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Title: Networking

By Mark Kelly Manager, Information
Systems McKinnon Secondary College Lecture notes
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

(Ethernets CSMA/CD)
Why network?
  • Efficiency Better, faster communication
    email, videoconferencing
  • Cost savings (email vs phone calls, physical
  • 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)

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,
  • 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,

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

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 computers 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
  • Its 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
  • Imagine mailing a house from Melbourne to Sydney
    one brick at a time.

  • 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.

Internet Addressing
Humans like working with names (e.g. but computers use IP numbers
(e.g. 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.
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).
  • A Networking Technology defines how packets are
    handled and what the hardware is like.
  • The only networking technology worth knowing is
  • Used everywhere by everyone (except a few odd
    people who arent worth worrying about)
  • Uses coaxial, UTP, fibre-optic cable, and
  • Ethernet defines both protocols (CSMA/CD) and
    cabling (e.g. UTP, thick coax, fibre), speeds etc.

Ethernet 10Base-huh?
10Base-Ttwisted 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
  • 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

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
If not, the node ignores the packet.
If so, the node opens the packet and reads its
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
  • 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
  • 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
  • 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
Coaxial cable
  • Can be daisychained with BNC (Bayonet) T-pieces
    and joined with I- pieces

(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 (cant 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 (WAPwireless access point)
  • short distances (e.g. 80m-200m), reduced by
  • Speeds of 54Mbps and increasing
  • Encrypted to prevent eavesdropping

  • Many PCs can connect to a base station, share its
  • 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
Robust central computers at the heart of a
network. File servers are the most common server
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
  • running services like DHCP to give out IP
    addresses to workstations
  • controlling internet services

Network Operating Systems
  • The most popular NOSes are
  • Novell Netware (better, more expensive at first,
    cheaper over time)
  • Microsoft Server 2003 (now dominant)
  • They offer similar services.

File Servers
Servers dont really have anything special in
terms of hardware. Expensive because of their
high-quality components, and scalability
  • Memory servers love lots of RAM.
  • Storage need large and fast hard disks often
    RAID (discussed soon)

File Servers vs Desktops 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
File Servers vs Desktops 2
Connectivity servers often have two or more
gigabit NICs to increase their data-throughput. Ro
bustness - 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.
Redundant Array of Independent 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
(spanning a logical single volume over several
physical disks for greater performance several
simultaneous disk reads/writes are
possible). RAID disks are usually "Hot Swap no
server downtime to replace sick disks. EXPENSIVE
needs justifying for small org
3-disk RAID array
Server farms
  • On 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

Network Topologies
  • A network topology is a logical (idealised) shape
    of a networks wiring. The main topologies
  • Bus
  • Star
  • Tree
  • Ring
  • Mesh

Each has its pros and cons cost, complexity,
reliability and susceptibility to
congestion. not examinable
Bus Topology
Many devices connect to a single cable backbone
cable as a daisychain. If the backbone breaks,
the entire segment fails like Christmas tree
Bus 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

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
  • RECOMMEND THIS for small networks!

Tree Topology
Combines bus and star topologies. It looks like
a tree. Very common in larger networks.
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.
not examinable
Mesh Topology
Multiple routes from one node to any other.
  Hardly ever found cabled in real-life in real
networks really only appears in The Internet to
give near-perfect reliability. DO NOT RECOMMEND
not examinable
Network Physical Security
  • File server failure can severely affect network
  • 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

Network Electronic Security
Passwords are not strong protection they can be
guessed, forgotten or stolen.
Network 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.
  • 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.

Network Security
TROJAN 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.
  • Exam case study will be a small organisations
  • 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

Mark Kelly McKinnon Secondary College kel_at_mckinno VCEIT Lecture Notes