GSM

The GSM logo is used to identify compatible handsets and equipment

GSM (Global System for Mobile communications: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. Its promoter, the GSM Association, estimates that 80% of the global mobile market uses the standard.[1] GSM is used by over 3 billion people across more than 212 countries and territories.[2][3] Its ubiquity makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signaling and speech channels are digital, and thus is considered a second generation (2G) mobile phone system. This has also meant that data communication was easy to build into the system. GSM EDGE is a 3G version of the protocol.

The ubiquity of the GSM standard has been an advantage to both consumers (who benefit from the ability to roam and switch carriers without switching phones) and also to network operators (who can choose equipment from any of the many vendors implementing GSM[4]). GSM also pioneered a low-cost (to the network carrier) alternative to voice calls, the short message service (SMS, also called "text messaging"), which is now supported on other mobile standards as well. Another advantage is that the standard includes one worldwide emergency telephone number, 112.[5] This makes it easier for international travellers to connect to emergency services without knowing the local emergency number.

Newer versions of the standard were backward-compatible with the original GSM phones. For example, Release '97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE).

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[edit] Technical details GSM cell site antennas in the Deutsches Museum

[edit] Cellular radio network

Main article: Cellular network

GSM is a cellular network, which means that mobile phones connect to it by searching for cells in the immediate vicinity.

There are five different cell sizes in a GSM network—macro, micro, pico, femto and umbrella cells. The coverage area of each cell varies according to the implementation environment. Macro cells can be regarded as cells where the base station antenna is installed on a mast or a building above average roof top level. Micro cells are cells whose antenna height is under average roof top level; they are typically used in urban areas. Picocells are small cells whose coverage diameter is a few dozen metres; they are mainly used indoors. Femtocells are cells designed for use in residential or small business environments and connect to the service provider’s network via a broadband internet connection. Umbrella cells are used to cover shadowed regions of smaller cells and fill in gaps in coverage between those cells.

Cell horizontal radius varies depending on antenna height, antenna gain and propagation conditions from a couple of hundred meters to several tens of kilometres. The longest distance the GSM specification supports in practical use is 35 kilometres (22 mi). There are also several implementations of the concept of an extended cell[12], where the cell radius could be double or even more, depending on the antenna system, the type of terrain and the timing advance.

Indoor coverage is also supported by GSM and may be achieved by using an indoor picocell base station, or an indoor repeater with distributed indoor antennas fed through power splitters, to deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna system. These are typically deployed when a lot of call capacity is needed indoors; for example, in shopping centers or airports. However, this is not a prerequisite, since indoor coverage is also provided by in-building penetration of the radio signals from any nearby cell.

The modulation used in GSM is Gaussian minimum-shift keying (GMSK), a kind of continuous-phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first smoothed with a Gaussian low-pass filter prior to being fed to a frequency modulator, which greatly reduces the interference to neighboring channels (adjacent- channel interference).

[edit] GSM frequencies

Main article: GSM frequency ranges

GSM networks operate in a number of different frequency ranges (separated into GSM frequency ranges for 2G and UMTS frequency bands for 3G). Most 2G GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands were already allocated. Most 3G GSM networks in Europe operate in the 2100 MHz frequency band.

The rarer 400 and 450 MHz frequency bands are assigned in some countries where these frequencies were previously used for first-generation systems.

GSM-900 uses 890–915 MHz to send information from the mobile station to the base station (uplink) and 935–960 MHz for the other direction (downlink), providing 125 RF channels (channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is used.

In some countries the GSM-900 band has been extended to cover a larger frequency range. This 'extended GSM', E-GSM, uses 880–915 MHz (uplink) and 925–960 MHz (downlink), adding 50 channels (channel numbers 975 to 1023 and 0) to the original GSM-900 band. Time division multiplexing is used to allow eight full-rate or sixteen half-rate speech channels per radio frequency channel. There are eight radio timeslots (giving eight burst periods) grouped into what is called a TDMA frame. Half rate channels use alternate frames in the same timeslot. The channel data rate for all 8 channels is 270.833 kbit/s, and the frame duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900 and 1 watt in GSM1800/1900.

[edit] Voice codecs

GSM has used a variety of voice codecs to squeeze 3.1 kHz audio into between 6.5 and 13 kbit/s. Originally, two codecs, named after the types of data channel they were allocated, were used, called Half Rate (5.6 kbit/s) and Full Rate (13 kbit/s). These used a system based upon linear predictive coding (LPC). In addition to being efficient with bitrates, these codecs also made it easier to identify more important parts of the audio, allowing the air interface layer to prioritize and better protect these parts of the signal.

GSM was further enhanced in 1997[13] with the Enhanced Full Rate (EFR) codec, a 12.2 kbit/s codec that uses a full rate channel. Finally, with the development of UMTS, EFR was refactored into a variable-rate codec called AMR-Narrowband, which is high quality and robust against interference when used on full rate channels, and less robust but still relatively high quality when used in good radio conditions on half-rate channels.

[edit] Network structure

The structure of a GSM network

The network behind the GSM seen by the customer is large and complicated in order to provide all of the services which are required. It is divided into a number of sections and these are each covered in separate articles.

• the Base Station Subsystem (the base stations and their controllers). • the Network and Switching Subsystem (the part of the network most similar to a fixed network). This is sometimes also just called the core network. • the GPRS Core Network (the optional part which allows packet based Internet connections). • all of the elements in the system combine to produce many GSM services such as voice calls and SMS.

[edit] Subscriber Identity Module (SIM)

Main article: Subscriber Identity Module

One of the key features of GSM is the Subscriber Identity Module, commonly known as a SIM card. The SIM is a detachable smart card containing the user's subscription information and phone book. This allows the user to retain his or her information after switching handsets. Alternatively, the user can also change operators while retaining the handset simply by changing the SIM. Some operators will block this by allowing the phone to use only a single SIM, or only a SIM issued by them; this practice is known as SIM locking, and is illegal in some countries.

[edit] Phone locking

Main article: SIM lock

Sometimes mobile phone operators lock mobiles which they sell to their own network. This is done because the price of the mobile phone is typically subsidised with revenue from subscriptions, and operators want to try to recoup this investment before a subscriber leaves for another operator.

A subscriber can usually contact the provider to remove the lock for a fee, utilize private services to remove the lock, or make use of software and websites available on the Internet to unlock the handset themselves. While most web sites offer the unlocking for a fee, some do it for free. The locking applies to the handset not to SIM card.

In some countries (e.g. Bangladesh, Hong Kong, Pakistan and others) all phones are sold unlocked. In others (e.g. Belgium, Finland, New Zealand and others) it is unlawful for operators to offer any form of subsidy on the phone's price.

[edit] GSM security

See also: UMTS security

GSM was designed with a moderate level of security. The system was designed to authenticate the subscriber using a pre-shared key and challenge-response. Communications between the subscriber and the base station can be encrypted. The development of UMTS introduces an optional USIM, that uses a longer authentication key to give greater security, as well as mutually authenticating the network and the user - whereas GSM only authenticates the user to the network (and not vice versa). The security model therefore offers confidentiality and authentication, but limited authorization capabilities, and no non-repudiation. GSM uses several cryptographic algorithms for security. The A5/1 and A5/2 stream ciphers are used for ensuring over-the- air voice privacy. A5/1 was developed first and is a stronger algorithm used within Europe and the United States; A5/2 is weaker and used in other countries. Serious weaknesses have been found in both algorithms: it is possible to break A5/2 in real-time with a ciphertext-only attack, and in February 2008, Pico Computing, Inc revealed its ability and plans to commercialize FPGAs that allow A5/1 to be broken with a rainbow table attack.[14] The system supports multiple algorithms so operators may replace that cipher with a stronger one.

On 28 December 2009 it was announced that Karsten Nohl, a 28-year-old German computer engineer, had cracked GSM's encrypting code. [15] [edit] Standards information

The GSM systems and services are described in a set of standards governed by ETSI, where a full list is maintained.[16]

The Global System for Mobile communications is the most popular cellular approach in the world. According to the GSM Association, there were more than 2 billion GSM subscribers worldwide by June, 2008, which the organization said is more than 86 percent of the world's cellular market. GSM was accelerated earlier this decade by Enhanced Data rates for GSM Evolution (EDGE) and is in the process of further speed boosts by High Speed Downlink Packet Access and High Speed Uplink Packet Access (HSDPA and HSUPA) approaches.

This tutorial explains the basic components, technologies used, and operation of Global System for Mobile Communication - GSM - systems. You will discover why mobile telephone service providers have upgraded from 1st generation analog systems to more efficient and feature rich 2nd generation GSM systems. You will also discover how 2nd generation systems are gradually evolving into 3rd generation broadband multimedia systems.

This tutorial starts with the system components and basic services that the GSM system can provide. You will learn that the key types of GSM devices include single mode and dual mode mobile telephones, wireless PCMCIA cards, embedded radio modules, and external radio modems. You will then discover the different types of available services such as multiple types of voice services, data services, group call, and messaging services.

Explained are the physical and logical radio channel structures of the GSM system along with the basic frame and slot structures. Described are the fundamental capabilities and operation of the GSM radio channel including channel coding, modulation types, speech coding, RF power control, and mobile assisted handover. You will learn how each GSM radio channel has 8 time slots per frame and that some of these are used for signaling (control channels) and others are used for user traffic (voice and data). Because the needs of voice and data communication are different, you will discover that the GSM system essentially separates circuit switched (primarily voice) and packet switched (primarily data) services.

Described are key functional sections of a GSM network components and how they communicate with each other. You will learn how and why GSM is evolving into 3rd generation broadband systems including GPRS, EDGE, and WCDMA.

Definition: GSM, which stands for Global System for Mobile communications, reigns as the world’s most widely used cell phone technology. Cell phones use a cell phone service carrier’s GSM network by searching for cell phone towers in the nearby area.

The origins of GSM can be traced back to 1982 when the Groupe Spécial Mobile (GSM) was created by the European Conference of Postal and Telecommunications Administrations (CEPT) for the purpose of designing a pan-European mobile technology.

It is approximated that 80 percent of the world uses GSM technology when placing wireless calls, according to the GSM Association (GSMA), which represents the interests of the worldwide mobile communications industry. This amounts to nearly 3 billion global people.

Cell phone carriers T-Mobile and AT&T use GSM for their cell phone networks. Sprint, Virgin Mobile and Verizon Wireless use the competing CDMA standard.

For practical and everyday purposes, GSM offers users wider international roaming capabilities than other U.S. network technologies and can enable a cell phone to be a “world phone”. More advanced GSM incorporates the earlier TDMA standard. GSM carriers have roaming contracts with other GSM carriers and typically cover rural areas more completely than competing CDMA carriers (and often without roaming charges, too).

GSM also has the advantage of using SIM (Subscriber Identity Module) cards in the U.S. The SIM card, which acts as your digital identity, is tied to your cell phone service carrier’s network rather than to the handset itself. This allows for easy exchange from one phone to another without new cell phone service activation.

GSM uses digital technology and is a second-generation (2G) cell phone system. GSM, which predates CDMA, is especially strong in Europe. EDGE is faster than GSM and was built upon GSM.

GSM Technology

General Information

GSM is also known as Global System for Mobile Communications, or simply Global System for Mobile. A technology started development in 1985 by a French company formerly known as Groupe Spécial Mobile. It's main competetor is CDMA, currently in use by Bell Mobility, Telus Mobility and Mobility Canada carriers.

Currently, only two main carriers in Canada are operating GSM networks. Microcell (Fido, Cityfone) and Rogers Wireless. Fido was the first carrier to start utilising this technology, followed by Rogers Wireless mainstream around 2001. Several companies in the United States have adopted GSM and it's spreading fast among AT&T Wireless, T-Mobile.

GSM operates on 4 different frequencies worldwide. However, only two are which are used in Canada, which are GSM-850 and GSM-1900.GSM-850 and GSM-1900 which operate at 1.9Ghz.

GSM calls are either based on data or voice. Voice calls use audio codecs called half-rate, full-rate and enhanced full-rate. Data calls can turn the cell phone into a modem operating at 9600 bps. An extended GSM feature is high speed circuit switched data, allowing the phone to transmit upto around 40 kbps.

GPRS

GPRS or General Packet Radio Service is an extended service of GSM Network adding the ability to surf the Internet on your phone at slightly higher speeds. GPRS Internet surfing is comparable to dial-up Internet service in it's speed, operating at around 4 to 5 Kilobytes per second.

Surfing the net on your mobile isn't exactly cheap compared to residential Internet services. It is generally billed by how much data you transfer and it can get costly! We would not recommend the consumer use GPRS technology in place of a desktop computer with an Internet connection. It's just too expensive.

Technical introduction to GSM modem technology

FACTS AND APPLICATIONS OF GSM/GPRS MODEM

The GSM/GPRS Modem comes with a serial interface through which the modem can be controlled using AT command interface. An antenna and a power adapter are provided. The basic segregation of working of the modem is as under: • Voice calls • SMS • GSM Data calls • GPRS

Voice calls: Voice calls are not an application area to be targeted. In future if interfaces like a microphone and speaker are provided for some applications then this can be considered.

SMS: SMS is an area where the modem can be used to provide features like: • Pre-stored SMS transmission • These SMS can be transmitted on certain trigger events in an automation system • SMS can also be used in areas where small text information has to be sent. The transmitter can be an automation system or machines like vending machines, collection machines or applications like positioning systems where the navigator keeps on sending SMS at particular time intervals • SMS can be a solution where GSM data call or GPRS services are not available

GSM Data Calls: Data calls can be made using this modem. Data calls can be made to a normal PSTN modem/phone line also (even received). Data calls are basically made to send/receive data streams between two units either PC’s or embedded devices. The advantage of Data calls over SMS is that both parties are capable of sending/receiving data through their terminals.

Some points to be remembered in case of data calls: • The data call service doesn’t come with a normal SIM which is purchased but has to be requested with the service provider (say Airtel). • Upon activation of data/fax service you are provided with two separate numbers i.e. the Data call number and the Fax service number. • Data calls are established using Circuit Switched data connections. • Right now the speed at which data can be transmitted is 9.6 kbps. • The modem supports speeds up to 14.4 kbps but the provider give a maximum data rate of 9.6 kbps during GSM data call. • Technologies like HSCSD (high Speed Circuit Switched Data) will improve drastically the data rates, but still in pipeline.

Applications And Facts About GSM Data Calls:

• Devices that have communication on serial port either on PC or in the embedded environment • Devices that want to communicate with a remote server for data transfer • This capability of data transfer can help in reducing processing requirements of the device • The basic aim is to provide a wireless solution keeping the existing firmware intact • The clients firmware continues to work without any modifications (no changes in the existing software required) • GSM data calls can be a good solution where data has to be transmitted from a hand-held device to a central server • The interface on two sides can be between PC’s as well as embedded devices

• Calls can be established by the terminals at either side to start data calls • The Modem remains transparent during data transfer after the call is established. • Call establishment utility to be provided in case PC terminals • Call establishment to be automated in case of embedded terminals. GSM converter can be an option where intelligence of establishing calls has to be put in case of embedded devices. Concept of GSM converter is discussed later in this document

Dial-Up Networks Using GSM Data Calls: Dial up networking is a utility available with Windows through a person can dial the Data call number of this modem from any PC and share the file system on either PC’s. This can be a good utility where both terminals are PC based. Sharing the file system remotely enables monitoring of devices remotely. Thus the modem can act as a piece of device which acts as a spy in the system. Can be a good debugging utility wherein a person can configure/monitor a remote PC based system and even rectify it. Some companies do sell their products with a GSM modem inside it just for this handy feature which allows them to configure the machines sitting anywhere in the world. Since the connection can have upper layer protocols like TCP/IP in this connection it becomes more reliable and useful.

GSM Converter: GSM converter will be an add-on device to be attached between a terminal which wants data transfer and the GSM modem. This GSM converter will take care of call establishment where the embedded device cannot make a call. The converter will remain transparent through-out the call once call is established. The GSM converter will be a very small piece of hardware possibly embedded inside the cable itself.

GPRS: This modem can be used to make a GPRS connection. Upon connection the modem can be used for internet connectivity of devices.

Key-Points in GPRS:

• The PC/Embedded device dials the Service Provider (say Airtel) • Data is routed through the ISP (Internet Service Provider) • GPRS is basically Packet Oriented service • Protocols like TCP/IP are inherent characteristics in GPRS • One has to talk in terms of IP addresses here not phone numbers • The implementation is more useful where PC’s want to communicate over GPRS • Although data transfer is done from embedded devices too but with reduced features • Since you are charged either on monthly flat rates or amount of data transfer taking place GPRS is anyday a cheaper option as compared to GSM data call. But GPRS services are not available everywhere. • The data rate rates in GPRS can go upto 40 kbps

Application areas in GPRS using this Modem:

• Applications where mobile devices want to upload data to a central server • Monitoring devices that are continuously logged on to the server. Since you are charged for the amount of data transfer hence a continuous connection can be maintained. • Virtual private networks • Radius servers

Virtual private networks

A virtual private network (VPN) is the extension of a private network that encompasses links across shared or public networks like the Internet. A VPN enables you to send data between two computers across a shared or public internetwork in a manner that emulates the properties of a point-to-point private link. The act of configuring and creating a virtual private network is known as virtual private networking. To emulate a point-to-point link, data is encapsulated, or wrapped, with a header that provides routing information allowing it to traverse the shared or public transit internetwork to reach its endpoint. To emulate a private link, the data being sent is encrypted for confidentiality. Packets that are intercepted on the shared or public network are indecipherable without the encryption keys. The portion of the connection in which the private data is encapsulated is known as the tunnel. The portion of the connection in which the private data is encrypted is known as the virtual private network (VPN) connection.

Figure 1: Virtual private network connection

VPN connections allow users working at home or on the road to connect in a secure fashion to a remote organization server using the routing infrastructure provided by a public internetwork (such as the Internet). From the user’s perspective, the VPN connection is a point-to-point connection between the user’s computer and an organization server. The nature of the intermediate internetwork is irrelevant to the user because it appears as if the data is being sent over a dedicated private link. VPN technology also allows a corporation to connect to branch offices or to other companies over a public internetwork (such as the Internet), while maintaining secure communications. The VPN connection across the Internet logically operates as a wide area network (WAN) link between the sites. In both of these cases, the secure connection across the internetwork appears to the user as a private network communication—despite the fact that this communication occurs over a public internetwork—hence, the name virtual private network. VPN technology is designed to address issues surrounding the current business trend toward increased telecommuting and widely distributed global operations, where workers must be able to connect to central resources and must be able to communicate with one another. To provide employees with the ability to connect to organization computing resources, regardless of their location, a corporation must deploy a scalable remote access solution. Typically, corporations choose either a department solution, where an internal information systems department is charged with buying, installing, and maintaining organization modem pools and a private network infrastructure; or they choose a value-added network (VAN) solution, where they pay an outsourced company to buy, install, and maintain modem pools and a telecommunication infrastructure. Neither of these solutions provides the necessary scalability, in terms of cost, flexible administration, and demand for connections. Therefore, it makes sense to replace the modem pools and private network infrastructure with a less expensive solution based on Internet technology so that the business can focus on its core competencies. With an Internet solution, a few Internet connections through Internet service providers (ISPs) and VPN server computers can serve the remote networking needs of hundreds or thousands of remote clients and branch offices. Common Uses of VPNs The next few sections describe the more common VPN configurations in more detail. Remote Access Over the Internet VPNs provide remote access to organization resources over the public Internet, while maintaining privacy of information. Figure 2 shows a VPN connection used to connect a remote access client to an organization intranet. This is known as a remote access VPN connection.

Figure 2: Using a VPN connection to connect a remote access client to an organization intranet Rather than making a long distance (or 1-800) call to an organization or outsourced network access server (NAS), the user dials a local ISP. Using the connection to the local ISP, the VPN client creates a VPN connection between the remote access computer and the organization VPN server across the Internet. Connecting Networks Over the Internet There are two methods for using VPNs to connect local area networks at remote sites: • Using dedicated lines to connect a branch office to an organization LAN. For example, rather than using an expensive long-distance dedicated circuit between the branch office and the corporate hub, both the branch office and the corporate hub routers can use a local dedicated circuit and local ISP to connect to the Internet. The VPN software uses the local ISP connections and the Internet to create a virtual private network between the branch office router and corporate hub router. • Using a dial-up line to connect a branch office to the Internet. Rather than having a router at the branch office make a long distance (or 1-800) call to a corporate or outsourced NAS, the router at the branch office can call a local ISP. The VPN client uses the connection to the local ISP to create a VPN connection between the branch office router and the corporate hub router across the Internet. This is known as a site-to-site VPN connection.

Figure 3: Using a VPN connection to connect two remote sites

In both cases, the facilities that connect the branch office and corporate offices to the Internet are local. The corporate hub router that acts as a VPN server must be connected to a local ISP with a dedicated line. This VPN server must be listening 24 hours a day for incoming VPN traffic. Connecting Computers Over an Intranet In some organization internetworks, the departmental data is so sensitive that the department’s LAN is physically disconnected from the rest of the organization internetwork. Although this protects the department’s confidential information, it creates information accessibility problems for those users not physically connected to the separate LAN.

Figure 4: Using a VPN connection to connect to a secured or hidden network

VPNs allow the department’s LAN to be physically connected to the organization internetwork but separated by a VPN server. The VPN server is not acting as a router between the organization internetwork and the department LAN. A router would connect the two networks, allowing everyone access to the sensitive LAN. By using a VPN server, the network administrator can ensure that only those users on the organization internetwork who have appropriate credentials (based on a need-to-know policy within the company) can establish a VPN connection with the VPN server and gain access to the protected resources of the department. Additionally, all communication across the VPN can be encrypted for data confidentiality. Those users who do not have the proper credentials cannot view the department LAN.

RADIUS:

A GSM phone is a type of mobile phone that uses the (G)lobal (S)ystem for (M)obile Communications to send and receive phone calls. GSM is a digital standard first offered commercially in 1991 and is currently the most popular mobile phone transmission technology in the world.

The GSM standard uses TDMA digital technology, which allows for three different voice calls to be placed in the same time slot, rather than one call using the old analog "cell" phones. This is possible through digital compression that GSM then builds upon with the addition of encryption. A GSM phone takes up the same amount of transmission space as the old technology, but has the additional benefit of added security.

One of the great benefits of a GSM phone is the addition of a SIM card, or "Subscriber Identification Module." This little chip slips into the back of GSM phones and provides all of the users' personal information. This includes contacts and calendar information in most cases, and more importantly the subscriber's personal identification information. Having this information on removable chip enables a GSM phone user to move a SIM card between mobile phones and still receive voice calls to the same number. It also prevents user from having to re-input personal information each time a new phone is purchased.

In Europe and most of Asia, GSM is the standard used by everyone. Having one technology is great, because users can simply move their chips to different phones if they travel to different countries or in most cases use the same phone. This is in contrast to the US, with so many competing standards and difficulty transferring between carriers.

The adoption of GSM technology and GSM phones as a standard also paved the way for the rise of text messaging in many countries. While text messaging is starting to become popular in North America, it is nowhere near as popular as it is in Europe and Asia. Carriers in the US in particular use various technologies in addition to GSM and must then route text messages through third party gateways. This is how a Sprint user can send a text message to a Verizon customer. Until a few years ago this wasn't possible and served to prevent text messaging from truly catching on.

GSM and GSM phones have found a significant boost due to Cingular Wireless becoming America's largest mobile provider. They have adopted GSM technology and promote the GSM phone's ease of use due to a swappable SIM card. Though the US still has many competing technologies, a GSM phone is the international choice. If you plan to travel frequently overseas, a GSM phone might be the wise decision.

Introduction Before deciding which technology is superior, let's talk a little more about these two tecnologies:

• CDMA: stands for Code Division Multiple Access. Both data and voice are separated from signals using codes and then transmited using a wide frequency range. Because of this, there are more space left for data transfer (this was one of the reasons why CDMA is the prefered technology for the 3G generation, which is broadband access and the use of big multimedia messages). 14% of the worldwide market goes to CDMA. For the 3G generation CDMA uses 1x EV-DO and EV-DV. It has a lot of users in Asia, specially in South Korea. • GSM: stands for Global System Mobile. Even though it is sold as "the latest technology" in several countries, this technology is older than CDMA (and also TDMA). But keep in mind that this doesn't mean that GSM is inferior or worse than CDMA. Roaming readiness and fraud prevention are two major advantages from this technology. GSM is the most used cell phone technology in the world, with 73% of the worldwide market. It has a very strong presence in Europe.

TDMA technology is the less used from the three main digital technologies (GSM, CDMA and TDMA) and we think it will gradually be replaced to CDMA or GSM. That's why the GSM vs CDMA war. At one corner, GSM operators say it is better "because it uses a SIM chip, it is the most used technology worldwide, it is more secure and it is more advanced". On the other corner, CDMA followers say it is better "because it is the 3G generation chosen technology and GSM will migrate to CDMA since CDMA is more advanced..."

But which one of these statements are correct? Acordingly to Nokia, "this discussion is not about technology anymore, but about market". We think this is the best way to describe the war between these two cell phone technologies.

In the beginning, GSM was in fact superior. It had more services and allowed more data transfer. But CDMA, facing the advantages of the competitor standard, soon delivered the same features found on GSM. Nowadays, it is not possible to say that GSM services are better than CDMA. Multimedia messages, video, high-speed Internet access, digital camera and even PDA function are some of the features we can found on both technologies. The new CDMA 1XRTT technology, which previews what G3 cell phones will bring, is more advanced than EDGE, technology from the beginning of 3G generation, allowing higher transfer rates.

Even the GSM SIM card advantage, that allows you to change your cell phone and keep your phone list, is being surplaced by some CDMA operators with a service that allows you to store your phone book on the operator's database, allowing you to recover your phone book even if your cell phone is stolen (which is not possible with GSM, since if your cell phone is stolen, your SIM card will be stolen together). Notice that recently a new accessory called SIM backup was released, which allows you to backup the data stored in your SIM card. Also some GSM operators are offering a similar backup service.

So, nowadays both technologies are equiparated in technology, but this picture won't be like that in the future. Afterall, CDMA evolution ground is wider and in a few years it will be superior than GSM. This means that GSM operators will disapear? Not at all. They will migrate over CDMA and the war will continue, because the existing CDMA operators chose to use 1xEV-DO and1XEV-DV technologies for their 3G network and the existing GSM operators have opted for a different technology, called WCDMA. Also, even though the current GSM operators will migrate to WCDMA, they still can use their existing GSM network. So users won't feel anything special when the operators shift to the new cell generation (3G), independently from the technology they choose. CDMA & GSM Cellular Technology Reference Page Wireless Communication Protocols and Standards

GSM

In 1989, GSM responsibility was transferred to the European Telecommunication Standards Institute (ETSI), and phase I of the GSM specifications were published in 1990. Commercial service was started in mid1991, and by 1993 there were 36 GSM networks in 22 countries, with 25 additional countries having already selected or considering GSM In addition to Europe, South Africa, Australia, and many Middle and Far East countries have chosen to adopt GSM. By the beginning of 1994, there were 1.3 million subscribers worldwide. The acronym GSM now (aptly) stands for Global System for Mobile telecommunications.

From the beginning, the planners of GSM wanted ISDN compatibility in services offered and control signaling used. The radio link imposed some limitations, however, since the standard ISDN bit rate of 64 Kbps could not be practically achieved.

The digital nature of GSM allows data, both synchronous and asynchronous data, to be transported as a bearer service to or from an ISDN terminal. The data rates supported by GSM are 300 bps, 600 bps, 1200 bps, 2400 bps, and 9600 bps.

The most basic teleservice supported by GSM is telephony. A unique feature of GSM compared to older analog systems is the Short Message Service (SMS). Supplementary services are provided on top of teleservices or bearer services, and include features such as international roaming, caller identification, call forwarding, call waiting, multiparty conversations, and barring of outgoing (international) calls, among others.

CDMA

Code Division Multiple Access (CDMA) is a digital air interface standard, claiming eight to fifteen times the capacity of traditional analog cellular systems. It employs a commercial adaptation of a military spread-spectrum technology. Based on spread spectrum theory, it gives essentially the same services and qualities as wireline service. The primary difference is that access to the local exchange carrier (LEC) is provided via a wireless phone.

Though CDMA’s application in cellular telephony is relatively new, it is not a new technology. CDMA has been used in many military applications, such as:

• Anti-jamming (because of the spread signal, it is difficult to jam or interfere with a Mobile Forensics..Understanding the Technology of GSM Vs CDMA

The mobile industry in India is divided between the two technologies GSM and CDMA. While the earlier service providers had adopted the GSM technology, the new players have been using CDMA technology and have notched up a significant share of the Indian market. Hence any discussion on Mobile Forensics need to take into account the presence of the two technologies.

It is necessary for us to understand the basic differentiation of the two technologies as they may have an impact on the Forensics. An attempt is made here to present the fundamental technical aspects about the two systems.

GSM stands for Global System for Mobile Communications and CDMA stands for Code Division Multiple Access. They represent different systems of sharing of the radio spectrum for communication.

Normally the radio spectrum can be shared by different users accessing the same frequency band without causing interference. The techniques used for this are TDMA (Time division multiple access), FDMA (Frequency division multiple access) and CDMA (Code division multiple access).

GSM (Global System for Mobile Communications) is a form of multiplexing, which divides the available bandwidth among the different channels. . GSM is a combination of Time and Frequency-Division Multiple Access (TDMA/FDMA). The FDMA part involves the division by frequency of the (maximum) 25 MHz bandwidth into 124 carrier frequencies spaced 200 kHz apart. Each of these carrier frequencies is then divided in time, using a TDMA scheme. The fundamental unit of time in this TDMA scheme is called a burst period and it lasts 15/26 ms (or approx. 0.577 ms). Eight burst periods are grouped into a TDMA frame (120/26 ms, or approx. 4.615 ms), which forms the basic unit for the definition of logical channels. One physical channel is one burst period per TDMA frame. Thus GSM allows eight simultaneous calls on the same radio frequency.

CDMA (Code Division Multiple Access) is a form of multiplexing (access to the same resource will be given to more than one user),which allows the use of a particular frequency for a number of signals, optimizing the use of available bandwidth. It is a cellular technology that uses spread-spectrum techniques. In CDMA technology every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence.

CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized (ADC) into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes; this enhances privacy and makes cloning difficult. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

GSM was first introduced in 1991 and until recently before the establishment of CDMA networks, GSM was the only mobile communication system present in the market. CDMA was first used during World War II by the English allies to foil German attempts at jamming transmissions. The allies decided to transmit over several frequencies, instead of one, making it difficult for the Germans to pick up the complete signal.

Since bandwidth is the major problem in the modern times the CDMA has a very clear advantage over the GSM in these terms. The number of channels(users) that can be allocated in a given bandwidth is comparatively higher for CDMA than for GSM. The cost of setting up a CDMA network is also comparatively less than the GSM network. Due to these advantages there is high probability that CDMA technology will dominate the future of mobile communications.

The technologies are normally evaluated on the following three parameters namely the data transmission capacity, security and radiation levels.

Following table indicates the data transmission of different technologies.:

Cellular technology Generation Data transmission capacity GSM 2G 56 Kps CDMA (IS-95B) 2.5G 64 Kps - 140 Kps CDMA 2000 3G 2 MBps

The idea of technology with superior security is not a new one. In 1935, a Russian researcher Dmitrii Vasilevich AGEEV, published his book "The basics of linery selection theory", where he explained the concept of coding the signals. After the WWII, Soviet and American military communication systems started to use the concept very widely because of many valuable advantages of the system. The origin concept of CDMA scheme was recommended by QUALCOMM (the famous communication provider in the US and worldwide), however Korean research institute, ETRI and companies like Hyundai, LG, and Samsung performed its realization for the first time in the world in 1995. As of today many countries have accepted it as a national standard of mobile communication and worldwide number of CDMA subscribers has climbed to over 100 million.

As already explained, CDMA uses a radically different approach to what GSM does. It assigns a unique "code" to put multiple users on the same wideband channel at the same time. The codes so-called "pseudo-random code sequence" is used by both the mobile station (handset) and the base station to distinguish between conversations. This gives a greater level of privacy and security to the communication.

As far as radiation level concerned, CDMA is the most harmless one among all existing technologies. Of course, it transmits microwaves while on standby mode, like other technologies do. However, CDMA technology checks 800 times per second its transmission level. Therefore, radiation level is 10 times less than GSM. Another important thing to point out is that CDMA system transmits signals only when the user starts conversation. Simply saying, when you're listening the other ends conversation, you are not affected by microwave as the speaking person does.

It appears that CDMA would be the dominating technology in future and Mobile Forensics has to gear itself to the requirements of the CDMA technology.

Architechture and Working Of GSM Networks

We have already read about how GSM technology had taken over mobile communication technologies and grown over to 214 countries around the world. Now it is important to learn how GSM network works and what is the architecture of GSM networks?. GSM network is consist of thee major systems, it can also be considered architecture of GSM networks. These three systems are SS, which is known to be The Switching System, BSS, it is The Base Station and the other important system is, The operation and support System for GSM networks.

Below all three systems are defined in details with sub systems of each system. The Switching System The Switching system is very operative system in which many crucial operations are conducted, SS systems holds five databases with in it which performs different functions. If we talk about major tasks of SS system it performs call processing and subscriber related functions. These five databases from SS systems are HLR, MSC, VLR, AUC and EIR. Let’s study each database in detail and learn what functions this little systems performs. HLR- Home Location Register:

HLR is database, which holds very important information of subscribers. It is mostly known for storing and managing information of subscribers. It contains subscriber service profile, status of activities, information about locations and permanent data of all sorts. When new connections are purchased, these subscribers are registered in HLR of mobile phone companies. MSC- Mobile Services Switching Center: MSC is also important part of SS, it handles technical end of telephony.It is build to perform switching functionality of the entire system. It’s most important task is to control the calls to and from other telephones, which means it controls calls from same networks and calls from other networks. Toll ticketing, common channel signaling, network interfacing etc are other tasks which MSC is responsible for.

VLR- Visitor Location Register: VLR performs very dynamic tasks; it is database which stores temporary data regarding subscribers which is needed by Mobile Services Switching Center-MSC VLR is directly connected to MSC, when subscribe moves to different MSC location, Visitor location register – VLR integrates to MSC of current location and requests the data about subscriber or Mobile station ( MS ) from the Home Location Register –HLR. When subscriber makes a call the Visitor location register-VLR will have required information for making call already and it will not required to connect to Home Register Location - HRL again. AUC- Authentication Center:

AUC is small unit which handles the security end of the system. Its major task is to authenticate and encrypt those parameters which verify user’s identification and hence enables the confidentiality of each call made by subscriber. Authentication center – AUC makes sure mobile operators are safe from different frauds most likely to happen when hackers are looking for even smallest loop wholes in systems. EIR – Equipment Identity Register: EIR is another important database which holds crucial information regarding mobile equipments. EIR helps in restricting for calls been stolen, mal functioning of any MS, or unauthorized access. AUC – Authentication center and EIR- Equipment Identity registers are either Stand-alone nodes or some times work together as combined AUC/EIR nodes for optimum performance. The Base Station System (BSS) The base station system have very important role in mobile communication. BSS are basically out door units which consist of iron rods and are usually of high length. BSS are responsible for connecting subscribers (MS) to mobile networks.All the communication is made in Radio transmission.The Base station System is further divided in two systems. These two systems, they are BSC, and BTS. Let’s study these two systems in detail.

BTS – The Base Transceiver Station: Subscriber, MS (Mobile Station) or mobile phone connects to mobile network through BTS; it handles communication using radio transmission with mobile station. As name suggests, Base transceiver Station is the radio equipment which receive and transmit voice data at the same time. BSC control group of BTSs. BSC – The Base Station Controller: The Base Station normally controls many cells, it registers subscribers, responsible for MS handovers etc. It creates physical link between subscriber (MS) and BTS , then manage and controls functions of it. It performs the function of high quality switch by handover over the MS to next BSC when MS goes out of the current range of BTS, it helps in connecting to next in range BTS to keep the connection alive within the network. It also performs functions like cell configuration data, control radio frequency in BTS. Data moves to MSC-Mobile switching center after BSC done processing it. MSC is switching center which acts as bridge between different mobile networks. Note: This image is graphical explaination of GSM Arhitecutre and Working of GSM Networks

Note: See the Video of GSM Arhcitechture to learn how GSM network works.

The Operation and Support System (OSS)

OMC- Operations and maintenance center is designed to connect to equipment of MSC- Mobile Switching Center and BSC-Base Station Controller. The implementation of OMC is called OSS-The Operations and Support System.OSS helps in mobile networks to monitor and control the complex systems.The basic reason for developing operation and support system is to provide customers a cost effective support and solutions. It helps in managing, centralizing, local and regional operational activities required for GMS networks. Maintaining mobile network organization, provide overview of network, support and maintenance activities are other important aspects of Operation and Support System

Prior to the end of the 20th century, the use of telephones were limited to the home or workplace. Then technology gave us the pager, the beeper and then the cellular phones.

Everybody will agree that cellular phone is better than the other types of phones because aside from its being handy it also offers differing varieties of features. You can now view movies, listen to radio, and take memorable photos all with the cellular phone handset. Although millions of people use it, it is undeniable that not everyone knows about the technology needed for cellular phones to work.

One such technology is GSM, how many of us know the correct meaning of this acronym? How about its uses?

GSM stands for "Global System for Mobile Communications". This refers to a digital cellular phone technology that is primarily based on a specified standard for how data is sent over a wireless network. GSM was taken over in 1989 by the ETSI (European Telecommunications Standards Institute) and they finalized the GSM standard in 1990. GSM cellular phones use a combination of Time and Frequency Division Multiple Access.

How does GSM work? The GSM works very differently as you compare it to its analog precursor. It can provide you with important features like a fax machine, encryption, text messaging (this is the most commonly used among its services), call forwarding, caller ID, call waiting and multi party conferencing. This is useful because you can talk to the other line without any interference from other calls. The reason for this is because, the frequency channel of GSM is divided into several time slots and as the data travels, there is a specified slot for it, away from the other data. Aside from this, there are also other important features that can be provided by the GSM. There are several system components and basic services that GSM system can provide to its users. To start with, the key types of GSM devices both include single mode and dual mode mobile telephones, embedded radio modules and even external radio modems.

Since there is a need to distinguish between voice and data communication, GSM has found a way of resolving it. The GSM system has made a significant separation of the circuits between these two important elements - the circuit switch refers to the primary voice service and the packet switch refers to the primary data service.

The main companies that offer a credible GSM service of in the United States are the AT&T and the Cingular companies that already merged into one company now. The second is T-Mobile.

Nicola Kennedy publishes articles and reports and provides news, views and information about communications and GSM and Satellite Telephones at Satellite Telephones Information.

This article may be reprinted in full so long as the resource box and the live links are included intact. All rights reserved. Copyright Satellite-Telephones.info

A GSM network is composed of several functional entities, whose functions and interfaces are defined.

Figure 1 shows the layout of a generic GSM network. The GSM network can be divided into three broad parts. The Mobile Station is carried by the subscriber, the Base Station Subsystem controls the radio link with the Mobile Station. The Network Subsystem, the main part of which is the Mobile services Switching Center, performs the switching of calls between the mobile and other fixed or mobile network users, as well as management of mobile services, such as authentication. Not shown is the Operations and Maintenance center, which oversees the proper operation and setup of the network. The Mobile Station and the Base Station Subsystem communicate across the Um interface, also known as the air interface or radio link. The Base Station Subsystem communicates with the Mobile service Switching Center across the A interface. Mobile Station The mobile station (MS) consists of the physical equipment, such as the radio transceiver, display and digital signal processors, and a smart card called the Subscriber Identity Module (SIM). The SIM provides personal mobility, so that the user can have access to all subscribed services irrespective of both the location of the terminal and the use of a specific terminal. By inserting the SIM card into another GSM cellular phone, the user is able to receive calls at that phone, make calls from that phone, or receive other subscribed services.

The mobile equipment is uniquely identified by the International Mobile Equipment Identity (IMEI). The SIM card contains the International Mobile Subscriber Identity (IMSI), identifying the subscriber, a secret key for authentication, and other user information. The IMEI and the IMSI are independent, thereby providing personal mobility. The SIM card may be protected against unauthorized use by a password or personal identity number. Base Station Subsystem

The Base Station Subsystem is composed of two parts, the Base Transceiver Station (BTS) and the Base Station Controller (BSC). These communicate across the specified Abis interface, allowing (as in the rest of the system) operation between components made by different suppliers.

The Base Transceiver Station houses the radio tranceivers that define a cell and handles the radiolink protocols with the Mobile Station. In a large urban area, there will potentially be a large number of BTSs deployed. The requirements for a BTS are ruggedness, reliability, portability, and minimum cost.

The Base Station Controller manages the radio resources for one or more BTSs. It handles radiochannel setup, frequency hopping, and handovers, as described below. The BSC is the connection between the mobile and the Mobile service Switching Center (MSC). The BSC also translates the 13 kbps voice channel used over the radio link to the standard 64 kbps channel used by the Public Switched Telephone Network or ISDN. Network Subsystem

The central component of the Network Subsystem is the Mobile services Switching Center (MSC). It acts like a normal switching node of the PSTN or ISDN, and in addition provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber. These services are provided in conjuction with several functional entities, which together form the Network Subsystem. The MSC provides the connection to the public fixed network (PSTN or ISDN), and signalling between functional entities uses the ITUT Signalling System Number 7 (SS7), used in ISDN and widely used in current public networks. The Home Location Register (HLR) and Visitor Location Register (VLR), together with the MSC, provide the callrouting and (possibly international) roaming capabilities of GSM. The HLR contains all the administrative information of each subscriber registered in the corresponding GSM network, along with the current location of the mobile. The current location of the mobile is in the form of a Mobile Station Roaming Number (MSRN) which is a regular ISDN number used to route a call to the MSC where the mobile is currently located. There is logically one HLR per GSM network, although it may be implemented as a distributed database.

The Visitor Location Register contains selected administrative information from the HLR, necessary for call control and provision of the subscribed services, for each mobile currently located in the geographical area controlled by the VLR. Although each functional entity can be implemented as an independent unit, most manufacturers of switching equipment implement one VLR together with one MSC, so that the geographical area controlled by the MSC corresponds to that controlled by the VLR, simplifying the signalling required. Note that the MSC contains no information about particular mobile stations - this information is stored in the location registers.

The other two registers are used for authentication and security purposes. The Equipment Identity Register (EIR) is a database that contains a list of all valid mobile equipment on the network, where each mobile station is identified by its International Mobile Equipment Identity (IMEI). An IMEI is marked as invalid if it has been reported stolen or is not type approved. The Authentication Center is a protected database that stores a copy of the secret key stored in each subscriber's SIM card, which is used for authentication and ciphering of the radio channel.

GSM

ARCHITECTURE

GSM Glossary

Information on GSM Architecture A GSM network consists of the following components:

 Mobile station. The GSM mobile station (or mobile phone) communicates with other parts of the system through the base-station system.

 GSM Base station system (BSS).

 Base transceiver station (BTS). The base transceiver station (BTS) handles the radio interface to the mobile station. The base transceiver station is the radio equipment (transceivers and antennas)

 Base station controller (BSC). The BSC provides the control functions and physical links between the MSC and BTS. It provides functions such as handover, cell configuration data and control of RF power levels in base transceiver stations. A number of BSCs are served by a MSC.

 GSM Switching System

 Mobile services switching center (MSC). The MSC performs the telephony switching functions of the system. It also performs such functions as toll ticketing, network interfacing, common channel signalling, and others.

 Home location register (HLR). The HLR database is used for storage and management of subscriptions. The home location register stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status.

 Visitor location register (VLR). The VLR database contains temporary information about subscribers that is needed by the mobile services switching center (MSC) in order to service visiting subscribers. When a mobile station roams into a new mobile services switching center (MSC) area, the visitor location register (VLR) connected to that MSC will request data about the mobile station from the HLR, reducing the need for interrogation of the home location register (HLR).

 Authentication center (AUC). The AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The authentication center (AUC) also protects network operators from fraud.

 Equipment identity register (EIR). The EIR database contains information on the identity of mobile equipment to prevent calls from stolen, unauthorized or defective mobile stations.

 Message center (MXE). The MXE is a node that provides integrated voice, fax, and data messaging.

 Mobile service node (MSN). The MSN is the node that handles the mobile intelligent network (IN) services.

 Gateway mobile services switching center (GMSC). A gateway mobile services switching center (GMSC) is a node used to interconnect two networks.

 GSM interworking unit (GIWU). The GIWU consists of both hardware and software that provides an interface to various networks for data communications. Through the GSM interworking unit (GIWU), users can alternate between speech and data during the same call.

 Operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of operation and support system is to offer support for centralized, regional, and local operational and maintenance activities that are required for a GSM network.

GSM System Architecture

In GSM system the mobile handset is called Mobile Station (MS). A cell is formed by the coverage area of a Base Transceiver Station (BTS) which serves the MS in its coverage area. Several BTS together are controlled by one Base Station Controller (BSC). The BTS and BSC together form Base Station Subsystem (BSS). The combined traffic of the mobile stations in their respective cells is routed through a switch called Mobile Switching Center (MSC). Connection originating or terminating from external telephone (PSTN) are handled by a dedicated gateway Gateway Mobile Switching Center (GMSC). The architecture of a GSM system is shown in the figure 2.1 below.

Figure 2.1: GSM Architecture (Source: Bettstetter et. all)

In addition to the above entities several databases are used for the purpose of call control and network management. These databases are Home Location Register (HLR), Visitor Location Register (VLR), the Authentication Center (AUC), and Equipment Identity Register (EIR).

Home Location Register (HLR) stores the permanent (such as user profile) as well as temporary (such as current location) information about all the users registered with the network. A VLR stores the data about the users who are being serviced currently. It includes the data stored in HLR for faster access as well as the temporary data like location of the user. The AUC stores the authentication information of the user such as the keys for encryption. The EIR stores stores data about the equipments and can be used to prevent calls from a stolen equipments.

All the mobile equipments in GSM system are assigned unique id called IMSI (International Mobile Equipment Identity) and is allocated by equipment manufacturer and registered by the service provider. This number is stored in the EIR. The users are identified by the IMSI (International Module Subscriber Identity) which is stored in the Subscriber Identity Module (SIM) of the user. A mobile station can be used only if a valid SIM is inserted into an equipment with valid IMSI. The ``real'' telephone number is different from the above ids and is stored in SIM.

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His knowledge of telecommunications has served, most notably, the American Heritage Invention and Technology Magazine and The History Channel. His interview on Alexander Graham Bell will air on the History Channel the end of 2006.

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He has been quoted in newspapers and magazines on issues regarding cell towers and has spoke at industry and non-industry conferences on cell tower related issues.

He is recognized as an expert on cell tower leases and due diligence processes for tower acquisitions. GSM History JANUARY 16, 2006 Architecture of the GSM network

A GSM network is composed of several functional entities, whose functions and interfaces are specified. Figure 1 shows the layout of a generic GSM network. The GSM network can be divided into three broad parts. The Mobile Station is carried by the subscriber. The Base Station Subsystem controls the radio link with the Mobile Station. The Network Subsystem, the main part of which is the Mobile services Switching Center (MSC), performs the switching of calls between the mobile users, and between mobile and fixed network users. The MSC also handles the mobility management operations. Not shown is the Operations and Maintenance Center, which oversees the proper operation and setup of the network. The Mobile Station and the Base Station Subsystem communicate across the Um interface, also known as the air interface or radio link. The Base Station Subsystem communicates with the Mobile services Switching Center across the A interface.

As John states, he presents a generic GSM architecture. Lucent, Ericsson, Nokia, and others feature their own vision in their own diagrams. But they all share the same main elements and parts from different vendors should all work together. The links below show how these vendors picture the GSM architecture. You can remember the different terms much better by looking at all these diagrams.

Lucent GSM architecture/ Ericsson GSM architecture / Nokia GSM architecture / Siemen's GSM architecture

General architecture of a GSM network

One of the most contentious battles being waged in the wireless infrastructure industry is the debate over the efficient use and allocation of finite airwaves. For several years, the world's two main methods -- Code-Division Multiple Access (CDMA) and Global System for Mobile communications (GSM) -- have divided the wireless world into opposing camps. Ultimately, the emergence of a victorious technology may owe more to historical forces than the latest wireless innovation, or the merits of one standard over the other.

CDMA's World War II Foundations CDMA, put into an historical context, is a recently patented technology that only became commercially available in the mid-1990s, but had its roots in pre-World War II America. In 1940, hollywood actress turned inventor, Hedy Lamarr, and co-inventor George Antheil, with World War II looming, co-patented a way for torpedoes to be controlled by sending signals over multiple radio frequencies using random patterns. Despite arduous efforts by the inventors to advance the technology from experiment to implementation, the U.S. Navy discarded their work as architecturally unfeasible. The idea, which was known as frequency- hopping, and later as frequency-hopping spread-spectrum technology (FHSS), remained dormant until 1957 when engineers at the Sylvania Electronic Systems Division, in Buffalo, New York took up the idea, and after the Lamarr-Antheil patent expired, used it to secure communications for the U.S. during the 1962 Cuban Missile Crisis. After becoming an integral part of government security technology, the U.S. military, in the mid-80s, declassified what has now become CDMA technology, a technique based on spread- spectrum technology.

What interested the military soon caught the eye of a nascent wireless industry. CDMA, incorporating spread-spectrum, works by digitizing multiple conversations, attaching a code known only to the sender and receiver, and then dicing the signals into bits and reassembling them. The military loved CDMA because coded signals with trillions of possible combinations resulted in extremely secure transmissions.

Qualcomm, which patented CDMA, and other telecommunications companies, were attracted to the technology because it enabled many simultaneous conversations, rather than the limited stop-and-go transmissions of analog and the previous digital option.

CDMA was not field tested for commercial use until 1991, and was launched commercially in Hong Kong in 1995. CDMA technology is currently used by major cellular carriers in the United States and is the backbone of Sprint's Personal Communications System (PCS). Along with Sprint, major users of CDMA technology are Verizon and GTE.

Advantages of CDMA include:

• Increased cellular communications security. • Simultaneous conversations. • Increased efficiency, meaning that the carrier can serve more subscribers. • Smaller phones. • Low power requirements and little cell-to-cell coordination needed by operators. • Extended reach - beneficial to rural users situated far from cells.

Disadvantages of CDMA include:

• Due to its proprietary nature, all of CDMA's flaws are not known to the engineering community. • CDMA is relatively new, and the network is not as mature as GSM. • CDMA cannot offer international roaming, a large GSM advantage.

The Euro-Asian Alternative: GSM

Analysts consider Qualcomm's major competitive disadvantage to be its lack of access to the European market now controlled by Global System for Mobile communications (GSM). The wireless world is now divided into GSM (much of Western Europe) and CDMA (North America and parts of Asia).

Bad timing may have prevented the evolution of one, single global wireless standard. Just two years before CDMA's 1995 introduction in Hong Kong, European carriers and manufacturers chose to support the first available digital technology - Time Division Multiple Access (TDMA). GSM uses TDMA as its core technology. Therefore, since the majority of wireless users are in Europe and Asia, GSM has taken the worldwide lead as the technology of choice.

Mobile Handset manufacturers ultimately split into two camps, as Motorola, Lucent, and Nextel chose CDMA, and Nokia and Ericsson eventually pushed these companies out and became the dominant GSM players.

Advantages of GSM:

• GSM is already used worldwide with over 450 million subscribers. • International roaming permits subscribers to use one phone throughout Western Europe. CDMA will work in Asia, but not France, Germany, the U.K. and other popular European destinations. • GSM is mature, having started in the mid-80s. This maturity means a more stable network with robust features. CDMA is still building its network. • GSM's maturity means engineers cut their teeth on the technology, creating an unconscious preference. • The availability of Subscriber Identity Modules, which are smart cards that provide secure data encryption give GSM m-commerce advantages.

In brief, GSM is a "more elegant way to upgrade to 3G," says Strategis Group senior wireless analyst Adam Guy.

Disadvantages of GSM:

• Lack of access to burgeoning American market.

Conclusion

Today, the battle between CDMA and GSM is muddled. Where at one point Europe clearly favored GSM and North America, CDMA, the distinct advantage of one over the other has blurred as major carriers like AT&T Wireless begin to support GSM, and recent trials even showed compatibility between the two technologies.

GSM still holds the upper hand however. There's the numerical advantage for one thing: 456 million GSM users versus CDMA's 82 million.

Other factors potentially tipping the scales in the GSM direction include : AT&T Wireless' move to overlay GSM atop its TDMA network means the European technology (GSM) gains instant access to North America's number two network.

Qualcomm's recently announced that Wideband-CDMA (WCDMA) won't be ready in Europe until 2005. This comes amidst reports that GSM's successor, General Packet Radio Services (GPRS) remains on target for deployment in 2001-2002.

For all of the historical and technological reasons outlined above, it appears that GSM, or some combination of GSM and CDMA, will become the long sought after grail for a global wireless standard. A universalization of wireless technologies can only stand to benefit the compatibility and development costs and demands on all wireless commerce participants.

What is the Difference Between GSM and CDMA? In cellular service there are two main competing network technologies: Global System for Mobile Communications (GSM) and Code Division Multiple Access (CDMA). Cellular carriers including Sprint PCS, Cingular Wireless, Verizon and T-Mobile use one or the other. Understanding the difference between GSM and CDMA will allow you to choose a carrier that uses the preferable network technology for your needs.

The GSM Association is an international organization founded in 1987, dedicated to providing, developing, and overseeing the worldwide wireless standard of GSM. CDMA, a proprietary standard designed by Qualcomm in the United States, has been the dominant network standard for North America and parts of Asia. However, GSM networks continue to make inroads in the United States, as CDMA networks make progress in other parts of the world. There are camps on both sides that firmly believe either GSM or CDMA architecture is superior to the other. That said, to the non-invested consumer who simply wants bottom line information to make a choice, the following considerations may be helpful.

Coverage: The most important factor is getting service in the areas you will be using your phone. Upon viewing competitors' coverage maps you may discover that only GSM or CDMA carriers offer cellular service in your area. If so, there is no decision to be made, but most people will find that they do have a choice.

Data Transfer Speed: With the advent of cellular phones doing double and triple duty as streaming video devices, podcast receivers and email devices, speed is important to those who use the phone for more than making calls. CDMA has been traditionally faster than GSM, though both technologies continue to rapidly leapfrog along this path. Both boast "3G" standards, or 3rd generation technologies.

EVDO, also known as CDMA2000, is CDMA's answer to the need for speed with a downstream rate of about 2 megabits per second, though some reports suggest real world speeds are closer to 300-700 kilobits per second (kbps). This is comparable to basic DSL. As of fall 2005, EVDO is in the process of being deployed. It is not available everywhere and requires a phone that is CDMA2000 ready.

GSM's answer is EDGE (Enhanced Data Rates for GSM Evolution), which boasts data rates of up to 384 kbps with real world speeds reported closer to 70-140 kbps. With added technologies still in the works that include UMTS (Universal Mobile Telephone Standard) and HSDPA (High Speed Downlink Packet Access), speeds reportedly increase to about 275—380 kbps. This technology is also known as W-CDMA, but is incompatible with CDMA networks. An EDGE-ready phone is required.

In the case of EVDO, theoretical high traffic can degrade speed and performance, while the EDGE network is more susceptible to interference. Both require being within close range of a cell to get the best speeds, while performance decreases with distance.

Subscriber Identity Module (SIM) cards: In the United States only GSM phones use SIM cards. The removable SIM card allows phones to be instantly activated, interchanged, swapped out and upgraded, all without carrier intervention. The SIM itself is tied to the network, rather than the actual phone. Phones that are card-enabled can be used with any GSM carrier.

The CDMA equivalent, a R-UIM card, is only available in parts of Asia but remains on the horizon for the U.S. market. CDMA carriers in the U.S. require proprietary handsets that are linked to one carrier only and are not card-enabled. To upgrade a CDMA phone, the carrier must deactivate the old phone then activate the new one. The old phone becomes useless.

Roaming: For the most part, both networks have fairly concentrated coverage in major cities and along major highways. GSM carriers, however, have roaming contracts with other GSM carriers, allowing wider coverage of more rural areas, generally speaking, often without roaming charges to the customer. CDMA networks may not cover rural areas as well as GSM carriers, and though they may contract with GSM cells for roaming in more rural areas, the charge to the customer will generally be significantly higher.

International Roaming: If you need to make calls to other countries, a GSM carrier can offer international roaming, as GSM networks dominate the world market. If you travel to other countries you can even use your GSM cell phone abroad, providing it is a quad-band phone (850/900/1800/1900 MHz). By purchasing a SIM card with minutes and a local number in the country you are visiting, you can make calls against the card to save yourself international roaming charges from your carrier back home. CDMA phones that are not card-enabled do not have this capability, however there are several countries that use CDMA networks. Check with your CDMA provider for your specific requirements.

According CDG.org, CDMA networks support over 270 million subscribers worldwide, while GSM.org tallies up their score at over 1 billion. As CDMA phones become R-UIM enabled and roaming contracts between networks improve, integration of the standards might eventually make differences all but transparent to the consumer. What is the difference between gsm and cdma When it comes to choice of anything in life, there will be pro's and con's on both sides of the coin. This is the same for cellular network providers, when it comes to delivery the best service for mobile phones. The end user is only interested in getting the best coverage and best speed when it comes to data transfer, and those two factors alone are just two of the many things which can be influenced by which technology your cellular network employs. There could be a preferable network that caters to your demands better than the other. So what is the difference between GSM and CDMA, the two leading technologies? Both GSM (Global System for Mobile Communications) and CDMA (Code Division Multiple Access) are technologies that work on radio frequencies, with the mobile phone handset being the antennae receiving the signal. The range of each technology is different, and they also have different rates and modulation schemes, and that is why handsets are different between the two technologies. GSM uses SIM cards (Subscriber Identity Module) whereas, CDMA based phones do not. In the case of GSM networks, it is the SIM card that is tied to the network, where on CDMA networks it is the handset itself that is linked to the carrier. This means that a SIM card can be placed in pretty much any handset and still receive GSM coverage, but once a CDMA phone's subscription has ended, the phone is outmoded. CDMA technology has a version of the SIM card, the RUIM (Removable User Identity Module) but is not as widely popular in the US because it is the handsets which must be linked to the carrier. Third Generation technology (3G) is used by both systems, so is fully compatible with both. A handset that is 3G compatible can be used for both GSM carriers and for CDMA signals. Both technologies utilise important aspects of 3G in order to try and improve their subscriber benefits. The better and more reliable a service can be provided, the more customer satisfaction there will be. What is the difference between GSM and CDMA when it comes to service? There have been reports that GSM drops a lot more calls than CDMA, but this is unfounded by any firm data. Both types of carrier have issues with dropped calls when moving from the range of one transmitter to the next. GSM is widely regarded as having much better coverage in rural areas though, and is certainly the dominant technology for mobile phones across Europe. The main issue with mobile phones is of course, coverage. GSM leads the way when it comes to coverage across the world, because it is seen as more versatile and has also been accepted and used in more places, especially within Europe, where it is the standard mobile phone communications technology. Being able to swap SIM cards between phones is a big positive, especially when visiting foreign countries, for cheap local SIM cards can be used to save on roaming charges. Roaming charges are often applied more on CDMA networks, because they often have to borrow services from GSM carriers in rural places, and therefore the consumer will likely be hit with roaming charges. For the end user, there is unlikely to be much concern as to what is the difference between GSM and CDMA as they both provide a similar service. The consumer will just want the best plan for their money, and the coolest handset with all the wonderful digital features. It is just how that service serves you from behind the scenes, which is the major difference. Subscribers in both camps will claim that one is better than the other, and there really is, as a phone user, not much to choose between the two. It will all come down to a personal preference when choosing a cellular phone.

Architechture and Working Of GSM Networks

We have already read about how GSM technology had taken over mobile communication technologies and grown over to 214 countries around the world. Now it is important to learn how GSM network works and what is the architecture of GSM networks?. GSM network is consist of thee major systems, it can also be considered architecture of GSM networks. These three systems are SS, which is known to be The Switching System, BSS, it is The Base Station and the other important system is, The operation and support System for GSM networks.

Below all three systems are defined in details with sub systems of each system. The Switching System The Switching system is very operative system in which many crucial operations are conducted, SS systems holds five databases with in it which performs different functions. If we talk about major tasks of SS system it performs call processing and subscriber related functions. These five databases from SS systems are HLR, MSC, VLR, AUC and EIR. Let’s study each database in detail and learn what functions this little systems performs. HLR- Home Location Register:

HLR is database, which holds very important information of subscribers. It is mostly known for storing and managing information of subscribers. It contains subscriber service profile, status of activities, information about locations and permanent data of all sorts. When new connections are purchased, these subscribers are registered in HLR of mobile phone companies. MSC- Mobile Services Switching Center: MSC is also important part of SS, it handles technical end of telephony.It is build to perform switching functionality of the entire system. It’s most important task is to control the calls to and from other telephones, which means it controls calls from same networks and calls from other networks. Toll ticketing, common channel signaling, network interfacing etc are other tasks which MSC is responsible for.

VLR- Visitor Location Register: VLR performs very dynamic tasks; it is database which stores temporary data regarding subscribers which is needed by Mobile Services Switching Center-MSC VLR is directly connected to MSC, when subscribe moves to different MSC location, Visitor location register – VLR integrates to MSC of current location and requests the data about subscriber or Mobile station ( MS ) from the Home Location Register –HLR. When subscriber makes a call the Visitor location register-VLR will have required information for making call already and it will not required to connect to Home Register Location - HRL again. AUC- Authentication Center:

AUC is small unit which handles the security end of the system. Its major task is to authenticate and encrypt those parameters which verify user’s identification and hence enables the confidentiality of each call made by subscriber. Authentication center – AUC makes sure mobile operators are safe from different frauds most likely to happen when hackers are looking for even smallest loop wholes in systems. EIR – Equipment Identity Register: EIR is another important database which holds crucial information regarding mobile equipments. EIR helps in restricting for calls been stolen, mal functioning of any MS, or unauthorized access. AUC – Authentication center and EIR- Equipment Identity registers are either Stand-alone nodes or some times work together as combined AUC/EIR nodes for optimum performance. The Base Station System (BSS) The base station system have very important role in mobile communication. BSS are basically out door units which consist of iron rods and are usually of high length. BSS are responsible for connecting subscribers (MS) to mobile networks.All the communication is made in Radio transmission.The Base station System is further divided in two systems. These two systems, they are BSC, and BTS. Let’s study these two systems in detail.

BTS – The Base Transceiver Station: Subscriber, MS (Mobile Station) or mobile phone connects to mobile network through BTS; it handles communication using radio transmission with mobile station. As name suggests, Base transceiver Station is the radio equipment which receive and transmit voice data at the same time. BSC control group of BTSs. BSC – The Base Station Controller: The Base Station normally controls many cells, it registers subscribers, responsible for MS handovers etc. It creates physical link between subscriber (MS) and BTS , then manage and controls functions of it. It performs the function of high quality switch by handover over the MS to next BSC when MS goes out of the current range of BTS, it helps in connecting to next in range BTS to keep the connection alive within the network. It also performs functions like cell configuration data, control radio frequency in BTS. Data moves to MSC-Mobile switching center after BSC done processing it. MSC is switching center which acts as bridge between different mobile networks. Note: This image is graphical explaination of GSM Arhitecutre and Working of GSM Networks

Note: See the Video of GSM Arhcitechture to learn how GSM network works.

The Operation and Support System (OSS)

OMC- Operations and maintenance center is designed to connect to equipment of MSC- Mobile Switching Center and BSC-Base Station Controller. The implementation of OMC is called OSS-The Operations and Support System.OSS helps in mobile networks to monitor and control the complex systems.The basic reason for developing operation and support system is to provide customers a cost effective support and solutions. It helps in managing, centralizing, local and regional operational activities required for GMS networks. Maintaining mobile network organization, provide overview of network, support and maintenance activities are other important aspects of Operation and Support System

What is a basic technical difference in CDMA technology and GSM Technology in telecom sector?

CDMA is by a service providerm such as Verizon, Sprint, AT&T, and so fourth. GSM is by a third-party service, so if your a big tech guy, you can basically create your own service. (which is very expensive. Hope this helps an good luck!

CDMA: code division multiple access is one of the method in encrypt a code.like FDMA.

GSM:

GSM (Global System for Mobile communications: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. Its promoter, the GSM Association, estimates that 80% of the global mobile market uses the standard.[1] GSM is used by over 3 billion people across more than 212 countries and territories.[2][3] Its ubiquity makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signaling and speech channels are digital, and thus is considered a second generation (2G) mobile phone system. This has also meant that data communication was easy to build into the system.

The ubiquity of the GSM standard has been an disadvantage to both consumers (who benefit from the ability to roam and switch carriers without switching phones) and also to network operators (who can choose equipment from any of the many vendors implementing GSM[4]). GSM also pioneered a low-cost (to the network carrier) alternative to voice calls, the Short message service (SMS, also called "text messaging"), which is now supported on other mobile standards as well. Another advantage is that the standard includes one worldwide Emergency telephone number, 112 [5] . This makes it easier for international travellers to connect to emergency services without knowing the local emergency number.

Newer versions of the standard were backward-compatible with the original GSM phones. For example, Release '97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE).