1.3.2 Computer networks, connections and protocols

Encryption is used to scramble information so that it can be sent safely without anyone else being able to read it. The information is encrypted with a password or key that is needed to read the information again. If you visit a website on the internet that starts with 'https://' then this means that all of the information you are looking at or sending is being securely encrypted.

Because the Internet is a mesh network, any data that is sent via the internet (email, photos, data entered using web page forms etc.) can be intercepted and the data could be misused. By using encryption, the data will not make sense unless it can be unscrambled.

The method of encryption is complex but given enough time, a powerful computer could still be used to "crack the code". In practice, this will not be routinely done and you can consider that your data is safe.

A simple way of encrypting a message is to use a long number known as a key. The key can be very long, but in this example we will use an eight digit key (01234567). Each letter in the original message is "moved" by the corresponding number in the key:

The first letter (The red T), is shifted 0 places, which means that it stays the same. The next letter, the red h, is shifted one place to give the blue letter i. This is repeated for each letter until the whole message is encrypted.

To decrypt the message, the process is reversed. The blue letter T is shifted backward zero places to give the red letter T. The next letter, the blue letter i, is shifted back 1 place to give the red letter h.

Of course, when we encrypt messages using a computer, we can use a lot more complicated method than this!

In the case of this protocol, it would be possible to still come into a lesson without following the protocol, but if you didn't follow the green cross code (protocol), then you could be injured or die, and if you didn't follow the bank protocol when you use an ATM machine to withdraw money from a "hole in the wall", then you will lose your bank card and you will not be able to get your money.

When a computer joins a network, the network assigns a special number called an IP address to the computer. Without an IP address, the computer will not be able to use the network. Every time the computer wants to use the network to send or receive data, it will use the IP address as part of the process.

Internet Protocol (IP) addresses were invented a long time ago and the original system had a four billion different addresses. These became known as IPv4 addresses. Each IP address is a string of four single byte numbers. Because the numbers are stored in single bytes, they can be any number between 0 and 255, which is the largest eight bit number. An IPv4 address looks like this: 192.168.1.14

When this protocol was created, no one ever expected there to be more than four billion computers, but that number was passed in 2017. The old IPv4 addresses (using 4 bytes or 32 bits) has been extended to a much large IPv6 address range.

An IPv6 address is represented as eight groups of four hexadecimal digits, each group representing 16 bits. The groups are separated by colons (:). An example of an IPv6 address is:

2001:0db8:85a3:0000:0000:8a2e:0370:7334

The IPv6 range uses 128-bit addressing to support approximately 340 trillion trillion (or 2 to the 128th power). Instead of the IPv4 address method of four sets of one- to three-digit numbers, IPv6 uses eight groups of four hexadecimal digits, separated by colons.

At the moment, many computers stick to the older IPv4 protocol but all new computers are "IPv6 ready" which means that they will be able to move over to the larger range at any time.

Click on this link to visit the What is my IP address website.

It will show you the address that is currently assigned to your computer. If you are using a school network, you may find that every computer on the network has the same IP address, which appears to break the rules around IP protocols. This is because each computer has one IP address on the school network, and the school's Internet router is given an address that is shared with everyone on the network.

Every single device that connects to a network, such as network interface cards and wireless interface cards, have a unique identifying number which is given to the device by the manufacturer and cannot be changed.

A MAC address is a 48 or 64 bit number and is used by a network to identify the computer. Every time a computer needs to send or receive data, the MAC address is used to direct the traffic.

Differences between IP and MAC address

This is essential information, you will be asked about this in your exam!

• IP addresses are used when sending data on a network, including the Internet

• MAC addresses are linked to the hardware, whereas IP addresses are assigned to the device by the network and can be changed

• An IP address can be fixed so it does not change. This is known as a static IP address. You will have to use a static IP address if you connect a device to the Internet and want other computers to be able to reach it all the time.

The Internet, is the largest network and connects literally billions of computers and equipment. Clearly, they must all be compatible and use the same standards to connect - otherwise they simply wouldn't work.

As new developments are made, all networks can work at faster speeds, using more secure and fail proof connections. It is important that any devices using these new technologies can still connect to the older parts of the network.

In order to do this,all manufacturers use special standards that are developed and administered by an independent and neutral organisation. In order for a new device (or web service) to work with the rest of teh network, it must use these standards.

IP and MAC addresses are examples of standards, as is ethernet. All three of these standards have been revised many times and whilst they are now a lot more capable and complicated compared to when they were first designed, they remain backwards compatible with older equipment.

Communication between devices connected together in networks can be very complex, but all devices work with each other because they use standard protocols. Communication is organised into "layers" and each device/or program communicates between these layers using standardized protocols. We use layers because:

• Reduces the complexity of the problem into manageable sub-problems

• Devices can be manufactured to operate at a particular layer

• Products from different manufacturers will work together.

TCP/IP

Transmission Control Protocol/Internet Protocol is one of the earliest network protocols that defines how data is sent between computers on a network and over the Internet.

Data is split into packets, and each packet has some additional information attached in a header. The header contains information such as the IP address of where the data came from, the destination IP address etc.

The protocol includes a method of error correction - if a packet is not received in a set amount of time, the system will re request it.

HTTP

The Hypertext Transfer Protocol is used by web servers and clients and is used to serve HTML web pages. A web server will store the web pages and other files such as images and these will be sent to a web browser when requested. Web pages are written in Hypertext Markup Language, and this can contain hyperlinks which allow access to other pages. HTTP was originally proposed by Tim Berners Lee and is the basis behind the World Wide Web. the WWW is a service that runs on the Internet. The Internet refers to the hardware that makes up the actually network.

HTPPS

HTTP documents are sent as "plain text" which means that any computer that intercepts the signal has full access to the contents of the pages. This could mean that usernames, passwords and other sensitive information can be easily intercepted and used fraudulently.

HTTPS (Hypertext Transfer Protocol - Secure) uses encryption to secure all the transmitted data. The data will be encrypted to make it illegible which prevents anyone from accessing information that was not meant for public consumption.

FTP

File Transfer Protocol is used when files (of any type) need to be transmitted over a network. It is possible to receive a list of files that are stored in a certain directory, and then move to a different directory, send, receive, delete and rename a file. This Protocol is used in networks when files need to be transfered. There is also a secure version of this protocol , called FTPS which uses a similar method of encryption as HTTPS

• The application layer is the scope within which applications, or processes, create user data and communicate this data to other applications on another or the same host. The applications make use of the services provided by the underlying lower layers, especially the transport layer which provides reliable or unreliable pipes to other processes. The communications partners are characterized by the application architecture, such as the client-server model and peer-to-peer networking. This is the layer in which all application protocols, such as SMTP, FTP, SSH, HTTP, operate. Processes are addressed via ports which essentially represent services.

• The transport layer performs host-to-host communications on either the local network or remote networks separated by routers.^[32] It provides a channel for the communication needs of applications. UDP is the basic transport layer protocol, providing an unreliable connectionless datagram service. The Transmission Control Protocol provides flow-control, connection establishment, and reliable transmission of data.

• The internet layer exchanges datagrams across network boundaries. It provides a uniform networking interface that hides the actual topology (layout) of the underlying network connections. It is therefore also the layer that establishes internetworking. Indeed, it defines and establishes the Internet. This layer defines the addressing and routing structures used for the TCP/IP protocol suite. The primary protocol in this scope is the Internet Protocol, which defines IP addresses. Its function in routing is to transport datagrams to the next host, functioning as an IP router, that has the connectivity to a network closer to the final data destination.

• The link layer defines the networking methods within the scope of the local network link on which hosts communicate without intervening routers. This layer includes the protocols used to describe the local network topology and the interfaces needed to affect the transmission of Internet layer datagrams to next-neighbor hosts.