Lesson 1

A set of protocols used to connect network devices to each other.

TCP/IP

This network model consists of a seven-layer architecture that organizes the sending of data from hosts across a network

The OSI (Open System Interconnection) model

This layer is responsible for the physical connections of the devices in the network. This layer is implemented through the use of devices such as hubs, repeaters, modem devices, and physical cabling.

Physical Layer or Layer 1

This layer is responsible for the error-free delivery of data to the receiving device or node. This layer is implemented through the use of devices such as switches and bridge devices, as well as anything with a network interface, like wireless or wired network cards.

Data Link Layer or Layer 2

This layer is responsible for the transmission of data between hosts in different networks as well as routing of data packets. This layer is implemented through the use of devices such as routers and some switches.

Network Layer or Layer 3

This layer provides services to the application layer and receives services from the network layer. It is responsible for the reliable delivery of data. It segments and reassembles data in the correct order for it to be sent to the receiving device. It may also handle the reliable delivery of data and any retries of data that are lost or corrupted (for example, TCP does this). This layer is often called the heart of OSI.

Transport Layer or Layer 4

This layer is responsible for connection establishment, session maintenance, and authentication.

Session Layer or Layer 5

This layer is responsible for translating data from the application layer into the format required to transmit the data over the network as well as encrypting the data for security if encryption is used.

Presentation Layer or Layer 6

This layer is responsible for network applications (like HTTP or FTP) and their production of data to be transferred over the network.

Application Layer or Layer 7