Networks For VCE Software Development ¾, 2007 Adrian Janson, Melbourne High School

What is a network? A network is two or more computers connected together for the purpose of: sharing resources (printers, files, software, hardware) communication

How are they classified? Their size: LAN, WAN Their size: LAN, WAN Their configuration: client-server, peer-to-peer (no servers) Their configuration: client-server, peer-to-peer (no servers) The rules they use to exchange data: protocols The rules they use to exchange data: protocols How they are linked together: cable, wireless How they are linked together: cable, wireless Their logical shape (topology): bus, tree, star, ring, mesh Their logical shape (topology): bus, tree, star, ring, mesh

Types of networks: Local Area Networks (LAN) One location Wide Area Networks (WAN) Centralised WAN: Servers in one location Distributed WAN: Servers distributed throughout the network (the Internet is an example of this) LAN WAN

Network configurations Client-server Client-server File server File server Files stored and accessed from central location Files stored and accessed from central location Application server Application server Applications installed and executed from central location. Applications installed and executed from central location. Often used in combination with file servers Often used in combination with file servers Peer-to-peer Peer-to-peer No servers No servers Applications installed on each PC, files shared Applications installed on each PC, files shared

Protocols A protocol is a convention or a standard that controls or enables the connection, communication and data transfer between computers on a network A protocol is a convention or a standard that controls or enables the connection, communication and data transfer between computers on a network Contains rules governing the syntax, semantics and synchronization of communication Contains rules governing the syntax, semantics and synchronization of communication May be implemented by hardware, software or a combination May be implemented by hardware, software or a combination Like two people agreeing to speak the same language… Like two people agreeing to speak the same language…

Communication protocols Communication protocols are specifically designed to control data transfer over a communications channel Communication protocols are specifically designed to control data transfer over a communications channel Some common examples: Some common examples: TCP/IP: Two protocols that control communication across the Internet and some networks TCP/IP: Two protocols that control communication across the Internet and some networks POP3, IMAP, SMTP: Protocols that can be used to send and receive POP3, IMAP, SMTP: Protocols that can be used to send and receive HTTP: Method of publishing and retrieving web pages HTTP: Method of publishing and retrieving web pages FTP: Protocol for sending and receiving files FTP: Protocol for sending and receiving files These examples are often referred to as the ‘Internet protocols’

Network Protocols Rules and conventions for communication between network devices The commonly used are Ethernet, Wi-Fi Others exist but are not as widely used

Ethernet Uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection) CS – Computers (or nodes) ‘listen’ to the network to see if there are any signals being transmitted MA – All computers (or nodes) can ‘hear’ what is being transmitted on the network at any one time CD – Collision detection: two computers (or nodes) could transmit at the same time, causing a collision

Ethernet What happens when there is a collision? Each computer (or node) waits a random amount of time and then retransmits The random time delay is usually enough to ensure the collision does not reoccur The Ethernet specified speed is 10Mb/s The Fast Ethernet standard increases this to 100Mb/s

Wi-Fi Based on the x standard Based on the x standard Cannot do collision detection and instead uses RTS/CTS Cannot do collision detection and instead uses RTS/CTS RTS: Request to send – packet sent by the sender RTS: Request to send – packet sent by the sender CTS: Clear to send – packet sent by the intended recipient that alerts all other nodes to be ‘quiet’ CTS: Clear to send – packet sent by the intended recipient that alerts all other nodes to be ‘quiet’

TCP/IP TCP/IP consists of two protocols: TCP and IP protocol TCP/IP consists of two protocols: TCP and IP protocol TCP (Transport Control Protocol) TCP (Transport Control Protocol) Used to divide data that needs to be transmitted into a number of packets, each with a sequence number Used to divide data that needs to be transmitted into a number of packets, each with a sequence number The TCP at the destination address assembles the data and notifies the sender if any packets are not received within a certain time (‘timeout’) The TCP at the destination address assembles the data and notifies the sender if any packets are not received within a certain time (‘timeout’) IP (Internet Protocol) IP (Internet Protocol) Defines how information gets sent between network nodes Defines how information gets sent between network nodes

TCP/IP: IP Address In order for packets to be able to be sent across the Internet or a network, each node must have a unique IP address (just like a street address) In order for packets to be able to be sent across the Internet or a network, each node must have a unique IP address (just like a street address) Domain Name Servers (DNS) translate URLs to IP addresses Domain Name Servers (DNS) translate URLs to IP addresses An IP address consists of 4 bytes (32 bits) An IP address consists of 4 bytes (32 bits) For example: For example:

TCP/IP: Packets TCP divides data to be sent into packets TCP divides data to be sent into packets Each packet contains: Each packet contains: A header consisting of: A header consisting of: a destination address a destination address a source address a source address the packet number the packet number the total number of packets the total number of packets a checksum a checksum and some other things… and some other things… The data itself (known as the payload) The data itself (known as the payload) A trailer A trailer

TCP/IP: From source to destination If a packet arrives at a destination with an incorrect checksum, it is discarded If a packet arrives at a destination with an incorrect checksum, it is discarded The path from the source to destination is in flux, therefore packets ‘get lost’, are corrupted or are duplicated The path from the source to destination is in flux, therefore packets ‘get lost’, are corrupted or are duplicated If a ‘timeout’ occurs or a packet is corrupted, a request for a resend of that packet is sent If a ‘timeout’ occurs or a packet is corrupted, a request for a resend of that packet is sent After several unsuccessful attempts at receiving a packet, the connection is broken After several unsuccessful attempts at receiving a packet, the connection is broken

Network Hardware Network hardware includes: Network hardware includes: Network Interface Controllers (NICs) Network Interface Controllers (NICs) Switches / Hubs Switches / Hubs Repeaters Repeaters Bridges Bridges Routers Routers Transmission media (cabling) Transmission media (cabling)

Network interface controller NICs provide a physical connection from a computer (or node) to the network NICs provide a physical connection from a computer (or node) to the network Can be integrated on the motherboard Can be integrated on the motherboard Each has a unique 48-bit MAC address Each has a unique 48-bit MAC address Stored in ROM Stored in ROM Media Access Control Media Access Control Acts like a name for the card Acts like a name for the card No two the same No two the same

Hubs Connects a number of NICs together Connects a number of NICs together Consists of a number of ports Consists of a number of ports Signals arriving at one port and sent to all other ports Signals arriving at one port and sent to all other ports Large number of collisions: a “dumb device” Large number of collisions: a “dumb device”

Switches Sends data only to the port that requires it – a “clever hub” Sends data only to the port that requires it – a “clever hub” Reduces collisions – and in many cases can eliminate them altogether Reduces collisions – and in many cases can eliminate them altogether Much better than hubs – traditionally were much more expensive, but this is no longer the case Much better than hubs – traditionally were much more expensive, but this is no longer the case

Repeaters As a network signal degrades as it travels over large distances, a repeater can be used to boost the signal As a network signal degrades as it travels over large distances, a repeater can be used to boost the signal Both switches and hubs act as repeaters Both switches and hubs act as repeaters 02/D-Link-DWL-G710-Range-Extender- 2.jpg

Bridges Network devices that can be used to connect two different physical networks together Network devices that can be used to connect two different physical networks together For example, a bridge could be used to join an ethernet network and a fast ethernet network or a star and a bus topology For example, a bridge could be used to join an ethernet network and a fast ethernet network or a star and a bus topology shop.ru/Modems/P6212.jpg

Routers Acts as a junction between two or more networks Acts as a junction between two or more networks Directs traffic in the same way as a switch, but can also translate and filter (firewall) Directs traffic in the same way as a switch, but can also translate and filter (firewall) Used to connect LANs to the Internet Used to connect LANs to the Internet For example, a router may connect to the Internet and be assigned an IP address by an ISP For example, a router may connect to the Internet and be assigned an IP address by an ISP IP addresses may exist within the LAN that duplicate those on the Internet, but the router ensures these are private to the LAN IP addresses may exist within the LAN that duplicate those on the Internet, but the router ensures these are private to the LAN m/Linksys+WRT54GS+Wireless+Ro uter/SF-1/PID

Bridges vs Routers Bridges and routers work in different ways (on different OSI layers – look up the definition of this if you want to know more) Bridges and routers work in different ways (on different OSI layers – look up the definition of this if you want to know more) Bridges are not able to convert from one protocol to another where routers can Bridges are not able to convert from one protocol to another where routers can B000H1L5W4.01._AA280_SCLZZZ ZZZZ_V _.jpg

Network Cabling Cables transmit data from one network node to another Cables transmit data from one network node to another Several types of cable exist, each having a particular bandwidth Several types of cable exist, each having a particular bandwidth Coaxial cable Coaxial cable UTP cable UTP cable Fibre optic cable Fibre optic cable Different types can be used within the same network, but this can affect bandwidth Different types can be used within the same network, but this can affect bandwidth

Coaxial cable Consists of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath Consists of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath Highly resistant to signal interference Highly resistant to signal interference Not used much today Not used much today Bayonet style connectors Bayonet style connectors Often associated with bus networks Often associated with bus networks Bandwidth: 10Mb/s Bandwidth: 10Mb/s m/sDefinition/0,,sid7_gci211806,00.h tml lts.asp?keyword=coaxial+cable &category=&searchtype=sss

UTP Cable Unshielded Twisted Pair (UTP) is the most popular cabling used currently Unshielded Twisted Pair (UTP) is the most popular cabling used currently Also comes in a Shielded Twisted Pair version, that prevent interference Also comes in a Shielded Twisted Pair version, that prevent interference Cables are twisted together to decrease interference Cables are twisted together to decrease interference Length limit is 100 metres Length limit is 100 metres Cheap Cheap

UTP Cable Connector on the end is called an RJ45 Connector on the end is called an RJ45 CAT5 is most common version and provides a bandwidth of 100Mb/s CAT5 is most common version and provides a bandwidth of 100Mb/s CAT5e can provide 1000Mb/s (or a gigabit/s) CAT5e can provide 1000Mb/s (or a gigabit/s) CAT6a is a future specification designed for 10Gb/s! CAT6a is a future specification designed for 10Gb/s! _5_cable TP_ethernet_cable_8pin_modular_ja ck_endings.jpg

Fiber Optic Cable Transmits light using the concept of critical angle Transmits light using the concept of critical angle As a result, cannot bend through tight angles As a result, cannot bend through tight angles Not affected by interference Not affected by interference Can carry multiple signals at the same time Can carry multiple signals at the same time Very hand bandwidth possible Very hand bandwidth possible Expensive and difficult to install Expensive and difficult to install S084/aa031778/

Wireless LANs Wireless network hardware is available Wireless network hardware is available Wireless router Wireless router Wireless NIC Wireless NIC Wireless Access Point (equivalent to a switch) Wireless Access Point (equivalent to a switch) Relatively cheap and easy to install Relatively cheap and easy to install Encryption a must! Encryption a must! WAP (Wireless Application Protocol) WAP (Wireless Application Protocol) WPA, WPA2 are better WPA, WPA2 are better

Wireless LANs x is a set of standards defining the way signals are formatted, the frequencies they use and ultimately, transfer speed x is a set of standards defining the way signals are formatted, the frequencies they use and ultimately, transfer speed a: (1999), max 54Mb/s a: (1999), max 54Mb/s b: (1999), max 11Mb/s b: (1999), max 11Mb/s g: (2003), max 54Mb/s g: (2003), max 54Mb/s n (draft): (2007), max 540Mb/s n (draft): (2007), max 540Mb/s Typical speeds are often half the max speeds due to other network traffic Typical speeds are often half the max speeds due to other network traffic Most devices are backwards compatible, for example a device might be bg Most devices are backwards compatible, for example a device might be bg mage:Linksys_Router.png

Topology The arrangement of nodes within a network The arrangement of nodes within a network Main types : Main types : Bus Bus Star Star Ring Ring Tree Tree Mesh Mesh mage:NetworkTopologies.png

Bus Contains a backbone which usually runs the length of the network Contains a backbone which usually runs the length of the network Ends are normally terminated using special connectors Ends are normally terminated using special connectors Often associated with coaxial cable Often associated with coaxial cable gn/ig/Computer-Network-Topologies/Bus- Network-Topology-Diagram.htm

Star In a star network, a central point is used to connect all other network nodes In a star network, a central point is used to connect all other network nodes The central point is usually a hub or a switch The central point is usually a hub or a switch Common network topology Common network topology Easy and cheap to implement Easy and cheap to implement gn/ig/Computer-Network-Topologies/Ring- Network-Topology-Diagram.htm

Ring All network nodes are connected in a ring All network nodes are connected in a ring A token is passed around the network from one computer to another A token is passed around the network from one computer to another Only the node that holds the token can transmit data Only the node that holds the token can transmit data No collisions No collisions Used to be implemented using coaxial cable and is sometimes used with fibre optic cable today Used to be implemented using coaxial cable and is sometimes used with fibre optic cable today Two rings transmitting data in different directions can be used Two rings transmitting data in different directions can be used gn/ig/Computer-Network-Topologies/Ring- Network-Topology-Diagram.htm

Tree A tree topology combines star and bus topologies A tree topology combines star and bus topologies Usually this takes the form of star networks linked by a network backbone (or a bus network) Usually this takes the form of star networks linked by a network backbone (or a bus network) Network-Topologies/Tree-Network-Topology-Diagram.htm

Mesh A mesh topolgy is one in which paths between network nodes are often changing as the status of nodes changes A mesh topolgy is one in which paths between network nodes are often changing as the status of nodes changes The Internet is a perfect example of a mesh topology The Internet is a perfect example of a mesh topology Network-Topologies/Mesh-Network-Topology-Diagram.htm