chapter 6: networks ocr computing for gcse © hodder education 2011

Chapter 6: Networks

OCR Computing for GCSE © Hodder Education 2011

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.


Advantages of a LAN

• 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.


LAN 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.


LAN hardware• Wireless access point

– Wireless technology has many advantages over wired networks.

• No building work needed

• Quick to add new workstations

• Flexible deployment of nodes

• Visitors can access network / internet

• But there are drawbacks– Slower performance– Security issues


Peer-to-peer networks

• All computers have the same status.• May be very slow because of

• data collisions• shared processor power

• Only suitable for small low traffic networks.


Client–server networks• One or more 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.

• Servers control network traffic.• Log usage of resources.• Provide security.• Clients have to log in – this identifies

users and assigns rights.• Big networks may have hundreds of

servers.


Network topologies

• The topology is the physical layout of the network.

• It affects • cost• performance• ease of installation.


Star topology

• Shared link to server(s)• Most common• Few data collisions• Fast• Can set up independent segments


Ring topology

• Ring topology• One common linking cable• Passes all nodes• One direction traffic• Fast performance

But any problems and the whole network goes down


Bus topology

• 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 affect whole network• Limited distance covered


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


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.


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 emails.

POP3 Post Office Protocol (version 3)

Another method for accessing emails, used by most webmail services.

Telnet Allows bidirectional text communications on a network.

IP addressing

• Each node on a network running IP has an IP address.

• It uniquely identifies the node.• Consists of four octets (8-bit bytes).• Written as four numbers separated by dots,

e.g. 212.1.45.67

• DNS servers convert domain names such as OCR.org.uk into IP addresses.


MAC addressing

• MAC – Media Access Control• This is a unique number on network interfaces.• Used to communicate with physical layer of

network.• Can use it to restrict access to a network.


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

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.


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.


Disasters

• Disasters do happen.• 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


chapter 6: networks ocr computing for gcse © hodder education 2011

Documents

gcse hodder education

networks ocr computing

network internet

network topologies

wans lan local area

site owner of network

peer networks

data packets