3.5 Computer networks

Computer network

A group of devices connected together so that they can communicate.

PAN – Personal Area Network

Devices connected and communicating over a small distance around one person.

LAN – Local Area Network

Devices connected and communicating over a small geographical area. They are often owned and controlled/managed by a single person or organisation.

WAN – Wide Area Network

Devices connected and communicating over a large geographical area. They are often under collective or distributed ownership.

Network protocol

A set of rules that allow devices/networks to communicate/transfer data.

TCP – Transmission Control Protocol

TCP is a transport layer protocol. It is used to establish communication between two end points and ensure that this is error free.

IP – Internet Protocol

IP is an internet layer protocol. IP is responsible for routing. An IP address is given to a device when it connects to a network. The IP address consists of four bytes of information and is typically represented as a dotted quad with each having a value in the range 0 to 255. An example is: 10.10.100.4

HTTP/HTTPS

HyperText Transfer Protocol HyperText Transfer Protocol Secure An application layer protocol concerned with sending and receiving web pages between a webserver and a client (browser). HTTPS adds encryption to the protocol allowing for secure data movement.

SMTP

Simple Mail Transfer Protocol An application layer protocol. To send emails to another email server/client.

IMAP

Internet Message Access Protocol An application layer protocol. To receive emails from an email server. To allow management of emails on the server.

Authentication

Authentication is the process of confirming someone is who they say they are. This can be completed by a variety of methods including username and password.

Encryption

Using an algorithm to convert a message into a form that is not understandable without the key to decrypt it.

MAC address (Media Access Control address)

A unique identifier assigned to a network device.

Firewall

A firewall is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules. A firewall generally has a set of rules that will either allow or deny traffic and these can be set to look at: • IP address (sender/destination) • Ports • MAC address (sender/destination) For example, a rule could block all incoming FTP traffic on ports 20 and 21.

MAC address filtering

MAC address filtering allows devices to access, or be blocked from accessing, a network based on the physical address embedded within the device’s network adapter.

TCP/IP model

The TCP/IP model is a protocol stack used when connecting a device to the Internet. It is made up of four layers: Application, Transport, Internet and Link.

Application layer

The application layer controls how data moves in and out of applications from the transport layer. Applications include email clients, web browsers and protocols such as HTTP, HTTPS and IMAP.

Transport layer

The transport layer breaks down messages into smaller chunks (packets). This layer sets up the communication between the two hosts and they agree settings such as the size of packets. Each packet is given a sequence number so the receiver can put the message back together again. The transport layer uses protocols such as TCP.

Internet layer

The Internet layer adds the source and destination IP addresses to the packet and packages the data for transmission. This layer is concerned with the routing of packets across the Internet.

Link layer

The link layer includes the network interface card and drivers necessary to send data out onto the network. The link layer is where the network hardware such as the NIC (network interface card) is located. OS device drivers also operate here.