E-Business

Introduction to

Computer Administration

Computer Network - Basic Concepts

Computer Networks Communication Model Transmission Modes Communication Types Classification Of Computer Networks

By Scale By Structure By Topology

Network Media Internetworking

Computer Network

A computer network is a group of interconnected computers.

It allows computers to communicate with each other and to share resources and information.

First Network : The Advanced Research Projects Agency (ARPA) funded the design of the "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defense

Communication Model

Communication Model Source

generates data to be transmitted Transmitter

Converts data into transmittable signals Transmission System

Carries data Receiver

Converts received signal into data Destination

Takes incoming data

Communication Model

Transmission Modes Simplex

One direction e.g. Television

Half duplex Either direction, but

only one way at a time e.g. police radio

Full duplex Both directions at the

same time e.g. telephone

Communication Types

Unicasting (one-to-one)

Multicasting (one-to-many)

Broadcasting (one-to-all)

Network Classification

By Size or Scale LAN WAN MAN CAN PAN

Local Area Network (LAN) Contains printers, servers and computers Systems are close to each other Contained in one office or building Organizations often have several LANS

Wide Area Networks (WAN) Two or more LANs connected Over a large geographic area Typically use public or leased lines

Phone lines Satellite

The Internet is a WAN

Metropolitan Area Network (MAN)

Large network that connects different organizations

Shares regional resources A network provider sells time

Campus Area Networks (CAN)

A LAN in one large geographic area Resources related to the same organization Each department shares the LAN

Personal Area Network (PAN)

Very small scale network Range is less than 2 meters Cell phones, PDAs, MP3 players

Network Classification

By Structure / Functional Relationship Client / Server Peer to Peer (P2PN)

Client/Server network

Nodes and servers share data roles Nodes are called clients Servers are used to control access Database software

Access to data controlled by server Server is the most important computer

Peer to peer networks (P2PN)

All nodes are equal Nodes access resources on other nodes Each node controls its own resources Most modern OS allow P2PN Distributed computing is a form Kazaa

Network Classification

By Topology / Physical Connectivity BUS STAR RING MESH TREE

Network Topology

Logical layout of wires and equipment Choice affects

Network performanceNetwork sizeNetwork collision detection

Bus Also called linear bus

One wire connects all nodes

Terminator ends the wires

Advantages Easy to setup Small amount of wire

Disadvantages Slow Easy to crash

Star All nodes connect to a hub

Packets sent to hub Hub sends packet to destination

Advantages Easy to setup One cable can not crash network

Disadvantages One hub crashing downs entire network Uses lots of cable

Most common topology

Ring

Nodes connected in a circle

Tokens used to transmit data Nodes must wait for token to send

Advantages Time to send data is known No data collisions

Disadvantages Slow Lots of cable

Mesh All computers connected together

Internet is a mesh network

Advantage Data will always be delivered

Disadvantages Lots of cable Hard to setup

Tree

Hierarchal Model

Advantages Scaleable Easy Implementation Easy Troubleshooting

Network Media

Links that connect nodes Choice impacts

Speed Security Size

Twisted-pair cabling

Most common LAN cable

Called Cat5 or 100BaseT

Four pairs of copper cable twisted

May be shielded from interference

Speeds range from 1 Mbps to 1,000 Mbps

Coaxial cable Similar to cable TV wire

One wire runs through cable

Shielded from interference

Speeds up to 10 Mbps

Nearly obsolete

Fiber-optic cable

Data is transmitted with light pulses

Glass strand instead of cable

Immune to interference

Very secure

Hard to work with

Speeds up to100 Gbps

Wireless Media Data transmitted through the air

LANs use radio waves

WANs use microwave signals

Easy to setup

Difficult to secure

Internetwork

An internetwork is the connection of two or more distinct computer networks or network segments via a common routing technology.

Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.

Internetwork - Extranet An extranet is a network or internetwork that is

limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities

by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Internetwork - Intranet An intranet is a set of networks, using the

Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity.

Most commonly, an intranet is the internal network of an organization

Internetwork - Internet

The Internet consists of a worldwide interconnection of governmental, academic, public, and private networks based upon the networking technologies of the Internet Protocol Suite.

It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the U.S. Department of Defense.

The Internet is also the communications backbone underlying the World Wide Web (WWW).

The Internet: Key Technology Concepts

Federal Networking Council definition of Internet highlights three important concepts that are basis for understanding the Internet: Packet switching TCP/IP communications protocol Client/server computing

Packet Switching

A method of slicing digital messages into packets, sending the packets along different communication paths as they become available, and then reassembling the packets once they arrive at their destination

Uses routers: special purpose computers that interconnect the computer networks that make up the Internet and route packets to their ultimate destination

Routers use computer programs called routing algorithms to ensure packets take the best available path toward their destination

Packet Switching

TCP/IP (Transmission Control Protocol/Internet Protocol)

Protocol: a set of rules for formatting, ordering, compressing and error-checking messages

TCP: Establishes the connections among sending and receiving Web computers, handles thee assembly of packets at the point of transmission, and their reassembly at the receiving end

IP: Provides the Internet’s addressing scheme TCP/IP is divided into 4 separate layers:

Network Interface Layer Internet Layer Transport Layer Application Layer

The TCP/IP Architecture and Protocol Suite

IP Addresses Internet address (also called IP address): a 32-

bit number expressed as a series of four separate numbers marked off by periods, such as 201.61.186.227

IPv4 the current version of IP. Can handle up to 4 billion addresses

IPv6 (next generation of IP) will use 128-bit addresses and be able to handle up 1 quadrillion addresses

Routing Internet Messages: TCP/IP and Packet Switching

Figure 3.6, Page 129

Domain Names and URLs Domain name: IP address expressed in natural

language Domain name system (DNS): allows numeric

IP addresses to be expressed in natural language Example: cnet.com = 216.200.247.134

Uniform resource locator (URL): addresses used by Web browsers to identify location of content on the Web

The Hierarchical Domain Name System

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Circuit switching

Circuit switching was the switching technique used in communication networks because it is simple enough to carry analog signals.

Eg. Phone system

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Contd..

Circuit switching provides traffic isolation and traffic engineering, but at the expense of using bandwidth inefficiently and signaling overhead. It is often said that these two drawbacks make circuits witching highly inflexible, especially in a highly dynamic environment such as the Internet..

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Packet switching

Packet switching is the basis for the InternetProtocol (IP) In packet switching, information flows are broken into variable-size packets (or fixed-size cells as in the case of ATM).These packets are sent, one by one, to the nearest router, which will look up the destination address, and then forward them to the corresponding next hop. This process is repeated until the packet reaches its destination. The routing of the information is thus done locally, hop-by-hop. Routing decisions are independent of other decisions in the past and in other routers;

Client/Server Computing

Model of computing in which very powerful personal computers (clients) are connected in a network with one or more server computers that perform common functions for the clients, such as storing files, software applications, etc.

The Client/Server Computing Model

Insight on Business: Peer-to-Peer Computing Goes to Work

Peer-to-peer computing an outgrowth of client/server computing model

Allows client computers to share resources without intervention of a central server

Most often used for sharing music and other file over the Internet, in violation of copyright laws

However, some new legitimate uses such as Groove Workspace, a P2P platform developed by Groove Networks

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What is network interface card?

A network interface card (NIC) is a circuit board or card that is installed in a computer so that it can be connected to a network. 

A network interface card provides the computer with a dedicated, full-time connection to a network. Personal computers and workstations on a local area network (LAN) typically contain a network interface card specifically designed for the LAN transmission technology 

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What is a Modem?

Definition: Traditional modems used on dialup networks convert data between the analog form used on telephone lines and the digital form used on computers. Standard dial-up network modems transmit data at a maximum rate of 56,000 bits per second (56 Kbps). However, inherent limitations of the public telephone network limit modem data rates to 33.6 Kbps or lower in practice.

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What is the difference between a router and a modem?

Routers and modems are two of the most common computer peripherals, yet many people don't know the function of each one. While the two devices may look similar, they each serve a difference purpose. Fortunately, the functions of the two devices are pretty easy to understand.

A router is a small box that allows multiple computers to join the same network (see below).

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Contd..

Routers Modem A modem is a device that

provides access to the Internet (see below).

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What is Hub?

A common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

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Contd..

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What is Switch?

In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.

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Contd..

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What is Router?

A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP.s network. Routers are located at gateways, the places where two or more networks connect. Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

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What is Network Gateway?

Definition: A network gateway is an internetworking system capable of joining together two networks that use different base protocols. A network gateway can be implemented completely in software, completely in hardware, or as a combination of both.

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What is Gateway?

A device that connects two local-area networks (LANs), or two segments of the same LAN that use the same protocol, such as Ethernet or Token-Ring.

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Thank you