You will need to know..
What is a Network?
It’s rare these days for anyone to have a standalone machine, that is a one that is not connected to anything, not even the internet. Any device which is connected with another is on a network, this could be a small company LAN or the largest network - the internet,
Networks: Advantages and Disadvantages
Networks allow us to share files and software, collaborate with colleagues, access our files from home. But there is a downside. Check the list below ( source: Craig and Dave).
Types of Networks: LANs and WANs
There are many different types of networks. For A level you need to focus on LANs and WANs.
The Internet Structure
The internet is a global system of interconnected computer networks. The internet facilitates a wide range of services, including the World Wide Web, email, internet telephony, and file sharing. In order to communicate to do any of those things, computers must use a common set of protocols referred to as the TCP/IP stack.
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Network Standards
When you travel internationally you use all sorts of plug adaptors which can get annoying. Did you know that early British plugs were manufacturer specific and not compatible? It took around half a decade to arrive at a standard for British plugs. We have mostly learnt from those mistakes and we now have standards which ensure products and services are compatible with each other.
Examples of network related standards are: character sets, HTML and network protocols. |
Network Protocols
Types of Protocols
To communicate over a network:
TCP - Transmission Control Protocol
IP - Internet Protocol
UDP - Used Datagram Protocol
TCP - Transmission Control Protocol
IP - Internet Protocol
UDP - Used Datagram Protocol
TCP/IP make up the rules of how data communicates over the internet. UDP is used ( instead of TCP) for rapid non critical data transfer ( using datagrams) where some loss is acceptable e.g. audio or video streaming. It uses an open two-way connection. It is less commonly used now because it is not as reliable as TCP.
To handle web page requests:
HTTP - Hypertext Transfer Protocol
HTTPS - Hypertext Transfer Protocol Secure
HTTP - Hypertext Transfer Protocol
HTTPS - Hypertext Transfer Protocol Secure
HTTP is the World Wide Web protocol. It is used for communication of HTML requests between a client and a server. HTTPS is HTTP with the added benefit of encryption and authentication.
To handle file transfers:
FTP: File Transfer Protocol
FTP: File Transfer Protocol
File Transfer Protocol and is used for sending files between computers often over a WAN using an FTP client which provides an easier interface saving you from knowing the actual commands,
To handle email:
POP - Post Office Protocol
IMAP - Internet Message Access Protocol
SMTP - Simple Mail Transfer Protocol
POP - Post Office Protocol
IMAP - Internet Message Access Protocol
SMTP - Simple Mail Transfer Protocol
SMTP handles outgoing mail ( to the server from a client or another server). POP retrieves the email from the server ( pops it off so it’s no longer there) and transfers it to your device). But if you want to read your email on your laptop and then read it again on your phone, you want the IMAP protocol. This is now more common because it keeps a copy of the email on the server.
Protocol Layers
To make things easier protocols are separated into layers. Each layer has its own responsibility and provides a service to the layer above it. This means that a manufacturers can create layer specific devices without worrying about how the other layers work.
Network layering also means that if something breaks we know which layer to focus on. |
The OSI Model has not really used anymore ( largely replaced by the simpler Internet protocol suite). However the OSI Model is helps us to troubleshoot any network problems. Find out more about the OSI model here.
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The TCP/IP stack
Data travels down the layers to be sent and up the layers to be received. Each layer adds information to the packets of data being sent so that it can be routed to the correct destination. Once received each layer strips off the information it has used to route the data back up the layers.
The Unique Role of Each Layer
Application Layer:
The Application Layer handles all those application web, email and file protocols.
Transport Layer:
Since application data is often large it must be split into segments by the Transport Layer.
Network Layer:
The Network Layer adds the source and destination IP addresses ( giving the approximate location like a sorting office).
Link Layer:
The Link layer adds the MAC address and is responsible for the actual physical connection between devices, Routers store just the MAC addresses for their devices, like your local postman.
Find out more here.
The Application Layer handles all those application web, email and file protocols.
Transport Layer:
Since application data is often large it must be split into segments by the Transport Layer.
Network Layer:
The Network Layer adds the source and destination IP addresses ( giving the approximate location like a sorting office).
Link Layer:
The Link layer adds the MAC address and is responsible for the actual physical connection between devices, Routers store just the MAC addresses for their devices, like your local postman.
Find out more here.
The World Wide Web
The World Wide Web is an interconnected system of public webpages and associated files accessible through the Internet.
The Domain Name System
The Domain Name System (DNS) is the Internet's system for mapping alphabetic names to numeric Internet Protocol (IP) addresses like a phone book maps a person's name to a phone number.
How does it work?
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TLD Server
A TLD nameserver maintains information for all the domain names that share a common domain extension, such as .com, . net, or whatever comes after the last dot in a URL. Authoritative Name Server This holds a copy of the regional phone book that matches IP addresses with domain names. |
Circuit Switching and Packet Switching
How is data actually sent over a network? The slow, but guaranteed way is circuit switching. The more efficient but less high quality way involves packet switching.
Circuit switching uses a dedicated path to send data. This means data delivery is guaranteed and arrives in order. The downside is that it bandwidth can’t be used by other data.
Packet switching is split into packets. Each packet has a header of information (including destination address and its position in the complete message). Each packet is placed on the network to travel on its own, At each node on the network the destination address is read and the best route is found. Therefore packets will not arrive in correct order. Packets need to be reordered at the destination.
This makes packet switching harder to intercept ( hack) because you’d need to get hold of each packet from a different route. Packet switching means that if one packet gets lost, you just need to resend one packet.
This makes packet switching harder to intercept ( hack) because you’d need to get hold of each packet from a different route. Packet switching means that if one packet gets lost, you just need to resend one packet.
Client Server versus Peer to Peer
This is really about which hardware is doing the heavy lifting.
Client server, where devices are reliant on services provided and managed by a central server.
Since the processing is carried out away from the user’s control client server can be more secure. Servers can have security software installed so that security is centralised. It can also be beneficial as browser may not support a client-side language. Or the client could have turned scripting off.
Peer-to-peer means that each device provides services and files to other devices on the network. So there is no need for a dedicated server.
This can be beneficial because there is no need pay for an expensive server. There is also no need to submit requests to a server and wait for response. Hence response times may be better for the client.
Client server, where devices are reliant on services provided and managed by a central server.
Since the processing is carried out away from the user’s control client server can be more secure. Servers can have security software installed so that security is centralised. It can also be beneficial as browser may not support a client-side language. Or the client could have turned scripting off.
Peer-to-peer means that each device provides services and files to other devices on the network. So there is no need for a dedicated server.
This can be beneficial because there is no need pay for an expensive server. There is also no need to submit requests to a server and wait for response. Hence response times may be better for the client.
Cloud Computing
We are all very familiar with cloud computing which allows the remote storage of data. It has many benefits: It allows the sharing of data between sites and client locations. It also provides extendable storage and built in back up. Although it has strong security, the control is outside the organisation.
Network Security
Example Security Threats
Preventing Security Breaches
Want to know more?
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