[PDF] UNIT 1: Introduction to Computer Networks - Aligarh Muslim University

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UNIT 1: Introduction to Computer Networks

Computer Engineering Section

University Women's Polytechnic

Aligarh Muslim University, Aligarh

February 22, 2020

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 1/113

Outline

Computer Networks: What and Why??

Applications of Computer Networks

Types of Network Connections

Categories of Networks: LAN, MAN & WAN

Network Topologies

Network Congurations: Server Based, Peer-to-Peer & Hybrid

Expanding Networks

Network Segmentation

Types of Servers

Network Performance Parameters: Bandwidth, Throughput,

Latency, Jitter etc.

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 2/113

Computer Network & Networking

A

Computer Net work

is a set of autonomous comput- ers and other devices connected together to exchange infromation and sharing resources.By autonomous we mean that no computer on the net- work can be forcibly start/stop by any other computer on the network.Another denition is - A group of computers and other devices connected together is called a network and the concept of connected computers sharing information and resources, is called

Net working

.Each device on the network is referred to asno de. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 3/113

Centralized Computing Vs. NetworkingI

In centralized computing there is a computer with single powerful CPU and a number of terminals are connected to it as shown in the gure on slide 6.All processing is performed within the boundaries of the same physical computer.User terminals are typically dumb ones, incapable of functioning on their own. They are cabled to the central computer.Sometimes these terminals have very little processing power and memory of their own and are called intelli- gent terminals . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 4/113

Centralized Computing Vs. NetworkingI I

This architecture places the tremendous burden on the central computer.In recent years, there have been signicant advances in the development of high performance personal comput- ers and networks.There is now an identiable trend in industry towards downsizing, i.e. replacing expensive mainframe com- puters with more cost eective networks of personal computers that achieve the same or even better results. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 5/113 Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 6/113

Why Networks??

Networks are all about:Sharing Resources.

Preserving Information.

Protecting Information.

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Sharing ResourcesI

Resource sharing means sharing H/W and S/W.

Hardware Resource Sharing:

Networked Computers can share:Printers, Fax Modem, Scanners, Hard Disks, Floppy Disks, CD-ROMS, Tape Backup Units, Plotters, Any device that can be attached to the

Network.Software Resource Sharing:

Software resources can be used more eectively over networks. With stand alone computers the software used on the computers must be present on each computer's hard disk, whether or not that computer is

used at that moment for the task the software performs.For a large number of stand alone computers S/W cost can become

more than expectations. It is also dicult and time consuming to install and congure the S/W individually on each computer. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 8/113

Sharing ResourcesI I

With a network we can install and congure the software on one com- puter (server) and can share it with other computers on the network.

We can also control the access to that S/W.Not all S/W will use a network even if one is installed on the server. Dif-

ferent S/W packages have dierent restrictions on how the software can legally be used on a network. We must check the S/W documentation to check what features the S/W provides in a networked environment. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 9/113

Preserving Information

Besides, information and resource sharing a network al-

lows information to be backed up to a central location.Important information can be lost by mistake or acci-

dentally when a stand alone computer has no backup means.It is also dicult to maintain regular backups on a num- ber of stand alone computers.In a networked environment when we take backup at a central location from all computers, we have one place to preserve it. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 10/113

Protecting Information

With stand alone computer, access to the computer

means access to the information on that computer.Networks provide an additional layer of security by means

of passwords.We can give each network user a dierent account name and password, allowing the network server to distinguish among those who need access to have it and protecting the information from tampering by those who do not. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 11/113

Components of a Data Communication SystemI

There arefivecomp onentsof a data communication sys- tem:1Message:The message is the info rmation(data) to b e communicated. Popular forms of information include text, numbers, pictures, audio, and video.2Sender:A sender is a device that sends the data mes- sage. It can be a computer, workstation, telephone handset, video camera, and so on.3Receiver:A receiver is a device that receives the mes- sage. It can be a computer, workstation, telephone handset, television, and so on. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 12/113

Components of a Data Communication SystemI I

4Transmission Medium:The transmission medium is the

physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, ber-optic cable, and radio waves Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 13/113

Components of a Data Communication SystemI II

5Protocol:A p rotocolis a set of rules that g overndata

communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 14/113

Transmission ModesI

The term

T ransmissionMo de

denes the direction of the ow of information between two communicating devices i.e. it tells the direction of signal ow between the two devices. There are three ways or modes of data transmission: Sim-

plex, Half duplex (HDX) & Full duplex (FDX)1Simplex- unidirectional, one can transmit other can only receive,

uses entire capacity of channel to send data in one direction. Ex- amples of simplex mode is loudspeaker, television broadcasting, television and remote, keyboard and monitor etc. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 15/113

Transmission ModesI I

2Half Duplex- b othstation can transmit and r eceivebut not at

the same time, entire capacity of the channel can be used for each direction. Example of half duplex is a walkie- talkie in which message is sent one at a time and messages are sent in both the directions. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 16/113

Transmission ModesI II

3Full Duplex- b othstations can transmit and receive simultane-

ously, either separate channels or channel can be divided between signals traveling in both directions. 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. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 17/113

Classication of Computer Networks

There is no generally accepted taxonomy for computer net- works but two criteria based on which they can be classied are

T ransmissionT echnology

and

Scale

.Based on tramission technology they may be classied as:Broadcast/ Multipoint Networks

Point-to-Point Networks

Based on scale (physical limits) they can be classied as:Local Area Network (LAN)

Metropolitan Area Network (MAN)

Wide Area Network (WAN)

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Broadcast NetworksI

1Broadcast networks have a single communication channel that is

shared or used by all the machines on the network. Short messages

called packets sent by any machine are received by all the others.2Broadcast systems generally use a special code in the address eld

for addressing a packet to all the concerned computers. This mode of operation is called broadcasting.3Some broadcast systems also support transmission to a subset of

the machines known as multicasting.4Upon receiving a packet, a machine checks the address eld. If the

packet is addressed to it then the packet is processed, otherwise the packet is ignored.5The channel's capacity is shared temporarily among the devices connected to the link. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 19/113

Broadcast NetworksI I

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Point-to-Point NetworksI

1A point-to-point connection is a direct link between two devices

such as a computer and a printer. It uses dedicated link between the devices.2The entire capacity of the link is used for the transmission between those two devices.3In point to point networks, there exist many connections between individual pairs of machines.4To move from sources to destination, a packet (short message) may follow dierent routes.5In point-to-point connection, there can only be a single transmitter and a single receiver. On the other hand, in multipoint connection, there is a single transmitter, and there can be multiple receivers. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 21/113

Point-to-Point NetworksI I

6The switching nodes are not concerned with the contents of data.

Their purpose is to provide a switching facility that will move data from node to node until they reach the destination. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 22/113

Classicaton Based on ScaleI

Local Area Networks (LANs)A Local Area Network (LAN) is a network that is restricted to smaller physical areas (few kilometers - typically upto 5 kms) e.g.

a local oce, school, house, University campus etc.On a `Local Area Network' data transfer speeds are higher than

WAN & MAN, and that can range from 10.0 Mbps (Ethernet

network) to 10 Gbps (10 Gigabit Ethernet).A LANs is usually implemented using any of the LAN Technolo-

gies i.e. Ethernet, Token Ring and FDDI (Fiber Distributed Data Interface).LAN Technologies are also referred to asPhysical and Data Link

Layers Protocols

. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 23/113

Classicaton Based on ScaleI I

Local Area Networks (LANs)Each LAN technolgy oers specic devices (meant for that technol- ogy only) and network layouts (topologies) for connecting several computers as LAN.The most prevalent LAN Technology isEthernet . It is standardized as

IE EE802.3

.The most common forms of Ethernet are 10BASE-T, 100BASE-T, and 1000BASE-T. All three use twisted pair cables. They run at

10 Mbit/s, 100 Mbit/s, and 1 Gbit/s, respectively.Fiber optic variants of Ethernet are also very common in larger

networks, oering high performance and longer distance (tens of kilometers with some versions).Also referred to asWiFi , Wireless LANs (WLANs) are standardized as

IE EE802.11

. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 24/113

Classicaton Based on ScaleI II

Local Area Networks (LANs)In general, network protocol stack software will work similarly on all varieties.LANs are restricted in size. It simplies network management. They are more reliable as compared to MAN and WAN. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 25/113

Metropolitan Area Network (MAN)I

A Metropolitan Area Network (MAN) is a network that connects two or more computers, communicating devices or networks in a single network that has geographic area larger than that covered by even a large `Local Area Network' but smaller than the region covered by a `Wide Area Network' (Typically from more than 5 km to 160 km).A Metropolitan Area Networks bridges a number of `Local Area Networks' with a ber-optical links which act as a backbone, and provides services similar to what Internet Service Provider (ISP)

provide to Wide Area Networks and the Internet.MANs can bridge Local Area Networks without any cables by using

microwave, radio wireless communication or infra-red laser which transmits data wirelessly. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 26/113

Metropolitan Area Network (MAN)I I

Distributed Queue Dual Bus (DQDB)

is the Metrop olitanA rea

Network (MAN) IEEE 802.6 standard for data communication.Using DQDB, networks can extend up to 100km-160km and op-

erate at speeds of 44 to 155Mbps. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 27/113

Wide Area Network (WAN)I

Wide Area Network is a computer network that covers relatively

larger geographical area such as a state, province or country.It provides a solution to companies or organizations operating from

distant geographical locations who want to communicate with each other for sharing and managing central data or for general com- munication.WAN is made up of two or more Local Area Networks (LANs) or Metropolitan Area Networks (MANs) that are interconnected with each other.In `Wide Area Network', Computers are connected through public networks, such as the telephone systems, ber-optic cables, and satellite links or leased lines. The `Internet' is the largest WAN in the world. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 28/113

Wide Area Network (WAN)I I

WANs are mostly private and are build for a particular organization by `Internet Service Providers (ISPs)' which connects the LAN of the organization to the internet. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 29/113

Other Special Types of NetworksI

1Home Area Network(HAN):As the name w ouldsuggest, a HAN

is the connection of network enabled devices in a domestic home.2Personal Area Network(PAN): As the name suggests, a personal area network is intended for personal

use within a range of a few ten meters.Mainly, the technologies used for creating personal area networks are

wireless. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 30/113

Other Special Types of NetworksI I

A notable example of WPAN is the Bluetooth technology, mostly found

on portable devices like smartphones, laptops, tablets, wearables, etc.Other PAN technologies are Zigbee, Wireless USB, etc.

Wireless BAN can work together with PAN technologies. For instance, a Bluetooth-connected smartphone can be used to sync data from wearables and various sensors present in the body.3Body Area Network(BAN): You can create a body area network by using wearable devices like smart- watches, tness bands, biometric RFID implants, and medical devices

placed inside the body like pacemakers.Wireless BAN is the primary form used to created such networks. It is

dened as per the IEEE 802.15.6 standard which describes a short-range, extremely low power wireless communication within or in a vicinity of the human body. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 31/113

Other Special Types of NetworksI II

4Near-me Area Network(NAN):

A near-me area network (NAN) is a communication network that focuses

on wireless communication among devices in close proximity.Unlike local area networks (LANs), where the devices are in the same

network segment and share the same broadcast domain.The devices in a NAN can belong to dierent proprietary network infras-

tructures (for example, dierent mobile carriers).If two devices are geographically close, the communication path between

them might, in fact, traverse a long distance, going from a LAN, through

the Internet, and to another LAN.Remember chatting with your friends on Facebook while all of you were

sitting in the same room. You were part of a NAN, even though you

might be on the networks of dierent carriers.A message from your device would traverse all the way to Facebook

servers over the internet come to your friend's device sitting right next to you. In a logical way, both the device are on some sort of network. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 32/113

Other Special Types of NetworksIV

5Storage Area Network(SAN):

SAN is a high-speed network of storage devices that also connects those

storage devices with servers.It provides block-level storage that can be accessed by the applications

running on any networked servers.Block-level storage is a type of storage in which each block (consisting

of several hard drives) of the storage system can be controlled as an individual hard drive, and the blocks are managed by a server operating system.SAN devices appear to servers as attached drives Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 33/113

Other Special Types of NetworksV

6Campus Area Network(CAN):

A network infrastructure covering the school, university, or a corporate

premises can be dubbed as campus area network.It can comprise of several LANs and connected to the internet using a

leased line or any other means. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 34/113

Other Special Types of NetworksVI

7Virtual Private Network(VPN):

A virtual private network (VPN) is a private network that is built over a public infrastructure.VPN is a type of computer network which doesn't have physical exis- tence.The devices that are part of a VPN could be present anywhere on the

earth, connected to each other over the internet.Security mechanisms, such as encryption, allow VPN users to securely

access a network from dierent locations via the Internet.VPNs are used by corporates to interconnect their oces located in

dierent places and give their remote employees access to company's resources.It has phased out another type of network known as Enterprise Private Network, a physical network created by organizations to link their oce locations. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 35/113

Network (LAN) TopologiesI

A network topology is the arrangement of a network, including its nodes and connecting lines.There are two ways of dening network geometry: thephysical topology and the logical (o rsignal) top ology .On a network the way in which connections are made is called the physical topology of the net work.Physical topology specicaly refers to the physical layout of the network, especially the locations of the computers & devices and how cable is run between them (Geographical arrangement of com- puters, devices and cables.).Logical (or signal) topologyrefers to the nature of the paths the signals follow from node to node. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 36/113

Network (LAN) TopologiesI I

In many instances, the logical topology is the same as the physical topology.But this is not always the case. For example, some networks (e.g. Hub based star and Token Ring) are physically laid out in a star conguration, but they operate logically as bus or ring networks. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 37/113

Physical Network (LAN) TopologiesI

1Bus Topology

On a bus network, the cable is just one or more wires, with no active electronics to amplify the signals or to pass them from one computer to

another.This makes the bus apassive topology.When one computer sends a signal up (or down) the wire, all the other

computers on the network receives the information.But, only one (the one with the address that matches the address en-

coded in the message) accepts the information. The rest discard the message.Only one computer at a time can send the message. Therefore, the number of computers attached to a bus can signicantly aect the speed of the network.A computer must wait until the bus is free before it can transmit.

These factors also aect star and ring networks.

Another important issue in bus network istermination.Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 38/113

Physical Network (LAN) TopologiesI I

As the bus is a passive topology, the electrical signal from a transmitting

computer is free to travel the entire length of the cable.Without termination, when the signal reaches at the end of the wire, it

bounces back and travels back up the wire.When a signal echoes back and forth along an unterminated bus, it is

calledringing.To stop signals from ringing we attach terminators at either end of the

bus. Terminators absorb the signals and stop ringing.Ethernet 10Base2(uses BNC T-Connecto rswith coaxial cable), also

referred to as thinnet

is an inexp ensivenet workbased on bus top ology.Ethernet 10Base5also referred to as thicknet is another n etworkbased

on bus topology. It uses thick coaxial cable compared to one used in thinnet. AdvantagesSimple, Reliable for small networks, Easy to use and install. Requires least amount of cable and therefore less expensive. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 39/113

Physical Network (LAN) TopologiesI II

Scalable: Its easy to extend a bus.

Repeaters can be used to boost the signals if a larger bus is required. DisadvantagesHeavy network trac can slow down a bus considerably.

Problems caused by terminators.

Dicult to troubleshoot.

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Physical Network (LAN) TopologiesIV

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Physical Network (LAN) TopologiesV

2Star Topology

Each computer on a star network communicates with a central device. The central device resends the message to all computers (in a broad- cast star network(hub based)) or only to the destination computer (in a switched star network).The central device in a star network can be anActive Hubor aPassive Hubor aSwitch.An active hubregenerates the electrical signal and sends it to all the

computers connected to it (broadcast star network).Active Hubs and Switches require electric power to run.

A passive hub such as wiring panel or punch-down blocks merely acts as a connection point and doesn't amplify or regenerates the electrical signal.Passive Hubs don't require electric power to run.

We can use

STP(Shielded Twisted P air),UTP (Unshilded Twisted P air) or

F iberOptic

cables to implement sta rnet works. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 42/113

Physical Network (LAN) TopologiesVI

A hyb ridhub/ switch can accomo dateseveral t ypesof cable in the same star network.Ethernet 10Base-T, 100Base-T (Fast Enternet), 1000Base-T (Gigabit

Ethernet) and 10000Base-T (10 G Ethernet)

a rew ellkno wnsta rnet-

works implemented with twisted pair cables (STP/UTP).In above star based ethernets, if medium (twisted pair cable) is replaced

by Fiber Optics then 'T' gets replaced by 'F' (e.g. 10Base-F etc.). AdvantagesIt is easy to modify and add new computers to a star network without

disturbing the rest of the network.The centre of the star is a good place to diagnose network faults.

Single computer failure do not bring down the whole star network. Several types of cable can be accomodated on same network. DisadvantagesIf central hub fails the whole network comes to halt.

Expensive compared to bus based networks.

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Physical Network (LAN) TopologiesVI I

Active Hub and Switch consume electricity.

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Physical Network (LAN) TopologiesVI II

3Ring Topology

On a ring network, each computer is connected to the next computer

with the last one connected to the rst.Each computer retransmits what it receives from the previous computer.

The messages

ow around the ring in one direction. Since each computer retransmits what it receives, a ring is anactive

networkand is not subject to the signal loss problem.There is no termination because there is no end to the ring.

Some ring networks dotoken passing.In token passing, a short message calledtokenis passed around the ring

until a computer whishes to send information to another computer. That computer captures the token modies it to adds an electronic address

and data, and sends it around the ring.Each computer in sequence receives the modied token and passes it to

the next computer until either the electronic address matches the address of a computer or the token returns to its origin. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 45/113

Physical Network (LAN) TopologiesIX

The receiving computer sends an acknowledgement to the originator

indicating that the message has been received.The sending computer then creates a fresh token and place it on the

network, allowing other computer to capture the token and begin trans- mitting.This all happens very quickly. A token can circle a ring 200 meters in diameter at about 10,000 times a second. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 46/113

Physical Network (LAN) TopologiesX

The topology of

IBM's T okenRing

LAN tec hnology(standa rdizedas

IEEE 802.5

) uses the similar kind of ring.Physical topology of token ring is star but logically it is a token passing

ring.Some other ring networks havet wocounter-rotating rings , that help

them recover from network faults.The topology ofFDDI (Fib erDistributed Data Interface) LAN technol-

ogy uses two counter-rotating rings. AdvantagesNo computer can monopolize the network as each computer is given

equal chance of capturing the token.Token passing makes ring topology perform better than bus topology

under heavy trac. DisadvantagesFailure of one computer on the ring can aect the whole network.

Dicult to trobuleshoot.

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Physical Network (LAN) TopologiesXI

Adding or removing computers disrupts the network.

4Mesh Topology

In a mesh network topology, each of the network node, computer and

other devices, are interconnected with one another.In a full mesh topology, every computer in the network has a connection

to each of the other computers in that network.The number of connections in this network can be calculated using the

formulan(n1)=2, wherenindicates the number of devices.Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 48/113

Physical Network (LAN) TopologiesXI I

This type of topology is very expensive as there are many redundant connections, thus it is not mostly used in computer networks. AdvantagesCan handle high amounts of trac, because multiple devices can trans- mit data simultaneously.A failure of one device does not cause a break in the network or trans-

mission of data (fault tolerant).Adding additional devices does not disrupt data transmission between

other devices.Easy to troubleshoot. DisadvantagesThe cost to implement is higher than other network topologies, making it a less desirable option.Building and maintaining the topology is dicult and time consuming. Becomes unmanagable as more and more devices join network. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 49/113

Hybrid TopologiesI

In today's networks we also see the

combinations of the topologies of bus, star and ring.A topology which is created by combining two or more topologies is referred to as ahybrid topol- ogy.Some popular hybrid topologies aresta r-bus& star-ring .Figure on next page illustrates each of them. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 50/113

Hybrid TopologiesI I

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Picking a Right Topology (Ethernet LANs)

You must look at following:Cost.

Scalability / Extendibility.

Ease of installation.

Bandwidth Capacity.

Ease of fault isolation/tolerance/Maintenance.

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Roles of a Computer on a NetworkI

A Computer can have one of the following three roles to play on a network:Client:A Computer which uses but don't p rovideNet workingResources. They are also known as nodes or workstations (only when they run UNIX or its avour)Server:A computer which p rovidesnet workresources. Peer: A computer which p rovidesas w ellas u sesresources. Can the role of a computer on a network be determined

by looking at the operating system it is using?:Clients run client operating system such as MS-DOS, OS/2 etc.

Peers run peer operating system such as Win 95/ Win 98/ Win NT workstation/ Win 2000 Professional/ Win XP (Professional and Home

Editions)/ Win Vista/7/8/10 (Home & Professional Editions) etc.Servers run Network Operating Systems such as Unix/ Linux/ HP-UX/

AIX/ Novell Netware/ Solaries/ Win NT/ Win 2000 Server/ Win 2000 Advanced Server/ Win 2000 Data Centre Server or higher versions. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 53/113

Roles of a Computer on a NetworkI I

Note that

simply lo okingat the op eratingsystem w e can't decide whether a computer on a Network is a client or a peer or a server as almost all server operating systems can also be used as client OS .So, a straight forward method to identify the role of a computer on a network is to look for its use on the network .Based on the roles of the computers attached to them networks can also be classied as:Server Based or Client/ Server Networks.

Peer-to-Peer Networks.

Hybrid Networks.

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Server Based NetworksI

Are identied by the presence of server(s) on the network. Server provides security and administration of the network. Client/ Server networks divide processing tasks between client and server.Clients (referred to as front ends) request services such as le storage and printing, and servers ( referred to as back ends ) deliver them.Server computers are typically more powerful than client comput-

ers. Their hardware is optimized to function as servers.Windows NT/ Server based networks are organized intodoma ins.

A domain is a logical grouping of network computers that share a central directo rydataba se . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 55/113

Server Based NetworksI I

A directory database contains user accounts and security informa- tion for the domain.In a domain the directory resides on the computers that are con- gured as domain controllers .A domain controller is a server that manages all security related user/ domain interactions and centralizes administration.

AdvantagesStrong central security.

Centralized storage and backup.

Ability to share resources.

Optimized dedicated server which are faster than peers when sharing resources. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 56/113

Server Based NetworksI II

Easy manageability of large number of users.

DisadvantagesExpensive dedicated servers.

Expensive Network Operating System and Client Licenses.

A dedicated network administrator.

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Server Based NetworksIV

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Peer NetworksI

There are no servers on a peer network.

Are dened by no central control over the network.

Users simply share resources.

Peer networks are organized into

w orkgroups . A workgroup is a logical grouping of networked computers that share resources (and strictly not the security information).Each Windows (server or client avour) computer in the workgroup maintains a local security database which contains a list of user

accounts and resource security information for that computer.As each computer in the workgroup maintains a local security

database, the administration of user accounts and resource se- curity is decentralized. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 59/113

Peer NetworksI I

A user must have a user account on each computer that the user needs to access.Any changes to the user account information such as changing a

password or adding new accounts must be made on each computer.As already discussed, access to individual resources can be con-

trolled if the user who shares the resource requires a password to access.Since there is no central security trust users will have to know the individual passwords for each resource they wish to access. This can be quite inconvenient.Peers are also not optimized to share resources. When a number of users are accessing the resources on a peer, they notice signicantly degraded performance. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 60/113

Peer NetworksI II

AdvantagesNo extra investment on server.

Easy Setup.

No network administrator required.

Ability of users to control the share of resources. Convenient for limited number of computers in close proximity. DisadvantagesAdditional load on computers because of resource sharing.

Inability of handling large networks.

Lack of central organization which can make data hard to nd. Requirement that users themselves administer the network.

Weak and insecure security.

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 61/113

Peer NetworksIV

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 62/113

Hybrid NetworksI

Hybrid computers have all types of computers operating on them

and generally have active domains and workgroups.It means that while most shared resources are located on servers,

users still have access to any resources being shared by the peers in their workgroup.It also means that network users don't have to logon to the domain

controller to access workgroup resources being shared by peers.If users log on to the network with proper username and password

they are eligible to enjoy \all shared" resources either they lie with

the domain controllers or with the peers.If users don't log on the network with proper username and pass-

word they are eligible to enjoy the resources contributed by the peers. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 63/113

Hybrid NetworksI I

AdvantagesAll advantages of Server based networks.

All advantages of Peer Networks.

DisadvantagesAll disadvantages of Server Based and Peer Networks. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 64/113

Hybrid NetworksI II

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 65/113

Expanding Networks: Principles & Devices

The objective is to expand a single network without breaking it intosub-networks.Following devices can be used for this purpose:

Repeater

.

Passive Hub

.

Active Hub

.

Switch

.

Bridge

.

Selection of device(s) strictly depends on a

va riety of factors.Hubs and Switches have alredy been discussed.

So, we will examine rest of the devices.

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 66/113

RepeatersI

All transmission media

attenuate (w eaken) the electronic signal that travel through them.Attenuation therefore limits the distance any medium can carry data.Adding a device thatampliesthe signal can allow it to travel

farther, increasing the size of the network.if we are connecting computers that are more than100/ 500 me-

ters apa rtusing a

10BASE-T/ 100BASE-T

Ethernet cable, w ewill

require a device that amlies signal to ensure data transmission.Devices that amplify signals in this way are calledRep eaters.

Two types of repeaters are there -

Ampliers

and

Signal-regenerato rs

(Boosters) .Amplierssimply amplify the entir eincoming signal including noise. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 67/113

RepeatersI I

Signal-regenerators (Boosters)

create an exact duplicate of incom- ing data by identifying it amid the noise, reconstructing it and

retransmitting only the desired information.They reduce noise. The signal is boosted to its original strength

and sent.Because repeaters simply deal with the actual physical signals on a network, they operate at

La yer1 (Physical La yer)

of

ISO-OSI

model.Theoretically, repeaters can be used to combine an unlimited num- ber of cable segments.Practically, network designs limit the number of repeaters. An active hub / switch/router is b yde faulta multip ortrep eater (signal-regenerator) . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 68/113

RepeatersI II

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 69/113

BridgesI

Bridges connect

net worksegments . Unlike a repeater, which simply passes all signals it receives, a bridge selectively determines t he app ropriatesegment to which it should pass a signal. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 70/113

BridgesI I

It does this by reading the

source and destination MA Caddresses of all the signals it receives.For the network shown in gure, the process takes place as follows:- The bridge receives all the signal from both segments A and B.

The bridge reads the destination address and

disca rds(lters) all s ignals from segment A that are addressed to computers on segment A, because

they do not need to crossover the bridge.Signals from segment A addressed to a computer on segment B are

retransmitted (regenerated) to segment B .The signals from segment B are treated in the same way. Bridges regenerate signals (physical layer activity) and read MAC addresses (data link layer addresses), so they are

La yer2

devices. In future we will learn that aswitch is actually a multip ort-port bridge . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 71/113

Assignment 2

Explain the following:

Bridge loop problem.

Spanning Tree Algorithm.

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 72/113

Network Segment

A net worksegment is a p ortionof a computer net work that is separated from the rest of the network by a device such as a repeater, hub, bridge, switch, router or gateway.Each segment can contain one or multiple computers or other hosts.The nature of a segment depends on the nature of the

device or devices used to interconnect end stations.Accrdingly, there may beLa yer1, La yer2 o rLa yer3

segments in a network. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 73/113

Collision & Broadcast DomainsI

Collision Domain

A collision domain is a network segment connected by a shared medium or through repeaters where data packets may collide with one another while being sent.A network collision occurs when more than one device attempts to send

a packet on a network segment at the same time, leading to collision.After a collosion has happened both devices must retransmit, one at a

time.

N otvery ecient

.Members of a network portion connected by a hub or bus are in the same collision domain. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 74/113

Collision & Broadcast DomainsI I

Broadcast Domain

A broadcast domain is the set of all devices on a network segment that

hear all broadcasts sent on that segment.When a host or server sends a network broadcast, every device on the

network receives it.For most of the hosts broadcast is of no use.

Too many broadcasts may result in

Broadcast Sto rms

which ma y o od the network. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 75/113

Network Segmentation

The process of breaking up a larger network into a number of smaller ones is referred to as net worksegmentation. Network segmentation is accomplished usingbridges, switches, routersandgateways.At some point of time we will have to break up one large network into a number of smaller ones.This is because as the network grows LAN trac also grows.

Possible causes of LAN trac congestion are:

Too many hosts in a collision domain.

Too many hosts in a broadcast domain.

Broadcast Storms.

Low Bandwidth.

In following slides we shall study

b ridges,switches, routers and gateways from the perspective of network segmentation . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 76/113

Bridge as Network Segmenter

Breaks the network into

collision domains . Clearly, it reduces network trac and improves bandwidth. Can't b reakthe b roadcastdomain(s) . Bridge doesn't stop broadcast, instead forwards it in every port except the port on which it is received.Makes forwarding decisions based onMA Ca ddresses. Improves existing network performance by breaking collision do- main(s), but can't be used to create internet works .This is because they can't lter the network based onLa yer-3 addresses (IP addresses) Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 77/113

Switch as Network SegmenterI

Like bridges, switches also break up

collision domains . Each port on a switch is a separate collision domain . They are employed to add functionality to an existing LAN. The main purpose of switches is to make a LAN work better i.e. to optimize its performance.Switches accomplish this by breaking up collision domain(s) and

thereby providing more bandwidth for LAN users.They "switch" frames(based on MA Caddresses) from one p ort

to another within the switched network.When a switch receives a broadcast it forwards the broadcast in

every port except the port on which it is received.Cleraly, theycan't b reakb roadcastdomain(s) . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 79/113

Switch as Network SegmenterI I

They don't fo rwardpack etsto other net works(i.e.) can't lter the network based on Layer-3 addresses (IP address).So, they arenot the devices fo rinternet working. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 80/113

Bridge vs. Switch

Both bridge and switch break up collision domains on a LAN. Looking at the way they do it, we conclude that a switch is just a multiport bridge .Still somedierences a rethere b etweenswitches and b ridges.

Following table summarizes them:

Particulars Bridge Switch

No. of PortsLess number of ports (2-16). Large number of ports (100 or more)

BuersNo Buers Buer for each link

Error CheckingDon't Perform error checking Perform error checking CostLow Cost Comparatively highDr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 82/113 Internetworking, Routable and Non-Routable ProtocolsI Before going into the details of other networking devices we need to discussInternetworking, Routable and Non- Routable Protocols.Internetworkingis the p rocesso rtechnique of connect- ing dierent networks by using intermediary devices such asroutersorgateways.Aninternet workneeds p rotocolsthat allo wit to identify each node on the network using following two things:1Address of the network.

2Address of the node (device) itself.

Network protocols that provide both of these features are said to be routable . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 83/113 Internetworking, Routable and Non-Routable ProtocolsI I

Some common routable protocols are:

TCP/ IP

(most p opularto day)

IPX/ SPX

(Internet workP acketExchange/ Sequenced P acketExc hange

(IPX/SPX) - Created by Novell for use on NetWare networks)DECnet(created b yDigital Equip mentCo rporation.)

AppleTalk

(w asa p roprietarysuite of net workingp rotocolsdevelop edb y

Apple Inc. for their Macintosh computers.)XNS(Xero xNe tworkSystems (XNS) is a computer net workingp rotocol

suite developed by Xerox).OSI(T heOp enSystems Interconnection p rotocolsis a p rotocolsuit developed jointly by the ISO and the ITU-T.

Not to b econfused with

ISO-OSI model

) Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 84/113 Internetworking, Routable and Non-Routable ProtocolsI II A protocol that needs only a device address (such as MAC address) and not a network address is referred to as a non-routable p rotocol .Some well known non-routable protocols are: LAT (Lo calArea T ransportProto colfrom DEC).

NetBEUI

(NetBios Extended User Interf acefrom Microsoft). Again, note that internetworking can only be realized using routable protocols. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 85/113

Router

Like bridges and switchs, routers also break up collision domains.Theydon't fo rwardthe net workb roadcast.When a

router receives a broadcast it simply discards it.So, routers are the only devices whichcan b reakthe

broadcast domains .Routersroute pack etsfrom one net workto another, which means they can lter the net workbased on la yer-

3 addresses (IP address).Clearly, they are the devices which are used to create

internetworks . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 86/113

Question???

How many collision and broadcast domains are there in the network shown below? Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 88/113

Answer

9

Collision Domains.

3

Broadcast Domains.

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 89/113

Brouter

A network device which combines the functions of a bridge and a router in one unite is called a b router .Fornon-routable p rotocolsb routerop eratesat La yer2 and is used as a bridge.Forroutable p rotocolsb routerop eratesat La yer3 and is used as a router.As networks continue to become more complex, a mix of routable and non-routable protocols has led to the need for a brouter. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 90/113

GatewayI

Routers can successfully connect networks with

simila r protocols .When the networks that must be connected, usecom- pletely dierent p rotocolsfrom each other, a mo rep ow- erful and intelligent device is required.Agatew ayis a device that can interp retand translate the dierent protocols that a reused on t wodistinct networks.This way a gateway is merely amulti-p rotocolrouter . Gateways can be comprised of software, dedicated hard- ware or a combination of both. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 91/113

GatewayI I

They operate at

all seven la yers of

ISO-OSI

mo del. A gateway can actually convert data so that it works with an application on a computer on the other side of the gateway.For example, a gateway can receive e-mail messages in one format and convert them into another format.This shows that how a gateway works at all layers. Therefore, we can connect networks with dierent pro- tocols and architectures using a gateway. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 92/113

OSI Model & Networking Devices

Types of Servers

Dierent servers do dierent jobs, from serving email and video to hosting Web sites.Some commonly used servers are:

File Server

Application Server

Mail Server

Web Server

Print Server

Real Time Communication Server (Internet Relay Chat)

Proxy Server

DNS Server

Database Server

Multimedia or Media Server

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 95/113

File Server

On a network, a le server is a computer responsible for the central storage and management of data les .Other computers on the same network can access these les.

A le server allows users to

sha reinfo rmationover a net workwithout having to physically transfer les by pen drive or some other external storage device .In its simplest form, a le server may be ano rdinaryPC that handles

requests for les and sends them over the network.In a more sophisticated network, a le server might be adedicated

network-attached storage (NAS) device .It serves as ar emoteha rddisk drive fo rother computers , allowing anyone

on the network to store les on it as if to their own hard drive.A program or mechanism that enables the required processes for le

sharing can also be called a le server.On the Internet, such programs often use theFile T ransferProto col

(FTP) . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 96/113

Application Server

The application server is viewed as part of a three-tier appli- cation development, consisting of a graphical user interface (GUI) server, an application server, and a database and trans- action server.More descriptively, it can be viewed as dividing an application into:1A rst-tier,front-end , Web browser-based graphicaluser i nterface, usu-

ally at a personal computer or workstation.2Am iddle-tier,application o rset of applications , possibly on a local area

network or intranet server.3A third-tier,back-end, database and transaction server , sometimes on a mainframe or large server.In many usages, the application server combines or works with a Web server and is called a Web application server. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 97/113

Mail Server

A mail server (sometimes also referred to an e-mail server) is a server that handles and delivers e-mail over a network, usually over the Internet.A mail server can receive e-mails from client computers and deliver them to other mail servers.A mail server can also deliver e-mails to client computers. A client computer is normally the computer where you read/write your e-mails, for example your computer at home or in your oce.Also an advanced mobile phone or Smartphone, with e-mail capabilities, can be regarded as a client computer in these circumstances. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 99/113

SMTP:Simple Mail T ransferProto col

POP:

P ostOce Proto col

Web Server

A w ebserver is a p rogramthat uses

HTTP (Hy-

pertext Transfer Protocol) to serve the les that form Web pages to users, in response to their re- quests, which are forwarded by their computers'

HTTP clients (browsers)

.The process is an example of theclient/server mo del.

All computers that

host W ebsites must have W eb server programs.Leading Web server programs includeApache (the most widely-installed Web server),

Micro soft'sIn-

ternet Information Server (IIS) etc. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 101/113

Print Server

A p rintserver , or p rinterserver , is a device that connects printers to client computers over a net work.It accepts print jobs from the computers and sends the jobs to the appropriate printers, queuing the jobs lo cally.A print server may be anet workedcomputer with one o rmo re shared printers.Alternatively, a print server may be adedicated device on the network, with connections to the LAN and one or more printers.Print server functionality may beintegrated with other devices such as a wireless router.A printer may have a built-in print server. Such printers are referred to as net workp rinters .HP laserjet p2015dnp rinterin w omen'sp olytechniclab is a network printer. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 102/113

Real Time Communication Server (IRC Server)

Internet Relay Chat (IRC) is an application layer protocol that facilitates communi- cation in the form of text .The chat process works on a client/server networking model.

IRC clients

a recomputer p rogramsthat a user can install on his system. These clients communicate with chat servers to transfer messages to other clients. IRC is mainly designed for group communication in discussion forums. But, it also allows one-on-one communication via private messages as well as chat and data transfer, including le sharing. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 103/113

Proxy Server

In computer networks, a proxy server is a

server (a computer system or an application) that acts as an intermediary fo rrequests from clients seeking resources from other servers.Aclient connects to the p roxyserver , requesting some service, such as a le, connection, web page, or other resource available from a dierent server .The proxy server evaluates the request and fulls it.

Today,

most p roxiesa rew ebp roxies , facilitating ac- cess to content on the World Wide Web.They provide anonymity and may be used tob ypass

IP address blocking

. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 104/113

DNS Server

The

Domain Name System ( DNS)

is the system and net work protocol used on the Internet. Ittranslates names of computers to numerical addresses ( IP addresses ) and vice versa .It simply involveslo okingup in tables , in which names are linked to numbers.DNS is a client-server system : a requestor (client) requests a name or address from a provider (DNS server ).The server returns a reply.

Searching a

numb erwith a name is called fo rwardlo okup .

Searching a

name with a numb er is called reverse lo okup . Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 105/113

Database Server

A database server is a computer system that provides other computers with services related to accessing and retrieving data from a database .Access to the database server may occur via a"fr ontend" running locally at a user's machine (e.g., phpMyAdmin), or "back end" running on the database server itself, accessed b y remote shell.Multimedia or Media Server A media server refers either to a dedicated computer appliance or to a specialized application software, ranging from an en- terprise class machine providing digital media on demand, to, more commonly, a small personal computer or NAS (Network Attached Storage) for the home, dedicated for storing various digital media (meaning digital videos/movies, audio/music, and picture les). Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 107/113

Network Performance MeasureI

Network Performance denes

ho wgo od the net workis.

Quality of Service (QOS)

is an overall measurement of network performance.FromQOS p ointof v iewfollo wingmeasures a recon- sidered important:Bandwidth.

Throughput.

Latency.

Jitter.

Error Rate.

Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 108/113

Network Performance MeasureI I

Bandwidth

Bandwidth is dened as a

range within a band of frequencies or wavelengths .Bandwidth is also dened as thea mountof data that can b e transmitted through a medium in a xed amount of time .For digital devices the bandwidth is usually expressed inbits per second (bps) or less frequently in bytes per second .For analog devices, the bandwidth is expressed incycles p er second or Hertz (Hz) .Anincrease in bandwidth in Hertz means an increase i nthe bandwidth in bits per second .It is not generally possible to send more data than dictated by the

Shannon-Ha rtley

Theo rem(Shannon channel capacit y

theorem). Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 109/113

Network Performance MeasureI II

Throughput

In general throughput means the

maximum rate of p roduction or the maximu mrate at which something can b ep rocessed.When used in the context of communication networks, such as Ethernet, throughput or network throughput is the rate of successful message delivery over a communication channel. Throughput is usually measured inbits p ersecond (bit/s o r bps) and sometimes in data pack etsp ersecond (p/s o rpps) .Latency

Network Latency

is the term used to indicate any kind of dela y

that happens in data communication over a network.The speed of light imposes a minimum propagation time on

all electromagnetic signals. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 110/113

Network Performance MeasureIV

It is not possible to reduce the latency below:

t=s=cm wheresis the distance andcmis the speed of light in the medium.This approximately means1 extra millis econdRTT (round- trip-time) fo r

100km

of distance b etweenhosts. Other delays also occur in intermediate nodes. Network connections in which small delays occur are called low-latency net works.Network connections which suer from long delays are called high-latency net works. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 111/113

Network Performance MeasureV

Jitter

Jitter

in an IP net worksis the va riationin the latency on a packet ow between two systems, when some packets take

longer to travel from one system to the other.Jitter results fromnet workcongestion and route changes .

Jitter is especially

p roblematicin real-time communications like IP telephony and video conferencing .Error Rate

In digital transmission, the

numb erof bit erro rs ( Ne) is the number of received bits of a data stream over a communica- tion channel that have b eenaltered due to noise, interference, distortion etc. Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 112/113

Network Performance MeasureVI

The bit erro rrate o r bit err orratio ( BER), is thenumb erof bit errors (Ne), divided by thetotal numb erof transferred bits (N) during a studied time interval.Mathematically, during the time interval
t,BERis expressed as follows:

BER=NeN

BER is a unitless performance measure, often expressed as a percentage. %BER=NeN 100Dr. J. Alam (CES)Unit 1: IntroductionFebruary 22, 2020 113/113