1. OCR GCSE Computing © Hodder Education 2013 Slide 1
Chapter 6: Networks
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2. OCR GCSE Computing © Hodder Education 2013 Slide 2
Index to topics
Network basics
Network topologies
Protocols and Protocolsaddressing
security
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3. OCR GCSE Computing © Hodder Education 2013 Slide 3
Chapter 6: Networks
LAN
A LAN is a Local Area Network.
It is a connected set of computers and other devices.
Each device is called a node.
A LAN is installed on one site.
It does not cover a wide geographical area.
All the infrastructure is owned by the organisation or individual who owns the LAN.
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Chapter 6: Networks
Advantages
It allows communications between workers.
It allows data to be shared.
It allows peripherals to be shared.
It allows computers to be upgraded more easily.
It allows distributed processing.
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Chapter 6: Networks
Disadvantages
Expertise required to set up a large network
Security issues from unauthorised access to data
Measures to secure a network include:
Passwords – strong passwords use a range of character types;
Changing passwords frequently;
Do not allow users to install software;
With wireless access, use encryption.
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Chapter 6: Networks
Hardware
NIC – network interface card
Each node needs a NIC to connect to the LAN.
Produces the electrical signals that carry data.
Hub
A device that connects nodes together.
Makes them act as a single segment.
Not smart – all data packets are transmitted.
Cheap devices – USB hubs useful in home computer installations.
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Chapter 6: Networks
Hardware
Switch a smart device that can create and connect to different segments of the network
This reduces network traffic because data is confined to the segment where it is needed rather than being broadcast to the whole network.
Routers
Routers work with data packets to send data between networks.
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Chapter 6: Networks
Hardware
Wireless access point
Wireless technology has many advantages over wired networks:
No building work needed
Quick to add new workstations
Flexible deployment of node
Visitors can access network / internet
But there are drawbacks:
Slower performance
Security issues
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Chapter 6: Networks
Network types: peer to peer
All computers have the same status.
May be very slow because of
data collisions
shared processor power
Only suitable for small, low traffic networks.
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Chapter 6: Networks
Network types: client server
At least one computer is designated as a server.
A high specification machine.
It offers services to client machines, such as centrally held software, data, file storage and peripheral access.
A server controls network traffic.
Logs usage of resources.
Provides security.
Clients have to log in – this identifies users and assigns rights.
Big networks may have hundreds of servers.
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Chapter 6: Networks
Network topology
The topology is the physical layout of the network.
It affects:
cost,
performance,
ease of installation.
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Chapter 6: Networks
Star topology
Shared link to server(s)
Most common
Few data collisions
Fast
Can set up independent segments
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Chapter 6: Networks
Ring topology
One common linking cable
Passes all nodes
One direction traffic
Fast performance
But any problems and the whole network goes down.
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Chapter 6: Networks
Bus topology
One common linking cable
Nodes connected off the cable
Cheap
But:
Slows down when heavy traffic
Lots of data collisions
Breakage to cable affects the whole network
Limited distance possible
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15. OCR GCSE Computing © Hodder Education 2013 Slide 15
Chapter 6: Networks
LANs and WANs
LAN
Local Area Network
Located on one site
Owner of network owns the infrastructure
WAN
Wide Area Network
Covers a large geographical area – may be worldwide
Infrastructure may be provided by telecoms companies
VPN
Virtual Private Network
Uses internet for infrastructure
Need for enhanced security
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Chapter 6.1 Networks
Protocols
Protocols are the rules for communication between devices.
Standard protocols encourage network development.
Network protocols are constructed in layers.
This allows independent development of small parts of a protocol.
Internet Protocol is a group of protocols that underlies the internet.
TCP/IP now the most important set of protocols.
Includes many special protocols.
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Chapter 6: Networks
Common protocols
Protocol
Meaning
Application
DNS
Domain Name System
Translates domain names such as ocr.org.uk into IP addresses.
TLS/SSL
Transport Layer Security / Secure Sockets Layer
Cryptographic protocols designed for secure communications.
FTP
File Transfer Protocol
For copying files from one host to another.
Gopher
An early means of searching for files on the Internet.
HTTP
Hypertext Transfer Protocol
For distributing hypermedia files – essentially web pages.
IMAP
Internet Message Access Protocol
One method for accessing s.
POP3
Post Office Protocol (version 3)
Another method for accessing s, used by most webmail services.
Telnet
Allows bidirectional text communications on a network.
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Chapter 6: Networks
IP addressing
Each node on a network has an IP address.
It uniquely identifies the node.
In IPv4 this consists of four octets (8-bit bytes).
Written as four numbers separated by dots, e.g
DNS servers convert domain names such as OCR.org.uk into IP addresses.
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Chapter 6: Networks
MAC addressing
MAC – Media Access Control.
This is a unique number on network interfaces.
Used to communicate with the physical layer of a network.
Can be used to restrict access to a network.
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20. Chapter 6: Networks Packets
Data is split into packets on an IP network.
Packets get sent by different routes according to availability.
Packets reassembled at receiving end.
Typical packet structure:
source address
destination address
Packet sequence number
data
checksum
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Chapter 6: Networks
The packet address is like the address on a letter
The data is sent from one router to another until it arrives at its destination. A B
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Chapter 6: Networks
Security
Transmitted data is vulnerable.
Users on a network do not need to see all the data.
Access levels
Users granted privileges.
Associated with login names.
Passwords
Must be changed regularly.
Passwords should be strong.
Encryption
Especially important on wireless networks.
WEP or WPA should be used.
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Chapter 6: Networks
Policies
Network owners should have policies to protect their assets.
Users have responsibilities.
Acceptable use policies are common.
Policy ensures that users understand what is expected of them.
Sanctions used if users misuse resources.
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Chapter 6: Networks
Disasters
Need to plan for worst case scenario.
Example strategies:
mirrors of systems;
use of disk protection technology such as RAID;
surge protectors — to minimise the effect of power surges on delicate electronic equipment;
uninterruptible power supply (UPS);
back-up generator in case of a power failure;
fire preventions — alarms, fire extinguishers;
anti-virus software and other security measures;
failover systems.
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