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NetworkingNetworking

For Information Processing and ManagementFor Information Processing and Management

By

Mark Kelly

Manager, Information Systems

McKinnon Secondary College

Lecture notes: Vceit.com

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What is a network – should I What is a network – should I panic?panic?

At its simplest, a network is two or more computers that are connected so they can exchange information and share resources.

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Networks can be classified by:

Types of networksTypes of networks

(LAN, WAN, Internet);

(Client-Server, P2P);

•Their size •Their servers

•How they are linked together (cable, wireless);

•Their ‘logical’ shape (bus, star, tree);

•How network messages travel (Ethernet’s CSMA/CD)

•The rules they use to exchange data (protocols – TCP/IP).

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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

Company image and “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)

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LANs – local areaLANs – local area

•Geographically limited, usually to one site.

•Can be cabled (usually UTP, fibre optic, coaxial) or wireless.

Types of networks, by sizeTypes of networks, by size

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WANs – Wide AreaWANs – 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.

Types of networks, by sizeTypes of networks, by size

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The internetThe internetMade 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)

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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

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Peer-to-Peer (P2P) networksPeer-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

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ProtocolsProtocolsCommunication 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.

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Human ProtocolsHuman 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.)

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Network ProtocolsNetwork 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)

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Choosing Choosing ProtocolsProtocolsSometimes 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.

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The King of Protocols – The King of Protocols – TCP/IPTCP/IPThe universal protocol for internet communications.

The backbone of the internet.

Made up of 2 complementary protocols…

TCP (Transport Control Protocol)

and

IP (Internet Protocol)

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Protocols – TCPProtocols – 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)

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Protocols – TCP/IPProtocols – TCP/IPIP (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 on internet conditions at that time.

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Protocols – TCP/IPProtocols – TCP/IPTCP 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.

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Packet SwitchingPacket SwitchingAny 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)

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Packet SwitchingPacket SwitchingWhy 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.

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AddressingAddressing•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 internet needs a unique identifying address so TCP/IP knows where packets are to be sent.

•This is an Internet Protocol, or IP address.

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Internet Internet AddressingAddressing

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.

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AddressingAddressing

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).

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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.

NETWORKING TECHNOLOGIES

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Ethernet – 10Base-huh?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.

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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.

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•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.

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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 not, the node ignores the packet.

If so, the node opens the packet and reads

its contents.

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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.

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Network Network HardwareHardwareThe main bits of network

hardware:

•Cables

•Network interface cards (NIC)

•Server (e.g. file server, proxy, DHCP, web servers)

•Switches (rarely, hubs)

•Routers – now home models have ADSL modem, wireless access point, switch, print server, coffee maker)

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The modem Modulator/demodulator

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.

Modulate = turn digital data into analogue sound for transmission over phone network. (when uploading)

Demodulate (when downloading) = convert sound back to digital data.

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Hardware - NICHardware - 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.

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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!)

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Hardware - NICHardware - 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

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Hardware – Hardware – Switches Switches and Hubsand 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.

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Switches Switches and hubsand 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)

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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

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Hardware – Hardware – RoutersRouters• 3 main roles…

• Route packets across networks and internet

• Security device that guards 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.

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Hardware – Hardware – RoutersRouters• 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

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Connections – UTPConnections – UTP

•UTP (Unshielded Twisted Pair) e.g. CAT5 (‘Category 5’)

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Connections – Connections – CoaxialCoaxial

Coaxial cable

•Now rare

•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

•Can be daisychained with BNC (Bayonet) T-pieces and joined with I- pieces

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Word of WisdomDO

NOTRECOMMEND

THIN OR THICKCOAXIAL

ALWAYS UTP or FIBRE OPTIC

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Connections – Fibre opticConnections – 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.

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Connections – Fibre OpticConnections – 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

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Connections – Cables and Connections – Cables and wirelesswirelessMany 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.

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Connections – WirelessConnections – 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

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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

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Connections – WirelessConnections – 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

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ServersServers

Robust central computers at the heart of a network.

File servers are the most common server type.

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File ServersFile ServersFile 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

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Network Operating Network Operating SystemsSystemsThe most popular NOSes are:

•Novell Netware (better, more expensive at first, cheaper over time)

•Microsoft Server 2003 (now dominant)

They offer similar services.

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File ServersFile ServersServers don’t really have anything special in terms of hardware.

Expensive because of their high-quality components, and “scalability” (expandability).

•Memory – servers love lots of RAM.

•Storage –need large and fast hard disks – often RAID (discussed soon)

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File Servers vs File Servers vs Desktops 1Desktops 1•CPU Processing power – not very important in a file

server

•Backup – most servers have inbuilt high-capacity tape backup drives to protect against data loss. Tape drives usually use QIC (Quarter Inch Cartridge) DAT (Digital audio tapes) tapes.

Servers are the muscle men in the computer world

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File Servers vs File Servers vs Desktops 2Desktops 2Connectivity – servers often have two or more gigabit NICs to increase their data-throughput.

Robustness - servers run all day for years, and need rugged high-quality components

Scalability –the ability to increase the size and power of equipment and networks as required e.g. add 8 hard disks, two power supplies, two NICs, two CPUs, lots of RAM etc.

Designing and engineering this expandability is expensive.

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R.A.I.D.R.A.I.D.Redundant Array of Independent [or Inexpensive] Disks) arrays for reliability and/or speed.

RAID uses a group of hard disks that work as a single disk under a RAID controller.

Flavours of RAID: RAID0 to RAID10 (RAID 1 + RAID 0) offer reliability and/or speed (at ever-increasing cost). Includes mirroring (for reliability) and striping (for speed).

RAID disks are usually "Hot Swap".

EXPENSIVE – needs justifying for small org

3-disk RAID array

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Server farmsServer farmsOn smaller networks, network services are performed by software in a single server.

On busy LANs, multiple servers share the work…

•Login servers – authenticate users•Proxy servers – cache downloads•DHCP servers – allocate IP addresses•Print servers –manage print job queues•Web/FTP servers – serve web pages or files•Email servers –handle email

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Network TopologiesNetwork TopologiesA network topology is a logical (idealised) shape of a network’s wiring. The main topologies:

•Bus

•Star

•Tree*

•Ring*

•Mesh*

Each has its pros and cons: cost, complexity, reliability and susceptibility to congestion.

*not examinable

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Bus TopologyBus Topology

Many devices connect to a single cable backbone cable as a daisychain. If the backbone breaks, the entire segment fails – like Christmas tree lights.

DO NOT RECOMMEND IT IN THE EXAM!

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Bus TopologyBus Topology•Relatively cheap and easy to install•Don't require much cabling •Gets congested with too many nodes•Not good for schools•OK for small LANs

•NEED COAXIAL CABLE AND NICs!

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* Star Topology ** Star Topology *

•central connection point (a switch) with cables branching to many computers.•Not a server with 4 NICs!!!

•If a cable fails, only one node will fail.•prone to traffic bottlenecks at the centre of the star•RECOMMEND THIS!

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Tree Topology*Tree Topology*

Combines bus and star topologies. It looks like a tree.Very common in larger networks.

*not examinable

e.g. one cable from a file server leads to a 24 port switch. Many cables branch from this switch to the computers in the computer room. They share the bandwidth of the incoming cable.

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Mesh Topology*Mesh Topology*

Multiple routes from one node to any other.  As used by The Internet to give near-perfect reliability.

*not examinable

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Network Physical Network Physical SecuritySecurityFile server failure can severely affect network users.

Server security:

•Locked in air-conditioned, alarmed room with barred windows, restricted keys•No user access to server•Uninterruptible power supply (UPS) protects against blackouts, brownouts and voltage spikes.•Accessible fire fighting equipment.•Locked floppy disk drives

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Network Electronic Network Electronic SecuritySecurity

Passwords are not strong protection – they can be guessed, forgotten or stolen.

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Network SecurityNetwork Security

Daily backups are vital. Massive cost and effort to recover a single megabyte of lost data.

Organisations need a data disaster recovery plan so they know what to do to recover from catastrophic data loss.

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EncryptionEncryption•A form of Electronic Security

•Makes data unreadable to unauthorised people even if a file is stolen.

• Web browsers use encryption to connect to a “Secure” SSL (Secure Socket Layers) site.

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Network SecurityNetwork SecurityTROJAN HORSES attempting to report ‘home’ or start a DOS/DDOS attack - can be blocked by a firewall.

FIREWALLS in hardware (routers) or software (e.g. Zone Alarm) check for unauthorised incoming or outgoing network traffic, e.g. port scanning, being enslaved to help with a distributed denial-of-service (DDOS) or spam attacks.

VIRUSES can disclose user passwords, steal information, destroy data, install “back doors” to let hackers in, clog print queues, disrupt Internet traffic, overload email servers etc. Keep scanners up to date.

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Remember

• Exam case study will be a small organisation’s LAN.• Choose between P2P or Client-Server• If Client-Server, choose NOS - MS Server 2003• Recommend…

– STAR topology, not bus– UTP - CAT5e or CAT6 cable, not coaxial– SWITCHES, not hubs– Wireless is now pretty cheap, reliable and flexible

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Thanks!

Mark Kelly

McKinnon Secondary College

kel@mckinnonsc.vic.edu.au

IPM Lecture Notes:

vceit.com