Networking For VCE IT By Mark Kelly Manager, Information Systems McKinnon Secondary College Lecture notes: Vceit.com
Networking Year 11 IT – all of the topics can be covered at a relatively simple level ITA – topologies and protocols are not in the study design and cannot be directly assessed Software Development – all topics are relevant Note – several complex issues have been grossly simplified in this presentation. For example, detailed differences between switches and routers at the transport level are not necessary in any VCE course and will only serve to frighten sensitive souls.
What is a network – should I panic? At its simplest, a network is two or more computers that are connected so they can exchange information and share resources.
Types of networks Networks can be classified by: • Their size (LAN, WAN, Internet); • Their servers (Client-Server, P2P); • The rules they use to exchange data (protocols – TCP/IP). • How they are linked together (cable, wireless); • Their ‘logical’ shape (bus, star, tree); • How network messages travel (Ethernet’s CSMA/CD)
Why network? • Efficiency – Better, faster communication – email, videoconferencing • Cost savings (email vs phone calls, physical travel), • Staff savings (e.g. networked helpdesk), • Equipment savings: printers, internet connections, internet cache, CD drives • Effectiveness – collaborative work is easier, access to resources is broader, group calendaring • Management - control over internet & printing, staff monitoring • Companyimageand “reach” – internet visibility makes any company international and accessible and “with it” • Customer service – many more ways to help customers (e.g. FAQ, downloads, online advice, email contact)
Types of networks, by size LANs – local area • Geographically limited, usually to one site. • Can be cabled (usually UTP, fibre optic, coaxial) or wireless.
Types of networks, by size WANs – Wide Area • Broad geographic coverage (e.g. state-wide, country-wide) • Connections use landline data cables (e.g. ISDN, ADSL), microwave, satellite. • Virtual Private Networks (VPN) can form a private network using the internet as a communication channel – much cheaper than leased ISDN lines.
The internet Made up of inter-networked WANs. No central boss. Users make and enforce rules. Uses all forms of media Mesh topology (many possible routes from A to B)
Server-Based Networks • Client/Server model • Automatically a pretty expensive choice compared to P2P • File server at the heart of the network • Server runs the Network Operating System (NOS) • Controls access to data and equipment • Runs ‘community’ programs • Offers control, security, centralisation, automation
Peer-to-Peer (P2P) networks • No server, cheap, simple, easy to run • All users have equal authority and rights • Little protection from each other • Used at home or in small orgs with trusted users • Share files, internet connection, printer • Internet music sharing networks (e.g. Kazaa) are P2P - no central computer; data and software on users’ computers. • P2P built into Win, Linux, Mac
Protocols Communication protocols are agreed sets of rules and procedures for computers to exchange information. Like humans agreeing to speak the same language during a conversation. For two computers to exchange data, they must be using the same protocols.
Human Protocols • during a phone call, saying “Uh huh”, “Mmmm” or “Yeah” while the other person speaks • nodding to show understanding • waiting for the other person to stop talking before you start • raising pitch of voice after a question • airline pilots speak English, refer to heights in feet, agree on which direction to turn to avoid collision, pronounce 9 as “niner”, spell out letters with words (Alpha, Bravo, Charlie etc.)
Network Protocols There is a standard protocol for each network communication task, such as: - how to send data over the Internet (TCP/IP) - how to send and receive email (POP, IMAP) - how to request and deliver web pages (HTTP) - how to request and deliver files (FTP)
Choosing Protocols Sometimes there is more than one choice of protocol for a task, such as how messages pass across a network (IPX/SPX vs TCP/IP, POP vs IMAP). As long as all the connected computers use the same protocol, it really does not matter which protocol is used (like diplomats agreeing on a language for negotiations) The internet only works because TCP/IP, POP, FTP and HTTP are universal standards, used by all shapes and sizes of computers.
The King of Protocols – TCP/IP The universal protocol for internet communications. The backbone of the internet. Made up of 2 complementary protocols… TCP (Transport Control Protocol) and IP (Internet Protocol)
Protocols – TCP • TCP (Transport Communication Protocol) • Breaks files into packets to be sent across the internet or a network. Each packet contains: • the address of the sender • the destination address • error-detecting checksum • a chunk of data (e.g. 1K)
Protocols – TCP/IP • IP (Internet Protocol)… • Once a file has been chopped into packets, the IP protocol delivers each packet to its destination. • each packet can take a different route from A to B, bouncing from router to router getting more precise with each hop. • the route is dynamically chosen for each packet, based on internet conditions at that time.
Protocols – TCP/IP TCP again… At the packets’ destination the receiving computer’s TCP re-assembles packets back into the original file. Recalculates checksum to see if packet is OK If packets are damaged, lost or delayed in transit, TCP will request the server to send the packet again.
Packet Switching Any protocol that breaks files into packets (like TCP/IP does) is called packet switching. (Compare with circuit switching used by telephones where a full-time path is set up for the duration of the communication)
Packet Switching • Why use packet switching? • A single bad bit in a file can ruin an entire file. • It’s quicker to re-send a portion of the file rather than the whole file. • Important with ‘noisy’ and unreliable communication paths, such as dial-up modem. • Many computers get to transmit some data, rather than 1 PC tying up a channel for ages with a huge transfer. • Imagine mailing a house from Melbourne to Sydney one brick at a time.
Addressing • Like telephones, every node on a network must have a unique identifier so the file server knows who is requesting information, and who is to be sent information. • This unique network address is hardwired into the network card of each computer. • Also, every active node of the internetneeds a unique identifying address so TCP/IP knows where packets are to be sent. • This is an Internet Protocol, or IP address.
Internet Addressing Humans like working with names (e.g. www.microsoft.com) but computers use IP numbers (e.g. 10.77.91.19). IP address has four ‘octets’ separated by dots, each octet can be between 0 and 255. Remember - all internet communications use IP addresses, not URLs. Only humans use URLs.
Addressing Domain name servers (DNS) – a distributed database on thousands of computers across the world - convert URLs into IP addresses. Like a phone book – look up a name (URL) to get a number (IP address).
NETWORKING TECHNOLOGIES • A “Networking Technology” defines how packets are handled and what the hardware is like. • The only networking technology worth knowing is Ethernet • Used everywhere by everyone (except a few odd people who aren’t worth worrying about) • Uses coaxial, UTP, fibre-optic cable, and wireless. • Ethernet defines both protocols(CSMA/CD) and cabling (e.g. UTP, thick coax, fibre), speeds etc.
Ethernet – 10Base-huh? 10Base-T=twisted pair (e.g. UTP). 10Mbps, max length 100m, RJ45 connectors. 10Base2 = uses thin coaxial (RJ58) cable – max length 195m. 10 Mbps. BNC connectors. 10Base5 = uses thick coaxial – max length 500m. Used mainly for backbones, cable TV. 10Base-F – fibre optic cable on 10Mbps networks – can get up to 2,000 megabits/sec (2Gbps) on the right network. 10Base-35 – broadband coaxial cable. Max length 3,600m.
How Ethernet Works Network devices compete for attention using Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Keep in mind: Only one signal can travel down a cable at a time. CS = Carrier Sense. Before transmitting over the network, a computer first "listens" and waits until there is no activity on the cable. When it sees its chance, it transmits.
MA = Multiple Access. When one Ethernet station transmits, all the stations on the cable hear the transmission • CD = Collision Detection. Carrier sense does not guarantee that two devices will not sense the same silence and transmit simultaneously, and cause a ‘collision’. CD detects this event. • Each node involved in the collision waits a random number of milliseconds, then repeats the transmission attempt. • The random waiting time prevents endless further collisions.
A ‘node’ is any device attached to a network that is capable of requesting and sending packets (e.g. Usually a PC, network printer) When a node wants to communicate to another node, it transmits its addressed packet. The packet travels to every node on the segment. Each node inspects the packet to see if it is addressed to him. If so, the node opens the packet and reads its contents. If not, the node ignores the packet.
Huh? Network segments? A network segment is a self-contained section of a network bounded by a bridge, router, or switch. Using segments reduces network congestion. Like classrooms in a school.
Network Hardware • The main bits of network hardware: • Cables • Network interface cards (NIC) • Server (e.g. file server, proxy, DHCP, web servers) • Switches (rarely, hubs) • Routers – now SOHO (Small Office / Home Office) combined boxes contain an ADSL modem, a router, wireless access point (WAP), switch, print server, coffee maker etc)
The modem Modulator/demodulator Modulate = turn digital data into analogue sound for transmission over phone network. (when uploading) Demodulate (when downloading) = convert sound back to digital data. Transmission speed is measured in bits per second (not bytes per second!) 56Kbps modem downloads at a theoretical maximum of approx 56,000 bits per second (about 7KB/sec). Can only transmit (upload) at 33.6kbps.
Hardware - NIC • The Network interface card (NIC) allows a stand-alone computer to connect to a network. • Can be cabled or wireless (radio) • Often now built into motherboards This old ‘combo’ NIC accepts both BNC (coaxial) and RJ45 (UTP) connectors.
Internet ChoicesNot all options are available to everyone, especially those not in major cities • ADSL, ADSL2 (256Kbps-24Mbps) • Cable (up to 5Mbps) • Satellite – 1 way or 2 way • Dialup (analogue, 56Kbps over phone lines) • WAN Wireless (e.g. iBurst) • ISDN (no way!)
Hardware - NIC • Network Interface Card • Rated by speed: 10, 100, or ‘Gigabit’ 1000Mbps. • For a NIC to work at its maximum speed, all the other network devices between it and the server must have at least the same bandwidth (data-carrying capacity). • ‘Auto-sensing’ e.g. 10/100/1000 NICs adjust themselves to the best possible speed. • Tip: go for GIGABIT NIC in servers
Hardware – Switches and Hubs Switches (and hubs) are connection points where cables can join up or be split. Typically, a single incoming cable is split into multiple outgoing cables.
Switches and hubs • Hubs and switches are the same except… • Dumb Hubs pass along all network traffic they receive (e.g. PA system) • Switches (“switching hubs”) are clever enough to only pass on relevant network traffic to recipients (like a phone call) • Switches greatly reduce network congestion. • Come in various sizes (number of ports)
WISDOM for U4O2 and exam • NEVER recommend hubs! • Switches are always best (unless an org has a free hub available for a tiny LAN) • No cost difference anyway • Switches make a network far faster HANDY SWITCH OPTIONS • Some switches have a fibre optic port • Some have a gigabit port
Hardware – Routers • 4 main roles… • Join dissimilar networks together, like a gateway (as the originalk routers used to be called) • Route packets across networks and internet • Act as a security device to guard the connection between a LAN and the outside world (another LAN or a WAN.) • Divide LANs into self-contained, protected areas, e.g. admin / student networks in a school.
Hardware – Routers • Act as a firewall at home, replacing software firewalls like Zone Alarm • Can be programmed to only allow authorised incoming and outgoing traffic. E.g. can block certain sites, forbid MP3 music files to enter. • Most home routers also have a built-in mini-switch but remember … a switch is not a router! • Home routers often combine: switch, ADSL modem, print server
Connections – UTP • UTP (Unshielded Twisted Pair) e.g. CAT6 (‘Category 6’)
Now extinct • Shielded from interference • Thick and thin varieties • Range: Thin-185m, thick-500m • Needs terminator at end of cable • Higher data capacity than UTP • Connectors can fail Connections – Coaxial EXTINCT Coaxial cable • Can be daisychained with BNC (Bayonet) T-pieces and joined with I- pieces
Word of WisdomDONOTRECOMMENDTHIN OR THICKCOAXIALALWAYS UTP (Cat6) or FIBRE OPTIC (for long distances or very high bandwidth)
Connections – Fibre optic • Made of glass (or plastic) • Optical, not electrical – little signal fade • Optical Signals created by LED or laser • Multiple signals on a single fibre • Resists EMI • Light signals bounce down Fibre Optic cable using Total Internal Reflection.
Connections – Fibre Optic • Core is as thin as a human hair • Not very flexible – needs thick protective coat • VERY fast • VERY high bandwidth • Very secure (can’t be tapped or snooped) • VERY long distance (>2km without repeaters) • Light weight, small size • Expensive adaptors to convert digital <> electrical signals
Connections – Cables and wireless Many fibre optic cable (‘FOC’) threads can be bound into a slim, single cable without their signals interfering with each other, giving massive data throughput. FOC is replacing old, heavy, expensive copper cables to cross oceans Warning! Sharks can damage your network! Sharks get over-excited by the electromagnetic fields radiated by copper cable. FO is silent.
Connections – Wireless • Data sent as radio signals between NICs and base stations (WAP=wireless access point) • short distances (e.g. 80m-200m), reduced by obstacles • Speeds of 54Mbps and increasing • Encrypted to prevent eavesdropping
Wireless • Many PCs can connect to a base station, share its bandwidth • PCs can “roam” and will automatically connect to the base station that has the strongest signal • Wireless NICs and antennae now built into laptops
Connections – Wireless • Good for temporary networks, or when PCs rarely needed in a location • Good for laptop-intensive places (e.g. classrooms, staffrooms). Great at home • Relatively expensive compared to cable, but a useful network add-on • Security concerns – never run it unsecured! Wireless base station & white radio antenna
Servers Robust central computers at the heart of a network. File servers are the most common server type.
File Servers • File servers run the Network operating system (NOS) which handles: • authenticating users during login • controlling users’ access to resources based on their rights • managing print queues • doing backups • running centralised software such as virus scanners • running services like DHCP to give out IP addresses to workstations • controlling internet services