Computer Networks - 6

In the OSI model, the physical layer is responsible for the transmission and reception of unstructured raw bit streams over a physical medium. Therefore, the unit exchanged is a bit.

In the context of the OSI model, PPDU stands for Presentation Protocol Data Unit, which is the data unit used at the presentation layer.

APDU stands for Application Protocol Data Unit. It is the unit of data used in the application layer of the OSI model.

The network layer is responsible for routing data, and the data unit it handles is called a packet. Bits are physical layer, frames are data link layer, and TPDU is transport layer.

The data link layer organizes data into frames for transmission across the physical medium. It handles framing, error control, and flow control at the link level.

The transport layer uses Transport Protocol Data Units (TPDU) to manage end to end communication. Other options refer to higher layer PDUs.

The application layer uses Application Protocol Data Units (APDU) to exchange information. This is the highest layer in the OSI model.

The communication subnet consists of the physical, data link, and network layers. Therefore, it lies below the transport layer, which handles end to end communication.

The physical layer is the lowest layer of the OSI model and is responsible for the transmission and reception of raw bit streams over a physical medium.

SPDU stands for Session Protocol Data Unit. It is the unit of data exchanged between session layer entities.

The physical layer is responsible for ensuring that the signal representing a bit is correctly interpreted at the receiving end, maintaining bit integrity.

Data frames vary in size depending on the network protocol and the payload, often ranging from a few hundred to a few thousand bytes.

Similar to the 0 bit case, the physical layer must ensure that a transmitted 1 bit is received as a 1 bit to maintain data accuracy.

The session layer manages sessions between applications and uses Session Protocol Data Units (SPDU) for its communication.

Frames are transmitted sequentially over the physical medium to ensure they can be reassembled and processed in the correct order by the receiver.

The data link layer takes packets from the network layer and encapsulates them into frames for transmission.

Acknowledgement frames are sent by the receiver to inform the sender that the data frame was received successfully.

The data link layer is responsible for both detecting errors (using checksums or CRC) and correcting them (often via retransmission).

If a frame is corrupted or lost, the data link layer protocol typically requests a retransmission to ensure reliable delivery.

The data link layer is responsible for framing, which involves creating frame boundaries to distinguish one frame from another and recognizing them at the receiver.

To define frame boundaries, the data link layer often attaches special bit patterns (flags) at both the beginning and the end of the frame.

Duplicate frames occur when a sender transmits a frame multiple times, often due to a timeout occurring before the acknowledgement is received.

The Medium Access Control (MAC) sublayer, which is part of the data link layer, handles access to the shared transmission medium.

Flow control is a primary function of the data link layer, ensuring that a fast sender does not overwhelm a slower receiver.