Dated: Aug. 13, 2004
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GSM, short for Global System for Mobile Communication, is the standard behinddigital 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 toprovide a full range of data and fax transmission on the move, providing thefirst true implementation of mobile phones.
GSM Technology
Before GSM, most countries have their own, incompatible analog mobile phonenetworks, working on different frequencies. This prevented phones being usedacross national boundaries. Analog phones are also not economical in their useof frequency brands, and with the explosive growth in mobile telephony in thelate 80s, radio capacity was being threatened.
Work started in 1982 and the first GSM service appeared in 1991, and by themiddle 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 setof problems. Although GSM digital transmission is more efficient than analogsystems, typically allowing three times the number of calls for the samefrequency spectrum, predicted demand suggested that GSM could clog up before theend of this century.
To solve this an additional frequency was specified at 1800 MHz. This iscommonly known as PCN or Personal Communication Network. PCN and GSM phones arenot compatible, however in near future dual standard phones will becomeavailable, allowing roaming between different service providers.
Key Features of GSM
SIMs
Each GSM phone contains a small smart card called a SIM or SubscriberIdentity Module. The SIM contains a microprocessor and memory, whichpersonalizes the phone. As well as storing passwords and the phone’s identity,It also contains details of the services enabled, store numbers and can storeincoming messages.
Because the SIM stores the whole personality of the phone it can be moved todifferent 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 MessagingService. SMS uses spare time in the control channel transmissions to insertshort messages. Coupled with computers, SMS can be transformed into a powerfulmessaging system.
SMS offers a real advantage to GSM in addition to transmission of data andfax providing 160 character messaging Guaranteed Delivery Acknowledgement ofreceipt Reception and transmission during phone calls.
SMS allows a text message to be sent to the display of any phone. If thephone is turned off, the message is stored by the service provider and thentransmitted as soon as the phone is turned on unlike congenital paging wheremessages can be lost.
As messages are received, they are stored on the SIM within the phone. Userscan retrieve them as required and they can even be received during the course ofa 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 PC’sor from desktops using simple communications applications, they can be directedto individual users or a group of numbers, and because they ride on the back ofa control signals, they are cheap to send.
Gateways exist that allow SMS messages to be converted to fax so that theyappear on fax machines. They can even be directed to email addresses. The onlylimit is 160-character length, which must include the destination fax number andaddress.
SMS is increasingly being used for subscription information services. Userscan already subscribe to financial information services, where marketinformation is sent either automatically or on demand.
Using a custom software interface, SMS provides an excellent vehicle for menuselection 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 underlyingtechnology of SMS is an ever-growing list. Besides the common use of justcommunicating with the "buddies” the SMS application family can beclassified 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 pricesensitivity, 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. Whenyou turn a GSM phone on, it looks for a base station. Once found, the basestation (which is the phone talks to) will check with your service provider tosee if you are a valid user. And if so connect you. If your service provider hasroaming agreements across national boundaries the technical aspects becomingmore complex, but for the user the process is quick and seamless. All you willsee is the name of local provider.
Unlike the analog phones, GSM phones are always checking to find thestrongest signals
From the local transmitters. As the phone moves out of range of a basestation, it will tell the base station to transfer it to the next. The most theuser will see is a current base transmitter. The consequence is that a GSM phoneknows more or less where it is.
Data/Fax/Email Transmissions
From the outset, GSM was designed to transmit data. Normal phone lines haveconditioned us to the idea that where voice can be transmitted, data can also besent. Unfortunately, with any wireless communication, other problems include.Radio is a far less reliable medium than a phone cable, being subject tointerference, loss and fading. The human brain is very good at compensating forthese aberrations – however, with data it is vital to ensure that nothing islost.
GSM performs an immense amount of processing to protect your data. The datais partitioned, reassembled and convoluted such that it can be checked andreconstructed, even if partially damaged in transmission. This processingincreases the complexity and cost of the phone, but it ensures reliable datatransmission at a throughput of 9600 Bps.
Depending upon the level of data reliability required, GSM has two differentmechanisms for sending data
- Transparent modes.
- Non Transparent Modes.
In Transparent mode no effort is made to correct errors, other than by thebasic protocols. This is ideal for applications where data is needed fast, butwhere error is acceptable. Typically this may be the case for applications likeVideo Conferencing or fax.
Non Transparent transmission checks each packet for errors and requestsretransmission, but ensures full data integrity. The method used to control NonTransparent transfer is RLP (Radio Link Protocol), which is an integral part ofthe GSM standard and is an error correction standard optimized for the wirelessenvironment. Because the checking is performed within the GSM hardware it isvery efficient mode of correction. Similar to data, GSM lets you send andreceive and receive faxes. Again, these can be sent in both Transparent and NonTransparent modes, although most service providers are currently onlyimplementing Non- Transparent Fax.
GSM Security
GSM was designed with security in mind and all voice data and fax isencrypted. The encryption password is programmed into the SIM module, and isknown only to the mobile telephone network. As yet there are no reports ofencryption having been cracked.
UP Next
GSM in an evolving standard. One of the next enhancements to reach the marketwill be a 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 willstart to integrate GSM with DECT, so that the same handset can make mobile callsor work through a local DCET wireless switchboard as a cordless phone.
Data speeds will also improve although not in the short term. Work hasalready begun on GSM’s successor – UMTS (Universal Mobile Telephone System)and GPRS (General Packet Radio Service), providing mobile communications in thenew millennium.
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