DefinitionDefinition

A computer network is a group of interconnected computers.

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

ComponentsComponents

A minimum of at least 2 computers Cables or wireless communication that

connect the computers to each other. A network interface device on each computer

(this is called a network interface card or NIC) A ‘Switch’ used to switch the data from one

point to another. Network operating system software.

Types of networkTypes of network

The three basic types of networks include:

Local Area Network (LAN)

Metropolitan Area Network (WAN)

Wide Area Network (WAN)

Local Area Network (LAN)

A LAN covers a relatively small area such as a classroom, school, or a single building

LANs are inexpensive to install and also provide higher speeds.

Metropolitan Area Network (MAN)

A MAN spans the distance of a typical metropolitan city

The cost of installation and operation is higher MANs use high-speed connections such as

fiber optics to achieve higher speeds.

Wide Area Network (WAN)

WANs span a larger area than a single city. These use long distance telecommunication

networks for connection, thereby increasing the cost.

The Internet is a good example of a WAN.

Network Configuration

Classification based on how computers behave in a network

Two classifications are: Peer-to-Peer networkPeer-to-Peer network Server based networkServer based network

Peer-to-Peer Networks

In a peer-to-peer network, the networked computers act as equal partners, or peers, to each other.

As peers, each computer can take on the client function or the server function alternately.

Client/Server Networks

In a client/server network arrangement, network services are located in a dedicated computer whose only function is to respond to the requests of clients.

The server contains the file,

print, application, security, and other services in a central computer that is continuously available to respond to client requests.

Networking hardware

Hub – electronic device (with a number of ports) used in a LAN to link groups of computers

Repeaters (also called amplifiers) – electronic devices that receive signals and amplify and send them along the network

Routers - electronic devices used to ensure messages are sent to their intended destinations

Gateway – consists of hardware and/or software that allows communications between dissimilar networks

Bridge – consists of hardware and/or software that allows communication between two similar networks

Network Topologies

A network topology describes the layout of the wire and devices as well as the paths used by data transmissions.

Bus TopologyBus Topology Also called linear bus One wire connects all

nodes Terminator ends the

wires

Network Topologies

Star TopologyStar Topology All nodes connect to a hub

Packets sent to hubHub sends packet to

destination

Ring TopologyRing Topology Nodes connected in a circle Tokens used to transmit

data

Network Topologies

Mesh TopologyMesh Topology All computers connected

together Internet is a mesh network

Tree TopologyTree Topology Hierarchal Model Combines characteristics of

linear bus and star topologies.

Communications Media

Communications ChannelCommunications Channel

To transfer data from one computer to another requires some type of link through which the data can be transmitted. This link is known as the communications channel.

To send data through the channel requires some type of transmission media, which may be either physical or wireless.

Physical Media

Twisted-pair cable Twisted-pair cable Pair of insulated copper wires Types

Shielded(STP) Unshielded(UTP)

UTP common in LAN Max. cable length – 100 meters Least expensive type of cable Used in many telephone systems

Physical Media

Co-axial cable Co-axial cable Consists of an insulated

center wire grounded by a shield of braided wire

Carries data as electromagnetic signals

Good resistance against interference

Used by the cable television industry

Physical Media

Fiber optic cable Fiber optic cable Core – cylinder of glass Bandwidth is greater, so it

can carry more data Not subject to interference Transfer rate – more than

100 mbps Expensive

Wireless Media

Microwave system Microwave system – transmits data via high-frequency

radio signals through the atmosphereSatellite system Satellite system – receive transmitted signals, amplify

them, and then transmit the signals to the appropriate locations

Wireless Media

Cellular technology Cellular technology – uses antennae resembling telephone

towers to pick up radio signals within a specific area (cell)

Infrared technology Infrared technology – transmits data as infrared light waves

from one device to another, providing wireless links between PCs and peripherals

InternetworkInternetworkAn 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.

IntranetAn intranet is a private LAN designed for

use by everyone within an organization. An intranet might consist of an internal e-mail system, a message board and one or more Web site portals that contain company news, forms, and personnel information

ExtranetA network that connects people

within your company with people who are outside your company--all within a secure, password-protected network that can be accessed from anywhere.

InternetA computer network consisting of a

worldwide network of computer networks that use the TCP/IP network protocols to facilitate data transmission and exchange

Internet Connections

Internet backbone : A set of high-speed networks that carry Internet traffic.These networks are provided by companies such as AT&T, GTE, and IBM

Internet service provider (ISP) : A company that provides other companies or individuals with access to the Internet

Internet Connections There are various technologies available that you can

use to connect a home computer to the Internet A phone modem converts computer data into an

analog audio signal for transfer over a telephone line, and then a modem at the destination converts it back again into data

A digital subscriber line (DSL) uses regular copper phone lines to transfer digital data to and from the phone company’s central office

A cable modem uses the same line that your cable TV signals come in on to transfer the data back and forth

Internet Connections

Broadband A connection in which transfer speeds are faster than 128 bits per second DSL connections and cable modems are

broadband connections The speed for downloads (getting data from

the Internet to your home computer) may not be the same as uploads (sending data from your home computer to the Internet)

Packet Switching

To improve the efficiency of transferring information over a shared communication line, messages are divided into fixed-sized, numbered packets

Network devices called routers are used to direct packets between networks

Open System Interconnection (OSI)

The International Organization for Standardization (ISO) established the Open Systems Interconnection (OSI) Reference Model

Each layer deals with a particular aspect of network communication

Network Protocols

Network protocols are layered such that each one relies on the protocols that underlie it

Sometimes referred to as a protocol stack

TCP/IP Protocol

TCP stands for Transmission Control Protocol TCP software breaks messages into packets,

hands them off to the IP software for delivery, and then orders and reassembles the packets at their destination

IP stands for Internet Protocol IP software deals with the routing of packets

through the maze of interconnected networks to their final destination

Internet Connections

Other protocols build on the foundation established by the TCP/IP protocol suite

Simple Mail Transfer Protocol (SMTP)File Transfer Protocol (FTP)TelnetHyper Text Transfer Protocol (HTTP)

Network Security

FIREWALLS :

Network Security

Firewalls can either be hardware and/or software based.

It sits at the gateway between the two networks, usually a private network and a public network such as the internet.

All traffic from inside to outside and vice versa, must pass through the firewall.

Only authorized traffic as defined by the local security policy, will be allowed to pass.

The firewall itself is immune to penetration.