Network Hardware and Software

What is a network?

A network consists of two or more computers that are linked in order to: share resources

(such as printers and CD-ROMs),

exchange files, or allow electronic

communications

How are they linked?

Computers on a network may be linked through: cables, telephone lines, radio waves,

satellites or wireless

technologies

The two basic types of networks include:

Local Area Networks (LAN)

Wide Area Networks (WAN)

LAN

WAN

Local area networks

LANs are confined to a relatively small area such as a school or a building

LANs usually have one computer designated as the file server

Other computers are connected to the network by cables connecting network interface cards in each computer

Wide Area Networks

WANs connect larger areas, such as whole states, or even the world.

Transoceanic cables and satellites are used to connect WANs

Protocol

A protocol is a set of rules that governs the communications between computers on a networkThese rules include guidelines that regulate the method of access, types of cabling and speed of data transfer

PROTOCOL =

SET OF RULES ABOUT

COMMUNICATIONS BETWEEN NETWORKS!

The most common protocols are:

Ethernet

Local Talk

Token Ring

FDDI

ATM

Protocol = a formal description of a set of rules and conventions that govern how devices on a network exchange information

Did you ever wonder what HTTP in web addresses was about? It stands for HyperText Transfer Protocol

Ethernet

Most widely used

Uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection

What does that mean?Each computer in the network ‘listens’ to the cable before sending anything through the network. If the network is clear, the computer will transmit.

If another computer is already transmitting on the cable, the computer will wait and try again when the line is clear

A bit like waiting for your younger sister to get off the telephone perhaps?

Ethernet (continued)Sometimes, two computers attempt to transmit at the same instant. When this happens, a collision occurs. Each computer then backs off and waits a random amount of time before attempting to retransmit.It is normal to have collisions using this method, but the delays caused by collisions and transmissions is small, and does not effect speed of transmission on the network

CSMA/CD =Carrier Sense Multiple

Access /Collision Detection

Ethernet (continued)

Ethernet protocol allows for data to be transmitted over twisted pair, coaxial or fiber optic cable at a speed of 10 Mbps

(more on that later)

Fast Ethernet

To allow for faster transmission, the Ethernet protocol has developed a new standard that supports 100 MbpsFast Ethernet requires the use of more expensive equipment and network cards

Gigabit Ethernet

The Ethernet protocol has also developed a new standard that allows transmission of 1 Gbps (gigabit per second)

One gigabit per second = one

thousand megabits per

second

Local Talk

Local Talk is a network protocol that was developed by Apple for Macintosh computersLocal Talk uses the CSMA/CA method (Carrier Sense Multiple Access with Collision Avoidance) which works in a similar way to CSMA/CDIt is a lot slower than Ethernet (only 230 Kbps)

Token RingToken ring protocol involves ‘token-passing’.

It is not as popular as Ethernet protocol

A single electronic ‘token’ moves around the ring from

one computer to the next. If a computer wishes to transit

and receives an empty token, it attaches data to the token which then proceeds around the ring until it comes to the computer the data is meant

for.

FDDI

Stands for Fiber Distributed Data InterfaceIs used mainly to connect two or more LANs, often over large distancesCan operate over fiber optic cable at 100 Mbps

ATM

Stands for Asynchronous Transfer Mode

Transmit data at a speed of 155 Mbps and higher

Works by transmitting all data in small packets of fixed size (other protocols transfer variable size packets)

Like FDDI , is most often used to connect two or more LANs

Where does TCP/IP fit into all this???

TCP/IP is the protocol that is used for the transmission of information over the Internet

IP (Internet Protocol) - the main delivery system for information over the Internet

TCP (Transport Control Protocol) - used to break apart and rebuild information that travels over the Internet

Network Hardware

Network hardware includes: Computers Peripherals Interface cards and Other equipment

needed to perform data processing and communications within the network

File servers

A very fast computer with a large amount of RAM and storage space along with a fast network interface cardThe network operating system software resides on this computer

Workstations

All computers connected to the file server on a network are called workstations

Network interface cardsThe network interface card (NIC) provides the physical connection between the network and the computer workstation.Most NICs are internal with the card fitting into an expansion slot in the computer.Three common network interface connections are Ethernet cards, Local Talk connectors and Token Ring cards

Ethernet cards

The most common Network Interface Cards are Ethernet cards

They contain connections for either coaxial or twisted pair cables, or both

Twisted pair cable

Co-axial cable

Concentrators / HubsA concentrator is a device that provides a central connection point for cables from workstations, servers and peripherals

Hubs are multi-slot concentrators

SwitchesWhile hubs provide an easy way to scale up and shorten the distance that the packets must travel to get from one node to another, they do not break up the actual network into discrete segments. That is where switches come in.

Switches (continued)A vital difference between a hub and a switch is that all the nodes connected to a hub share the bandwidth among themselves, while a device connected to a switch port has the full bandwidth all to itself.

Think of a switch as a ‘clever’ hub

Repeaters

A signal loses strength as it passes along a cable, so it is often necessary to boost the signal with a device called a repeater

A repeater might be a separate device, or might be part of a concentrator

Bridges

A bridge is a device that allows you to segment a large network into two smaller, more efficient networks

Routers

A router translates information from one network to anotherThe router directs traffic to prevent “head-on” collisionsIf you have a LAN that you want to connect to the Internet, you will need a router to serve as the translator between information on your LAN and the Internet

Routers (continued)

CablingNetwork cabling is the medium through which information usually moves from one network device to anotherThere are several different types of cable commonly used in LANSSome networks use a variety of cable types within the one network

Unshielded Twisted Pair (UTP) Cable

Twisted pair cables come in two varieties: shielded and unshielded. Unshielded (UTP) is the most popularShielded twisted pair is used only in environments where there may be electrical interference

UTP (continued)UTP has four pairs of wires inside the jacket

Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs

UTP Connector

The standard connector for UTP cabling is an RJ-45. It looks like a telephone style connection

Coaxial cableCoaxial cable has a single copper conductor at its centre with a plastic layer between the centre conductor and the braided metal shield

Although coaxial cabling is difficult to install, it is highly resistant to signal interference

Coaxial cable connectors

The most common type of connector used with coaxial cables is the BNC connector

Fiber Optic Cable

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materialsIt transmits light rather than electronic signalsIt is the standard for connecting networks between buildings, due to its immunity to the effects of moisture and light

Fiber Optic (continued)

Fiber optic cable has the ability to transmit signals over much longer distances than coaxial or twisted pairIt can also carry information at vastly greater speedsFiber optic cable is more difficult to install than other cabling

Wireless LANSWireless networks use high frequency radio signals to communicate between the workstations and the fileserver or hubs.Disadvantages of wireless networks are: they are expensive (relatively), provide poor security, are susceptible to interference and are slower than cabled networks

Network Operating Software

Network operating systems co-ordinate the activities of multiple computers across a network

The two major types of network OS are: Peer-to-peer Client/server

Peer to peer network OSIn peer to peer network OS, there is no file server or central management source; all computers are considered equal

Peer to peer networks are design primarily for small to medium LANS

AppleShare and Windows for Workgroups are examples of programs that can function as peer to peer

Client/Server network OSClient/server network OS centralise functions and applications in one or more dedicated file servers.

The file server provides access to resources and provides security

Novelle Netware and Windows NT Server are examples of client/server network operating systems

Topology

The physical topology of a network refers to the configuration of cables, computers and other peripherals.

The main types of network topologies are: Linear Bus Star Ring Tree or Hybrid

Linear BusA linear bus topology consists of a main run of cable with a terminator at each end. All servers workstations and peripherals are connected to the linear cable

Star

A star network is designed with each node (file server, workstation, peripheral) connected directly to a central network hub or server

Ring

A ring network is one where all workstations and other devices are connected in a continuous loop. There is no central server

Tree or hybrid

A tree or hybrid topology combines characteristics of linear bus and star and/or ring topologies.It consists of groups of star-configured workstations connected to a linear bus backbone cable