My ContentTelecommunicationComponent of Communications SystemCommunication Channel Guided Media Twisted Pair Characteristics Disadvantages Coaxial Cable (Coax) Characteristics Disadvantag Fiber Optics Characteristics Disadvantag Unguided Media Microwaves Characteristics Disadvantag Broadcast radio Characteristics Disadvantag Cellular Radio Characteristics Disadvantag Satellite Characteristics Disadvantag Infra Red (IR) Characteristics DisadvantagCommunication mode Simplex Duplex Half Duplex Full DuplexISDN (Integrated Service Digital Network) 1988Multiplexing Analog Techniques FDM (Frequency Division Multiplexing) Advantages Disadvantages WDM (Wavelength Division Multiplexing) Digital Techniques Time Division Multiplexing (TDM) Types of TDM Synchronous TDM Asynchronous TDMApplications of MultiplexingModulationTypes of ModulationNeed for ModulationStandards and Protocols Protocols StandardsStandards organizations
Telecommunication
Transmission channels, Mode, and Media, ISDN, PSDN, Multiplexing, Modulation, Standards and Protocols.
Telecommunication
"Telecommunication" is defined as the art and science of communicating over a distance by telephone, telegraph and radio. It is the transmission, reception and the switching of signals, such as electrical or optical, by wire, fiber, or electromagnetic (i.e. through the air) means.
O'Neil and Everett define telecommunications is like communications, except that it involves communicating electronically across distances (generally over telephone lines) without any changes occurring to the original message. All forms of information may be sent electronically : voice, text, data, graphics, and video.
Another definition is given to 'telecommunications' technology as 'the electronic communication of information over distance' (Mitchell, Hendricks and sterry, 1993) The key word "electronic" in this definition refers to the present day use of telecomunications, which involves the use of technology for signaling, purposes.
Kooker and Brey state that telecommunicationis is broadly defined as "the process by which information gets transferred electronically from one place to another. They also pointed out some examples of telecommunications in our society, such as basic telephone system, cellular and mobile phones, credit card verification network facsimile transmission, broadcast and cable TV / radio etc.
Telecommunications network is a collection of terminal nodes in which links are connected so as to enable telecommunication between the terminals. The transmission links connect the nodes together. The nodes use circuit switching massage switching or packet switching to pass the signal through the currect links and nodes to reach the connect destination terminal. Each terminal in the network usually has a unique address so messages or connections can be routed to the correct recipients. The collection of addresses in the network is called the address space.
In telecommunication, a communications system is a collection of individual communication networks, transmission system, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and interoperation to form an integrated whole. The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls and operate in union. Telecommunications is a method of communication (e.g. for sports broadcasting mass media, Journalism, etc.)
Component of Communications System
The following are the basic components for working of a communication system :
i. Transmitter :
The transmitter sendis the massage and the receiver receives the massage. The medium is the channel over which the message is sent and the protocol is the set of rules that guides how the data is transmitted from enoding to decoding. The message of course is central to all the components. The message is the data that is being communicated.
ii. Transmitter :
The transmitter its the device that sends the massage. It can be a computer, workstation, telephone, handset. video camera and so on.
iii. Medium :
The transmission medium is the physical path by which a massage travels from sender to receiver. It can consist of twisted pair wire, coavial cable, fiber-optic cable, laser or radio waves (terrestrial or satellite microwave)
iv. Receiver :
The receiver is the device that receives the massage. It can be a computer, workstation, telephone, handset. television and so on.
v. Message :
The message is the transmission (data) to be communicated. It can consist of text, number, pictures, sound or video Or any combination of these.
vi. Protocol :
A protocol is a set of rules that governs data communication. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating. Just as a person speaking german connot be understood by a person who speaks only Japanese.
Communication Channel/ Transmission Channel / Communication Media /Medium
Communication Channel
Guided Media. Unguided Media (wireless media)
i.Twisted Pair. i. Microwave
ii. Coaxial. ii. Radio ware
iii. Fibre optics. iii. Cellular
iv . Infrared
v . Satellite
Guided Media
i. Twisted Pair :
Speed 10 mbps to 10 gbps.
Characteristics
• Most Popular
• Used in LAN and local telephone lines,
• Can carry voice and data signals.
• Copper wires pair are insulated by plastic.
• Wires are twisted together in order to reduce noise.
• It is of two types, Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP).
• Inexpensive and easy to install and maintain.
Disadvantages
• Unsuitable for long distance.
• Speed is less than Coaxial cable or fibre optics.
ii. Coaxial Cable (Coax) :
Speed 10 mbps to 100 mbps.
Characteristics
• It is used for video transmissions for television or for long-distance telephone lines and LANs.
• Single solid copper wire care that is covered by insulating material.
• Copper mesh is used to cover the insulated copper wire to protect from electromagnetic waves.
• Carries both analog and digital signals.
• Carries high frequency range signals.
• It is of two types, thicknet and thinnet.
Disadvantages
• Expensive than twisted pair.
• Not compatible with twisted pair cables.
iii. Fiber Optics :
Speed 100 gbps
Characteristics
i. Used for internet orb long distance communication.
• Digital signals are sent as light pulses which are translated back into electrical signals.
• Fine glass strand surrounded by glass cladding and protective layer.
• Glass cladding reflects light back into the core, guiding the light along the wire.
• Thousands of transmissions can be carried on a single strand.
• Secure and has very low signal loss.
Disadvantages
• Expensive difficult to install and modify.
• Difficult to repair.
Unguided Media
i. Microwaves :
Speed 1 mbps to 10gbps.
Characteristics
• Used for high speed transmission.
• Information is sent via microwaves from ground based transmitting and receiving stations.
• Text, sound, and graphics are converted into microwave pulses and transmitted.
• Microwave stations (a. k. a repeater stations) must be placed every 50 kilometres to receive, amplify and then pass the signal along.
Disadvantages
• It cannot pass thru obstacles.
• Can only use line of sight transmission.
ii. Broadcast radio :
Speed 1 mbps to 10 mbps.
Characteristics
• Used for cordless phones, AM and FM radio transmission for both voice and data.
• Can travel long distances and penetrates buildings.
• Requires a transmitter to send broodcast radio signals and a receiver to receive it.
• The receivers uses an antenna to receive the signals.
• An example of the short-range broadcast radio in bluetooth.
- Used in computers, mobiles, printers etc.
-Transmit data at a rate of 1 Mbps.
Disadvantages
• Unidirectional and insecure.
iii. Cellular Radio :
Speed 10 mbps to 1 gbps.
Characteristics
• Used in wireless modems and cellular telephone.
• Users high-frequency radio waves to transmit voice and digital data.
• Can cannot notebooks or mobile computer to the celluar telephone to access the web or send and receiver the email etc.
Personal Communications Services (PCS) is a set of technologies used for digital cellular devices like laptops, cellular telephones etc.
Disadvantages
• It required complex infrastructure.
• Well planned frequency spectrum distribution.
iv. Satellite :
Speed 1 mpps to 10 gbps.
Characteristics
• Is used for global communication.
• Satellite are placed in space and they orbit the earth.
• Receives microwave signals from the earth station.
• Satellites magnify the signals and retransmit them back.
• The data transfer speed its very high.
• It avoids the cost of cabling and repeater stations.
• The transmission from the earth station to a satellite is called uplink. The transmission from the satellite to the earth station is called the downlink.
Disadvantages
• It is expensive and not easy to repair and maintain.
• Weather and sunspots cause signal disturbance.
v. Infra Red (IR) :
Speed 1gbps.
Characteristics
• Used in remote controls for televisions. Optical mouse and entertainment devices.
• Sends signals using infrared light wave that is invisible to us and is just above the red end of the colour spectrom.
• It works over a moderate bandwidth 115 kbps and works up to few meters.
• IRDA port is fixed to transfer data
• Alternative to short-range range channel like bluetooth.
Disadvantages
• It has short range and low bandwidth.
• It requires a light of sight transmission.
Communication mode
Transmission Mode means transfering of data between two device. Its another name data communication Mode/Data transmission Mode.
The term transmission mode defines the direction of the flow of information between two communication devices. The way in which data is transmitted from one place to another is called data transmission mode. It indicates the direction of flow of information. Data transmission modes are also referred to as directional modes.
Transmission
Simplex Duplex
Half Duplex
Full Duplex.
Simplex Mode (A to B only)
• Data can flow is only one direction.
• i.e. communication is unidirectional.
• In this mode, a sender can only data but can't receive it. similarly, a receiver can only receive data but can't send it.
• Some Examples of simplex Mode
• Keyboard or Mouse inputs to CPU
• CPU outputs to monitor.
• Computer to printer.
• Scanner to computer.
• Radio and TV Transmission.
Half Duplex Mode. [(A to B) or (B to A)]
• Data can flow in both direction but in one direction at a time.
• When one device is sending the other can only receive and vice versa.
• For Examples :
• Walkie Talkie
• Internet Browser
Full Duplex Mode [(A to B) and (B to A)]
• Data can flow in both direction at the same time.
• It is bidirectional
• Data can be sent in both directions simultaneously.
• We can send as well as we receive the data.
• Example of full duplex is a telephone network in which there is communication between two persons by a telephone line, through which both can talk and listen at the same time.
ISDN (Integrated Service Digital Network) 1988
• ISDN is integrated service Digital Network.
• Used in communication of digital transmission of voice, data, and other network service over the traditional circuit.
• It integrate voice data + image, video ete on some data line.
• Before ISDN classic telephone system was used transport voice and some special service for data.
• ISDN was first define in 1988 in CCITT red book.
• Key feature of ISDN is integrated speech and data on same line.
• ISDIN standards define serveral kinds of interface.
i. BRI (Basic Rate Interface)
ii. PRI (Primary Rate Interface)
iii. N - ISDN
iv. B - ISDN
• ISDN WORK on 64 kbps digital communication channel.
• ISDN provide different channel to provide access to various services. BRI provide 2 Barrier channel (B) and 16 kps Data Channel (D).
• B channel is used for end to and digital connection and for voice and data and D channel carry information for B channel.
PSDN
BLANK
Multiplexing
Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a signal data link.
picture plz
• Multiplexing is a technique in which multiple data stream can combine and send through single medium.
• Process of combining data stream is called multiplexing device used for multiplexing is called multiplexer.
• Multiplexer is a device which take n input line and gives one output line.
• Multiplexer follow many to one approach
• On the receiving end we use demultiplexer which separate singnal into multiple signals.
Multiplexing techniques are used in telecommunication, in which different telephone calls can carried into single wire.
Multiplexing Techniques
Analog Techniques. Digital Techniques
FDM (Frequency Division Multiplexing) TDM (Time Division Multiplexing)
WDM (Wavelength Division Multiplexing) Synchronous
Asynchronous
Analog Multiplexing
The process of combining multiple and log signals into one signal is called analog multiplexing. It multiplexes the analog signals according to their frequency or wavelength.
Multiplexing requires that the multiple signals be kept apart so that they do not overlap with each other and thus can be separated at the receiving end. This can be achieved by separately the signal in frequency.
There are two types of analog multiplexing.
i. Frequency Division Multiplexing
ii. Wavelength Division Multiplexing
i. Frequency Division Multiplexing
Frequency division multiplexing is an analog technique. It is most popular multiplexing technique. We use this techniques extensively in TV and radio transmission. This technique combines multiple signals into one signal and transmitted over the communication channel. Frequency division multiplexing its also known as FDM. In this technique, the bandwidth of the communication channel should be greater than the combined bandwidth of individual signals.
Advantages
1. It transmits multiple signals simultaneously.
2. In frequency division multiplexing, the demodulation process is easy.
3. It does not need synchronization between transmitter and receiver.
Disadvantages
1. It needs a large bandaridth communication channel.
ii. Wavelength Division Multiplexing
Wavelength division multiplexing is an analog technique. It is the most important and most popular method to increase the capacity of an optical fiber. We know that wavelength and frequency are inversely proportional to each other. wavelength means (i.e. longer wavelength means two frequency and shorter wavelength means high frequency).
Therefore, the working principle of wavelength division multiplexing is similar to frequency division multiplexing. The only difference is in wardength division multiplexing optical signals are used instead of electrical signals. In wavelength division multiplexing, optical signals are transmitted through f iber optic cables wavelength division multiplexing is a technology in which multiple optical signals (laser light) of different wavelength or colors are combined into one signal and is transmitted over the communication channel. Thus multiple signals are transmitted simultaneously over a single communication channel. Wavelength division multiplexing is a technology that increases the bandwidth of a communication channel (optical f iber) by simultaneously allowing multiple optical signals through it.
Digital Multiplexing
The process of combining multiple digital signals into one signal is called digital multiplexing.
Time Division Multiplexing (TDM)
Time Division Multiplexing is a technique in which multiple signals are combined and transmitted one after another on the same communication channel.
At the receiver side, the signals are separated and received. Each signal is received by a user at a different time.
Time Division Multiplexing is also simply referred to as TDM. It is the digital multiplexing technique.
In frequency division multiplexing, all signals of different frequencies are transmitted simultaneously. But in time division multiplexing, all signals operate with the same frequency are transmitted at different times.
In frequency division multiplexing, the sharing of a channel is done on the basic of frequency. But in time division multiplexing, the sharing of a channel is done on the basis of time.
Types of TDM
Time division multiplexing is mainly two type.
i.Synchronous TDM
ii.Asynchronous TDM
i. Synchronous TDM
In synchronous time disision Multiplexing. each device (transmitter) in allotted with a fixed time slot, regardless of the fact that the device (transmitter) has any data to transmit on not. The device has to transmit data within this time slot. If the device (transmitter) does not have any data to send then its time slot remains emply.
picture
ii. Asynchronous TDM
In Asynchronous time division multiplexing, the time slots are not fixed (i.e. time slots are flexible). The asynchronous TDM is also known as statistical time division multiplexing.
picture
Applications of Multiplexing
• Communication System
• Computer memory
• Telephone System
•TV broadcasting
•Telemetry
• Satellites
• Circuit Switching
Modulation
• Baseband signals
- Voice (0-4 KH2)
- TV (0-6 MH2)
• A Signal may be sent in its baseband format when a dedicated wired channel is available.
• Otherwise, it must be converted to passband.
The process of shifting the baseband signal to passband range is called Modulation.
The process of shifting the. passband signal to base band frequency is called Demodulation.
Reasons for Modulation:
- simultaneous transmission of several signals.
- Practical design of antennas.
- Exchange of power and bandwith
Modulation is the process of mixing a low energy message signal with the high energy carrier signal to produce a new high energy signal which carries information to a long distance.
or Modulation is the process where some parameter of the carrier wave is varied in accordance with the modulating signals .
Modulation
Analog Modulation Digital Modulation
Continuous Wave Modulation Pulse Modulation ASK
Amplitude Modulation (AM) PAM FSK
Frequency Modulation (FM) PWM PSK
Phase Modulation (PM) PPM
PCM
Need for Modulation
1. Reduction in the height of antenna.
2. Avoids mixing of signals.
3. Increases the range of communication
4. Multiplexing is possible.
5. Improve quality of reception.
Standards and Protocols
Protocols
• A protocols is a set of rules that govern data communications.
• Syntax : The term syntax refers to the structure or format of the data.
• Semantics : The word semantics refers to the meaning of each section of bits.
• Timing : The term timing refers to when data should be sent and how fast they can be sent.
Standards
• Standards provide guidelines to manufacturers, vendors, government agencies, and other service providers.
• De facto - Standards that have not been approved by on organized body but have been adopted as standards through widespread use.
• De Jure - Those standards that have been legislated by an officially orecognized body.
Standards organizations
• International organization for standardization (ISO).
• International Telecommunication Union Telecommunication standards sector (ITU-T).
• American National Standards Institute (ANSI).
• Institute of Electrical and Electronics Engineers (IEFE).
• Forums.
• Regulatory Agencies.
/ Some of the standards organizations of relevance for communication protocols are the International organization for standardization (ISO), the international Telecommunication union (ITU), the institure of Electrical and Electronics Engineers (IEEE), and the internet Engineering Task Force (IETF).
The IETF maintains the protocols in use on the internet. The IEEE controls many software and hard are protocols in the electronics industry for commercial and consumer devices. The ITU is an umbrella organization of telecommunication engineers, designing the public switched telephone network (PSTN), as well as many radio communication systems. For marine electronics the NMEA standards are used. The world wide web consortium (W3C) produces protocols and standard for web technologies.
OSI standardization : A lesson learned from ARPANET, the predecessor of the Internet, was that standardization of protocols is not enough, because protocols also need a framework to operate. In the OSI model, communicating system are assumed to be connected by an underlying physical medium providing a basic transmission mechanism. The layers above it are numbered (from one to seven), the nth layer is referred to as (n)-layer. Each layer provides service to the layer above it (or at the top to the application process) using the services of the layer immediately below it. The layers commune cate with each other by means of an interface, called a service access point. Corresponding layers at each system are called peer entities. To communicate, two peer entities at a given layer use an (n)-Protocol, which is implemented by using services of the (n-1) layer.
No comments:
Post a Comment