INTRODUCTION DATA COMMUNICATION TELECOMMUNICATIONS SYSTEM COMPONENTS 1/28/2015. Satish Chandra satish0402.weebly.com

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1 INTRODUCTION DATA COMMUNICATION Satish Chandra satish0402.weebly.com The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. The data communications are the exchange of data between two devices via some form of transmission medium such as awire cable. TELECOMMUNICATIONS SYSTEM COMPONENTS Tele (Far) + Communications Early telecommunications smoke signals and drums visual telegraphy (or semaphore in 1792) Telegraph and telephone Telegraph (1839) Telephone (1876) Radio and television Telephony Voice and Data Simplified Communications Model Simplified Communications Model The key elements of this model are: Source generates data to be transmitted Transmitter converts data into transmittable signals Transmission System carries data from source to destination Receiver converts received signal into data Destination takes incoming data 1

2 Simplified Data Communications Model Simplified Data Communications Model Assume a PC user wants to send an message m to another user. The process is modeled as follows: User keys in message m comprising bits g buffered in source PC memory. Input data is transferred to I/O device (transmitter) as sequence of bits g(t) using voltage shifts. Transmitter converts these into a signal s(t) suitable for transmission media being used. Whilst transiting media signal may be impaired so received signal r(t) may differ from s(t). Receiver decodes signal recovering g (t) as estimate of original g(t). Which is buffered in destination PC memory as bits g being the received message m. Communication Systems COMMUNICATIONS COMPONENTS Basic components of a communication system Communication technologies Communication devices Communication channels Communication software Communication Technology Applications Communication Channels e mail voice mail instant messaging Twitter newsgroups telephony videoconferencing chat rooms collaboration groupware global positioning system (GPS) A channel is a path between two communication devices Channel capacity: How much data can be passed through the channel (bit/sec) Also called channel bandwidth The smaller the pipe the slower data transfer! Consists of one or more transmission media Materials carrying the signal Two types: Physical: wire cable T1 Wireless: Air lines destination network server T3 lines T1 lines T1 lines 2

3 Physical Transmission Media Physical Transmission Media A tangible media Examples: Twisted pair cable, coaxial cable, Fiber optics, etc. Twisted pair cable: One or more twisted wires bundled together Md Made of copper Coaxial Cable: Consists of single copper wire surrounded by three layers of insulating and metal materials Typically used for cable TV Fiber optics: Strands of glass or plastic used to transmit light Very high capacity, low noise, small size, less suitable to natural disturbances plastic outer coating woven or braided metal insulating material copper wire twisted pair cable optical fiber core glass cladding protective coating twisted pair wire Wireless Transmission Media Broadcast Radio Distribute signals through the air over long distance Uses an antenna Typically for stationary locations Can be short range Cellular Radio A form of broadcast radio used for mobile communication High frequency radio waves to transmit voice or data Utilizes frequency reuse Wireless Transmission Media Microwaves Radio waves providing high speed transmission They are point to point (can t be obstructed) Usedfor satellitecommunication Infrared (IR) Wireless transmission media that sends signals using infrared light waves Communication Satellite Geo stationary orbit Transponder C band (Downlink/Uplink 4/6 GHz) Ku band (Downlink/Uplink 11/14 GHz) VSAT Earth Station Physical Transmission Media Wireless Transmission Media Wireless channel capacity: 3

4 DATA FLOW Simplex Transmission Simplex: One direction only Half Duplex Transmission Full Duplex Transmission half duplex: Both directions but only one direction at a time full duplex: send and receive both directions at once NETWORK A network is aset of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. A link can be a cable, air, optical fiber, or any medium which can transport a signal carrying information. TYPE OF CONNECTION Point to Point - single transmitter and receiver Multipoint - multiple recipients of single transmission 4

5 personal computer personal computer personal computer CATEGORY OF TOPOLOGY personal computer personal computer personal computer personal computer personal computer personal computer host computer printer file server Mesh Topology Star Topology Bus Topology Ring Topology 5

6 Hybrid Topology: NETWORKS growth of number & power of computers is driving need for interconnection also seeing rapid integration of voice, data, image & video technologies three broad categories of communications networks: Local Area Network (LAN) Wide Area Network (WAN) Metropolitan Area Network (MAN) Categories of Networks Local Area Networks (LANs) Short distances Designed to provide local interconnectivity Wide Area Networks (WANs) Long distances Provide connectivity over very large areas Metropolitan Area Networks (MANs) Provide connectivity over areas such as a city, a campus Local Area Networks smaller scope Building or small campus usually owned by same organization as attached devices data rates much higher switched LANs, eg Ethernet wireless LANs Local Area Networks (LAN) An isolated LAN connecting 12 computers to a hub in a closet Wide Area Networks span a large geographical area cross public rights of way rely in part on common carrier circuits alternative technologies used include: circuit switching packet switching frame relay Asynchronous Transfer Mode (ATM) 6

7 Wide Area Networks Metropolitan Area Networks MAN middle ground between LAN and WAN private or public network high speed large area A heterogeneous network made of four WANs and two LANs THE INTERNET Internet evolved from ARPANET first operational packet network applied to tactical radio & satellite nets also had a need for interoperability led to standardized TCP/IP protocols THE INTERNET The Internet has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use. Hierarchical organization of the Internet 7

8 Internet Elements Internet Architecture Example Configuration MULTIPLEXING Bandwidth utilization is the wise use of available bandwidth to achieve specific goals. Efficiency can be achieved by multiplexing; i.e., sharing of the bandwidth between multiple users. MULTIPLEXING Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the link can be shared. Multiplexing is the set of techniques that allows the (simultaneous) transmission of multiple signals across a single data link. As data and telecommunications use increases, so does traffic. THE CONCEPT OF MULTIPLEXING Multiplexing to refer to the combination of information streams from multiple sources for transmission over a shared medium Multiplexor is a mechanism that implements the concept Demultiplexing refers to the separation of a combination back into separate information streams Demultiplexor to refer to a mechanism that implements the concept 8

9 Multiplexing and Demultiplexing MULTIPLEXING IN NETWORKS Sharing th e medium Main pur pose is? MULTIPLEXING IN NETWORKS MULTIPLEXING each sender communicates with a single receiver all pairs share a single transmission medium multiplexor combines information from the senders for transmission in such a way that the demultiplexor l can separate the information i for receivers. MULTIPLEXER EXAMPLE NETWORK SHARING Network Resources (bandwidth) divided into pieces pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into pieces frequency division time division 9

10 FDM TDM frequency FDM and TDM Example: 4 users time Spectrum AM: 535 khz to 1.7 MHz TV: (VHF, channels 2 6) and (UHF, channels 7 13) Unlicensed vs. licensed cell phone (800 MHz, 1800/1900 MHz) Wi Fi (2.4 GHz, 5 GHz) frequency time Categorization of Multiplexing Frequency Division Multiplexing FDM is an analog multiplexing technique that combines analog signals. FDM: Multiplexing Process FDM: Demultiplexing Process 10

11 FDM: Example Assume that a voice channel occupies a bandwidth of 4 khz. We need to combine three voice channels into a link with a bandwidth of 12 khz, from 20 to 32 khz. Show the configuration, using the frequency domain. Assume there arenoguard bands. FDM: Example Shift (modulate) each of the three voice channels to a different bandwidth. We use the 20 to 24 khz bandwidth for the first channel, the 24 to 28 khz bandwidth for the second channel, and the 28 to 32 khz bandwidth for the third one and then combine them. FDM: Bandwidth Five channels, each with a 100 khz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 khz between the channels to prevent interference? Wave Division Multiplexing WDM is an analog multiplexing technique to combine optical signals. WDM: MULTIPLEXING & DEMULIPLEXING TIME DIVISION MULTIPLEXING TDM is a digital multiplexing technique for combining several low rate digital channels into one high rate one. In synchronous TDM, the data rate of the link is n times faster, and the unit duration is n times shorter. 11

12 TDM TDM TDM TDM Frequency Division Multiplex Separation of spectrum into smaller frequency bands Channel gets band of the spectrum for the whole time Advantages: no dynamic coordination needed Channels k i works also for analog signals Disadvantages: k 3 k 4 k 5 k 6 waste of bandwidth, if traffic distributed unevenly inflexible guard spaces t 12

13 Why FDM is for analog signals and TDM is for digital signals? FDM stands for frequency division multiplexing and it is used only in case of analog signals because analog signals are continuous in nature and the signal have frequency. TDM stands for time division multiplexing and it is used only in case of digital signals because digital signals are discrete in nature and are in the form of 0 and 1s. and are time dependent. ADVANTAGES & DISADVANTAGES OF TDM & FDM In TDM, different users share the same channel based on time slots allotted to them. Each user or source is given a particular time slot to send its information. 1. The entire channel BW is available for a particular time interval unlike in FDM where the channel BW is split into smaller segments. This enables higher data rates. 2. All users share the same frequency, so spectrum efficiency is increased. Available channel BW is no more a constraint ENDS 13