Explain the working of Lower four layers of OSI model in brief. (Don't copy paste answer plz)

Hey Sherlie,

I hope the following answers your question.

Transport Layer
The main techniques implemented by the transport layer is basically 1) the reliable TCP protocol and the 2) unreliable UDP protocol which basically sums up the 2 most major and common modes of data delivery. Just to mention another protocol, SPX (Sequenced Packet Exchange) and IPX (Sequenced Packet Exchange) which are part of the Novell System.

The transport layer is also responsible for 'segmenting' the data thrown at it by the application layer at the sender side, and reassembling is back at the receivers end. Some important concepts to know regarding the transport layer include: connection-oriented, connection less, error recovery, acknowledgment, flow control, and windowing.

Analogy: You arrive at a city, and you want to know which house is yours.

Network Layer
The network layer defines end-to-end packet delivery and locating end system using logical addressing – IP addresses. Routers are high level switches are implemented up till this layer and it helps these devices determine the best path to transfer the data within an internetwork through the routes learning via routing protocols. In a nutshell, this layer allows communication between end systems from different networks. There are two types of packets associated with this layer – data packets and routing update packets. Protocols include - IP, IPX, AppleTalk.

Analogy: You book an airplane ticket which states your source country and your destination country.

Data Link Layer
Defines how to transmit data over a network media (how to place network layer packets onto the network media – cable or wireless) with physical addressing. Allows communication between end systems within the same network. Protocols include: LAN – Ethernet, WAN – HDLC, PPP, Frame Relay, ATM. Basically means, now that you have known your source and destination you must find a route or a path by which you can actually reach your destination.

Analogy: Airplanes heading to the same country take different paths or routes to avoid collision.

Physical Layer
Defines specifications for communication between end systems and the physical media (how to place data link layer frames onto the media). Defines connector shapes, number of pins, pin usages or assignments, electrical current levels, and signal encoding schemes. Example Ethernet, RS-232, V.35.

Analogy: Its the actual airplane you travel in

------------------------------------------------------------------------------------------
To sum up, all layers have a small function example, in the transport layer the UDP protocol includes a checksum which is used for error detection. Other layers respond to errors in ways such as dropping the data packet/segment/frame and reporting back to sender or fixing the error itself.

Great answer. i liked the analogies very much.
thank you so much.

Glad you understood