Transcript Networks, Interfacing & Handshaking

A-Level Computing
networks, protocols and interfacing
Objectives
• Know what a basic network consists of
• Understand the benefits of using a network
• Know how devices connect and communicate
over a network
Interfacing
• Computer devices all work differently
• Need to connect to each other and same
computer
• An interface is the hardware and software
needed for the processor to be able to
communicate with a device
Interfacing
• Processors and in turn computers are being
developed all the time
• Devices on one computer must be able to talk
to another
• It is important to adopt standards so that if the
processor changes then the device can still
communicate
Interfacing
• Sometimes the interface hardware comes on
an interface board, which has to be fitted into a
computer
• The device can just be
connected to a socket.
This is the port through which
signals to and from the device travel
Interfacing
• Most PCs come with at least a serial port (for
mouse or modem)
• Being replaced by a USB
(Universal Serial Bus) port.
Handshaking
• When two devices need to communicate, one
device sends a message to the other....
'Are you ready to receive data?'
• When the other is ready, it sends a signal back
to the first device....
'Yes, I am ready to receive data'
• ...and then communication can begin
Networks
• A network consists of a number of computers
and peripherals connected together
Networks
• hardware can be shared (eg.a number of
computers can use the same printer)
• software can be shared (eg a number of
workstations can all load up a program from a
file server)
• data can be shared (eg a number of computers
can access the same database stored on a file
server)
• computers may communicate between each
other (messages / email
Networks
• viruses can be spread to all computers on a
network
• hackers may access computers on a network.
• network failure means nobody can use the
computers
• networks may be slower than using standalone
computers
• complex cabling may be expensive to install
Local Area Network
• A LAN (local area network) is a method of
connecting computers together in a small area
• Building or small site
• Computers and peripheral devices are linked
via physical connections (cables)
Topologies
• The physical layout of a network
• How computers (nodes) connect to one
another
• Bus Network
• Star Network
• Ring Network
Star Network
Star Network
• Each node is connected to a host computer
• The host controls the network
• WAN with big mainframe computers use this
topology
Star Network
• Pros:
• If one cable fails, the whole network doesn’t
• Easy to isolate faults
• Consistent performance
• Each node has its own connection to the
server
• Messages sent directly, more secure
• Simple to extend
Star Network
• Cons:
• Costly to install (length of cable)
• Cabling is major cost in networking
• Distributed star networks are collection of
‘stars’ connection boxes linking a ‘string’ of
stars
Bus Network
Bus Network
• Common in a LAN
• All devices share a single cable
• Data travels in all directions from one computer
to another
• Works well if ‘channels’ on network are too
crowded
Bus Network
• Pros:
• Very cheap and easy to install
• Easy to add more nodes to network without
disruption
• Cons:
• Cable goes down....whole network breaks!
• Hard to isolate faults
• Heavy load of traffic slows network down
Ring Network
Ring Network
• No central computer controlling the network
• Every computer communicates with any other
in the ring
• Sends messages with an address
• Messages passed in one direction
Ring Network
• Pros:
• No depending on central computer
• Transmission of signals nice and simple
• Can send lots of signals
• Cons:
• one node breaks....cant send signals
Mesh Network
Mesh Network
• Every computer acts as a router to every other
computer
• Nodes can break down but signals can still be
passed to others
• Very expensive when using network with lots of
nodes
Wide Area Network
• A WAN (wide area network) is a network over a
large scale (city-city, countries etc.)
• Can be made up of connected LAN’s
• Connected by telephone or satellite links
Wide Area Network
• Public telephone network
• Dedicated leased lines
• Radio Waves
• Fibre Optic Cable
• Microwaves (limited
to 30 miles apart)
• Satellites orbiting
planet Earth
Modems
• Sending data over long distances
• Internet using phone lines
• Modems convert digital signals on computer to
analogue to transmit over phone lines
• Modem at other node converts analogue back
to digital
Standards
• It is important that networks adopt standards
• Common methods of sending data and
consistent data formats.
• If they did not operate in the same way the
workstations would not be able to communicate
with each other.
Standards
• http://www.bbc.co.uk
• HTTPs: HyperText Transfer Protocol, used for
a website over the internet
• FTP: File Transfer Protocol
• VoIP: Voice over Internet Protocol
Wireless Networks
• Radio waves can be used to transmit data from
one computer to another.
• Wireless networks are becoming very popular
as there is no need to lay a lot of cables.
• Each computer in a wireless network needs a
wireless network card installed.
• A wireless hub is connected to the network and
transmits and receives data from the
computers.
Wireless Networks
Wireless Networks
• Pros:
• no need for cabling.
• computers can be used anywhere within
range of the signal.
• For example laptops can be moved around
and still use the network.
Wireless Networks
• Cons:
• data transmission speeds can be slow.
• data signals can only be received within a
limited range.
• security may be a problem as people may
be able to pick up the data signals outside
your premises.
• Careful setting up of the network is needed.