NetworksNetworks

For VCE Software For VCE Software Development ¾, Development ¾, 20072007Adrian Janson,Adrian Janson,Melbourne High SchoolMelbourne High School

What is a network?What is a network?

A network is two A network is two or more or more computers computers connected connected together for the together for the purpose of:purpose of: sharing resources sharing resources

(printers, files, (printers, files, software, software, hardware)hardware)

communicationcommunication

How are they classified?How are they classified?

Their size: LAN, WANTheir size: LAN, WAN Their configuration: client-server, peer-Their configuration: client-server, peer-

to-peer (no servers)to-peer (no servers) The rules they use to exchange data: The rules they use to exchange data:

protocolsprotocols How they are linked together: cable, How they are linked together: cable,

wirelesswireless Their logical shape (topology): bus, tree, Their logical shape (topology): bus, tree,

star, ring, meshstar, ring, mesh

Types of networks:Types of networks:

Local Area Networks Local Area Networks (LAN)(LAN) One locationOne location

Wide Area Networks Wide Area Networks (WAN)(WAN) Centralised WAN: Centralised WAN:

Servers in one locationServers in one location Distributed WAN: Distributed WAN:

Servers distributed Servers distributed throughout the throughout the network (the Internet network (the Internet is an example of this)is an example of this)

LAN

WAN

Network configurationsNetwork configurations Client-serverClient-server

File serverFile server Files stored and accessed Files stored and accessed

from central locationfrom central location Application serverApplication server

Applications installed and Applications installed and executed from central executed from central location.location.

Often used in combination Often used in combination with file serverswith file servers

Peer-to-peerPeer-to-peer No serversNo servers Applications installed on Applications installed on

each PC, files shared each PC, files shared

ProtocolsProtocols

A protocol is a convention A protocol is a convention or a standard that controls or a standard that controls or enables the connection, or enables the connection, communication and data communication and data transfer between transfer between computers on a networkcomputers on a network

Contains rules governing Contains rules governing the syntax, semantics and the syntax, semantics and synchronization of synchronization of communicationcommunication

May be implemented by May be implemented by hardware, software or a hardware, software or a combinationcombination

Like two people agreeing to Like two people agreeing to speak the same language…speak the same language…

Communication protocolsCommunication protocols

Communication protocols are Communication protocols are specifically designed to control data specifically designed to control data transfer over a communications channeltransfer over a communications channel

Some common examples:Some common examples: TCP/IP: Two protocols that control TCP/IP: Two protocols that control

communication across the Internet communication across the Internet and some networksand some networks

POP3, IMAP, SMTP: Protocols that can POP3, IMAP, SMTP: Protocols that can be used to send and receive emailbe used to send and receive email

HTTP: Method of publishing and HTTP: Method of publishing and retrieving web pagesretrieving web pages

FTP: Protocol for sending and FTP: Protocol for sending and receiving filesreceiving files

These examples are These examples are often referred to as the often referred to as the ‘Internet protocols’‘Internet protocols’

Network ProtocolsNetwork Protocols

Rules and conventions Rules and conventions for communication for communication between network between network devicesdevices

The commonly used The commonly used are are Ethernet, Wi-FiEthernet, Wi-Fi

Others exist but are not Others exist but are not as widely usedas widely used

EthernetEthernet Uses an access method called Uses an access method called

CSMA/CD (Carrier Sense Multiple CSMA/CD (Carrier Sense Multiple Access/Collision Detection)Access/Collision Detection) CS – Computers (or nodes) ‘listen’ CS – Computers (or nodes) ‘listen’

to the network to see if there are to the network to see if there are any signals being transmittedany signals being transmitted

MA – All computers (or nodes) can MA – All computers (or nodes) can ‘hear’ what is being transmitted on ‘hear’ what is being transmitted on the network at any one timethe network at any one time

CD – Collision detection: two CD – Collision detection: two computers (or nodes) could computers (or nodes) could transmit at the same time, causing transmit at the same time, causing a collisiona collision

EthernetEthernet What happens when there is a What happens when there is a

collision?collision? Each computer (or node) waits a Each computer (or node) waits a

random amount of time and then random amount of time and then retransmitsretransmits

The random time delay is usually The random time delay is usually enough to ensure the collision enough to ensure the collision does not reoccurdoes not reoccur

The Ethernet specified speed The Ethernet specified speed is 10Mb/sis 10Mb/s

The Fast Ethernet standard The Fast Ethernet standard increases this to 100Mb/sincreases this to 100Mb/s

Wi-FiWi-Fi

Based on the 802.11x Based on the 802.11x standardstandard

Cannot do collision Cannot do collision detection and instead detection and instead uses RTS/CTSuses RTS/CTS RTS: Request to send – RTS: Request to send –

packet sent by the packet sent by the sendersender

CTS: Clear to send – CTS: Clear to send – packet sent by the packet sent by the intended recipient that intended recipient that alerts all other nodes to alerts all other nodes to be ‘quiet’be ‘quiet’

TCP/IPTCP/IP

TCP/IP consists of two TCP/IP consists of two protocols: TCP and IP protocolprotocols: TCP and IP protocol TCP (Transport Control Protocol)TCP (Transport Control Protocol)

Used to divide data that needs to be Used to divide data that needs to be transmitted into a number of transmitted into a number of packets, each with a sequence packets, each with a sequence numbernumber

The TCP at the destination address The TCP at the destination address assembles the data and notifies the assembles the data and notifies the sender if any packets are not sender if any packets are not received within a certain time received within a certain time (‘timeout’)(‘timeout’)

IP (Internet Protocol)IP (Internet Protocol) Defines how information gets sent Defines how information gets sent

between network nodes between network nodes

TCP/IP: IP AddressTCP/IP: IP Address

In order for packets to be able In order for packets to be able to be sent across the Internet to be sent across the Internet or a network, each node must or a network, each node must have a unique IP address (just have a unique IP address (just like a street address)like a street address)

Domain Name Servers (DNS) Domain Name Servers (DNS) translate URLs to IP addressestranslate URLs to IP addresses

An IP address consists of 4 An IP address consists of 4 bytes (32 bits)bytes (32 bits) For example: 255.255.255.255For example: 255.255.255.255

TCP/IP: PacketsTCP/IP: Packets TCP divides data to be TCP divides data to be

sent into packetssent into packets Each packet contains:Each packet contains:

A header consisting of:A header consisting of: a destination addressa destination address a source addressa source address the packet numberthe packet number the total number of packets the total number of packets a checksuma checksum and some other things…and some other things…

The data itself (known as The data itself (known as the payload)the payload)

A trailerA trailer

TCP/IP: From source to TCP/IP: From source to destinationdestination

If a packet arrives at a If a packet arrives at a destination with an incorrect destination with an incorrect checksum, it is discardedchecksum, it is discarded

The path from the source to The path from the source to destination is in flux, therefore destination is in flux, therefore packets ‘get lost’, are packets ‘get lost’, are corrupted or are duplicatedcorrupted or are duplicated

If a ‘timeout’ occurs or a If a ‘timeout’ occurs or a packet is corrupted, a request packet is corrupted, a request for a resend of that packet is for a resend of that packet is sentsent

After several unsuccessful After several unsuccessful attempts at receiving a attempts at receiving a packet, the connection is packet, the connection is brokenbroken

Network HardwareNetwork Hardware

Network hardware Network hardware includes:includes: Network Interface Network Interface

Controllers (NICs)Controllers (NICs) Switches / HubsSwitches / Hubs RepeatersRepeaters BridgesBridges RoutersRouters Transmission Transmission

media (cabling)media (cabling)

Network interface Network interface controllercontroller

NICs provide a physical NICs provide a physical connection from a connection from a computer (or node) to computer (or node) to the networkthe network

Can be integrated on Can be integrated on the motherboardthe motherboard

Each has a unique 48-Each has a unique 48-bit MAC addressbit MAC address Stored in ROMStored in ROM Media Access ControlMedia Access Control Acts like a name for the Acts like a name for the

cardcard No two the sameNo two the same

http://en.wikipedia.org/wiki/Network_card

HubsHubs

Connects a number Connects a number of NICs togetherof NICs together

Consists of a number Consists of a number of portsof ports

Signals arriving at Signals arriving at one port and sent to one port and sent to all other portsall other ports

Large number of Large number of collisions: a “dumb collisions: a “dumb device”device” http://en.wikipedia.org/wiki/Ethernet_hub

SwitchesSwitches

Sends data only to the Sends data only to the port that requires it – a port that requires it – a “clever hub”“clever hub”

Reduces collisions – and Reduces collisions – and in many cases can in many cases can eliminate them eliminate them altogetheraltogether

Much better than hubs – Much better than hubs – traditionally were much traditionally were much more expensive, but more expensive, but this is no longer the this is no longer the case case

http://en.wikipedia.org/wiki/Network_switch

RepeatersRepeaters

As a network signal As a network signal degrades as it degrades as it travels over large travels over large distances, a distances, a repeater can be repeater can be used to boost the used to boost the signalsignal

Both switches and Both switches and hubs act as hubs act as repeatersrepeaters

http://www.unitedsale.net/products/image-02/D-Link-DWL-G710-Range-Extender-2.jpg

BridgesBridges

Network devices that Network devices that can be used to can be used to connect two different connect two different physical networks physical networks togethertogether

For example, a bridge For example, a bridge could be used to join could be used to join an ethernet network an ethernet network and a fast ethernet and a fast ethernet network or a star and network or a star and a bus topologya bus topology

http://www.stream-shop.ru/Modems/P6212.jpg

RoutersRouters

Acts as a junction between Acts as a junction between two or more networkstwo or more networks

Directs traffic in the same Directs traffic in the same way as a switch, but can also way as a switch, but can also translate and filter (firewall)translate and filter (firewall)

Used to connect LANs to the Used to connect LANs to the InternetInternet For example, a router may For example, a router may

connect to the Internet and be connect to the Internet and be assigned an IP address by an assigned an IP address by an ISPISP

IP addresses may exist within IP addresses may exist within the LAN that duplicate those on the LAN that duplicate those on the Internet, but the router the Internet, but the router ensures these are private to the ensures these are private to the LANLAN

http://shopproducts.howstuffworks.com/Linksys+WRT54GS+Wireless+Router/SF-1/PID-20664068

Bridges vs RoutersBridges vs Routers

Bridges and routers Bridges and routers work in different ways work in different ways (on different OSI layers (on different OSI layers – look up the definition – look up the definition of this if you want to of this if you want to know more)know more)

Bridges are not able to Bridges are not able to convert from one convert from one protocol to another protocol to another where routers canwhere routers can

http://images.amazon.com/images/P/B000H1L5W4.01._AA280_SCLZZZZZZZ_V61775592_.jpg

Network CablingNetwork Cabling

Cables transmit data Cables transmit data from one network node from one network node to anotherto another

Several types of cable Several types of cable exist, each having a exist, each having a particular bandwidthparticular bandwidth Coaxial cableCoaxial cable UTP cableUTP cable Fibre optic cableFibre optic cable

Different types can be Different types can be used within the same used within the same network, but this can network, but this can affect bandwidthaffect bandwidth

Coaxial cableCoaxial cable

Consists of a round Consists of a round conducting wire, surrounded conducting wire, surrounded by an insulating spacer, by an insulating spacer, surrounded by a cylindrical surrounded by a cylindrical conducting sheath conducting sheath

Highly resistant to signal Highly resistant to signal interferenceinterference

Not used much todayNot used much today Bayonet style connectorsBayonet style connectors Often associated with bus Often associated with bus

networksnetworks Bandwidth: 10Mb/sBandwidth: 10Mb/s

http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci211806,00.html

http://www.fotosearch.com/results.asp?keyword=coaxial+cable&category=&searchtype=sss

UTP CableUTP Cable

Unshielded Twisted Pair Unshielded Twisted Pair (UTP) is the most popular (UTP) is the most popular cabling used currentlycabling used currently

Also comes in a Shielded Also comes in a Shielded Twisted Pair version, that Twisted Pair version, that prevent interferenceprevent interference

Cables are twisted Cables are twisted together to decrease together to decrease interferenceinterference

Length limit is 100 metresLength limit is 100 metres CheapCheap

UTP CableUTP Cable

Connector on the end is Connector on the end is called an RJ45called an RJ45

CAT5 is most common CAT5 is most common version and provides a version and provides a bandwidth of 100Mb/sbandwidth of 100Mb/s

CAT5e can provide CAT5e can provide 1000Mb/s (or a 1000Mb/s (or a gigabit/s)gigabit/s)

CAT6a is a future CAT6a is a future specification designed specification designed for 10Gb/s!for 10Gb/s!

http://en.wikipedia.org/wiki/Category_5_cable

http://en.wikipedia.org/wiki/Image:UTP_ethernet_cable_8pin_modular_jack_endings.jpg

Fiber Optic CableFiber Optic Cable Transmits light using the concept of critical Transmits light using the concept of critical

angleangle As a result, cannot bend through tight anglesAs a result, cannot bend through tight angles Not affected by interferenceNot affected by interference Can carry multiple signals at the same timeCan carry multiple signals at the same time Very hand bandwidth possibleVery hand bandwidth possible Expensive and difficult to installExpensive and difficult to install

http://www.fotosearch.com/PDS084/aa031778/

Wireless LANsWireless LANs

Wireless network Wireless network hardware is availablehardware is available Wireless routerWireless router Wireless NICWireless NIC Wireless Access Point Wireless Access Point

(equivalent to a switch)(equivalent to a switch) Relatively cheap and Relatively cheap and

easy to installeasy to install Encryption a must!Encryption a must!

WAP (Wireless Application WAP (Wireless Application Protocol)Protocol)

WPA, WPA2 are betterWPA, WPA2 are better

Wireless LANsWireless LANs

802.11x is a set of standards 802.11x is a set of standards defining the way signals are defining the way signals are formatted, the frequencies they formatted, the frequencies they use and ultimately, transfer use and ultimately, transfer speedspeed 802.11a: (1999), max 54Mb/s802.11a: (1999), max 54Mb/s 802.11b: (1999), max 11Mb/s802.11b: (1999), max 11Mb/s 802.11g: (2003), max 54Mb/s802.11g: (2003), max 54Mb/s 802.11n (draft): (2007), max 802.11n (draft): (2007), max

540Mb/s540Mb/s Typical speeds are often half the Typical speeds are often half the

max speeds due to other network max speeds due to other network traffictraffic

Most devices are backwards Most devices are backwards compatible, for example a device compatible, for example a device might be 802.11bgmight be 802.11bg

http://en.wikipedia.org/wiki/Image:Linksys_Router.png

TopologyTopology

The arrangement of The arrangement of nodes within a networknodes within a network

Main types :Main types : BusBus StarStar RingRing TreeTree MeshMesh

http://en.wikipedia.org/wiki/Image:NetworkTopologies.png

BusBus

Contains a backbone Contains a backbone which usually runs which usually runs the length of the the length of the networknetwork

Ends are normally Ends are normally terminated using terminated using special connectorsspecial connectors

Often associated with Often associated with coaxial cablecoaxial cable

http://compnetworking.about.com/od/networkdesign/ig/Computer-Network-Topologies/Bus-Network-Topology-Diagram.htm

StarStar

In a star network, a In a star network, a central point is used central point is used to connect all other to connect all other network nodesnetwork nodes

The central point is The central point is usually a hub or a usually a hub or a switchswitch

Common network Common network topologytopology

Easy and cheap to Easy and cheap to implementimplement

http://compnetworking.about.com/od/networkdesign/ig/Computer-Network-Topologies/Ring-Network-Topology-Diagram.htm

RingRing All network nodes are All network nodes are

connected in a ringconnected in a ring A token is passed around A token is passed around

the network from one the network from one computer to anothercomputer to another

Only the node that holds Only the node that holds the token can transmit the token can transmit datadata

No collisionsNo collisions Used to be implemented Used to be implemented

using coaxial cable and is using coaxial cable and is sometimes used with fibre sometimes used with fibre optic cable todayoptic cable today

Two rings transmitting Two rings transmitting data in different directions data in different directions can be usedcan be used

http://compnetworking.about.com/od/networkdesign/ig/Computer-Network-Topologies/Ring-Network-Topology-Diagram.htm

TreeTree

A tree topology A tree topology combines star combines star and bus and bus topologiestopologies

Usually this Usually this takes the form takes the form of star of star networks linked networks linked by a network by a network backbone (or a backbone (or a bus network)bus network)

http://compnetworking.about.com/od/networkdesign/ig/Computer-Network-Topologies/Tree-Network-Topology-Diagram.htm

MeshMesh

A mesh topolgy is A mesh topolgy is one in which paths one in which paths between network between network nodes are often nodes are often changing as the changing as the status of nodes status of nodes changeschanges

The Internet is a The Internet is a perfect example of a perfect example of a mesh topology mesh topology http://compnetworking.about.com/od/networkdesign/ig/Computer-

Network-Topologies/Mesh-Network-Topology-Diagram.htm