FRP Chapter 14 Communication and Computer …...Notes By Shivali Jaggi 1 Chapter 14 Communication and Computer Networks Network It is an interconnected collection of autonomous computers

Notes By Shivali Jaggi 1

Chapter 14 Communication and Computer Networks

Network It is an interconnected collection of autonomous computers

Network Goals 1. Resource sharing --- All programs, data and peripherals are available to anyone on the network irrespective to

the physical location of the resource and the user. 2. High Reliability --- A file could be replicated on two or three machines, so if one of them is unavailable

(hardware crash), the other copies could be available. 3. Cost Factor --- Personal Computers (PC’s) have a much better price/performance ratio than micro ones. 4. Communication Medium --- A file that was updated/modified on a network, can be seen by the other users on

the network immediately.

Network Applications 1. Sharing of data, programs and peripherals 2. Access to remote programs. 3. Access to remote databases. 4. Value-added communication facilities.

Advantages 1. Speed --- Sharing and transferring files within Networks are very rapid. Thus saving time, while maintaining the

integrity of the file. 2. Security --- Sensitive files and programs on a network are passwords protected so no illegal copying of

programs is there. 3. Centralized Software Management --- Software can be loaded on one computer eliminating that need to spend

time installing on independent computers. 4. Resource Sharing --- Resources such as, printers, fax machines and modems can be shared. Therefore is

cheaper than to have these on many systems. 5. Improve Communications --- E-mail aids in personal and professional communication. Electronic mail on a

LAN can enable staff to communicate within the building having tot to leave their desk.

Disadvantages 1. Cabling can be expensive to install and replace. 2. A fault with the server will prevent the whole network from working. 3. Security measures are needed to restrict access to the network. 4. WANs are vulnerable to hackers and viruses. 5. Server faults stop applications being available 6. Network faults can cause loss of data and resources 7. User work dependent upon network 8. Could degrade in performance 9. Resources could be located too far from users 10. Network management can become difficult for very large networks

Evolution of Internet

ARPANET NSFnet Internet Advanced Research Projects Agency NETwork

National Science Foundation

World wide Network of Computer Networks

• Started in 1969 • By U.S. Department of

Defense and different universities

• Was shut down in 1990

• Started in 1980s • By a federal agency – National Science

Foundation • High capacity network to be used

strictly for academic and engineering researches

• Government funding was discontinued in 1995

• Started in 1990’s • Inter-networking of ARPANET, NSFnet

and other private networks resulted into Internet

• Use common set of rules for communication called as Protocols

• For Internet protocol name is TCP/IP (Transmission Control Protocol / Internet Protocol)

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Some Important terms of Internet

• Gateway ---- It is a device that connects dissimilar networks • Backbone --- It is central interconnecting structure that connect one or more networks just like trunk of a tree

Tree Network • Interspace ---- It is a client/serve software program that allows multiple users to communicate online with

real time audio, video and text chat in dynamic 3D environments • TCP ---- It is responsible for dividing the file/message into packets on the source server and also for

reassembling the received packets at the destination computer. • IP ---- It is responsible for handling the address of destination computer so that each packet is routed

to its proper destination. • Nodes ---- The computers that are attached to a network are known as nodes, also known as workstation. • Server ---- Computer that facilitates the sharing of data, software and hardware resources (e.g. printer,

modem etc.) on the network is known as server. There are two types of servers, characteristics and difference is given below :-

Non-Dedicated server Dedicated server 1. Used on small networks 1. Used on bigger networks 2. In it a workstation can double up as a server 2. In it a workstation can not double up as a server 3. Facilitates resource sharing between workstations 3. Workstations can only access data, software and

hardware resources from the server, not other workstations. 4. It is slower and requires more memory 4. It is faster and requires less memory as compared with

non-dedicated server 5. Networks using such a server is known as Peer-to-Peer networks

5. Networks using such a server is known as Master/Slave networks

• NIU ---- Network Interface Unit is an interpreter (device) that helps establish communication between the server and workstations. Some important point related to NIU :-

a) Each NIU has a unique number known as node address. b) It is also known as Terminal Access Point (TAP) c) It is also called as Network Interface Card (NIC) d) NIC manufactures assigns a unique physical address known as MAC Address

Network Switching Techniques These are three switching techniques given below :-

Circuit Switching ---- 1. The complete physical connection between two computers is established and then data are transmitted from

the source computer to the destination computer. 2. The important property of this switching technique is to setup an end-to-end path (connection) between

computers before any data can be sent.

Message Switching ---- 1. The source computer sends data or the message to the switching office which sends the data to another

switching office until the data is delivered to the destination computers. 2. Its working principle is known as store and forward

Packet Switching ---- 1. It places a tight upper limit on block size i.e. a fixed size of packet is transmitted across the network. 2. This improves the performance as the access time (time taken to access a data packet) is reduced, 3. Thus, the throughput (measure of performance) of the network is improved.

Ring Network

Star Network

Bus Network

Backbone Network

Gateways

Gateways




Difference between Message and Packet Switching

Message Switching Packet Switching 1. There is no limit on block size 1. It places a tight upper limit on block size i.e. a fixed size of packet 2. Data packets are stored on the disk 2. All the packets of fixed size are stored in main memory 3. Access time of data packets is large than

packet switching 3. Access time of data packets is large than message switching

4. Throughput of the network is slow as compared to packet switching

4. Throughput of the network is improved as compared to message switching

A Comparison of Circuit-Switched and Packet Switched Networks

Item Circuit Switching Packet Switching 1. Dedicated Copper Wire Yes No 2. Bandwidth Available Fixed Dynamic 3. Potentially Wasted Bandwidth Yes No 4. Store and Forward Transmission No Yes 5. Setup of an end-to-end path (i.e Call Setup) Required Not Needed 6. Each packet follow same route Yes No 7. When can congestion occur At setup time On every packet

Transmission Media The communication media is divided into two categories :-

1. Guided Media ---- includes cables for transmission. The basic types are :- a. Twisted Pair Cables b. Coaxial Cables c. Optical Fiber Cables

2. Unguided Media ---- includes waves through air, water or vacuum for transmission. The basic types are:- a. Micro Wave b. Radio Wave c. Satellite d. Infrared e. Laser

Twisted Pair Cables Cables without a shield are called Unshielded Twisted Pair (UTP). As shown in Fig below:-

Insulators Conductor

Important point related to twisted pair cables :- • The wire comes in pairs and the pair are twisted around each other • VGM (Voice Grade Medium) for telephone wiring • DGM (Data Grade Medium) a high quality cable used for LAN applications • It stops signal interference that is crosstalk (Bleeding of signals from one wire to another) which can corrupt

signals and cause network errors. • The degree of reduction in noise interference is determined by the number of turns per foot. Increasing the

number of turns per foot reduces the noise interference. • To further improve noise rejection, a foil or wire braid shield is woven around the twisted pairs. Cables with a

shield are called Shielded Twisted Pair (STP). As shown is figures A and B given below :-

Fig A Fig B

Single Twisted Pair




Advantages :- 1. It is simple 5. It is very inexpensive 2. It is physically flexible 6. Easy to add additional network devices, therefore supports large 3. It can be easily connected number of network devices 4. It is easy to install and maintain 7. It has a low weight

Disadvantages :- 1. High attenuation (signal loss) limits individual runs to 100 meters 2. Repeaters should be used to carry signals for long distances 3. Its low bandwidth makes it unsuitable for broadband applications 4. Maximum data rate without conditioning 1Mbps and with conditioning 10 Mbps

UTP cable is available in five grades (or categories) :- Type Description

CAT 1 Only for VGM, no data transmission CAT 2 DGM, 4 Mbps CAT 3 DGM, 10 Mbps CAT 4 DGM, 16 Mbps CAT 5 DGM, 1000 Mbps

Coaxial Cable

Important point related to Coaxial pair cables :-

• Coaxial Cable consists of two conductors. • The inner conductor is held inside an insulator with the other conductor woven around it providing a shield.

An insulating protective coating called a jacket covers the outer conductor. • The outer shield protects the inner conductor from outside electrical signals. • Coaxial cables are used for Cable TV (in CATV form) and Ethernets. • This cable allows higher data rates to be transferred than the Twisted Pair cable.

Advantages :- 1. Can be used for broadband transmissions i.e. many channels transmitted simultaneously 2. Offer higher bandwidths upto 400 MBPS 3. Data transmission is better than Twisted Pair cable 4. Low cost due to less total footage of cable, hubs not needed 5. Lower attenuation (disturbance)than twisted pair

Optical Fiber

Jacket Thin Glass Rods Cladding Core

Disadvantages :- 1. Expensive as compared to Twisted Pair cables 2. They are not compatible with twisted pair cables 3. Limited in network speed 4. Limited in size of network 5. One bad connector can take down entire network

Parts of Fiber Optic Cable :- 1. Core -- the glass or plastic through which light travels 2. Cladding -- the covering of the core that reflects light

back to the core 3. Protective Coating -- Protects the cable from hostile

environment, also called as jacket

Fiber Optical Cable with multi-tubes




Important point related to Fiber Optical cables :-

• It consists of thin strands of glass or glass like material that carry light from a source at one end to a detector at the other end

• Light sources used are either LEDs (Light Emitting Diodes) or LDs (Laser Diodes) • Data transmitted is modulated onto light using frequency modulation techniques • Bandwidth is very high, for LEDs is 20 to 150 Mbps and for LDs even higher

Comparison table for Guided Media

Cable Type Cable Sub Type

Maximum Segment Length

Bandwidth Supported Installation Cost Interference

Twisted Pair UTP 100 meters 100 Mbps Easy Cheapest High STP 100 meters 500 Mbps Moderate Moderate Moderate

Coaxial Thinnet 185 meters 10 Mbps Easy Cheap Moderate Thicknet 500 meters 10 Mbps Hard Moderate Low

Fiber Optic Multi node 2 Kms 100 Mbps Very hard Expensive None Single node 100 Kms 2 Gbps Very hard Expensive None

Micro Wave How it works :-

• Microwave Signals are used to transmit data instead of cable which are similar to radio and television signals and are used for long distance communications

• Microwave transmission consists of transmitter, receiver and the atmosphere. • This transmission is also known as Line-of-Sight transmission. The Transmit station must be in visible

contact with the receive station. • Parabolic antennas are mounted on towers to send a beam to other antenna far away. • The higher the tower, higher is the range. With 100 meter high tower a distance of 100 Km is feasible.

Advantages :- 1. Can be used for broadband transmissions where many

channels are handled in parallel 2. Guarantee Secure Transmission: cannot tap into cable. 3. Noise, Radio-Frequency, Electrical and Magnetic

Immunity 4. Longer distances than copper wire 5. Smaller and lighter than copper wire 6. Faster transmission rate

Disadvantages :- 1. Difficult to install 2. Connecting two fibers or a fiber to a light

source is a difficult process 3. Light can reach the receiver out of phase 4. Difficult to solder and slice 5. Limited physical arc of cable. Bend it too

much & it will break! 6. Expensive than all cables 7. Connection losses are common problem

Advantages :- 1. Cheaper than the cabling system 2. Ability to communicate over oceans 3. Low cost land purchase: each tower occupies

small area. 4. They can carry high quantities of information due

to their high operating frequencies. 5. High frequency/short wavelength signals require

small antenna.

Disadvantages :- 1. Insure communication 2. Susceptible to weather effects (like rain, snow

and fog) and other objects like birds etc. 3. Reflected from flat surfaces like water and metal 4. Refracted by atmosphere, thus causing beam to

be projected away from receiver. 5. The code of design, implementation and

maintenance is high




Radio Wave also known as RF (Radio Frequency) Propagation

How it works :- • Uses Radio Frequency which uses continuous sine waves for transmission • Radio wave transmission consists of transmitter, receiver • The transmitter encodes message onto sine wave and transmits it with radio wave which is decoded by the

receiver at other end • Antennas are used to radiate and capture the signals

Types of RF (Radio Frequency) Propagation:-

Advantages :-

1. Radio wave transmission offers mobility 2. Cheaper than the cabling system 3. Low cost land purchase: each tower occupies small area. 4. It offers ease of communication

Disadvantages :- 1. Radio wave communication is an insecure communication 2. Susceptible to weather effects (like rain, snow and fog) and other objects like birds etc.

Satellite Satellites are transponders that are set in a geostationary orbit directly over the equator.

How it works :- • The earth station consists of a satellite dish that functions as an antenna and communication equipment to

transmit and receive data from the satellite passing overhead. • The satellite has transponders -- a unit that receives data signals transmitted from earth station, amplify them,

and retransmits on another earth station.

Advantages :-

1. The area coverage through satellite transmission is very large 2. The laying and maintenance of intercontinental cable is difficult and expensive. 3. The heavy usage of intercontinental traffic makes the satellite commercial attractive 4. Satellite can cover large areas on Earth

Disadvantages :- 1. Technological limitations preventing the development of large, high gain antennas on the satellite platform 2. Over crowding of available bandwidths due to low antenna gains 3. The high investment cost and insurance cost associated with probability of failure 4. High atmospheric losses

Ground Wave Ionosphere Line-of-Sight




Infrared Infrared transmission is usually limited to a small area, e.g. one room, with the transmitter pointed towards the receiver. The hardware is inexpensive and does not require an antenna. Infrared light is used to send data. Example TV remotes, wireless speakers etc. Laser The laser transmission requires direct line-of-sight. It is unidirectional like microwave, but has higher speed than microwave. The laser transmission requires the use of a laser transmitter and a photosensitive receiver at each end. The laser transmission is point-to-point transmission between buildings.

Data Communication Technologies

Data Channel A channel is a medium used to carry information or data from one point to another BAUD It is a unit of measurement for the information carrying capacity of a communication channel

Baud Rate It is the measure of the modulation rate, the number of discrete signalling events per second – not of the data transfer rate.

Data Transfer Rates

The data transfer rate represents the amount of data transferred per second by a communication channel or a computing or a storage device.

BandWidth It is the width of the range of frequencies that an electronic signal uses on a given transmission medium

Bus One or more conductors that serves as a common connection for related group of devices

Datagram A packet switching service in which a packet carries information for routing from source to destination without establishing a connection between them and the network is known as datagram.

Internetworking The communication of devices among multiple networks is called as internetworking.

Hertz Frequency is measured in cycles per second known as Hertz. (KHz – KiloHertz, MHz – MegeHertz, GHz – GigaHertz, THz – TeraHertz)

Connectionless Data Transmission

A protocol for exchanging data in an unplanned fashion or without prior coordination is known as Connectionless Data Transmission

Connection Oriented Data Transmission

A protocol for exchanging data in which a logical connection is established between end points is known as Connection Oriented Data Transmission

Virtual Circuits A packet switching service in which a connection is established between two stations at the start of transmission, all the packets follows the same route, they need not to carry the complete address asnd arrive in sequence.

Transmission Medium The physical path between the transmitters and the receivers in a communication system

Serial Transmission In serial transmission, each unit of data being transferred travels in sequence

Parallel Transmission

In parallel data transmission the transmission of character of a word is transmitted over different lines and usually simultaneously.

Synchronous Transmission

In Synchronous Transmission, data bytes are send one after the other at regular intervals. The data forms a continuous stream of bits spaced at equal intervals, with no space between consecutive bytes.

Asynchronous Transmission

In Asynchronous Transmission each character is transmitted separately, that is one character at a time. Each character is preceded by a start bit, which tells the receiving device where the character coding begins and is followed by a stop bit, which tells the receiving device where the character coding ends.

bps : bits per second Bps : Bytes per second kbps : kilo bits per second Kbps : Kilo Bytes per second mbps : million bits per second Mbps : Million Bytes per second

TYPES OF NETWORKS

The three basic types of networks include: LAN, MAN and WAN.

LOCAL AREA NETWORK (LAN) Developed in 1970s A LAN is a group of computers and network devices connected together, usually within the same building.




Characteristics of LAN :- • Size : LAN’s are restricted in size, typically connects computer in a single building or campus (Inter-

processor distance can span from 10 m to 1 Km) • Medium : optical fibers, coaxial cables, twisted pair, wireless. • Data rates : High speed networks (0.2 to 100 mbps), speeds adequate for most distributed systems • Error rates : very less errors • Problems : Multi media based applications • Topologies : Typically used in bus or ring topologies

LAN configuration consists of:- • A file server - stores all of the software that controls the network, as well as the software that can be shared by

the computers attached to the network. • Workstations - computers connected to the file server (Mac or PCs). These are less powerful than the file server • Cables - used to connect the network interface cards in each computer. • Peripherals – such as scanner, speaker and printer connected to LAN and can be used by any workstation.

METROPOLITAN AREA NETWORK (MAN) Developed in 1980s Metropolitan Area Network (MAN) covers larger geographic areas, such as cities. Often used by local libraries and government agencies often to connect to citizens and private industries. Cable TV is best suitable example of MAN.

Characteristics of MAN :- • Size : Generally covers towns and cities (50 kms) • Medium : optical fibers, cables. • Data rates : adequate for distributed computing applications, A typical standard is DQDB (Distributed Queue

Dual Bus) • Message routing is fast.

WIDE AREA NETWORK (WAN) Developed in 1960s Wide Area Networks (WANs) connect larger geographic areas, such as London, the UK, or the world. In this type of network dedicated transoceanic cabling or satellite uplinks may be used. Example :- Internet

Characteristics of WAN :- • Size : Generally covers large distances (states, countries, continents). • Medium : communication circuits connected by routers. • Store-and-Forward technique : Routers forwards packets from one to another following a route from the

sender to the receiver. Hosts are typically connected (or close to) the routers. • Problems : delays if using satellites. • Data rates : 20 - 2000 Kbits/s (approx 1mbps) • Error rates : 1000 times than of LAN’s error rate • Not suitable for distributed computing.

Workstations

Cables

File

Scanner

Printer




TYPES OF TOPOLOGY Topology : The pattern of interconnection of nodes in a network is called as topology. Point-to-Point Link : In a P-P network each station receives exactly from one transmitter, and each transmitter transmits to exactly one receiver. Topology Factors : There a number of factors that helps in deciding the topology, they are:- Cost -- The network installation cost should be minimized Flexibility -- Topology should provide easy reconfiguration of the network. Reliability -- Topology should help the location of the fault to be detected and means of isolating it Bus or Linear Topology

Characteristics of Bus Topology :- • Bus networks use a common backbone to connect all devices. A single cable (the backbone) functions as a shared

communication medium that devices attach or tap into with an interface T-connector. • The transmission form any station travels the length of the bus, in both direction, and can be received by all stations • The bus has terminators at both the ends which absorbers the signal, removing it from the bus. • Data is transmitted in small blocks known as data packets.

Advantages of Bus Topology :-

1. Easy to implement and extend 2. Well suited for temporary or small networks not requiring high speeds (quick setup) 3. Cheaper than other topologies, i.e. cost effective as only a single cable is used. 4. Short cable length and simple wiring layouts

Disadvantages of Bus Topology :- 1. Limited cable length and number of stations. 2. If there is a problem with the cable, the entire network goes down. 3. Maintenance costs may be higher in the long run. 4. Proper termination is required (loop must be in closed path). 5. It works best with limited number of nodes; heavy network traffic can slow a bus. 6. It is slower than the other topologies. 7. It is difficult to troubleshoot the bus, i.e. fault diagnosis and isolation is difficult.

Star Topology

Characteristics of Star Topology :- • Each node (file server, workstations, and peripherals) connected directly to a central network hub or

concentrator. • Data on a star network passes through the hub or concentrator before continuing to its destination. • The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the

data flow. • Twisted pair cable, coaxial cable or fiber optic cable can also be used.

Advantages of Star Topology :- 1. Better performance: Passing of Data Packet through unnecessary nodes is prevented. 2. Isolation of devices: Each device is inherently isolated by the link that connects it to the hub, thus any non-

centralized failure does not affect the network. 3. Benefits from centralization: The central nature allows the inspection of traffic through the network. Also

faults are easily detected and isolated by disconnecting the failure node from the system.

Terminator

T-Connector




4. Simplicity: The topology is easy to understand, establish, and navigate. Also it has Simple Access Protocols 5. Easy of Service: It is easy to reconfigure the network.

Tree Topology

Ring Topology

Disadvantages of Star Topology :- 1. Central Node Dependency: High dependence of the system

on the functioning of the central hub. The failure of the central hub renders the network inoperable, immediately isolating all nodes.

2. Difficult to Expand: The addition of a new node involves a connection all the way to central hub. Wiring up of the system can be very complex.

3. Long cable length: It is expensive because all network cables must be pulled to one central point, requires more cables, congestion in cable ducts.

4. Network size is limited by the number of connections that can be made to the hub.

Workstations

File Server

Terminator

T-Connectors

Characteristics of Tree Topology :- • This is a combination of linear bus and star

topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. This topology is also known as hybrid topology.

• This bus/star hybrid approach supports future expandability of the network much better than a bus or a star alone.

• There is no need to remove the packet from the medium because when a signal reaches the end of the medium, it is absorbed by the terminators.

Advantages of Tree Topology :- 5. Point-to-point wiring for individual segments. 6. Supported by several hardware and software

venders.

Disadvantages of Tree Topology :- 1. Overall length of each segment is limited by the type

of cabling used. 2. If the backbone line breaks, the entire segment goes

down. 3. More difficult to configure and wire than other

topologies.

A

B

C

D

Characteristics of Ring Topology :- • In this each computer is connected to the next computer with

the last one connected to the first. • Each node retransmits the data it receives from the previous

computer, after passing the data through each node, it returns to the sender node, which removes it.

• The message flows around the ring in one direction. • The ring network does not subject to signal loss problem as a

bus network experiences. • There is no termination because there is no end to the ring.




Advantages of Ring Topology :- 1. Very orderly network where every device has access to the token and the opportunity to transmit, that is each

node has equal access. 2. Performs better than a star topology under heavy network load as it is capable of high speed data transfer 3. Can create much larger network using Token Ring 4. Does not require network server to manage the connectivity between the computers 5. Short Cable Length : Amount of cable used is less than other topologies 6. Suitable for Optical Fibers as data travels in one direction only.

Disadvantages of Ring Topology :- 1. One malfunctioning workstation or node failure can create problems or failure of the entire network 2. Network Reconfiguration is difficult, that is Moves, adds and changes of devices can affect the network 3. Network adapter cards and MAU's are much more expensive than Ethernet cards and hubs 4. Difficult to diagnose faults in the network

Mesh Topology

Characteristics of Mesh Topology :- • Each node is connected to more than one node to provide an alternative route in the case the host is either

down or too busy. • It is an extension to P-P network

Advantages of Mesh Topology :- 1. It is excellent for long distance networking because it provides extensive backup, rerouting and pass through

capabilities 2. Communication is possible between any two nodes, either directly or by passing through 3. this topology is ideal for distributed networks

Types of Mesh Topology :- 1. Fully connected : The type of network topology in which each of the nodes of the network is connected

to each of the other nodes in the network with a point-to-point link – this makes it possible for data to be simultaneously transmitted from any single node to all of the other nodes.

Disadvantages of Fully connected : The physical fully connected mesh topology is generally too costly and complex for practical networks, although the topology is used when there are only a small number of nodes to be interconnected.

2. Partially connected : The type of network topology in which some of the nodes of the network are connected to more than one other node in the network with a point-to-point link – this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network.

Disadvantages of Fully connected : In most practical networks that are based upon the physical partially connected mesh topology, all of the data that is transmitted between nodes in the network takes the shortest path between nodes, except in the case of a failure or break in one of the links, in which case the data takes an alternate path to the destination. This makes that node over busy and also requires that the nodes of the network possess some type of logical 'routing' algorithm to determine the correct path to use at any particular time.

Graph Topology

Characteristics of Graph Topology :- • In this nodes are connected together in an arbitrary fashion • It is not necessary that all the nodes are connected • If a path is established in two nodes via one or more links,

it is called a connected graph



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Network Devices Modem Modem is a computer peripheral that allows you to connect and communicate with other computer via telephone lines

Characteristics :- Modem converts digital signals to A/F (Audio Frequency) tones which are in the frequency range that the telephone lines can transmit and also it can convert transmitted tones back to digital information.

Digital Data :- The data that consists of a sequence of discrete elements is called as digital data. The signals can be either high or low there is no intermediate form. Computer generated signals are digital signals.

Analog Data :- Data represented by a physical quantity that is considered to be continuous variable or whose magnitude is made directly proportional to data or to a suitable function of data is known as analog data

Modulation :- The technique which converts digital signals to analog form is known as modulation. Three types of modulation techniques are used : AM (Amplitude Modulation), FM (Frequency Modulation), PM (Phase Modulation)

Demodulation :- The technique which converts analog signals to digital form is known as demodulation

BaseBand :- Transmission of signals without modulation is known as baseband

BroadBand :- The data signals are passed through a modem and transmitted over one of the frequency bands of the cable, this transmission technique is called as broadband.

Types of Modems :- Modem comes in two varieties --- 1. Internal Modem -- Modem that are fixed inside within the computers 2. External Modem -- Modem that are connected externally to a computer as other peripherals are connected

RJ-45 Registered Jack – 45 RJ – 45 is an eight wire connector, which is commonly used to connect computers on the LAN especially Ethernets. 3

Ethernet :- Ethernet is an LAN architecture that uses either a Bus or a Star topology and supports data transfer rates of upto 10 Mbps. It uses an Ethernet card that contains connections for either coaxial or twisted pair cables (or both). If it is designed for coaxial cables, it will have a BNC connection and if it is designed for twisted pair, it will have a RJ-45 connection.

Side View of Ethernet NIC HUBS Hub is a hardware device used to connect several computers together. Hub basically acts as signal splitter, it accepts signal through its input port and outputs it to the output ports. A concentrator is a device that provides a central connection point for cables from workstations, servers and peripherals.

Types of HUB :- There are three main types of hubs ---- 1. Passive Hubs :

• Passive hubs allow the signal to pass from one computer to another without any change. • These types of hubs do not help in rectifying/enhancing the signals they pass on in the network. • It is very hard to get any help from the passive hubs while troubleshooting in case if there is any fault in

the hardware or the network.

RJ-45

BNC

AUI

BNC port




2. Active Hubs : • Active hub stores the input signals received from input port for sometime, electrically amplifies the

signals and forwards it. • Some active hubs come with a feature that helps in transmitting data that has high priority before the data

that has lower priority. • Some active hubs help in synchronizing data communication by retransmitting the packets, which are not

properly received at the receiving computer. • Active hubs also help in troubleshooting at certain level.

3. Intelligent Hubs : • An intelligent hub provides all the features of a passive and an active hub; it also provides some features,

which help in managing the network resources effectively and efficiently. • An intelligent hub itself finds out the problem in the network, diagnoses it and tries to rectify it without

letting the problem hamper the performance of the network. • Intelligent hub can decide which packet goes in which output line, this helps in controlling and

minimizing data traffic in the network, which results in improved performance of the network/LAN. • An intelligent hub also adopts the changes in the network very easily and it also supports different

technologies without need of changing anything in configuration. SWITCH

• Switch is a device that is used to segment networks into different subnetworks called as subnets or LAN segments.

• Segmenting the network into small subnets prevents traffic overloading in the network. • A switch is responsible for filtering (transferring data in a specific way) and for forwarding packets between

LAN segments. • LANs that are segmented by a switch are called as switched LANs

REPEATERS • Repeater boost signal strength that weakens along a cable during long distance transmission from one point to

another by electrically amplifying the signal it receives and rebroadcasts it. • They are used when the total length of your network cable exceeds the standards set for the type of cable

being used.

Types of Repeaters :- 1. Amplifier --- It merely amplifies all incoming signals over the network, that is it amplifies both the signals

and any concurrent noise. 2. Signal Repeater --- It collects the inbound packet and then retransmits the packet as if it were strrting from

the source station. BRIDGES

• A bridge is a network device that establishes an intelligent connection between two local networks with different type of cables.

• Bridge knows which computers are on which side of the bridge, so they only allow those messages that need to get to the other side to cross the bridge.

• A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments.

Subnets




ROUTERS

• A router is a network device that is used to separate different segments in a network to improve performance and reliability.

• For Internet connection a router is used as a translator.

Routers can :-

GATEWAY

• A gateway is a network device that connects dissimilar networks. It establishes an intelligent connection between a local network and external networks with completely different structure.

• It operates at the highest layer of network abstraction • A gateway node often acts as a proxy server and a firewall (a barrier that protects your network from

uninvited intruders, unauthorized users, and hackers).

LAN Design

Good Network Design : The 80 – 20 Rule

80 percent of the traffic on a given network segment is local (designed for the target in the same workgroup) and not more than 20 percent of the network traffic should need to move across the backbone ( the spine that connects various segments or subnetworks). LAN Hardware

Hardware Symbols Used

Repeaters

Hubs

Bridges

Switches

Routers

When to use Hub / Bridge / Switch / Router

• Connection between two computers –– Install NIC card in both computers • If distance between computer increases –– Use Repeaters • If many computers are to be attached –– Use multi-port repeater called Hub (Problem – can

not filter the traffic)

o Direct signal traffic efficiently, i.e. it selects the best path to route a message, based on the destination address and origin.

o Route messages between any two protocols, i.e. it can handle different protocols.

o Route messages between linear bus, star, and star-wired ring

o Route messages across fiber optic, coaxial, and twisted-pair cabling

Internet LAN 1

LAN 2

LAN 3

Using Repeaters :-One basic rule of using repeaters is 5–4–3 Rule. The maximum path between two stations on the network should not be more than 5 segments with 4 repeaters between those segments and no more than 3 populated segments.

Using Bridge :- Bridge implements the Spanning Tree Protocol to build a loop free network topology. This means that on a network, one or more bridges may be blocked if they are forming a loop.



http://fcit.usf.edu/Network/glossary.htm#linear_bus

http://fcit.usf.edu/Network/glossary.htm#star

http://fcit.usf.edu/Network/glossary.htm#star_wired_ring

http://fcit.usf.edu/Network/glossary.htm#fiber

http://fcit.usf.edu/Network/glossary.htm#coaxial

http://fcit.usf.edu/Network/glossary.htm#twisted


• If want to filter the traffic also –– Use smart Hub called Bridge (filter traffic based on MAC address)

• If want to replace multiple bridges –– Use multi-port bridge called Switch (Provides – dedicated bandwidth , Problem – can not stop traffic destined for different LAN segment from traveling to all other LANs)

• If want to stop traffic from flowing to –– Use Router (filters network traffic based on IP address) other unwanted LAN segments

When to replace Hubs with Switches

1. when number of nodes on the network grows 2. if utilization is over 40 percent on Ethernet networks 3. OR if utilization is above 70 percent on Token Ring or FDDI networks

Network component checklist

For Building a small LAN For connecting offices and departments For connecting Dispersed office sites • Clients computers with NICs

installed • Seervers • Hub • Cabling • Networking Operating System

software

• Clients computers with NICs installed • Seervers • Hub • Switches • Cabling • Networking OS software • Routers for shared Internet access

(optional)

• Clients computers with NICs installed • Seervers • Hub • Switches • Routers at each location for WAN

connections / shared Internet access • Access server for dialup access for remote

users • Cabling • WAN service (ISDN / Leased line etc.) • Network OS Software

Network Component Chart

Transmission Speed of Cables




Case Study Computer Network Problem (Very Imp 4 marks question always comes in board exams) “Kanganalay Cosmetics” is planning to start their offices in four major cities in Uttar Pradesh to provide cosmetic product support in its retail fields. The company has planned to set up their offices in Lucknow at three different locations and have named them as “Head office”, “Sales office”, & “Prod office”. The company’s regional offices are located at Varanasi, Kanpur & Saharanpur. A rough layout of the same is as follows :

Answer the following questions :-

1. Suggest the cable layouts (topologies) to connect the all the Lucknow offices and effective methodology to connect the rest of offices at UP.

2. Name the branch where the server should be installed. Justify your answer. 3. Suggest the device to be procured by the company for connecting all the computers within each of its offices, and out of

the following devices : a) Hubs b) Routers c) Switches

4. The company is planning to link its head office situated in Lucknow with the office at Saharanpur. Suggest an economic way to connect it; the company is ready to compromise on the speed of connectivity. Justify your answer.

Answers :-

1. The cable layouts are :- Star topology at the Lucknow offices and an Intranet connection among rest of offices at UP.

2. The branch where the server should be installed is the Head office, because the number of computers are more that the other offices

3. The routers are placed between the Head office to Kanpur office, Kanpur office to Saharanpur office, and Saharanpur office to Varanasi office (because Intranet connection is used). The switches are placed at the Varanasi, Saharanpur, Lucknow, Prod and Head offices (because number of computers in these offices is large). The hub is placed at sales office (because number of computers in this office is small).

4. An economic way of connecting is Dial-Up or Broadband as it connects two computers at an economic rate though it provides lesser speed than other expensive methods.

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Approximate distances between these offices is as follows : Place from Place to Distance Head office Sales office 15 KM Head office Prod office 8 KM Head office Varanasi Office 295 KM Head office Kanpur Office 195 KM Head office Saharanpur office 408 KM

Number of computers :

Head office 156 Sales office 25 Prod office 56

Varanasi Office 85 Kanpur Office 77

Saharanpur office 65



FRP Chapter 14 Communication and Computer …...Notes By Shivali Jaggi 1 Chapter 14 Communication and Computer Networks Network It is an interconnected collection of autonomous computers

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