1.3.3a. + b. Networks –Characteristics of Networks, the importance of standards and protocols and the Internet Structure

A group of connected computers that can share data and communicate with each other.

To allow users to share files, hardware, internet connections and other services efficiently.

A set of rules used to ensure the successful transmission of data between devices. This allows standardisation as different devices have different OS/hardware, and they allow for data to be exchanged in a predictable way

The process of dividing the complex task of networking into smaller, more manageable sections.

-To apply Protocols in order -To provide independence of layers -Hides details from previous or next layers -Each layer does a specific job -Breaks tasks down into manageable units -Improved troubleshooting as you can more easily identify the layer that causes the issue -Each layer only communicates with adjacent layers -Hardware/software can be manufactured to fit into one specific layer -Allows for standards for individual tasks/layers to be developed

A set of specifications that ensure different hardware and software systems are compatible with each other. They are necessary so that networks remain secure, capable of working with other products and efficient.

• Application • Transport • Internet • Link

A protocol is utilised based on the application operating at this layer, e.g. SMTP/IMAP for messaging service or HTTPS for browser based service. The layer then encrypts the data, before passing it data on to the transport layer to be sent. When receiving data, this is received from the transport layer. The received message is unpacked, ready for display, and then decrypted.

File Transfer Protocol (FTP), HTTP (Hyper Text Transfer Protocol), HTTPS (Hyper Text Transfer Protocol Secure) SMTP (Simple Mail Transfer Protocol) IMAP (Internet Message Access Protocol)

Manages data transmission between devices, ensuring it arrives reliably and in the correct order. It is responsible for establishing an end-to-end connection and maintaining conversations between application processors. Once the connection is made, the transport layer splits the data into packets. Each packet includes its number/sequence, the total number of packets and the port number that the packet should use. Packets are numbered so that they can be reassembled in the correct order.

Transmission Control Protocol (TCP), User Datagram Protocol (UDP)

This layer adds a source IP address and a destination IP address to each packet. The router uses the IP address to figure out where to route each data packet to.

Internet Protocol (IP)

This layer passes and receives data across a wireless network (to WAN / other machine). It also adds the source and destination MAC addresses to the packet. It both receives data from the internet layer to send, when sending, and passes (layered) data back up to internet layer when receiving.

Transmission media, e.g. copper twisted pair cables, fibre-optic or wi-fi

When a user types in a URL the domain name is sent to a DNS server. If it has the domain name in its lookup table it return the corresponding IP address to the web browser. Otherwise, it queries other DNS servers higher in the hierarchy until it finds the correct address. A request for the web page or resource is sent to the web server using the IP address. The requested web page or resource is then sent to the user’s web browser.

A LAN is a network which covers a small geographical area – such as a house. All the hardware for a LAN is owned and managed by the organisation using it. They are usually connected using Unshielded Twisted Pair cables, fibre optic, and Wi-Fi. They enable users to share resources and internet connection and be managed/monitored centrally (basically all the resource sharing advantages of peer-to-peer and all the central management advantages of client-server).

A wide area network covers a large geographical area, such as a city or multiple nations. The most famous example is the Internet. The hardware for a WAN is owned and managed by telecommunications companies. LANs physically located in different areas are connected to form a WAN. They are operated by telephone lines, fibre optic cables and satellite links.

A dedicated communication path of fixed bandwidth is established between 2 devices for the duration of a transmission and dedicated hardware resources are used for each connection. All packets are sent along this one route. This technique is used in traditional phone networks.

The dedicated bandwidth ensures a reliable and consistent connection, which makes it beneficial for data that needs a constant link end-to-end like real-time video.

A lot of potential bandwidth can be wasted. This means that the line cannot be used by others at the same. It is less secure if data is intercepted.

Data is split into small packets, and sent across the network independently of each other. At each node a packet is sent down the least congested path. They may be sent along multiple different paths or not in order. They are then reordered at the destination. Hardware is used for multiple different connections.

Data is more secure if intercepted as, because they may travel along different routes, its unlikely that all packets will be intercepted at once. It is more affordable and efficient than circuit switching as all bandwidth is used at once, meaning that less resources are wasted and that multiple users can share the same connections at once.

As packets can take different routes to the same destination, some may arrive out of order or be delayed, resulting in variable performance.