Network switching subsystem (NSS)

Network switching subsystem (NSS) is the component of a GSM system that carries out switching functions and manages the communications between mobile phones and the Public Switched Telephone Network (PSTN). It is owned and deployed by mobile phone operators and allows mobile phones to communicate with each other and telephones in the wider telecommunications network. The architecture closely resembles a telephone exchange, but there are additional functions which are needed because the phones are not fixed in one location. Each of these functions handle different aspects of mobility management and are described in more detail below.
The Network Switching Subsystem, also referred to as the GSM core network, usually refers to the circuit-switched core network, used for traditional GSM services such as voice calls, SMS, and circuit switched data calls.
There is also an overlay architecture on the GSM core network to provide packet-switched data services and is known as the GPRS core network. This allows mobile phones to have access to services such as WAP, MMS, and Internet access.
All mobile phones manufactured today have both circuit and packet based services, so most operators have a GPRS network in addition to the standard GSM core network.

Equipment identity register (EIR)

Equipment identity register (EIR)
The equipment identity register is often integrated to the HLR. The EIR keeps a list of mobile phones (identified by their IMEI) which are to be banned from the network or monitored. This is designed to allow tracking of stolen mobile phones. In theory all data about all stolen mobile phones should be distributed to all EIRs in the world through a Central EIR. It is clear, however, that there are some countries where this is not in operation. The EIR data does not have to change in real time, which means that this function can be less distributed than the function of the HLR. The EIR is a database that contains information about the identity of the mobile equipment that prevents calls from stolen, unauthorized or defective mobile stations. Some EIR also have the capability to log Handset attempts and store it in a log file.

[edit] Other support functions
Connected more or less directly to the GSM core network are many other functions.

[edit] Billing centre (BC)
The billing centre is responsible for processing the toll tickets generated by the VLRs and HLRs and generating a bill for each subscriber. It is also responsible for to generate billing data of roaming subscriber.

[edit] Short message service centre (SMSC)
The short message service centre supports the sending and reception of text messages.

[edit] Multimedia messaging service centre (MMSC)
The multimedia messaging service centre supports the sending of multimedia messages (e.g., images, audio, video and their combinations) to (or from) MMS-enabled Handsets.

[edit] Voicemail system (VMS)
The voicemail system records and stores voicemails

Visitor location register (VLR)

[edit] Visitor location register (VLR)

[edit] Description
The visitor location register is a temporary database of the subscribers who have roamed into the particular area which it serves. Each base station in the network is served by exactly one VLR, hence a subscriber cannot be present in more than one VLR at a time.
The data stored in the VLR has either been received from the HLR, or collected from the MS. In practice, for performance reasons, most vendors integrate the VLR directly to the V-MSC and, where this is not done, the VLR is very tightly linked with the MSC via a proprietary interface.
Data stored include:
IMSI (the subscriber's identity number).
Authentication data.
MSISDN (the subscriber's phone number).
GSM services that the subscriber is allowed to access.
access point (GPRS) subscribed.
The HLR address of the subscriber.

[edit] Other GSM core network elements connected to the VLR
The VLR connects to the following elements:
The V-MSC to pass needed data for its procedures; e.g., authentication or call setup.
The HLR to request data for mobile phones attached to its serving area.
Other VLRs to transfer temporary data concerning the mobile when they roam into new VLR areas. For example, the temporal mobile subscriber identity (TMSI).

[edit] Procedures implemented
The primary functions of the VLR are:
To inform the HLR that a subscriber has arrived in the particular area covered by the VLR.
To track where the subscriber is within the VLR area (location area) when no call is ongoing.
To allow or disallow which services the subscriber may use.
To allocate roaming numbers during the processing of incoming calls.
To purge the subscriber record if a subscriber becomes inactive whilst in the area of a VLR. The VLR deletes the subscriber's data after a fixed time period of inactivity and informs the HLR (e.g., when the phone has been switched off and left off or when the subscriber has moved to an area with no coverage for a long time).
To delete the subscriber record when a subscriber explicitly moves to another, as instructed by the HLR.

Authentication centre (AUC)

Authentication centre (AUC)

[edit] Description
The authentication centre (AUC) is a function to authenticate each SIM card that attempts to connect to the GSM core network (typically when the phone is powered on). Once the authentication is successful, the HLR is allowed to manage the SIM and services described above. An encryption key is also generated that is subsequently used to encrypt all wireless communications (voice, SMS, etc.) between the mobile phone and the GSM core network.
If the authentication fails, then no services are possible from that particular combination of SIM card and mobile phone operator attempted. There is an additional form of identification check performed on the serial number of the mobile phone described in the EIR section below, but this is not relevant to the AUC processing.
Proper implementation of security in and around the AUC is a key part of an operator's strategy to avoid SIM cloning.
The AUC does not engage directly in the authentication process, but instead generates data known as triplets for the MSC to use during the procedure. The security of the process depends upon a shared secret between the AUC and the SIM called the Ki. The Ki is securely burned into the SIM during manufacture and is also securely replicated onto the AUC. This Ki is never transmitted between the AUC and SIM, but is combined with the IMSI to produce a challenge/response for identification purposes and an encryption key called Kc for use in over the air communications.

[edit] Other GSM core network elements connected to the AUC
The AUC connects to the following elements:
the MSC which requests a new batch of triplet data for an IMSI after the previous data have been used. This ensures that same keys and challenge responses are not used twice for a particular mobile.

[edit] Procedures implemented
The AUC stores the following data for each IMSI:
the Ki
Algorithm id. (the standard algorithms are called A3 or A8, but an operator may choose a proprietary one).
When the MSC asks the AUC for a new set of triplets for a particular IMSI, the AUC first generates a random number known as RAND. This RAND is then combined with the Ki to produce two numbers as follows:
The Ki and RAND are fed into the A3 algorithm and the signed response (SRES) is calculated.
The Ki and RAND are fed into the A8 algorithm and a session key called Kc is calculated.
The numbers (RAND, SRES, Kc) form the triplet sent back to the MSC. When a particular IMSI requests access to the GSM core network, the MSC sends the RAND part of the triplet to the SIM. The SIM then feeds this number and the Ki (which is burned onto the SIM) into the A3 algorithm as appropriate and an SRES is calculated and sent back to the MSC. If this SRES matches with the SRES in the triplet (which it should if it is a valid SIM), then the mobile is allowed to attach and proceed with GSM services.
After successful authentication, the MSC sends the encryption key Kc to the base station controller (BSC) so that all communications can be encrypted and decrypted. Of course, the mobile phone can generate the Kc itself by feeding the same RAND supplied during authentication and the Ki into the A8 algorithm.
The AUC is usually collocated with the HLR, although this is not necessary. Whilst the procedure is secure for most everyday use, it is by no means crack proof. Therefore a new set of security methods was designed for 3G phones.

Home location register (HLR)

Home location register (HLR)

[edit] Description
The home location register (HLR) is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. There can be several logical, and physical, HLRs per public land mobile network (PLMN), though one international mobile subscriber identity (IMSI)/MSISDN pair can be associated with only one logical HLR (which can span several physical nodes) at a time.
The HLR stores details of every SIM card issued by the mobile phone operator. Each SIM has a unique identifier called an IMSI which is the primary key to each HLR record.
The next important items of data associated with the SIM are the MSISDNs, which are the telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the number used for making and receiving voice calls and SMS, but it is possible for a SIM to have other secondary MSISDNs associated with it for fax and data calls. Each MSISDN is also a primary key to the HLR record. The HLR data is stored for as long as a subscriber remains with the mobile phone operator.
Examples of other data stored in the HLR against an IMSI record is:
GSM services that the subscriber has requested or been given.
GPRS settings to allow the subscriber to access packet services.
Current location of subscriber (VLR and serving GPRS support node/SGSN).
Call divert settings applicable for each associated MSISDN.
The HLR is a system which directly receives and processes MAP transactions and messages from elements in the GSM network, for example, the location update messages received as mobile phones roam around.

[edit] Other GSM core network elements connected to the HLR
The HLR connects to the following elements:
The G-MSC for handling incoming calls
The VLR for handling requests from mobile phones to attach to the network
The SMSC for handling incoming SMS
The voice mail system for delivering notifications to the mobile phone that a message is waiting
The AUC for authentication and ciphering and exchange of data (triplets)

[edit] Procedures implemented
The main function of the HLR is to manage the fact that SIMs and phones move around a lot. The following procedures are implemented to deal with this:
Manage the mobility of subscribers by means of updating their position in administrative areas called 'location areas', which are identified with a LAC. The action of a user of moving from one LA to another is followed by the HLR with a Location area update while retrieving information from BSS as base station identity code (BSIC).
Send the subscriber data to a VLR or SGSN when a subscriber first roams there.
Broker between the G-MSC or SMSC and the subscriber's current VLR in order to allow incoming calls or text messages to be delivered.
Remove subscriber data from the previous VLR when a subscriber has roamed away from it.

Mobile switching center (MSC)

Mobile switching center (MSC)

Description
The mobile switching center (MSC) is the primary service delivery node for GSM, responsible for handling voice calls and SMS as well as other services (such as conference calls, FAX and circuit switched data). The MSC sets up and releases the end-to-end connection, handles mobility and hand-over requirements during the call and takes care of charging and real time pre-paid account monitoring.
In the GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent directly digitally encoded to the MSC. Only at the MSC is this re-coded into an "analogue" signal (although actually this will almost certainly mean sound encoded digitally as PCM signal in a 64-kbit/s timeslot, known as a DS0 in America).
There are various different names for MSCs in different contexts which reflects their complex role in the network, all of these terms though could refer to the same MSC, but doing different things at different times.
The gateway MSC (G-MSC) is the MSC that determines which visited MSC the subscriber who is being called is currently located. It also interfaces with the PSTN. All mobile to mobile calls and PSTN to mobile calls are routed through a G-MSC. The term is only valid in the context of one call since any MSC may provide both the gateway function and the Visited MSC function, however, some manufacturers design dedicated high capacity MSCs which do not have any BSSs connected to them. These MSCs will then be the Gateway MSC for many of the calls they handle.
The visited MSC (V-MSC) is the MSC where a customer is currently located. The VLR associated with this MSC will have the subscriber's data in it.
The anchor MSC is the MSC from which a handover has been initiated. The target MSC is the MSC toward which a Handover should take place. A mobile switching centre server is a part of the redesigned MSC concept starting from 3GPP Release 5.

General Architecture of the BTS.

A BTS in general has the following units:
Transceiver (TRX)
Quite widely referred to as the driver receiver (DRX). Basically does transmission and reception of signals. Also does sending and reception of signals to/from higher network entities (like the base station controller in mobile telephony)
Power amplifier (PA)
Amplifies the signal from DRX for transmission through antenna; may be integrated with DRX.
Combiner
Combines feeds from several DRXs so that they could be sent out through a single antenna. Allows for a reduction in the number of antenna used.
Duplexer
For separating sending and receiving signals to/from antenna. Does sending and receiving signals through the same antenna ports (cables to antenna).
Antenna
This is also considered a part of the BTS.
Alarm extension system
Collects working status alarms of various units in the BTS and extends them to operations and maintenance (O&M) monitoring stations.
Control function
Control and manages the various units of BTS including any software. On-the-spot configurations, status changes, software upgrades, etc. are done through the control function.
Baseband receiver unit (BBxx)
Frequency hopping, signal DSP, etc..

BTS in Mobile Communication

BTS in Mobile Communication
A GSM BTS network is made up of three subsystems: • The Mobile Station (MS) • The Base Station Sub-system (BSS) – comprising a BSC and several BTSs • The Network and Switching Sub-system (NSS) – comprising an MSC and associated registers
Though the term BTS can be applicable to any of the wireless communication standards, it is generally and commonly associated with mobile communication technologies like GSM and CDMA. In this regard, a BTS forms part of the base station subsystem (BSS) developments for system management. It may also have equipment for encrypting and decrypting communications, spectrum filtering tools (band pass filters) etc. antennas may also be considered as components of BTS in general sense as they facilitate the functioning of BTS. Typically a BTS will have several transceivers (TRXs) which allow it to serve several different frequencies and different sectors of the cell (in the case of sectorised base stations). A BTS is controlled by a parent base station controller via the base station control function (BCF). The BCF is implemented as a discrete unit or even incorporated in a TRX in compact base stations. The BCF provides an operations and maintenance (O&M) connection to the network management system (NMS), and manages operational states of each TRX, as well as software handling and alarm collection. The basic structure and functions of the BTS remains the same regardless of the wireless technologies.

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls. A central office is the physical building used to house inside plant equipment including telephone switches, which make telephone calls "work" in the sense of making connections and relaying the speech information.
The term exchange can also be used to refer to an area served by a particular switch (typically known as a wire center in the US telecommunications industry). It is sometimes confused with other concepts of telephone geography, such as NPA or area code. More narrowly, in some areas it can refer to the first three digits of the local number. In the three-digit sense of the word, other obsolete Bell System terms include office code and NXX. In the United States, the word exchange can also have the legal meaning of a local access and transport area under the Modification of Final Judgment (MFJ).

Broadband In data communications

Broadband in data can refer to broadband networks or broadband Internet and may have the same meaning as above, so that data transmission over a fiber optic cable would be referred to as broadband as compared to a telephone modem operating at 56,000 bits per second.
However, broadband in data communications is frequently used in a more technical sense to refer to data transmission where multiple pieces of data are sent simultaneously to increase the effective rate of transmission, regardless of data signaling rate. In network engineering this term is used for methods where two or more signals share a medium.[1]

[edit] In DSL
The various forms of digital subscriber line (DSL) services are broadband in the sense that digital information is sent over a high-bandwidth channel above the baseband voice channel on a single pair of wires.[1]

[edit] In Ethernet
A baseband transmission sends one type of signal using a medium's full bandwidth, as in 100BASE-T Ethernet. Ethernet, however, is the common interface to broadband modems such as DSL data links, and has a high data rate itself, so is sometimes referred to as broadband. Ethernet provided over cable modem is a common alternative to DSL.

[edit] In video
Broadband in analog video distribution is traditionally used to refer to systems such as cable television, where the individual channels are modulated on carriers at fixed frequencies.[2] In this context, baseband is the term's antonym, referring to a single channel of analog video, typically in composite form with an audio subcarrier.[3] The act of demodulating converts broadband video to baseband video.
However, broadband video in the context of streaming Internet video has come to mean video files that have bitrates high enough to require broadband Internet access in order to view them.
Broadband video is also sometimes used to describe IPTV Video on demand

Broadband In telecommunication

Broadband In telecommunication

Broadband in telecommunications refers to a signaling method that includes or handles a relatively wide range of frequencies, which may be divided into channels or frequency bins. Broadband is always a relative term, understood according to its context. The wider the bandwidth, the greater the information-carrying capacity. In radio, for example, a very narrow-band signal will carry Morse code; a broader band will carry speech; a still broader band is required to carry music without losing the high audio frequencies required for realistic sound reproduction. A television antenna described as "normal" may be capable of receiving a certain range of channels; one described as "broadband" will receive more channels. In data communications an analogue modem will transmit a bandwidth of 56 kilobits per seconds (kbit/s) over a telephone line; over the same telephone line a bandwidth of several megabits per second can be handled by ADSL, which is described as broadband (relative to a modem over a telephone line, although much less than can be achieved over a fibre optic circuit).

CDMA Technology

CDMA Technology

Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne and CDMA2000 (which are often referred to as simply "CDMA"), which use CDMA as an underlying channel access method.
One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a bandwidth of frequencies. This concept is called multiplexing. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum" signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.

TDMA Technology

TDMA Technology

Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using his own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, and combat-net radio systems. For usage of Dynamic TDMA packet mode communication, see below.

TDMA frame structure showing a data stream divided into frames and those frames divided into time slots.
TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.

FDMA Technology

FDMA Technology

Frequency Division Multiple Access or FDMA is a channel access method used in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, allowing them to utilize the allocated radio spectrum without interfering with each other. Multiple Access systems coordinate access between multiple users. The users may also share access via different methods such TDMA, CDMA, or SDMA. These protocols are utilized differently, at different levels of the theoretical OSI model.

FDMA requires high-performing filters in the radio hardware, in contrast to TDMA and CDMA.
FDMA is not vulnerable to timing problems as TDMA. Since a predetermined frequency band is available for the entire period of communication, stream data (a continuous flow of data that may not be packetized) can easily be used with FDMA.
Due to the frequency filtering, FDMA is not sensitive to near-far problem which is pronounced for CDMA.

Control System

Control System

A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems.
There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls. There is also fuzzy logic, which attempts to combine some of the design simplicity of logic with the utility of linear control. Some devices or systems are inherently not controllable.
The term "control system" may be applied to the essentially manual controls that allow an operator to, for example, close and open a hydraulic press, where the logic requires that it cannot be moved unless safety guards are in place.
An automatic sequential control system may trigger a series of mechanical actuators in the correct sequence to perform a task. For example various electric and pneumatic transducers may fold and glue a cardboard box, fill it with product and then seal it in an automatic packaging machine.
In the case of linear feedback systems, a control loop, including sensors, control algorithms and actuators, is arranged in such a fashion as to try to regulate a variable at a setpoint or reference value. An example of this may increase the fuel supply to a furnace when a measured temperature drops. PID controllers are common and effective in cases such as this. Control systems that include some sensing of the results they are trying to achieve are making use of feedback and so can, to some extent, adapt to varying circumstances. Open-loop control systems do not directly make use of feedback, but run only in pre-arranged ways.

RF Engineering

RF Engineering, also known as Radio Frequency Engineering is a field, in particular within electronics, that deals with devices which are design to operate in the Radio Frequency spectrum. These devices operate within the range of about 3 Hz up to 300 GHz.
RF Engineering is incorporated into almost everything that transmits or receives a radio wave which includes, but not limited to, Mobile Phones, Radios, WiFi and walkie talkies.
RF Engineering is a specialized field, to properly produce quality results an in-depth knowledge of Mathematics, Physics and general electronics theory is required. Even with this, the initial design of an RF Circuit usually bears very little resemblance to the final physical circuit produced as alteration to the design is often required to achieve the required results.

Teletraffic Engineering

Introduction
Traffic engineering uses statistical techniques such as queuing theory to predict and engineer the behaviour of telecommunications networks such as telephone networks or the Internet.
The field was created by the work of A. K. Erlang in whose honour the unit of telecommunications traffic intensity, the Erlang, is named. The derived unit of traffic volume also incorporates his name. His Erlang distributions are still in common use in telephone traffic engineering.
The crucial observation in traffic engineering is that in large systems the law of large numbers can be used to make the aggregate properties of a system over a long period of time much more predictable than the behaviour of individual parts of the system.
The queueing theory originally developed for circuit-switched networks is applicable to packet-switched networks.
The most notable difference between these sub-fields is that packet-switched data traffic is self-similar. This is a consequence of the calls being between computers, and not people.

Teletraffic Engineering

Teletraffic engineering is the application of traffic engineering theory to telecommunications. Teletraffic engineers use their basic knowledge of statistics including Queueing theory, the nature of traffic, their practical models, their measurements and simulations to make predictions and to plan telecommunication networks at minimum total cost. These tools and basic knowledge help provide reliable service at lower cost. Because the approach is so different to different networks, the networks are handled separately here: the PSTN, broadband networks, mobile networks, and networks where the possibility of traffic being heavy is more frequent than anticipated

Air Traffic Control

Air Traffic Control
Air traffic control radar at London Heathrow Airport
Air Traffic Control Systems
Air Traffic Control (ATC) Radars
Secondary Surveillance Radar (SSR) (Airport Surveillance Radar)
Ground Control Approach (GCA) Radars
Precision Approach Radar (PAR) Systems
Distance Measuring Equipment (DME)
Radio Beacons
Radar Altimeter (RA) Systems
Terrain-Following Radar (TFR) Systems

Radar Antenna System

Antenna design
Radio signals broadcast from a single antenna will spread out in all directions, and likewise a single antenna will receive signals equally from all directions. This leaves the radar with the problem of deciding where the target object is located.
Early systems tended to use omni-directional broadcast antennas, with directional receiver antennas which were pointed in various directions. For instance the first system to be deployed, Chain Home, used two straight antennas at right angles for reception, each on a different display. The maximum return would be detected with an antenna at right angles to the target, and a minimum with the antenna pointed directly at it (end on). The operator could determine the direction to a target by rotating the antenna so one display showed a maximum while the other shows a minimum.
One serious limitation with this type of solution is that the broadcast is sent out in all directions, so the amount of energy in the direction being examined is a small part of that transmitted. To get a reasonable amount of power on the "target", the transmitting aerial should also be directional

Radar System

Radar is a system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for radio detection and ranging.[1][2][3] The term has since entered the English language as a standard word, radar, losing the capitalization. Radar was originally called RDF (Radio Direction Finder) in the United Kingdom.
A radar system has a transmitter that emits either microwaves or radio waves that are reflected by the target and detected by a receiver, typically in the same location as the transmitter. Although the signal returned is usually very weak, the signal can be amplified. This enables radar to detect objects at ranges where other emissions, such as sound or visible light, would be too weak to detect. Radar is used in many contexts, including meteorological detection of precipitation, measuring ocean surface waves, air traffic control, police detection of speeding traffic, and by the military.

Optical Fiber Communication

An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications. Fibers are used instead of metal wires because signals travel along them with less loss, and they are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.
Light is kept in the core of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. Fibers which support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those which can only support a single mode are called single-mode fibers (SMF). Multi-mode fibers generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 550 meters (600 yards).
Joining lengths of optical fiber is more complex than joining electrical wire or cable. The ends of the fibers must be carefully cleaved, and then spliced together either mechanically or by fusing them together with an electric arc. Special connectors are used to make removable connections

Wireless Local Loop

Definition and Overview
DefinitionSometimes called radio in the loop (RITL) or fixed-radio access (FRA), WLL is a system that connects subscribers to the public switched telephone network (PSTN) using radio signals as a substitute for copper for all or part of the connection between the subscriber and the switch. This includes cordless access systems, proprietary fixed radio access, and fixed cellular systems.
OverviewIndustry analysts predict that the global WLL market will reach millions of subscribers by the year 2000. Much of this growth will occur in emerging economies where half the world's population lacks plain old telephone service (POTS). Developing nations like China, India, Brazil, Russia, and Indonesia look to WLL technology as an efficient way to deploy POTS for millions of subscribers—without the expense of burying tons of copper wire.
In developed economies, WLL will help unlock competition in the local loop, enabling new operators to bypass existing wireline networks to deliver POTS and data access. So the question isn't will the local loop go wireless, but when and where. This tutorial discusses the basics of WLL and examines the markets and future for this technology.

Cordless Systems

Cordless Systems
nResidential – a single base station can provide in-house voice and data support
nOffice
nA single base station can support a small office
nMultiple base stations in a cellular configuration can support a larger office
nTelepoint – a base station set up in a public place, such as an airport .

nModest range of handset from base station, so low-power designs are used
nInexpensive handset and base station, dictating simple technical approaches
nFrequency flexibility is limited, so the system needs to be able to seek a low-interference channel whenever used

Satellite Communications

Satellite ,is in effect,a microwave relay station.It is used to link two or more ground–base microwave transmitter/receiver,known as earth stations
Some satellites are natural, like the Moon, which is the natural satellite of the earth. Other satellites are made by scientists and technologists to go around the earth and do certain jobs

OR

A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, other elliptical orbits and low (polar and non-polar) Earth orbits.
For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of submarine communication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting, for which application of other technologies, such as cable, is impractical or impossible.

What is ATM ?

ATM (asynchronous transfer mode) is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path.
Because ATM is designed to be easily implemented by hardware (rather than software), faster processing and switch speeds are possible. The prespecified bit rates are either 155.520 Mbps or 622.080 Mbps. Speeds on ATM networks can reach 10 Gbps. Along with Synchronous Optical Network (SONET) and several other technologies, ATM is a key component of broadband ISDN (BISDN).
ATM also stands for automated teller machine, a machine that bank customers use to make transactions without a human teller.

OR

Short for Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.

What is VOIP?

What is VoIP?

VoIP (voice over IP) is an IP telephony term for a set of facilities used to manage the delivery of voice information over the Internet.VoIP involves sending voice information in digital form in discrete packets rather than by using the traditional circuit-committed protocols of the public switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service

OR

Introduction VOIP is an acronym for Voice Over Internet Protocol, or in more common terms phone service over the Internet. If you have a reasonable quality Internet connection you can get phone service delivered through your Internet connection instead of from your local phone company. Some people use VOIP in addition to their traditional phone service, since VOIP service providers usually offer lower rates than traditional phone companies, but sometimes doesn't offer 911 service, phone directory listings, 411 service, or other common phone services. While many VoIP providers offer these services, consistent industry-wide means of offering these are still developing.

ISDN Technology

Integrated Services Digital Network (ISDN)

Definition: ISDN is a network technology that supports digital transfer of simultaneous voice and data traffic. Similar to DSL in this respect, an ISDN Internet service works over ordinary telephone lines. ISDN Internet service generally supports data rates of 128 Kbps.
ISDN emerged as an alternative to traditional dialup networking during the 1990s. The relatively high cost of ISDN service, though, limited its popularity with residential customers at the outset. More recently, the much higher network speeds supported by newer broadband technologies like DSL have drawn many consumers away from ISDN service.
ISDN technology today has limited applications as a networking solution. Some customers who live in rural areas of the U.S. subscribe to ISDN Internet as an alternative to satellite Internet. ISDN phone service also remains fairly common in some European countries.
Also Known As: Integrated Services Digital Network

Metropolitan Area Network (MAN) Network

Metropolitan Area Network (MAN)

A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks. Metropolitan area networks can span up to 50km, devices used are modem and wire/cable

OR

A Metropolitan Area Network (MAN) is a large computer network that spans a metropolitan area or campus. Its geographic scope falls between a WAN and LAN. MANs provide Internet connectivity for LANs in a metropolitan region, and connect them to wider area networks like the Internet.

WAN Networks

What is a WAN?

A wide area network (WAN) is a geographically dispersed telecommunications network. The term distinguishes a broader telecommunication structure from a local area network (LAN). A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network (MAN.

WAN (Wide Area Network)
Covers a long distance [more than 1 kilometer ( > 1 km)]
Usually spans several locations (even world wide)
Usually has a larger number of users (100's or even 1000's)
Implemented as a client-server model

LAN Network

Definition: A local area network (LAN) supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN.
Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist.

OR

Definition: local area network (LAN): A computer network that covers a relatively small area. Most LANs cover a single building or group of buildings. A system of LANs can be connected over any distance through telephone lines and radio waves, creating a wide-area network.

NETWORK: Two or more computers which are linked together and which share resources like data, programs and peripherals (like printers) are networked.

Types of Networks
LAN (Local Area Network)
Covers a short distance (usually less than 1 kilometer [<> 1 km)]
Usually spans several locations (even world wide)
Usually has a larger number of users (100's or even 1000's)
Implemented as a client-server model Peer to Peer Networks
All computers on the network have the potential to share resources that they have control over
NOT a client-server model (in the strict sense of that concept)
usually confined to a small area (an office or a lab)
Usually has a small number of users (around 2 to 25 users)
considered to be less secure than a LAN or a WAN
see above for more details NOTE: you may have hybrids (combinations) of LANs, WANs and Peer-to-Peer networks
Intranets vs The Internet
The Internet is a collection thousands of Wide-Area and Local-Area networks with servers (http, ftp, chat, ...) on them. The Internet uses TCP/IP as the primary networking protocol to communicate with all these machines.
Intranets are local networks that do not have access to the outside world (they are self-contained). They are like the Internet but they are private.

DSL service of Internet

DSL (Digital Subscriber Line ):-

•DSL is a broadband data communications technology that uses uses existing copper local loop telephone connections.
•The term “DSL” has relevance that also extends across both ISDN and “T Carrier” service.
•In the majority of new installations, and for purposes here, DSL is a digital data service that uses frequencies above the voice band to provide fast (up to 1.5 Mbs) network connections

DSL Las Vegas NV services is a method for moving data over regular phone lines. A dsl internet service provider offers a DSL circuit that is much faster than a regular phone connection, and the wires coming into the subscriber?s premises are the same (copper) wires used for regular phone service. A DSL circuit must be configured to connect two specific locations, similar to a leased line. A commonly discussed configuration of Las Vegas dsl allows downloads at speeds of up to 1.544 megabits (not megabytes) per second, and uploads at speeds of 128 kilobits per second. This arrangement is called ADSL: ?Asymmetric? Digital Subscriber Line. Another common configuration is symmetrical: 384 Kilobits per second in both directions. In theory ADSL allows download speeds of up to 9 megabits per second and upload speeds of up to 640 kilobits per second. DSL connections are now a popular alternative to Leased Lines and ISDN, being faster than ISDN and less costly than traditional Leased Lines. An advantage of using Las Vegas dsl connections over traditional cable lines is that DSL is more secure. Las Vegas DSL service is not a shared network service like cable modems, which means that one end-user can not see what's on a neighbor's computer using DSL. The dsl internet service is a private dedicated connection from the end-user to the network.

Mobiles Theory

A mobile phone (also known as a handphone,[1] wireless phone, cell phone, cellular phone, cellular telephone or cell telephone) is a long-range, electronic device used for mobile voice or data communication over a network of specialized base stations known as cell sites. In addition to the standard voice function of a mobile phone, telephone, current mobile phones may support many additional services, and accessories, such as SMS for text messaging, email, packet switching for access to the Internet, gaming, Bluetooth, infrared, camera with video recorder and MMS for sending and receiving photos and video, MP3 player, radio and GPS. Most current mobile phones connect to a cellular network of base stations (cell sites), which is in turn interconnected to the public switched telephone network (PSTN) (the exception is satellite phones).
A mobile phone proper typically has a telephone keypad, more advanced devices have a separate key for each letter. Some mobile phones have a touchscreen.
Contents[hide]
1 History
2 Handsets
2.1 Features
2.2 Applications
2.3 Media
2.4 Power supply
2.5 SIM card
3 Terminology
3.1 Related non-mobile-phone systems
4 Privacy
5 See also
6 References
7 Further reading
8 External links
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