topic 4

A network is an arrangement of two or more computing devices connected together in order to communicate with each other and share resources.

to share data and software to share printers, hard drives and other hardware peripherals. to share internet connections and services. to provide centralised support and backup services. to enable the rabid deployment of new software and updates to enable people to communicate with each other using services. to support collaborative working

LAN (Local Area Network) a network that covers a relatively small geographical area. WAN (Wide Area Network) a network that covers a large geographical area and connects together multiple LANs.

internet protocol address a unique identifier assigned to each device connected to a network. • most devices use a dynamic IP address • this is allocated to them from a communal pool when they connect to the internet and returned when they disconnect. • next time they connect, the IP address will be different. a device such as a router, is permanently connected to the internet with a static IP address that never changes.

1) the senders large file is broken up into smaller packets. 2) packets are directed to their destination by routers. routers inspect the packets and decide the most efficient path to the next router. 3) packets take different routes across the network. they may nit arrive in the correct order. 4) the receiving computer reassembles them in the correct order using information in the packet headers.

transmission speed is faster for wired. latency is very low for wired (good)

file size = time x data transfer rate time (s) = file size (bits) / data transfer rate (bps) data transfer rate = file size / time speed (data transfer rate) = size / time (time)

Post Office Protocol Internet –. Mail server → client used by client to retrieve emails from a main server. all of the emails are downloaded when there is a connection between client and server. messages are deleted from the email server once they have been downloaded. • get email from a mail server • emails are removed, once downloaded to a client

Simple Mail Transfer Protocol provides the rules for sending email messages from client to server and then from server to server until it reacges its destination. • used to send email between email servers • it is not to receive emails Email uses these protocols to communicate with mail servers. SMTP is used to send the email

Internet Message Access protocol messages do not have to be deleted. they can be read and stored on the message server. • a set of rules that email client programs use to download emails from a mail server. • this protocol leaves the emails on the server so they can be accessed by a different application.

Application: user interface Transport: create a channel and packets Internet: addressing Link: physical transmission After Tea I Link

From client A, the information that needs to be sent from an application in the application layer, is sent down to the transport layer. It is then split into packets. The packets are sent to the internet layer. Addresses are added to the packets. They are sent to the link layer. There, they are converted into signals and sent across the transmission medium. At the receiving end, the signals are converted to data and sent to the internet layer. There, the addresses are removed. The data is sent up to the transport layer, where the many packets are joined back up together in the right order. The data is sent up to the corresponding application on the application layer. The data is processed for client B.

in a star network, each computer or client is connected individually to a central point or node, which can be a hub or switch. + data is only sent to the intended computer directly + network traffic is kept to a minimum + if one fails, all of the others will continue to operate, + it is easy to add new devices without disrupting the network. • if the central point fails, then so will the entire network. • requires a lot of cable because each computer connects individually to the central component.

Firewalls are software. They are designed to monitor and block incoming and outgoing connections to a network. Firewalls protect a system from hackers. If a hacker is already inside the system, they may be prevented from doing extra damage by the firewall blocking outgoing traffic • a firewall protects a network connected to a WAN such as the internet. it can be provided by hardware or software. firewalls can be configured to prevent communications from entering the network and also programs and users from accessing the internet from within the netwokrk.

application - HTTP, HTTPS, SMTP, POP, IMAP Transport - TCP Internet - IP Link - Ethernet, Wi-Fi

Application Contains the applications that exchange data Transport Determines how the data being sent gets to its destination Splits up data and puts it into packets Internet Deals with the IP addresses Adds addresses to the packets Link Responsible for converting the packets to signals that can be sent across transmission media

The sending computer used protocols in the application layer first. These protocols are responsible for how user applications, such as email and web browsers, package their data to be sent online. Then protocols in the transport layer establish a channel between the two devices and split the data into packets. In the internet layer (or network layer), addressing is carried out. The addresses of the sending and receiving devices are added to the packet header. Finally the link layer (or network interface layer) is responsible for transporting the raw data over the transmission medium. This includes generating the right type of signal for the connection type - light for fibre and electrical for ethernet. The receiving computer follows the same processes but in reverse. The signal is translated into data The addresses are taken off The packets are reconstructed The data is rendered for the application.

The sending computer used protocols in the application layer first. These protocols are responsible for how user applications, such as email and web browsers, package their data to be sent online. Then protocols in the transport layer establish a channel between the two devices and split the data into packets. In the internet layer (or network layer), addressing is carried out. The addresses of the sending and receiving devices are added to the packet header. Finally the link layer (or network interface layer) is responsible for transporting the raw data over the transmission medium. This includes generating the right type of signal for the connection type - light for fibre and electrical for ethernet. The receiving computer follows the same processes but in reverse. The signal is translated into data The addresses are taken off The packets are reconstructed The data is rendered for the application.