This document contains all of the required infomation to learn and understand for your GCSE examinations for J277 Computer Science. These revision summary notes helped myself and others achieve grade 9s in computer science and so can you!
Computer Networks, Connections and Protocols
Ip Address = a unique code that can be used to locate a website and send a user to it
Domain Name = a domain can be entered by a user to be sent to the location of the ip
address (it is an easier form of input rather than a long code)
Domain Name Server = a DNS server has a database that maps domain names to IP
addresses so it can translate the human friendly domain name into an IP address
When a user types in a URL:
- The URL is sent to a local DNS server where it is translated into an IP address
- If the IP address is found, it is passed back to the browser
- If not found, it is checked at the next DNS server - if still not found, an error message
is displayed
Advantages of DNS servers:
- Humans do not need to remember difficult numerical addresses
- If an IP address is changed, the user can still use the same domain name whilst the
server updates the database
- Having many distributed DNS servers means everyone has access to all addresses
from their local DNS server
Uniform Resource Locator (URL) = an address of a particular page on a website (identical
to to domain of home page but with added data at the end to show page)
Media Access Control (MAC Address) = a unique code assigned by the product
manufacturer to identify a computer - products may have multiple, one for wired and one for
ethernet / wireless or bluetooth
Network Interface Card (NIC) = hardware used to hold the MAC address found in a
computer
Wide Area Network (WAN) = a collection of computers and networks connected together
using resources supplied by a ‘third party carrier’. It uses cables, telephone lines, satellites
and radio waves to connect the components, which are usually spread over a wide
geographical location
Circuit Switching = the process of setting up a dedicated line between two locations to
allow for a phone call to take place
,Packet Switching = the process of breaking a large piece of data into smaller segments to
then send it to its destination.
Each packet is given a header containing:
- The IP (Internet Protocol) address it is going to
- The IP address it has come from
- The sequence number of the packet
- The number of packets in the whole communication
- Error checking data
After being sent along different routes, packets are reassembled in the right order upon
arrival
Local Area Network (LAN) = consists of a collection of computers and peripheral devices
(such as printers) connected together, often on a single site (usually covers a small
geographical area). A LAN is often owned / managed by a single organisation or person
Benefits of Networking Computers:
- Resources are shared = files stored on a file server (can be accessed by all),
peripheral devices can be joint used and all computers use the same internet
connection
- Centralised management = security managed centrally, software can be distributed
and files are backed up centrally
Negatives of Networking Computers:
- Administration = managing a large network can be complicated
- Security = viruses may be able to infiltrate a network and spread between computers
Network Topologies = the way computers are connected together in different layouts
Star Network = all computers have their own cable connecting them to a hub, switch or
computer which acts as a server
Advantages:
- If one cable fails, the other workstations are not affected
- Consistent performance, even when the network is heavily used
Disadvantages:
- Can be costly to install because there is a lot of cabaling and extra hardware (e.g. a
switch)
- If the server / central switch fails, the whole network goes down
, Mesh Network = used to connect small offices to entire cities by connecting all nodes
(computers) together in a system. To connect to the internet, only one node needs to be
physically linked via a modem - which shares its connection with other nodes around them
Full Mesh Network = all nodes are connected together
Partial Mesh Network = some nodes are not directly connected (more common in larger
systems)
Advantages:
- Using fewer cables means it costs less to set up a network, particularly over a large
area of coverage
- The more nodes installed, the bigger and faster the wireless network becomes
- New nodes are automatically incorporated into the network without needing any
adjustments by a network administrator
- If one node is faulty / blocked, the system finds a new route to send data
Router = designed to route data packets across a wide area network such as the Internet.
Each router in a network acts as a node and packets are passed from router to router to
reach their destination
Switch = a component of a LAN that learns the MAC address of each individual device
connected to it locally. Its function is to forward packets being sent to recipient using
recipients MAC address and the port it is connected to
Network Interface Card (NIC) = required to connect any network enabled device (a physical
component) which can either operate wirelessly or be wired using an ethernet cable
Selecting Cable Types:
- Twisted pair copper cable = lightweight, inexpensive and easily installed
(commonly used to connect devices in LANs)
- Copper coaxial cable = has a high bandwidth, can transmit data very quickly along
large distances and there is less distortion / interference in comparison to twisted pair
cable (commonly used in cable TV and broadband)
- Fibre Optics = even higher bandwidth, transmission is faster, they do not break as
easily as copper cables and are not affected by electromagnetic interference
Wireless Access Point (WAP) = receives data from a network via its physical connection.
The transmitter then converts this data into radio waves which are transmitted, devices on
the network receive radio signal via a WI-FI adaptor
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