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Communication is a way which we communicate one to another, the same is used as computer terminology to communicate a computer or device to another computer or device. When we communicate, we are sharing information. This can be local or remote. The data communications are the exchange of data between two devices via some form of transmission medium.
2: Transmission media:
A transmission medium can be broadly defined as anything that can carry information from a source to a destination for example:
For verbal communication, transmission media is air, for data communication among computers transmission medium can be either a wire or wireless medium.
When we talk about transmission media over computer network, we have two option first one is guided media and second one is unguided media.
Guided media which are those that provide a channel from one device to another includes twisted-pair cable, coaxial cable, and fiber cable. As well as guided media have advantage it’s have also many disadvantage like installation & maintenance, cost of wire very high & unable to move devices etc. To avoid these disadvantages we use Wireless-Technology.
Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Signals are normally broadcast through free space.
3: Wireless Technology:
Wireless Technology is a terminology in which you can connect two or more computer or device without using cables. Signals are normally broadcast through free space and thus are available to anyone who has device capable of receiving them. Wireless communication started in 1895 when Hertz was able to send frequency signals. Latter, Marconi devised a method to send telegraph-type massages over the Atlantic Ocean.
IEEE has defined the specifications for a wireless Communication, which covers the physical and data link layers. It’s work on IEEE 802.11 standard. Minimum speed is 11 maps & maximum speed is 54 Mbps.
5: Topology of wireless Technology (Structure)
There are two wireless structures in which wireless works
5.1 Ad hoc:
In ad hoc technology, wireless client communicate directly with each other without the use of wireless access point or wired network. Ad hoc mode connects wireless line together when there is no access point preferred.
In this mode, wireless and possible wired clients communicate with each other through a wireless access point, wireless client uses the wireless access point to access the resources of wired network.
In computer networking, wireless access point is a device that connects wireless communication devices together to form a wireless network.
6: Types of Wireless Technology:
We can divide wireless transmission into three broad groups:
- Wi – Fi
- Radio waves & Microwaves
6.1 WI – FI:
Wi – Fi is a brand originally licensed by the Wi – Fi Alliance to describe the underlying technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications. It was developed to be used for mobile computing devices, such as laptops, in LANs, but is now increasingly used for more services, including Internet and VoIP phone access, gaming, and basic connectivity of consumer electronics such as televisions and DVD players, or digital cameras. More standards are in development that will allow Wi – Fi to be sued by cars in highways in support of an Intelligent Transportation System to increase safety, gather statistics, and enable mobile commerce (IEEE 802.11p). Wi – Fi and the Wi – Fi CARTIFIED logo are registered trademarks of the Wi – Fi Alliance – the trade organization that tests and certifies equipment compliance with the 802.11x standards.
Wi – Fi networks can be monitored and used to read and copy data (including personal information) transmitted over the network when no encryption is used.
Microwave technology has been used extensively by the broadcast and cable television industries, as well as in other telecommunications applications, since the early 1950s. Today, microwaves are employed by telecommunications industries in the form of both terrestrial relays and satellite communications.
Microwaves are a form of electromagnetic radiation with frequencies ranging from several hundred MHz to several hundred GHz and wavelengths ranging from approximately 1 to 20 centimeters. Because of their high frequencies, microwaves have the advantage of being able to carry more information than ordinary radio waves and are capable of being beamed directly from one point to another. In addition to their telecommunications applications (which include telephony and computer networking, as well as television), microwaves are used in cooking, police radar, and certain military applications.
Since microwave is a “line-of-sight” technology (i.e., because a microwave transmission cannot penetrate the earth’s surface, it will not extend beyond the horizon), long-distance terrestrial transmission of messages is accomplished via a series of relay points known as “hops”. Each hop consists of a tower (often atop a mountain) with one antenna (typically a parabolic antenna) for receiving and another for retransmitting. Hops typically are spaced at 25-mile intervals.
Prior to the widespread use of communications satellites in television industries, terrestrial microwave relays frequently is used to deliver programmed from broadcast networks to their affiliates, or to deliver special event programming, such as sports, to local stations. Beginning in the 1950s, terrestrial microwave relays were employed to supplement expensive telephone land lines for long distance transmission of programming. Microwave mobile units (vans with microwave transmitters attached) have also been used in television news reporting since the late 1950s.
Microwave technology was vital to the development of the community antenna television (CATV) industry. Before microwave technology became available in the early 1950s, local CATV systems were limited in channel selection to those stations that could be received over-the-air via tall “master” antennas. I such situations, a CATV system could flourish only within 100-150 miles of the nearest broadcast television markets. Microwave relays, however, made it possible for CATV systems to operate May hundreds of miles from television stations. The new technology thus was a boon to remote communities, especially in the rural areas, which could not have had television otherwise Microwave also introduced the possibility for CATV operators to select which broadcast signals they would carry sometimes allowing them to bypass closer signals in order to provide their customers with more desirable programming—perhaps from well-funded stations in large cities. For this reason, it was microwave technology above all that prompted the earliest efforts by the Federal Communications Commission to regulate CATV. By the late fifties, some concern had been voiced by broadcasters as to the legality of the retransmission—and, in effect, sale—of their signals by CATV system and CATV-serving microwave outfits.
Historically, then, terrestrial microwave technology accomplished many of the television programming tasks for which communication satellites are used today. Terrestrial relays still exist and serve many important functions for television. In recent years, they have also been enlisted for non-television applications such as computer networking and the relaying of long distance telephone messages. Some companies that began as terrestrial microwave outfits have also diversified into satellite program delivery.
6.2(a) Types of Microwave Relay:
It is usually used when the cabling is difficult and cost of expensive but thus uses line-of-line system. The undirected dishes that are used or terrestrial microwave must be aligned. Microwaves are unidirectional. When an antenna transmits microwave waves, they can be narrowly focused. This means that the sending and receiving antennas need to be aligned.
Its covers large distance compare to other technology. When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned. A sending antenna sends waves that can be received by any receiving antenna.
6.3 Infrared Technology:
Infrared waves, with frequencies form 300 GHz to 400 THz (wavelength form 1 mm to 770mm); can be used for short-range communication. Infrared waves, having high frequencies, cannot penetrate walls. This advantageous characteristic prevents interference betw3en one system and another; a short-range communication system in one room cannot be affected by another system in the next room. When we use our infrared remote control, we do not interfere with the use of the remote by our neighbors; however this same characteristic makes infrared signals useless for long-range communication. In addition, we cannot use infrared waves outside a building because the sun’s rays contain infrared waves that can interfere with the communication.
Infrared radiation is the region of the electromagnetic spectrum between microwaves and visible light. In infrared communication an LED transmits the infrared signal as non-visible light. At the receiving end a photodiode or photoreceptor detects and captures the light pulses, with are then processed to retrieve the information they contain. Some common applications of infrared technology are listed below.
- Communication devices Navigation systems
- Car locking systems Mobiles
- Computers TVs, VCRs, CD players, stereos
- Mouse 11. Toys
- Environmental control systems
- Home security systems
6.3(a) Applications of IR:
The infrared band, almost 400 THz, has an excellent potential for data transmission. Such a wide bandwidth can be used to transmit digital data with a very high data rate. The Infrared Data Association (IrDa), an association for sponsoring the use of infrared waves, has established standards for using these signals for communication between devices such as keyboards, mice, PCs, and printers. For example, some manufactured provide a special port called the IrDA port that allows a wireless keyboard to communicate with a PC. The standard originally defined a data rate or 75 kbps for a distance up to 8m. The recent standard defines a data rate of 4 Mbps.
Infrared signals defined by IrDA transmit through line of sight: the IrDA port on the keyboard needs to point to the PC for transmission to occur.
Infrared technology offers several important advantages as a form of wireless communication. Advantages and disadvantages of IR are first presented, followed by a comparative listing of radio frequency (RF) advantages and disadvantages.
6.3(b) Advantages of IR:
- Low power requirements: therefore ideal for laptops, telephones, personal digital assistants
- Low circuitry costs for the entire coding/decoding circuitry
- Simple circuitry: no special or proprietary hardware is required, can be incorporated into the integrated circuit of product
- Higher security: directionality of the beam helps ensure that data isn’t leaked or spilled to nearby devices as it’s transmitted
- Few international regulatory: IrDA (Infrared Data Association) regulate the functionality of devices will ideally be useable by international travelers, no matter where they may be
- High noise immunity: not as likely to have interference from signals from other devices
6.3(c) Disadvantage of IR:
- Line of sight: transmitters and receivers must be almost directly aligned (i.e. able to see each other) to communicate
- Blocked by common materials: people, walls, plants, etc. can block transmission
- Short range: performance drops off with longer distances
- Light, weather sensitive: direct sunlight, rain, fog, dust, pollution can affect transmission
- Speed: data rate transmission is lower than typical wired transmission
≈> Advantages of RF:
- Not line of sight
- Not blocked by common materials: can penetrate most solids and pass through walls
- Longer range
- Not light sensitive
- Not as sensitive to weather/environmental conditions
≈> Disadvantages of RF:
- Interference: communication devices using similar frequencies – wireless phones, scanners, wrist radios and personal locators can interfere with transmission
- Lack of security: easier to “drop” on transmissions since signals are spread out in space rather than confined to a wire
- Higher cost than infrared
- Federal Communications Commission (FCC) licenses required for some products
- Lower speed: data rate transmission is lower than wired and infrared transmission
In addition to the above noted advantages and disadvantages of IR and RF technology, there are other issues that are also pertinent to the consideration of wireless communication systems. Health, safety and security issues are now discussed.
Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephone, notebooks, computer (Desktop & laptop), cameras, printers, coffee makers, and so on A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneously; the devices, sometimes called gadgets, find each other and make a network called a Pico net. A Bluetooth LAN can even be connected to the Internet if one of the gadgets has this capability. A Bluetooth LAN, by nature, cannot be large. If there are many gadgets that try to connect, there is chaos.
Bluetooth was originally started as a project by the Ericsson Company. It is named for Herald Blaatand, the king of Denmark (940-981) who united Denmark and Norway. Blaatand translates to Bluetooth in English.
Today, Bluetooth technology is the implementation of a protocol defined by the IEEE 802.15 standard. The standard defines a wireless personal-area network (PAN) operable in an area the size of a room or a hall.
GSM is short for “Global System for Mobile” Communications, which is on off the leading digital cellular system. The GSM standard for digital cell phone was established in Europe in the mid 1980s. GSM has now become the international standard in Europe, Australia and mush of Asia and Africa.
In covered areas, cell-phone users can buy one phone that will work anywhere where the standard is supported. To connect to the specific service providers in these different countries, GSM users simply switch “Subscriber Identification Module (SIM) cards. SIM cards are small removable disks that slip in and out of GSM cell phones. They store all the connection data and identification no. you need to access a particular wireless service provider.
GSM uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency. TDMA is short of Time-Division Multiple Access, a technology for delivering digital wireless service using time-division multiplexing (TDM). TDMA works by dividing a radio frequency into time slots and then allocation slots to multiple calls. In this way, a single frequency can support multiple, simultaneously data channel.
GSM digitizes and compress voice data, then sends it down a channel with other streams of user data, each in its own time slots. GSM system use encryption to make phone calls more secure. GSM operates in the 900-MHz bands in Europe and Asia, and in the 1900-MHz band in the United States. It is used in United States.
CDMA is short for Code-Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing system, such as GSM that uses TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with pseudo-random digital sequence. CDMA is a form of spread spectrum, which simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range. Each user’s signal is spread over the entire bandwidth by a unique spreading code. At the receiver end, that same unique code is used to recover the signal.
CDMA is military technology 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 German to pick up the complete signal.
Wireless in local loop is a system that connects subscriber to the “Public Switched Telephone Network (PSTN)” using radio signals as a substitute for other connecting media. It is analogous with local telephone service, but much more capable. A WLL system serves a local area by deploying multiplicities of multichannel transmit/receive base station (transceivers) that are within line-of-sight of the intended customers. Each customer is equipped with a mini-station of low power, into which the telephone is connected. The WLL unit consists of a radio transceiver and the WLL interface assembled in one metal box. Two cables and a telephone connector are the only outlets form the box; one cable connects to a directional antenna and a phone receptacle to connect to a common telephone set. A fax or modem could also be connected for fax or computer communication.
When calls are made from the telephone, it signals the base station for a connection, which is subsequently established through a switch centre, exactly as in conventional telephone. An incoming call is identified at the switch centre and routed to the base station assigned to server the telephone being called. The wireless connection is then made, and the call is completed in a conventional manner.
The infrastructure design of WLL system typically uses an advanced transmission technology such as CDMA that permits support of large subscriber bases through orderly expansion of the base station clusters. Such system can support a mixture of rural and urban coverage, permitting modern telephone services to be economically extended to less advantaged population groups. Services like public payphone can also be supported.
The point to point transmission occur through the air over a terrestrial microwave platform rather than through copper or fiber cable; therefore, fixed wireless does not require satellite feeds or local phone service. The advantages of fixed wireless include the ability to connect with users in remote areas without the need for laying new cables and the capacity for broad bandwidth that is not impeded by fiber cable capacities.
The WLL system can operate with GSM Handset/Mobile units, as well as with WLL compatible Subscriber Units.
Advantage of WLL:
- Lacking exterior plant, reliability is greatly enhanced; as well designed WLL facilities do not significantly suffer from weather damage, vandalism, and accidents.
- WLL system offers better bandwidth than tradition telephone systems.
- Most important, because the WLL system has much better bandwidth than traditional telephone systems, superior customer service features and quality can be provided.
WLL system support high quality transmission, signaling service, and all the most advanced customer service features.
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