CSC 423 Lecture Materials

8/10/2019 CSC 423 Lecture Materials

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CSC 423 : COMPUTER NETWORKS

* Introduction to Networking* Classification/Types of Networks

- LAN, WAN, INTRANET, EXTRANET, INTERNET

* LANDefinition, Scope, Components, Topology

* Internetworking

* Interconnectivity, Standards, Protocols.

Textbooks

1. Computer Networks and Internets with Internet Applications, 3

rd

EditionAuthor: Douglas E-Comer

2. Data and Computer Communications, 3rdEdition

Author ; Williams Stallings.


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COMPUTER NETWORKS BASICS- Evolution of Computer Networks

* Batchoriented configuration

* Timesharing Multi-user

* SingleUser

* LAN

* Private WANs (Metropolitan)* Publicly Switched Data Networks (WAN)

* Internet

* Intranet

Motivation/Benefits of Networks

* Fast communicationdata/messages:- The first data networks were developed to share large scalecomputational power

- Information

- Software

* Sharing of resourcesData / Messages

- information

- software

- hardwareprocessor, memory, printer, modem, remote devices

e.t.c

* Cost effectiveness

* Convenience

* Delivered new paradigmsGlobal village, digital economy, information society, common humanity.

delivered new servicese-services e.g. e-mail, web browsing,, e-purse, e-banking, e-commerce,virtual- learning, virtual lab etc. ftp, teleconferencing etc.

Network Types

- LAN, MAN, WAN, INTRANET, INTERNET- LAN

* Definition & Scope

* Benefits

* Requirements

* Pointtopoint t/Direct & shared LAN

* Topology / Architecture


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-A network is a set or collection of nodes or points which are linked or connected togethere.g. network of roads, a network of fuel depots, a network of product distributors.

- Computer Network refers to a set or collection of computers that are linked or connectedtogether in some pattern.

Historical development of computer Networks

* Development of multi-user systems

* Limitations of multi-user systems

* Development of top-end PCs

* Limitations of PCs

- Motivation/Benefits of computer networks* Fast Communication

** Messages / Information

** Data

** Software

** Access to specified remote devices

* Sharing of computer resources

** Messages / information

** Data

** Software

** Devices e.g. printers, moderns, telephone lines.

** RAM space


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** Processor** Hard disk space

* Cost

* Convenience


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LAN Contd

* General Introduction

* PointtoPoint versus shared LAN

No. of direct = (N2N) / 2

Connections

* Locality of reference principle- Temporal locality of reference

- Physical locality of reference

* Requirements

* Topology / Architecture

Discuss the different lines (cables, cards, connector & other accessories)available in the market based on star, Ring & Bus architecture.


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LAN Contd

The decreasing cost and increasing performance of micros have led to a continuing integration of micro-technology into every facet of business, education, and government.

SingleSite organizations i.e. organizations whose communication occurs across relatively short distancessuch as a building or a group of offices, benefit from LAN.

- The initial motivation for LAN was the need to share expensive resources such as laser printers and high-capacity, high-speed mass storage devices etc. among a number of users termed WORKGROUP. This is adirect economic benefit.

- LAN allows the high-speed exchange of essential information between workgroup members in anorganization. This promotes efficiency and productivity.

- LAN provides the catalyst to increase the range of potential applications for PCs.

- LAN could be a visible contributor to increased profitability or some other productivity metric in the caseof non-profit organisations)

TerminologyCLIENTSWorkstations running host applications.

The term SERVER refers to a software application that offers a well-defined service to network users. Aserver application can be run on special-purpose hardware or an ordinary PC. In the latter case, the PC

often has minimum configuration requirements. The most common types of servers are Web servers, mailservers, File Servers, Print servers, Communication Servers, & Database servers etc.

SERVER could be dedicated or non-dedicated

A dedicated server is set up to provide one or more services to users on the network.

A non-dedicated server can simultaneously function as a workstation and one or more servers. LANsconnecting non-dedicated servers are also referred to as PEER-TO-PEER NETWORKS.


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Direct

Point-to-point & shared LANs

Direct Point-to-point

The first computer communication systems all used the direct point-to-point pattern ofcommunication. In this pattern, each communication channel or medium connectedexactly two computers, and was available to those computers exclusively. Known as apoint-to-point network or mesh network, the scheme has three useful properties.

First, because each connection is installed independently, appropriate hardware can beused. For example the transmission capacity i.e. the bandwidth of the underlying circuit

and the modems used do not need to be the same on all connections. Second, becausethey have exclusive access, the connected computers can decide exactly how to senddata across the connection. They can choose a frame format, an error detectionmechanism and a maximum frame size. More important, because each connection isindependent of others, the details can be changed whenever the owners of the attachedcomputers agree to make a change. Third, because only two computers have access tothe channel, it is easy to enforce security and privacy. No other computers handle data,and no other computers can obtain access.

However, the main disadvantage of direct point-to-point connection becomes apparentwhen more than two computers need to communicate with one another. In a point-to-pointscheme that provides a separate communication channel for each pair of computers, thenumber of connections grows quickly as the size of the set increases. For example, twocomputers need only one connection, three computers need three connections, and fourcomputers need 6 connections.


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The total number of connections grows more rapidly as the total number of computers. Mathematically,the number of connections needed for N computers is proportional to the square of N :

DIRECT CONNECTIONS REQUIRED = (N2 - N) /2= N(N-1)/2

These connections are expensive in terms of cabling cost. Local Area Networks (LANs) were devisedas alternatives to expensive, dedicated point-to-point connections. Each LAN consists of a singleshared medium, usually a cable, to which many computers attach. The computers take turn to use themedium to communicate with one another.

LAN concept is supported by a fundamental principle of computer networking known as LOCALITYOF REFERENCE. It states that communication among a set of computers is not random, but insteadallows two patterns. First, if a pair of computers communicates once, the pair is likely to communicate

again in the near future and then periodically. This pattern is called TEMPORAL LOCALITY OFREFERENCE to imply a relationship over time. Second, a computer tends to communicate most oftenwith other computers that are nearby. This second pattern is called PHYSICAL LOCALITY OFREFERENCE to emphasize the geographic relationship.

The locality reference principle is easy to understand because it applies to human communication.For example, people communicate most often with others who are nearby (e.g. working together).Furthermore, if an individual communicates with someone (e.g a friend or family members), theindividual is likely to communicate with the same person again.

Requirements

Computers hardware-Workstations /Clients

-Servers


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Computer Software

-Network Operating System (OS)

-Server applications (Network versions of application software)-Client OS

-Client applications

Communication hardware

-Network Cards (NAC/NIC)Switches/Hubs

-Cables-Accessories

-Protocol Software

Peopleware

-Network Administrator/Manager-Network Engineer

-Network Programmer

-Database Administrator

-Web designer

-Network user


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NETWORK ARCHITECTURE OR TOPOLOGY

Network designs have three categories : Star network, Ring network, and Bus network.

- A Star network: Contains a central connecting device called or Hub or Switch andone or more workstations connected to the central device, forming a Star.

The Star arrangement is logical. e.g. Ethernet 10 Base T, Asynchronous TransferMode (ATM).

- In a Ring network, there is no central system, rather, a series of computer systemscommunicate with one another from one node to the next node in one direction only

(closed loop). The ring arrangement is logical e.g. IBM Token Ring, Fibre DistributedData Interconnect (FDDI).

- The Bus network is a kind of Broadcast topology characterised by a singlecommunication channel shared by all communicating computers e.g. consists of asingle, long cable to which computers attach.

In the Bus network, one computer is allowed to transmit message onto the bus whileothers are required to receive or not to transmit, at any one time e.g. EthernetThicknet and Thinnet (10 Base 2)

In the Bus network, the message usually bears the address of the intended receivers sothat others will share it.


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NETWORK TOPOLOGY (contd.)

STAR

Switch

Client A Client B Client C Server Client D


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RING

Broadcast methodA message can be sentfrom a PC to multiple destinations at the sametime.

Client A

Client C

Client D

Server

Client B


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BUS

Broadcast

Client D Client C

Server Client A Client B

Bus (cable)

Terminal

Broadcastmethod

Terminal


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TOPOLOGY

Network design or ArchitectureThe way a network is physically connected together. Ithas effect on network selection and management.

Common topology are: Star, Ring, Bus, Distributed Star.

Factors that influence choice of topology:-

- The complexity & cost of network cable installation

- Redundant, or fail-safe design

- Fault isolation

- Strategy for physically expanding and reconfiguring the network.

Ring - Provides redundancy through the use of a backup cable path which can be usedfor network reconfiguration resulting from media failure.

- Provides built-in hardware features to isolate failed station loops from the activering.

StarIt is the superior choice for fault detection and isolation.

BusMore difficult to diagnose since there is no built-in means to isolate faulty cablesegments


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Star - Asynchrous Transfer Mode (ATM) uses an electronic switch or a hub to

which computers are attached by means of fibre optics cables.

- Twisted Pair Ethernet (10 Base T)

Twisted pair wiring

RingIBM Token RingConcept of TOKEN (Broadcasting)

- Fibre Distributed Data Interconnect (FDDI)

- Copper Distributed Data Interconnect (CDDI)

- Uses two layers of rings in a counter rotating form. Outer carries data, while inner is used when theouter ring fails.

BusEthernetThicknet & Thinnet (Broadcasting)

* Carrier Sense Multiple Access (CSMA)

* Carrier Sense Multiple Access / Collision

1stCollision applies a delay of o to d

Subsequent collision applies a delay of o to ndwhere nis an even

factorthis scheme is referred to as the Binary Exponential Back off

Hub/

Switch


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HARDWARE ADDRESSING IN LAN & FRAME TYPE IDENTIFICATION

LAN Technologies use an Addressing Scheme to provide direct communication.

Each workstation on the LAN is assigned a unique numeric value called a PHYSICAL ADDRESS, HARDWARE

ADDRESS or MEDIA ACCESS ADDRESS (MAC ADDRESS)

Each Packet or Data Frame transmitted from a Workstation on a LAN consists of two address fieldsSOURCEaddress field, DESTINATION address field.

Senders address makes it easy for the receiver to generate a reply to the sender in case of errors or for

acknowledgement.

Categories of Addressing

Static:Hardware manufacturer-assigned. Does not change except NIC is changed.

Configurable:provides a mechanism for users to set the addressmanual through setting of switches or electronicusing EPROM. Configuration usually done once when NIC is f irst installed.

Dynamic: Aphysical address is assigned to a workstation when the workstation first boots. It uses a random number

that does not correspond to any other workstation's address.

Unicasting - a single destination address

Broadcastingmakes a copyof message available to all connected computers on the network. A reservedBROADCAST address is needed in the DESTINATION field e.g. 11111111 could specify broadcast & 10000001 thestations address

i.e. either address in the destination field could lead to forwarding of the packet to receiving hosts Operating System.

MulticastingA restricted form of Broadcasting. NIC is programmed with specs of which multicast frames

i.e. destination addresses to accept or reject.


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Packet Frame

Packet / Frame formats

Frame Header Frame Data Area or Payload

General format

Frame header contains info. Such as Source & Destination addresses.

Frame Data Area or Payload contains information or message being sent.

Preamble Dest Source Frame Data CRC

Address. Addr type

Ethernet frame format

Syn Dest Addr Source Addr Frame type Data Error Checking code

8Bytes 6bytes 6bytes 2 46-1500 4


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INTERNETWORKING COMPONENTS & SYSTEMS

InternetworkingConnecting multiple physical networks into a large, logically

uniform communication system.

Motivation

- Constraints of specific networks e.g. LANs provide high speed communication

within a short distance.

- Diverse networking requirements by large organizations implies multiple

physical networks.

- Choice of different networks suited to different tasks.

Concept of universal service:


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INTERCONNECTIVITY, STANDARDS, PROTOCOLS

Network entities :Computers, Applications, Networks

Multivendor disparate products exist for these entities. For Interconnectivity & Inter-operability orOPENNESS between diverse, disparate products, upward compatibility, there is need to have certaincommon denominators in network entities design & implementation.

These common denominators are provided by many national and international organizations.

Protocol refers to rules, conventions, guidelines, agreed to/adopted by a group of stakeholders for the

design & implementation of products.

A protocol or protocol suite adopted by a group & widely circulated and accepted becomes a

STANDARD.

Standards could be :

- Dejure - National - Universal

- Defactor - International

Examples of Standards and Regulations Organizations:

ISOInternational Standards Organization

IEEEInstitute of Electrical & Electronic Engineers

ITUInternational Telecommunications Union

CCITTConsultative Committee in International Telegraphy and Telephony

NCCNational Communications Commission

SONStandards Organization of Nigeria


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ANSI American National Standards Institute

ECMA European Computer Manufacturers Association

DoD Department of Defense, United States of American

Develop your note on the history & functions of the above bodies especially in the areas of Computers& Networking.

Connectivity levels / layers : Communications is made possible generally by 3 layers / levels

- Cognitive, - Understanding the concept

- Language - Expression

- Transmission - Physical means of communication

Independent layers but each depends on at least one other layer for effectiveness.

OSI (Open Systems Interconnection) reference model of ISO.

X.200 of CCITT

TRANSMISSION CONTROL PROTOCOL / INTERNET PROTOCOL (TCP/IP)LAN Protocolsieee series


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TCP/IP was the first set of protocols developed for use in an internet. It is a result of protocol research and developmentconducted on the experimental packet-switched networkthe ARPANET, funded by the Defense Advanced ResearchProjects Agency (DARPA) of USA, and is generally referred to as the TCP/IP protocol suite.

Indeed, researchers who devised TCP/IP also developed the internet architecture described earlier. Work on TCP/IP beganin the early 1980s, about the same time that Local Area Networks (LANs) were being developed. The military was among thefirst organisations to have multiple physical networks. Consequently it was among the first to realize the need for universalservice.

Research on internetworking and TCP/IP protocols has produced dramatic results. Inter-networking has become one of themost important ideas in modern networking. In fact internet technology has revolutionized computer communication. Mostlarge organisations already use internetworking as the primary computer communication mechanism. Smaller organisationsand individuals have started to do so as well. The TCP/IP technology has made this possible.

Communication task for TCP/IP are organized into five relatively independent layers :

OSI Model TCP/IP Model

Application

Presentation

Session

Transport

Network

Data Link

Physical

Process/Application

Host-to-Host

(Transport)

Internet

Network

Interface layer

Physical


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The model is a framework for defining standards for linking heterogeneous computers.

The OSI is concerned with the exchange of information between a pair of open systems and not and

with the internal functioning of each individual system.

The OSI model/architecture has seven layers which are listed with a brief definition as follows :

* PhysicalConcerned with mechanical, electrical functional and procedural

characteristics of physical links

* Data linkProvides for the reliable transfer of data across the physical link.

* Network - Responsible for establishing, maintaining, and terminating network connections

* TransportProvides reliable, transparent transfer of data between end points.

* SessionEstablishes, manages, and terminates sessions between cooperating applications

* PresentationPerforms transformations on data to provide standardised application interface e.g.encryption, text compression.

* ApplicationProvides services to users of the OSI environment e.g. transaction services, file

transfer etc.


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The Physical and Network Interface Layers of the TCP/IP model use existing Physical and

Data link standards, such as Ethernet and Token Ring, thereby making TCP/IP hardware-

independent.

As a result, the protocol is widely used to connect heterogeneous systems.

The Internet layer provides procedures needed to allow data to traverse multiple

interconnected networks. The Internet Protocol (IP) is used at this layer to provide the routing

function across multiple networks.

The Transport layer (Host-to-Host) provides the requirements needed for data to be exchanged

reliably regardless of the nature of the applications that are exchanging data. The Transmission

Control Protocol (TCP) is the most commonly used protocol to provide this functionality.

Finally, the Application layer contains the logic needed to support the various user applications.


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The TCP/IP Protocol

Transmission Control Protocol/Internet Protocol

The Internet concept :

a. The illusion of a single network that TCP/IP software provides to users and applications


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host computer

router

b. The underlying physical structure in which a computer attaches to one physical network, and routers

interconnect the networks.

net 3

net 1

net 2

net 6

net 5

net 4


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A routeris a special-purpose computer dedicated to the task of interconnecting networks. A router

can interconnect networks that use different technologies including different media, physical

addressing schemes, or data frame formats.

An Internetconsists of a set of networks interconnected by routers. The internet scheme allows each

organization to choose the number and type of networks, the number of routers to use to

interconnect them, and the type of interconnection.

Host Computer :TCP/IP defines the term host computerto refer to any computer system that

connects to an internet and runs applications. A host can be as small as a PC or as large as a

mainframe.


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Application layer

Transport layer

Internet layer

Network Interface layer

Physical

TCP/IP PROTOCOL SUITE

SMTP TELNET FTP DNS HTTP

TCP UDP NETWORKVOICE PROTOCOL (VoIP)

IP

ICMP ARP RARP

LAN Protocols


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Simple Mail Transfer Protocol (SMTP) Handles the transfer of emails using

UDP or TCP as underlying protocols.

TELNET It is a remote log-in protocol that uses TCP as the underlying

protocol.

File Transfer Protocol (FTP) It is the protocol that gives access to

data/software files stored in folders for general use. It uses TCP as the

underlying protocol.

Domain Name Service (DNS) This protocol resolves domain names to IP

addresses and vice versa. It uses UDP as the lower transport protocol.


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Internet Control Message Protocol (ICMP) a special purpose set of messages that are used between

internetwork nodes to resolve problems in packet processing.

These messages include :

Echo request, Source quench, Routing change request,

Time stamp request / Reply.

Address Resolution Protocol (ARP)

used to map the 32-bit IP address to a MAC address e.g. (anEthernet 48-bit address). The ARP is necessary because there is no preestablished relationship

between IP and MAC address.

Address resolution / Binding can be done in 3 different ways:

- Table lookup, Closed form computation, Message exchange.

Reverse Address Resolution Protocol (RARP) It is a who am l broadcast that is transmitted by a

new station entering the network. The broadcast is responded to by a RARP server that maps the

Requesters MAC address to an IP address appropriate to the internetwork configuration.

Connectionless & Connection-oriented Services

Connectionless - A characteristic of a network system that allows a computer to send data to any

other computer at anytime. Connectionless networks are analogous to a postal system in which each

letter carries the address of the recipient; letters can be sent at any time. It is an extension of packet

Switching.

Connection-oriented- A characteristic of a network system that requires a pair of a computers to establish a connection

before sending data. Connection-oriented networks are similar to a telephone system in which a call must be placed

and answered before communication can begin.

TCP/IP includes both servicesthe fundamental delivery service is connectionless, however, a reliable connection-oriented service uses the underlying connectionless service.

An Internet Packet is called an IP Datagram.


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TCP Transmission Control Protocol

It is an End-to-End protocol because it provides connection directly from an application on one computerto an application on a remote computer.

The connections are called VIRTUAL CONNECTIONS because they are achieved by software.

It provides Reliable Transport Service.

From an application program's point of view, the service offered by TCP has seven major features:

- Connection orientation

- Point-to-Point

- Complete reliability : Exact delivery ,no duplication, no data missing or out of order

- Full duplex communication

- Stream Interface

- Reliable Connection Startup

- Graceful Connection Shutdown

User Datagram Protocol (UDP)

It is a connectionless transport protocol that permits an application to send a message to anydestination at anytime. When using a connectionless transport protocol, the sending applications mustspecify a destination with each message it sends. An application using UDP can send a sequence ofmessages, where each message is sent to a different destination.


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Hardware Frame, IP datagram, Fragmentation, Maximum Transmission

Unit, Encapsulation

IP datagram is encapsulated in a Hardware frame.

Each hardware technology has a maximum amount of data that a Frame can carry; this

limit is known as Maximum Transmission Unit (MTU). Thus, a datagram must be less

or equal to an MTU in size, or it cannot be encapsulated.

The Router uses the technique known as FRAGMENTATION to divide the datagram

into smaller pieces called Fragments, which are then transmitted independently.

Hardware Hardware Frame data

Frame Header

IP Header IP data area

IP Header Original datagram data area

IP Header data 1 IP Header data 2 IP Header data 3


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TCP/IP continued

IP Addresses

Internet as a single, uniform Virtual Network.

To guarantee uniform addressing of routers and hosts, the protocol software defines an

addressing scheme for all computers on the internet .

Each host has a unique IP Address used by Application programs & higher layers of protocol softwarefor communication.

Each host has a unique 32-bit number known as IP address.

IP address is different from MAC physical address.

Network number Host number

Classful IP addressing

0 8 16 24 31

Class A

Class B

Class C

Class D

Class E

Prefix suffix

C prefix suffix

1 0 prefix suffix

1 1 0 prefix suffix

1 1 1 0 multicast address

1 1 1 0 reserved for future use


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Dotted Decimal Notation

32-bit Binary Number Equivalent Dotted

00000010111111100000000100000000 2.254.1.0

IANAInternet Assigned Number Authority

ICANNInternet Corporate for Assigned Names and Numbers

Subnet & Classless Addressing

0 Address mask or 31 32 Actual host address 63

The mask specifies the boundary between prefix & suffix.

1bits mark network prefix0 bits mark host or suffix portion

Classless Inter-Domain RoutingCIDR

IP address/mask

e.g. 200.218.56.18/20

Subnet mask

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CSC 423 Lecture Materials