|
Welcome to the new home of the Celtnet Mobiles in formation site. This page is the second in a series of eight articles that takes you through how mobile phones work. You can either page through the aritcles, below, or you can use the navigation menu on the left to find the page you want.
In this description of how a mobile phone actually functions I’m going to concentrate on digital (ie 2nd generation) mobile phones, as these are by far the most prevalent telephones used today (indeed, the general description given here will also apply to 3rd generation phones).
Although, in strict electronic terms, a mobile phone is one of the most complex pieces of equipment that people regularly use on a daily basis the principle of how a digital mobile phone works is relatively simple and can be summarized by the components show on the schematic on the left. In effect, the phone is simply a means of converting the owner’s voice into a digital signal that can be transmitted via the phone’s antenna to a receiving station. At the same time the telephone receives an incoming signal from the receiving station via its antenna which the phone converts into the voice of the person on the other end of the call.
Of course, the situation is a little more complicated that this as there are other components to the phone — such as the keypad, the LCD screen, memory to hold the telephone’s operating system, memory to hold contacts and images, a camera etc. Yet all these devices are peripheral, for at the heart of the telephone lies a single microprocessor that handles most of the phone’s operations and it is this that performs the hard work of making mobile telephone calls actually work and be intelligible.
What Happens When you Switch a Mobile Phone On
We will now look at what happens when a mobile telephone’s owner actually makes a call. The phone is charged and there is sufficient energy in the battery for a telephone call to be made. As soon as the telephone is turned on the mobile phone’s operating system is loaded from RAM. This generally loads a start-up screen and ‘bots-up’ (starts) the phone ready for operation. Once the operating system is loaded into the telephone’s RAM then a call can be made.
Most phones today have a SIM (Subscriber Identity Module) card that is a specialized form of flash memory. This card stores information such as address books, contacts, calendars. But it also holds other very important data that the user cannot normally access. Indeed, the first time a new mobile phone is used (actually, to be precise, the first time a new SIM card is used in a phone) a number held on the SIM card called the International Mobile Subscriber Identifier (IMSI) number is transmitted to the network. The network then looks this number up in a database to ensure the SIM card is registered there. If this is the case then a number called the Temporary Mobile Subscriber Identity (TMSI) is encrypted and sent back to the phone where it is stored in the SIM card. In all subsequent calls the phone uses this TMSI number to identify itself by broadcasting the number to the network.
Each time a call is made the TMSI is transmitted to the network. The transmission of this number is followed by a complex series of events — each designed to verify that the phone and the phone’s owner are who they actually claim to be. Once the TMSI has been broadcast to the network the network then locates the corresponding IMSI number for the phone from its database and this information is used to determine which services (news, web access etc) the subscriber has signed-up for. A special component of the network, called the Authentication Centre then broadcasts a random number to the phone. This number, combined with a secret authentication number held on the SIM card itself are then fed into an algorithm (a sequence of mathematical formulae) within the phone’s CPU that generates a new number which the phone transmits back to the network. The network then runs the original random number and the user’s authentication code through an equivalent algorithm to generate its own result. Only if the numerical results from the phone and from the network match is the call given the ‘all clear’ to connect. This ensures that authentication can be made without the phone ever having to transmit its own secret authentication code from its SIM. This ensures that it is much more difficult to ‘clone’ (ie duplicate one phone to another so that a thief can make telephone calls that are charged to the original owner’s account) with digital phones that it was with analogue phones.
Once this initial verification is made the SIM card feeds the random number generated by the network and its own authentication number into a second algorithm that generates an encryption key which is used to encode and decode all data both sent from and received by the phone during the subsequent connection (whether or not data or voice information is accessed).
Though not performed during every connection to the network, a further security check is often made by the network. In this case, the network beams a signal to the phone that interrogates it for its International Mobile Equipment Identity (IMEI) number (which is held in the handset’s own memory. This is a 10-digit number unique to the handset (and you can generally access yours by typing *#06# into your phone). The phone then transmits this number to the network, which checks it against its equipment register. If the phone is registered as stolen then the connection is cut and, depending on the phone, a signal may be sent to block the phone completely so that it cannot be used again. This is why it’s important to note your phone’s IMSI number at purchase (or at the very least the first time you switch the phone on) so that, if stolen, the handset can be rendered useless to the thief and/or any subsequent purchases.
At this point, all security checks have been made and the telephone is now registered to the network and ready to make a call. The usual thing to do at this point is to dial a call using the telephone’s keypad. This is modelled on the numeric keypad of landline telephones for the sake of familiarity. Though, as phones are increasingly used for data and message transmission the keypads can access a wide range of characters and some phones now come with full computer keypads. There is also a move away from the traditional numeric keypad, such as in Apple’s iPhone which uses a touch sensitive bezel that is similar to the one found on Apple’s iPod range of music players. However, despite what the input method may look like, they are all devices for inputting numbers or alphanumeric messages into the phone.
Not found what you're looking for? Search the web:
One Million People CampaignIf you can spare $1 then help support this site and change someone's life forever? Learn how and why on the One Million People campaign page. Or donate $10 and get my guide to spices ebook or The Recipes of Africa eBook as a gift for your donation! |
GPS Tuner Atlas Full version with North America Basic map content Atlas, is an outdoor navigational software for windows mobile devices, with built-in Tele Atlas maps, raster maps, and user generated custom calibrated maps.
If you are in search of company for your iPhone application development then visit Perception System
Bangalore: Verity Technologies, a mobile applications company with focus on Authentication and Identity Management Services, today announced a strategic alliance with Kores (India) Limited, a 76 year old highly diversified business house with all India network and market leadership in stationery and office products. Kores has relationships with most Indian Banks. The alliance paves way for Kores to distribute Verity’s highly acclaimed Blue ID, a new generation technology – that secures financial transactions, manage access and provides biometric identity to masses on a pan India basis.
Perception System has professional Iphone Games developers to built different levels of iPhone games as per your cost, budget and requirements within a certain period of time. Perception System http://perceptionsystem.com/iphone-game-development.html , offers great value at affordable cost to deliver our customers high quality game services.
Perception System know-how to proves quality and cost effective porting solutions. If you want our iPhone porting services please contact us at http://www.perceptionsystem.com Perception System offer both operator specific and handset specific porting services.
A handy app, SmartTouch Mobile enhances your Windows Mobile device functionality with a suite of widgets, enabling smooth access to branded content and services.
iPhone 3G is the coolest mobile phone launched lately, even though it is cheaper than its earlier version but there are a lofty subscription charges involved. You can spare yourself from these costs and gift yourself a free iPhone 3G.
iPhone is a revolutionary cell phone and has changed the cell phone industry completely. But it is cell phone which is out of reach of many. There are a lot of websites which are offering free iPhones.
Are you one of the thousands of people with an old mobile phone languishing in the corner? If you are then why not contact Envirofone.com they could give you up to £150 for your old phone. It’s better than having that old phone sitting around doing nothing. Read the full story to find out more…
While there still aren’t any physical copies of cell phone directories in our times yet, it is already possible to know the names and addresses of any cell phone number if you will use a cell phone lookup website. If you still aren’t aware with this, then read on this article and we will explain it to you more and more.
A cell phone lookup resource is an online tool that any person can use to search and retrieve any essential information about a cell phone number owner. For example, through a cell phone lookup tool, you can know the full legal name of the person behind the number.
click here for the full story
printer version