Communication Systems Part 11

The Data Link Layer in the OSI model focuses on managing reliable and efficient communication between two adjacent devices connected via physical media like coaxial cables, telephone lines, or wireless connections.

The Data Link Layer provides services to the Network Layer, enabling data packets to be transmitted accurately and efficiently. These services include framing, error control, and flow control.

Framing is the process of dividing data packets from the Network Layer into smaller units called frames that can be easily transmitted over the physical network. It adds control information to the data, ensuring proper delivery.

Character count framing uses a count field to indicate the length of the data in each frame, but can fail if the character count itself is corrupted.

Byte/character stuffing involves inserting special bytes to identify the start and end of frames. However, it can be tricky with longer characters like UNICODE.

Bit stuffing is used for variable-length characters and involves inserting a '0' bit after every five consecutive '1' bits to prevent misinterpretations.

Physical layer coding violations exploit coding differences at the physical layer to identify frame boundaries. This allows for special patterns to mark the start and end of frames.

Error control mechanisms ensure that data is transmitted accurately and efficiently. It helps detect and correct errors introduced during transmission through noisy channels.

Flow control helps prevent overwhelming the receiving device with data by regulating the rate of data transmission, ensuring that the data is received effectively.

Connectionless services offer no guarantees of reliable delivery and order of packets. They are simple and suitable for less demanding applications.

Acknowledged connectionless services send packets with acknowledgments, providing confirmation of delivery without establishing a dedicated connection between devices.

Acknowledged connection-oriented services establish a virtual circuit between devices before sending packets. They ensure the reliable delivery of data in sequence with acknowledgments.

A physical layer coding scheme where data is encoded using a high-low or low-high pair for each bit, allowing frames to be delimited by consecutive high or low signals.

Errors that occur in bursts, meaning multiple bits in a row are affected. These are more challenging to correct than isolated errors.

Codes designed to detect errors but not correct them. They typically involve calculating a checksum that can verify data integrity.

Codes designed to both detect and correct errors. They add redundant bits to the data, allowing the receiver to identify and fix errors.

A method of encoding data that adds redundancy by calculating parity bits at specific positions within the codeword. These parity bits help detect and correct single bit errors.

A category of error-correcting codes capable of correcting single errors. These codes are particularly effective when dealing with burst errors that occur within a limited range.

A type of error-correcting code capable of handling bursts of errors. It achieves this by sending data in columns, rearranging it at the receiver, and correcting errors in a specific direction.

The original message in an error-correcting code before redundancy is added to create a codeword.

The extra bits added to a message in an error-correcting code to provide redundancy and enable error detection and correction.

A codeword is the complete data unit transmitted after redundancy bits are incorporated into the message. It includes both the message and redundancy bits.