel transmissions to insert short messages. Coupled with computers, SMS can be transformed into a powerful messaging system.
SMS offers a real advantage to GSM in addition to transmission of data and fax providing 160 character messaging Guaranteed Delivery Acknowledgement of receipt Reception and transmission during phone calls.

SMS allows a text message to be sent to the display of any phone. If the phone is turned off, the message is stored by the service provider and then transmitted as soon as the phone is turned on unlike congenital paging where messages can be lost.

As messages are received, they are stored on the SIM within the phone. Users can retrieve them as required and they can even be received during the course of a phone call.
Linking phones to a PC or Organizer makes these SMS messages more flexible. Messages can be input from a Key Board, they can be broadcast from mobile PCs or from desktops using simple communications applications, they can be directed to individual users or a group of numbers, and because they ride on the back of a control signals, they are cheap to send.

Gateways exist that allow SMS messages to be converted to fax so that they appear on fax machines. They can even be directed to email addresses. The only limit is 160-character length, which must include the destination fax number and address.

SMS is increasingly being used for subscription information services. Users can already subscribe to financial information services, where market information is sent either automatically or on demand.

Using a custom software interface, SMS provides an excellent vehicle for menu selection of data. If the data is concise, the whole process could run over SMS; alternatively SMS could provide the low cost menu system prior to data transfer.

The list of SMS applications and mobile services based on the underlying technology of SMS is an ever-growing list. Besides the common use of just communicating with the "buddies the SMS application family can be classified into two groups :

Customer Oriented.
Corporate Oriented.

The main types of consumer applications based on SMS are:

Simple Person to Person Paging
Voice and Fax mail notification.
Internet Email Alerts
Ring tones
Chat
Information services

Corporate applications that use the SMS are currently few and far between. The reasons are the older age of corporate mobile phone users and their price sensitivity, particularly since the company usually pays mobile phone bills
The main corporate applications based on SMS are:

Corporate Email
Customer Service
Vehicle Positioning
Job Dispatch
Remote Point of Sale?

Roaming

GSM phones are designated to work wherever there is a service operator. When you turn a GSM phone on, it looks for a base station. Once found, the base station (which is the phone talks to) will check with your service provider to see if you are a valid user. And if so connect you. If your service provider has roaming agreements across national boundaries the technical aspects becoming more complex, but for the user the process is quick and seamless. All you will see is the name of local provider.

Unlike the analog phones, GSM phones are always checking to find the strongest signals
From the local transmitters, as the phone moves out of range of a base station, it will tell the base station to transfer it to the next. The most the user will see is a current base transmitter. The consequence is that a GSM phone knows more or less where it is.

Data/Fax/Email Transmissions

From the outset, GSM was designed to transmit data. Normal phone lines have conditioned us to the idea that where voice can be transmitted, data can also be sent. Unfortunately, with any wireless communication, other problems include. Radio is a far less reliable medium than a phone cable, being subject to interference, loss and fading. The human brain is very good at compensating for these aberrations however; with data it is vital to ensure that nothing is lost.

GSM performs an immense amount of processing to protect your data. The data is partitioned, reassembled and convoluted such that it can be checked and reconstructed, even if partially damaged in transmission. This processing increases the complexity and cost of the phone, but it ensures reliable data transmission at a throughput of 9600 Bps.
Depending upon the level of data reliability required, GSM has two different mechanisms for sending data :

Transparent Modes
Non Transparent Modes

In Transparent mode no effort is made to correct errors, other than by the basic protocols. This is ideal for applications where data is needed fast, but where error is acceptable. Typically this may be the case for applications like Video Conferencing or fax.

Non Transparent transmission checks each packet for errors and requests retransmission, but ensures full data integrity. The method used to control nontransparent transfer is RLP (Radio Link Protocol), which is an integral part of the GSM standard and is an error correction standard optimized for the wireless environment. Because the checking is performed within the GSM hardware it is very efficient mode of correction. Similar to data, GSM lets you send and receive and receive faxes. Again, these can be sent in both Transparent and Nontransparent modes, although most service providers are currently only implementing Non- Transparent Fax.

GSM Security

GSM was designed with security in mind and all voice data and fax is encrypted. The encryption password is programmed into the SIM module, and is known only to the mobile telephone network. As yet there are no reports of encryption having been cracked.

UP Next

GSM in an evolving standard. One of the next enhancements to reach the market will be dual-mode phones, which operate on both the 900 MHz and 1800 bands. They will be followed by triple mode phones, which will also incorporate the US1900 MHz bands, giving truly global coverage. Further down the line, phones will start to integrate GSM with DECT, so that the same handset can make mobile calls or work through a local DCET wireless switchboard as a cordless phone.

Data speeds will also improve although not in the short term. Work has already begun on GSM's successor UMTS (Universal Mobile Telephone System) and GPRS (General Packet Radio Service), providing mobile communications in the new millennium.


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