Download Stand Alone Computers Computer Network Local Area Network

GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
Candidates should be able to:
a. Explain the advantages of networking stand-alone computers into a LAN
b. Describe H/W needed to connect stand-alone computers into a LAN, including
hub/switches, wireless access points
c. Explain the different roles of computers in a client-server and a peer-to-peer network
d. Describe, using diagrams or otherwise, the ring, bus and star network topologies
e. Describe the differences between a LAN and a WAN such as the Internet
f. Explain the terms IP addressing, MAC addressing, packet and protocols
g. Explain the need for security measures in networks, such as user access levels, suitable
passwords and encryption techniques
h. Describe & justify network policies such as acceptable use, disaster recovery, failover,
back-up, archiving
Stand Alone Computers
Stand Alone refers to any computer or device that is not connected to any other computer
or device via a network.
Computer Network
A computer network is a collection of computers (and other hardware components) that are
connected together to allow the sharing of resources and information.
Local Area Network (LAN)
Networked computers / devices are located fairly close to each other geographically, for
example, all of the computers in a school or small business, or a small home network. Can
be wired or wireless.
Each device is called a Node.
The entire infrastructure is owned by the organisation / individuals who own the LAN.
Why Use a LAN?
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Allows communications between workers
Allows data / files / information to be shared
Peripherals can be shared e.g. printers
Computers can be upgraded more easily (also virus scans)
Logon from any connected machine
Distributed processing (e.g. run a single program simultaneously at various sites)
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GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
Data Packets
When a file is sent across a network, it is not all sent in one go, but piece by piece. Before
any data is sent it is split up into little pieces called Packets. In addition to the data that is
being sent, each packet also contains important information about where it has been sent
from, where it is going to and how to reassemble it at the other end!
Packets from the same data file may travel on different routes across a network before
arriving at their destination address to be reassembled.
LAN Hardware
A variety of hardware is needed to connect nodes to a network and to allow them to
communicate and transfer data efficiently and effectively without loss of data...
Network Interface Controller/Card (NIC)
Each node on the network needs a NIC to connect to a LAN. The NIC allows computers to
communicate over a computer network by providing physical access to the network and a
unique address for each individual node (Media Access Control - MAC address).
Hub
A Hub is a device that connects nodes together, enabling them act as a single segment.
Hubs are not intelligent; they simply pass on all data packets received from one node to all
other nodes connected to the network. If data is being sent from multiple nodes at the
same time, collision may occur, and data will need to be retransmitted. They are cheap
devices – USB hubs are often used in home networks.
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GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
Switch
A Switch is used to connect network segments. Nodes can communicate directly with each
other via a Switch without the risk of data collisions. With 4 computers (e.g., A, B, C, and D)
on 4 switch ports, A and C can transfer data back and forth, while B and D also do so
simultaneously, and the two conversations will not interfere with one another.
A
B
C
D
Router
A router is a device that forwards data packets between computer networks. When the
router receives a data packet it reads the address information in the packet to determine its
ultimate destination. Then, using information in its routing table or routing policy, it directs
the packet to the next network on its journey. This continues until the data packet reaches
its final destination.
Wireless Access Point (WAP)
(not to be confused with Wireless Application Protocol!)
A Wireless Access Point is a device that allows wireless devices to connect to a wired
network using Wi-Fi, Bluetooth or related standards. The WAP usually connects to a router
(via a wired network), and can relay data between the wireless devices (such as computers
or printers) and wired devices on the network.
Advantages of wireless networks include:
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No building work needed
Quick to add new workstations
Flexible deployment of nodes
Visitors can access network / internet
They also bring their disadvantages with slower performance and security issues heading
the list.
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GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
Types of Network
Peer-to-Peer
Some small networks do not differentiate between the computers connected to them: they
all have equal status. They can share files and peripherals, and so provide some of the usual
advantages of any network, but are prone to data collisions, meaning that the overall speed
of the network is reduced. In addition, each peer computer may be accessed by any other
peer, which may cause it to slow down.
Peer-to-Peer networks can be implemented over the internet, where they are
predominantly used to facilitate illegal file-sharing.
Client-Server
This is probably the most common architecture for a network. A dedicated, high-spec
machine handles centralised storage of data and processing of shared files as well as
services such as printing and internet access. The computers accessed by end-users are
called Clients which request services from the Server(s). Servers are also responsible for
handling the security and general functionality of the network. It is normal for organisations
to have multiple servers, each having its own dedicated function. Multiple servers can be
stacked together to create a Data Centre. Servers tend to be virtualised to increase
efficiency and decrease energy consumption.
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GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
Network Topologies
Topology refers to the physical layout of the network. This will affect the cost, performance
and ease of installation of a network.
Star Topology
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Shared link to server(s)
Most common type of network topology
Few data collisions
Fast
Can set up independent segments
Hub can be another node, or switch etc...
Ring Topology
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One common linking cable
Passes all nodes
One direction traffic
Fast performance
If one node fails, the whole network fails
Bus Topology
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One common linking cable
Nodes connected off the cable
Cheap
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Slows down when heavy traffic
Lots of data collisions
Breakage to cable affect whole network
Limited distance covered
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GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
Wide Area Network (WAN)
Computers are located in various distant locations geographically. For instance, multinational businesses that have offices in different countries may all need to access the same
network to share resources. Effectively, a WAN is the result of joining two or more
geographically separate LANs via satellite, fibre-optic cables, telephone lines or a
combination of these. The infrastructure of a WAN may be provided by telecoms
companies.
The largest WAN in existence is the Internet.
Virtual Private Network (VPN)
A VPN is a network that uses a public telecoms infrastructure, such as the Internet, to
provide remote offices or individual users with secure access to their organisation's
network. It works by using the shared public infrastructure while maintaining privacy
through security procedures and tunnelling protocols that send data through a "tunnel" that
cannot be "entered" by data that is not properly encrypted. An additional level of security
involves encrypting not only the data, but also the originating and receiving network
addresses.
Network Protocols
In computer networks, a protocol refers to a set of common rules that enable different and
unrelated devices to communicate with each other. Having a set of common standards
promotes the development of networks (how much easier would international relations be
if everyone in the world spoke just one language?).
Network protocols are constructed in layers, meaning that small parts of a particular
protocol can be developed independently, without interfering with the rest of its
functionality.
The Internet protocol suite is the set of communications protocols used for the Internet and
other similar networks. It is commonly known as TCP/IP, because of its most important
protocols: Transmission Control Protocol (TCP) and Internet Protocol (IP), which were the
first networking protocols defined in this standard.
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GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
TCP/IP Includes many special protocols, some of which are described in the table below:
Protocol
DNS
Meaning
Domain Name System
TLS/SSL
Transport Layer Security /
Secure Sockets Layer
File Transfer Protocol
FTP
Gopher
HTTP
Hyper Text Transfer Protocol
IMAP
POP3
Telnet
Internet Message Access Protocol
Post Office Protocol (version 3)
SMTP
Simple Mail Transfer Protocol
Application
Translates domain names such as
mrfraser.org into IP addresses
Cryptographic protocols designed for
secure communications
For copying files from one host to
another
An early means of searching for files on
the internet
For distribution of hypermedia files (web
pages)
Used to send /receive email
Used to send /receive email
Bidirectional text communications on a
network.
Used to send /receive email
IP Addressing
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Each node on a network running IP has a unique IP address.
It uniquely identifies the node.
IPv4 (Internet Protocol Version 4) consists of four octets (8-bit bytes).
• Written as four numbers separated by dots, e.g. 76.74.128.90
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DNS servers convert domain names such as mrfraser.org into IP addresses.
76 . 74 . 128 .
90
01001100 . 01001010 . 10000000 . 01011010
MAC Addressing
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MAC – Media Access Control
Unique number to identify individual network interfaces.
Used to communicate with physical layer of network.
Can be used to restrict access to a network.
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GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
Network Security
When data is being transmitted across a network it is possible that it might be intercepted
by unauthorised people and misused. This is a particular issue with wireless networks,
where signals are more easily captured.
Access levels
Users on a network do not need to see all the data. As with a DB, different users have
different needs so can be given different permissions. Checks can be made when a user logs
on to a network – their userID / password are checked against a DB of authorised users and
appropriate privileges are granted based on a set of rules determined by the network
manager. Access privileges will range from Access Administrator rights (access all areas)
down to lowest levels where users are restricted to viewing / editing specific files. As well as
enhancing security, this also makes life easier for the average user by removing access to
lots of unnecessary data and files.
Passwords
Each userID is password protected. Hackers may try to access accounts by guessing likely
passwords. Brute force methods can be used in which a software program will use every
possible combination of characters until the correct password is found. Passwords can be
made more difficult to guess by increasing the number of characters used, mixing upper and
lower case letters and including numbers and characters. Regularly changing a password will
also enhance security.
Encryption
If data could be intercepted by an unauthorised person, security can be maintained by
encrypting data before it is transmitted across the network.
It is harder to enforce security across a wireless network as anyone within range could
potentially access the data being transmitted within it. An older method of encrypting data
within a wireless network is known as WEP (Wired Equivalent Privacy). This method
encrypts data using a single password as the encryption key but is not particularly secure. A
more robust method is to use WPA (Wi-Fi Protected Access), which uses a similar method
but dynamically generates a new 128-bit key for each packet sent. WPA also includes a
message integrity check to ensure that data packets are not interfered with. WPA2 is the
successor of WPA and is even more robust through its use of stronger algorithms. Provided
a long enough password is used, WPA2 is virtually uncrackable… unless someone reveals the
key.
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GCSE Computing A451
Unit 6.1 – Networks
www.mrfraser.org
Network Policies
Most organisations rely on their networks, and as such adopt policies for network users to
abide by so that the integrity and reliability of the network can be maintained. Usually,
there will be sanctions in place for any breach of network policy.
Most typically, an organisation will have an Acceptable Usage Policy in which users are
required to sign an agreement stating that they will adhere to the rules set out by the
network administrator. Such policies will ensure that users understand what is expected of
them when utilising the network.
Network Failure & Disaster Recovery
If it all goes Pete Tong it is handy to have a plan B. This will minimise disruption to the
network and loss of data and money. A good disaster recovery plan should consider:
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Preventive Measures to stop disasters happening in the first place
Detective Measures to discover unwanted events
Corrective Measures to restore the system in the event of a disaster
Regular backups should be made and stored off site
Data that is no longer in daily use can be archived (removed from live system and stored
elsewhere).
Preventive measures can include:
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mirrors of systems
use of disk protection technology such as RAID
surge protectors — minimise effect of power surges on 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 (backup system – switched to automatically in case of error)
Keywords
Client–Server
Hub
LAN
NIC
Packet
Peer-to-Peer
Topology
WAN
Network in which server computers provide services for client workstations.
Device that channels a number of input signals into one output line.
Local area network
Network interface card/controller
A unit of data sent on a packet switching network.
Network in which all the computers are of equal status.
The layout of a network.
Wide area network
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