chapter 1: computer network fundamentals guide to computer network security

Chapter 1: Computer Network Chapter 1: Computer Network FundamentalsFundamentals

Guide to Computer Network Security

Kizza - Guide to Computer Network SecuriKizza - Guide to Computer Network Securityty

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Computer communication networksComputer communication networks

A Computer network is a distributed A Computer network is a distributed system consisting of loosely coupled system consisting of loosely coupled computers and other devices. computers and other devices.

To form a network, there are To form a network, there are communicating rules or protocols communicating rules or protocols each device in the network must each device in the network must follow to communicate with another. follow to communicate with another.

Ethernet

Laptop computer

Laptop computer Workstation

Laser printer

IBM Compatible


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Internetworking technology enables multiple, Internetworking technology enables multiple, diverse underlying hardware technologies, and diverse underlying hardware technologies, and different software regimes to interconnect different software regimes to interconnect heterogeneous networks and bring them to heterogeneous networks and bring them to communicate smoothlycommunicate smoothly

The network elements (computing elements), The network elements (computing elements), network software(operating systems and network software(operating systems and browsers), and users all work together browsers), and users all work together exchanging information and utilizing the exchanging information and utilizing the resources in the networkresources in the network

The network elements may be of diverse The network elements may be of diverse technologies and software may be as different technologies and software may be as different as possible but the whole combo works in as possible but the whole combo works in unison.unison.


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Computer Networks TypesComputer Networks Types

There are several types of There are several types of networks:networks:

LAN – Local Area networksLAN – Local Area networksWAN – Wide Area networksWAN – Wide Area networksMAN – Metropolitan Area NetworkMAN – Metropolitan Area Network


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Data Communication Media Data Communication Media TechnologyTechnology

Data movement in computer networks Data movement in computer networks is either analog or digitalis either analog or digital– In analog format data is sent as a In analog format data is sent as a

continuous electromagnetic wave with a continuous electromagnetic wave with a constant frequency signal called a carrier.constant frequency signal called a carrier.

– The carrier signal has three characteristics:The carrier signal has three characteristics:Amplitude modulation –each bit is represented by Amplitude modulation –each bit is represented by a different amplitude of the carrier wave.a different amplitude of the carrier wave.Frequency modulation- each bit is represented by Frequency modulation- each bit is represented by a different frequency of the carrier wavea different frequency of the carrier wavePhase Shift modulation – shifts in the wave Phase Shift modulation – shifts in the wave encode binary information.encode binary information.

– In digital encoding binary data is In digital encoding binary data is represented as electrical voltage.represented as electrical voltage.


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Transmission MediaTransmission Media

This is a physical medium between two This is a physical medium between two transmitting elementstransmitting elementsThe quality, dependability, and overall The quality, dependability, and overall performance of a computer network performance of a computer network depends on the transmission mediumdepends on the transmission mediumThese media fall into the following These media fall into the following types:types:– Wired Transmission consisting of:Wired Transmission consisting of:

Copper wire – insulated copper wires. Copper wire – insulated copper wires. Traditionally used because copper has low Traditionally used because copper has low resistance to electrical currents.resistance to electrical currents.Twisted pair - a pair of wires of insulated copper Twisted pair - a pair of wires of insulated copper wires each wrapped around the other.wires each wrapped around the other.


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Coaxial cables – insulated dual conductor cables Coaxial cables – insulated dual conductor cables with inner conductor in the core.with inner conductor in the core.Optical fiber – small medium made of glass and Optical fiber – small medium made of glass and plastics and conducts optical raysplastics and conducts optical rays

– Wireless networks fall one of the following Wireless networks fall one of the following three categories depending on distance as three categories depending on distance as follows:follows:

Restricted proximity networkRestricted proximity network: this network : this network involves local area networks (LANs) with a involves local area networks (LANs) with a mixture of fixed and wireless devices. mixture of fixed and wireless devices. Intermediate/Extended network:Intermediate/Extended network: this this wireless networkwireless network is actually made up of two fixed is actually made up of two fixed LANS components joined together by a wireless LANS components joined together by a wireless component. The bridge may be connecting LANS component. The bridge may be connecting LANS in two nearby buildings or even further. in two nearby buildings or even further. Mobile network. Mobile network. This is a fully wireless This is a fully wireless network connecting two network elements. One network connecting two network elements. One of these elements is usually a mobile unit which of these elements is usually a mobile unit which connects to the home network (fixed) using connects to the home network (fixed) using cellular or satellite technology. cellular or satellite technology.


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– The three types of wireless The three types of wireless communication are connected using the communication are connected using the following basic technologies:following basic technologies:

Infrared - Infrared - uses pulses of infrared light to uses pulses of infrared light to carry coded instructions to the receiving carry coded instructions to the receiving network element. network element.

High-Frequency Radio – using High-Frequency Radio – using electromagnetic radio waves or radio electromagnetic radio waves or radio frequencies (RF transmission)frequencies (RF transmission)

Microwave – This is a higher frequency Microwave – This is a higher frequency version of radio communication. It is capable version of radio communication. It is capable of being focused in a single directionof being focused in a single direction

Others include Laser wavesOthers include Laser waves


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Network TopologiesNetwork TopologiesComputer networks, whether LANs, MANs, or Computer networks, whether LANs, MANs, or WANs are constructed based on a topology. WANs are constructed based on a topology. There are several topologies including:There are several topologies including:– (i ) Mesh – allows multiple access links to a (i ) Mesh – allows multiple access links to a

network elementnetwork element– (ii) Tree – except the root, every element in (ii) Tree – except the root, every element in

the network can only be accessed through the network can only be accessed through its predecessors its predecessors

– (iii) Bus – all elements are on a shared line(iii) Bus – all elements are on a shared line– (iv) Star – communication between any two (iv) Star – communication between any two

elements in the network must go through elements in the network must go through central nodecentral node

– (v) Ring – each element in the network is (v) Ring – each element in the network is directly connected to two neighbors forming directly connected to two neighbors forming a ring.a ring.


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Network Connectivity and ProtocolsNetwork Connectivity and Protocols

These are operational These are operational modalities/procedures for moving packets modalities/procedures for moving packets between network transmitting elementsbetween network transmitting elements

There are two widely used of protocol There are two widely used of protocol suites:suites:– OSI – open systems interconnection of the OSI – open systems interconnection of the

international standards organization (ISO)international standards organization (ISO)– TCP/IP – most widely used.TCP/IP – most widely used.

Both of these proposed suites are based Both of these proposed suites are based on layered tacks of serviceson layered tacks of services


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Network ServicesNetwork Services

Network work effectively when network Network work effectively when network services move data in the network. These services move data in the network. These services fall into two categories:services fall into two categories:– Connection services to facilitate the exchange of Connection services to facilitate the exchange of

data between the two network communicating end-data between the two network communicating end-systems with as little data loss as possible and in as systems with as little data loss as possible and in as little time as possible.little time as possible.

– Switching services to facilitate the movement of data Switching services to facilitate the movement of data from host to host across the length and width of the from host to host across the length and width of the network mesh of hosts, hubs, bridges, routers and network mesh of hosts, hubs, bridges, routers and gateways gateways


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Two connection services are provided by most digital Two connection services are provided by most digital networks:networks:– connected oriented services – offer prior connection connected oriented services – offer prior connection

controls in a form of three-way handshakecontrols in a form of three-way handshake– Connectionless service – no handshake is needed no Connectionless service – no handshake is needed no

prior information and no warnings.prior information and no warnings.

Two switching services are providedTwo switching services are provided : :– Circuit switching – The network must reserve all Circuit switching – The network must reserve all

resources needed for the communication session before resources needed for the communication session before any communication begins. Example: any communication begins. Example: telecommunications sessions.telecommunications sessions.

– Packet switching networks are referred to as Packet switching networks are referred to as Packet networks. There are two types of these Packet networks. There are two types of these networks.networks.

– Virtual circuit networks – logical connection is needed Virtual circuit networks – logical connection is needed before a packet is sent before a packet is sent

– Datagram and networks - Datagram and networks -


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Network Connecting devicesNetwork Connecting devices

The computing elements in a network The computing elements in a network (LAN, WAN) are interconnected using (LAN, WAN) are interconnected using connecting devices commonly referred connecting devices commonly referred to as nodes to as nodes

There are several types:There are several types:– Hub – the simplest connecting devices. It Hub – the simplest connecting devices. It

takes in inputs and retransmits them takes in inputs and retransmits them verbatim. verbatim.

– Bridge – it is similar to the hub, however, Bridge – it is similar to the hub, however, bridges filter incoming data packets for bridges filter incoming data packets for addresses before the packets/ frames are addresses before the packets/ frames are re-transmittedre-transmitted


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– Switch - this a newer version of a bridge with Switch - this a newer version of a bridge with high a performance capacity and can high a performance capacity and can accommodate higher numbers of interfaces accommodate higher numbers of interfaces

– Router – general purpose nodes that Router – general purpose nodes that interconnect two or more heterogeneous interconnect two or more heterogeneous networks. They are dedicated special purpose networks. They are dedicated special purpose computers with their own Address Resolution computers with their own Address Resolution Protocol (ARP) and IP addresses Protocol (ARP) and IP addresses

– Gateway – this is a more versatile device that Gateway – this is a more versatile device that can provide translation of and between can provide translation of and between networking technologies such as OSI and networking technologies such as OSI and TCP/IP. TCP/IP.

Because of this, Gateways can connect two or more Because of this, Gateways can connect two or more autonomous networks.autonomous networks.

They perform all functions of a router and more.They perform all functions of a router and more.


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Network TechnologiesNetwork Technologies

Network technologies in each network Network technologies in each network category.category.– LAN Technologies LAN Technologies

Star-based Ethernet (IEEE 802.3) LANStar-based Ethernet (IEEE 802.3) LAN

Token Ring/IEEE 805.2Token Ring/IEEE 805.2

Other LAN technologiesOther LAN technologies– Asynchronous Transfer Mode (ATM) with the goal to Asynchronous Transfer Mode (ATM) with the goal to

transport real time voice, video, text, email, and transport real time voice, video, text, email, and graphic data. ATM offers a full array of network services graphic data. ATM offers a full array of network services that make it a rival of the Internet network. that make it a rival of the Internet network.

– Fiber Distributed Data Interface (FDDI) is a dual-ring Fiber Distributed Data Interface (FDDI) is a dual-ring network which uses a token ring scheme with many network which uses a token ring scheme with many similarities to the original token ring technology.similarities to the original token ring technology.

– AppleTalk, the popular Mac users’ LAN.AppleTalk, the popular Mac users’ LAN.


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– WAN Technologies:WAN Technologies:Integrated Services Digital Network (ISDN)Integrated Services Digital Network (ISDN)X.25 X.25 Other WAN TechnologiesOther WAN Technologies

– Frame Relay is a packet switched network with the ability to Frame Relay is a packet switched network with the ability to multiplex many logical data conversions over a single multiplex many logical data conversions over a single connection. It provides flexible efficient channel bandwidth connection. It provides flexible efficient channel bandwidth using digital and fiber optics transmission. It has many similar using digital and fiber optics transmission. It has many similar characteristics to X.25 network except in format and characteristics to X.25 network except in format and functionality.functionality.

– Point-to-point ProtocolPoint-to-point Protocol (PPP) is the Internet Standard for (PPP) is the Internet Standard for transmission of IP packets over serial lines. The point-to-point transmission of IP packets over serial lines. The point-to-point link provides a single, pre-established communications path link provides a single, pre-established communications path from the ending element through a carrier network, such as a from the ending element through a carrier network, such as a telephone company, to a remote network. These links can telephone company, to a remote network. These links can carry datagram or data-stream transmissions. carry datagram or data-stream transmissions.

– xDirect Service LinexDirect Service Line (xDSL) is a technology that provides an (xDSL) is a technology that provides an inexpensive, yet very fast connection to the Internet. inexpensive, yet very fast connection to the Internet.

– Switched Multi-megabit Data ServiceSwitched Multi-megabit Data Service (SMDS) is a (SMDS) is a connectionless service operating in the range of 1.5-100Mbps; connectionless service operating in the range of 1.5-100Mbps; any SMDS station can send a frame to any other station on the any SMDS station can send a frame to any other station on the same network. same network.

– Asynchronous Transfer Mode (ATM) is already discussed as a Asynchronous Transfer Mode (ATM) is already discussed as a LAN technology. LAN technology.

chapter 1: computer network fundamentals guide to computer network security

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