Mod3 PartB

Basic Transmission and Receipt

The sender encapsulates packets into frames and transmits them to the receiver. Frame headers are never passed to the network layer.

Data Link Layer

The second layer of the OSI model responsible for node-to-node delivery, framing, flow control, error detection, and correction.

Framing

The process of encapsulating network layer packets into frames by adding headers and trailers.

Error Detection

Identifying whether an error has occurred during transmission.

Error Correction

Identifying and fixing the errors in transmitted data.

Flow Control

Regulates data flow between sender and receiver to prevent overwhelming the receiver.

Elementary Data Link Protocols

Basic protocols with simplifying assumptions such as reliable machines, unidirectional communication, and independent processes.

Unidirectional Communication

Data flows in only one direction—from sender to receiver.

Independent Processes

Assumption that the sender and receiver operate independently.

Reliable Machines and Processes

Assumption that hardware and software are fault-free.

Utopia Protocol

A protocol with no flow control or error correction; assumes a perfect network.

Sender (in Utopia)

Runs in the data link layer of the source machine, transmitting data.

Receiver (in Utopia)

Runs in the data link layer of the destination machine, receiving data.

Drawback of Utopia

Ignores the possibility of transmission errors or flow overload.

Stop-and-Wait Protocol

Flow control protocol where the sender sends one frame and waits for acknowledgement before sending the next.

Line Rate

Maximum rate at which data can be transmitted over a communication channel.

Buffering

Temporary data storage to handle speed mismatches between sender and receiver.

Processing Ability

The capacity of the receiver to handle incoming frames.

Error-Prone Channels

Communication channels where frames can be damaged or lost.

Damaged Frame

A frame altered in transit, usually detected by hardware.

Lost Frame

A frame that never arrives at the receiver.

Acknowledgement (ACK)

A control message sent to confirm receipt of a frame.

Timer

A mechanism used to trigger retransmission if an acknowledgement is not received in time.

Delayed Delivery Problem

A retransmitted frame may arrive after the original was received, causing confusion.

Duplicate Frame Problem

Retransmissions may be mistaken as new frames.

Solution to Duplicates

Use sequence numbers in frame headers so the receiver can detect and discard duplicates.

Sequence Number

A number in the frame header to differentiate new transmissions from duplicates.

ARQ (Automatic Repeat reQuest)

Protocol that ensures error correction by retransmitting unacknowledged frames.

PAR (Positive Acknowledgement with Retransmission)

Another name for ARQ, emphasizing acknowledgement-based retransmission.

Disadvantage of ARQ

Extra overhead, complexity, and potential delay due to retransmissions.

Improving Efficiency

Use bidirectional transmission and allow multiple frames to be sent before requiring acknowledgements.

Bidirectional Transmission

Communication happens in both directions between sender and receiver.

Piggybacking

Technique of combining acknowledgements with data frames to reduce overhead.

Forward Channel

Path for data transmission from sender to receiver.

Reverse Channel

Path for data from receiver back to sender.

Control Frame

A frame used only to carry control information like acknowledgements.

Piggybacking Disadvantage

Delaying acknowledgements may lead to inefficiencies if the reverse traffic is low.

“Free Ride” Concept

Acknowledgement is attached to the next outgoing frame without extra cost.

Sliding Window Protocol (SWP)

Protocols where sender and receiver maintain windows of allowable frame numbers to send/receive.

Sending Window

Set of sequence numbers the sender is allowed to transmit.

Receiving Window

Set of sequence numbers the receiver is allowed to accept.

Fixed Window Size

A constant number of frames allowed in flight.

Dynamic Window Size

A variable-sized window based on network conditions.

Advantage of Dynamic Window

Adapts to congestion or processing speed, improving performance.

One-Bit Sliding Window

Simplified protocol with a window size of 1, essentially functioning like stop-and-wait.

Go-Back-N Protocol

Sender continues sending multiple frames but must go back and resend all frames after a lost or damaged one.

Receive Window = 1

Receiver only accepts the next expected frame and discards others.

Selective Repeat Protocol

Receiver buffers out-of-order frames and only asks for retransmission of missing ones.

Buffering in Selective Repeat

Temporarily stores received frames even if earlier frames are missing.

Automatic Repeat reQuest (ARQ)

Retransmits frames that are not acknowledged.

Positive Acknowledement with Retransmission (PAR)

Acknowledges correct frames and retransmits unacknowledged ones.

Sliding Window Protocol (SWP)

Allows multiple frames in flight, using windows to manage flow and errors.