• layer 1 physical device. connects more than one ethernet together to share the same medium, takes electrical signal from one place and sends it to every channel(broadcasts), doesnt matter who the recipent is, so it was obsolete kind of technology basically. — was not efficent — was wasting a lot of bandwidth — was not needed as it made a lot of collisions, because all the devices were sharing the same medium the chances of collision were very high. — Operates in half-duplex mode, meaning devices can only send or receive data at one time, not simultaneously. — Creates a single collision domain, meaning if two devices try to send data at the same time, a collision will occur and the data will have to be re-sent.

• layer 2 (data link layer) device which are used to join two ethernets only but the difference is instead like hubs who used to broadcast it to every device switches are a little more intelligent meaning they see for device MAC address through nic on the ports and when they recieve the data they send it to destination address through the mac address they have , meaning they know where to send the data without the collision problem.

— collision domain is very low as in the full duplex mode its rare to be collided when the switches know macs —works on full duplex mode, meaning the data can be sent nd recieved simultaneously thereby increasing the efficiency by a threshfold. — Builds a MAC address table (or CAM table) to store the MAC addresses of connected devices and the port they are connected to. This allows the switch to forward frames only to the intended recipient. — Each port on a switch is its own collision domain, which significantly reduces the number of collisions.

• routers are the most intelligent, work on 3rd layer or network layer which mean they deal with ip addresses(logical address of devices) meaning they help in connection of two networks and help in transferring of data packets from one point to another in very efficent as they have all the paths stored in something known as routing tables. they also help in deciding whether to send the data on to the next network or keep the data in same network — essential for inter-communication meaning necessary for connecting the internet with office/college network to the Internet. — Use IP addresses to make routing decisions and forward packets between different networks. — Connect different broadcast domains. — Can be used to implement security policies and filter traffic between networks.

The Open Systems Interconnection (OSI) model is a conceptual framework that standardizes the functions of a telecommunication or computing system in seven distinct layers.

• Layer 7: Application Layer - The layer closest to the end user. This is where application-specific protocols like HTTP (for web browsing), FTP (for file transfer), and SMTP (for email) operate.
• Layer 6: Presentation Layer - Responsible for data translation, encryption, and compression. It ensures that data from the application layer is in a readable format for the application layer of the destination system.
• Layer 5: Session Layer - Manages sessions between applications. It establishes, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end.
• Layer 4: Transport Layer - Provides reliable data transfer between end systems. The two most common protocols are TCP (Transmission Control Protocol), which is connection-oriented and reliable, and UDP (User Datagram Protocol), which is connectionless and less reliable. This layer also handles port numbers.
• Layer 3: Network Layer - Responsible for logical addressing (IP addresses) and routing of packets across different networks. Routers operate at this layer.
• Layer 2: Data Link Layer - Provides reliable transit of data across a physical link. It deals with physical addressing (MAC addresses) and framing. Switches operate at this layer.
• Layer 1: Physical Layer - Defines the physical characteristics of the network, such as the type of cables, connectors, and signaling. Hubs operate at this layer.