X) TCP / IP / Client-server Model

A protocol is a set of rules that specify how two or more devices communicate with one another. In a protocol stack, protocols are used in a series of functional layers and ensuring the data is sent from one layer to another layer, before being sent out onto the media for transmission.

A method of modular communication, where data is taken from the layer above, the data is then given some additional information, then passed to the layer below. The process of a layer taking data from the data packet recived, then passes the rest of the data to the layer above.

This layer uses appropriate protocols relating to whatever application is being used to transmit data. Protocol Examples: HTTP, HTTPS, POP3, FTP, SMTP.

This layer is responsible for establish an “end to end” connection. Once a connection has been made, the data is split and is transmitted as packets. At the receiving end, the layer confirms that all packets have been received and requests data if any are missing.

For each packet a source IP address and destination IP address is added. E.g. 127.56.87.2 : 80 Socket = IP Address : Port Number

This layer represents the physical connection between the various network nodes. The Media Access Control Address (MAC Address) is added to each packet. The packets are then sent based on their destination IP Address.

The MAC Address is a unique identifier, 12 digit hexadecimal code. This identifier is used to identify a specific physical device. E.g. 4B:24:A2:73:0E:F1 281 Trillion possibilities.

Once the data packets have been received, it is passed back up through the layers. - The link layer removed the MAC address

A port is used to alert a specific application to deal with data sent to a computer. They are used by protocols to specify what data is being sent. HTTP - 80 HTTPS - 443 POP3 - 110 SMTP - 25 FTP - 20

An encrypted protocol that allows secure communication between nodes across a network. Secure Shell tunnelling is used to pass data through where otherwise it might have been blocked.

Mail servers are dedicated computers which are responsible for storing and provide access to emails. SMTP- Used to send emails between the mail server and their destination. POP3- Downloads emails stored on a server to a local client. IMAP- Manages emails on a server so multiple clients can access the same email account.

Some computers are dedicated to host websites and provide resources. Data stored are either in the format of HTML or JavaScript and are then separated down into their constituents parts. These text elements are broken down further and rendered on the client browser. Images, Videos or scripts are also downloaded as the webpage is rendered. Web servers make use of protocols such as HTTP to ensure that all data is handled correctly.

A unique identifier for a host computer or network node trying to connect over IP on a network.

Used 4 (octets) groups of 8 bits written in decimal-dotted notation: 10101011.00001111.10101010.11100010 Example: 5D26:93AC:0007:492F Range of: 0.0.0.0 - 255.255.255.255 2 ^ 32 = 4.3 Billion Addresses

X.Y.Z.0 - represents the entire network X.Y.Z.255 - represents the broadcast address, used for sending data simultaneously to all hosts on a network. 127.X.Y.Z - represents loopback, in which a host’s IP software, treats an outgoing packet as incoming.

IPv4 = 256^4 = 4.3 Billion combinations Not enough for the level of devices being manufactured. IPv6- 128 bits (8 octets) Example: 5D26:93AC:0007:492F:5D26:93AC:0007:492F IPv6 = 256 ^ 16= 3.4x10^38 possible addresses Every atom covering the Earth’s surface +100 times over.

IP Address broken down into a Network ID and Host ID. For this example, 16 bits represent each sub ID. IP Address: 142.67.57.253 Network ID: 142.67.0.0 Host ID: 0.0.57.253

The more hosts in each network, the fewer networks that can be created. 210.54.101.0 /24 Network ID = 24 bits –> 3 octets Network ID = 210.54.101 = 16.8 million Host ID = 0.0.0.0 = 256

The subnet mask is used to define the Network ID and this can be segmented to however the administrator sees fit.

142.27.114.56 / 24 IP Address = 10001110.00011011.01110010.00111000 All Network ID bits set to 1. All Host ID bits set to 0. SubNet = 11111111.11111111.11111111.00000000 1 AND 1 = 1 0 AND 1 = 0 1 AND 0 = 0 0 AND 0 = 0 Network ID = 10001110.00011011.01110010.00000000

Example of an address that is considered to be private: 10.0.0.1 - 10.255.255.255 This address is non-routable across the Internet and reserved for LANs or private WANs. This reduces the need for every computer to have its own unique public address.

Devices using IP addresses cannot access the internet directly. A client having a single IP address is shared across all hosts on a private IP address. NAT is responsible for converting IP addresses as they pass over the board are between public and private address spaces.

The translation device (router) records the source and destination address for a request. It then communicates on the host’s behalf with the destination IP address, when a respond returns it sends it back to the host address.

A method of routing data through additional ports, it is used to provide services to clients on the internet.