Reliable Data Transfer RDT2.1 Overview
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Questions and Answers

Match the following terms with their descriptions in the context of packet transmission:

ACK = Acknowledgment from the receiver NAK = Negative acknowledgment from the receiver Checksum = Data integrity verification method Sequence Number = Unique identifier for each packet

Match the scenarios with the corresponding actions taken by the sender:

If ACK/NAK is corrupted = Sender retransmits the packet If not sure what happened = Sender waits for a response If duplicate packet needs to be sent = Sender adds a sequence number If receiving an ACK = Sender can send the next packet

Match the sender and receiver responsibilities:

Sender = Waits for ACK or NAK from the receiver Receiver = Delivers data to the application layer

Match the terms related to packet transmission mechanisms:

<p>Stop and Wait = Sender sends one packet and waits for response Retransmission = Sending the same packet again due to loss Sequence Numbering = Ensures correct packet order Data Delivery = Final step of showing data to user applications</p> Signup and view all the answers

Match the types of acknowledgements with their purposes:

<p>ACK = Indicates that a packet was received correctly NAK = Indicates that a packet had an error Retransmit = Sender action for receiving a NAK Error Detection = Mechanism to identify bit errors</p> Signup and view all the answers

Match the reliable data transfer protocols with their characteristics:

<p>rdt1.0 = Reliable transfer over a reliable channel rdt2.0 = Channel with bit errors using checksums Sender = Sends data into the underlying channel Receiver = Reads data from the underlying channel</p> Signup and view all the answers

Match the types of errors with their recovery mechanisms:

<p>Bit Errors = Detected using checksums Packet Loss = Not covered in rdt1.0 but requires handling NAK Reception = Informs the sender to retransmit ACK Reception = Confirms successful packet receipt</p> Signup and view all the answers

Match the terms with their correct explanations in data transfer protocols:

<p>Error Detection = Identifies issues in transmitted packets Acknowledgement = Feedback from receiver to sender Negative Acknowledgement = Feedback indicating packet errors Packet = Basic unit of data transmitted in rdt</p> Signup and view all the answers

Match the terms related to TCP with their meanings:

<p>Timeout = Indicates a loss event in TCP ACK = Acknowledgment message received from the receiver MSS = Maximum Segment Size RTT = Round Trip Time for packet delivery</p> Signup and view all the answers

Match the pipelined protocols with their characteristics:

<p>Go-back-N = Receiver only sends cumulative ack Selective Repeat = Receiver sends individual ack for each packet</p> Signup and view all the answers

Match the roles of sender and receiver in Go-back-N protocol:

<p>Sender = Starts timer for oldest unacked packet Receiver = May receive duplicate ACKs</p> Signup and view all the answers

Match the following transport-layer services with their descriptions:

<p>Multiplexing = Sending multiple signals over a single channel Connection-oriented transport = Establishes a connection before data transfer Connectionless transport = No need for a session establishment Reliable data transfer = Ensures data is received accurately</p> Signup and view all the answers

Match the following TCP concepts with their details:

<p>Segment structure = The format of data packets in TCP Flow control = Prevents overwhelming the receiver Connection management = Handles the creation and termination of connections Reliable data transfer = Guarantees delivery of data packets</p> Signup and view all the answers

Match the following networking topics with their importance level:

<p>Multiplexing and demultiplexing = Critical for efficient use of channels TCP congestion control = Prevents network congestion Unreliable channel characteristics = Affects protocol complexity Reliable data transfer protocols = Essential for data integrity</p> Signup and view all the answers

Match the following terms in networking with their definitions:

<p>Connection management = Involves establishing and terminating connections Flow control = Regulates the speed of data transmission UDP = A connectionless transport protocol TCP = A connection-oriented transport protocol</p> Signup and view all the answers

Match the following concepts with their transport layer categories:

<p>Layer 4 = Transport layer Layer 2 = Link layer Layer 3 = Network layer Layer 5 = Application layer</p> Signup and view all the answers

Match the following principles of reliable data transfer with their attributes:

<p>Reliable data transfer = Ensures messages are delivered accurately Multiplexing = Combines multiple signals into one Connection-oriented transport = Requires a handshaking process Connectionless transport = Sends data without prior connection</p> Signup and view all the answers

Match the following types of transport with their characteristics:

<p>Connection-oriented = Requires coordination before data exchange Connectionless = Data is sent without prior handshake UDP = Faster but less reliable TCP = More reliable but slower</p> Signup and view all the answers

Match the following components of connection-oriented transport with their functions:

<p>Segment structure = Defines how TCP packets are formatted Flow control = Manages the data flow rate Connection management = Handles establishing connections Reliable data transfer = Confirms receipt of data packets</p> Signup and view all the answers

Study Notes

Reliable Data Transfer - RDT2.1

  • Problem: RDT1.0 assumes a perfect channel. RDT2.0 introduces a channel with bit errors.
  • Solution: Checksums detect errors, but a mechanism is needed for the receiver to inform the sender about problems.
  • Methods:
    • ACK (Acknowledgement): The receiver confirms successful packet reception.
    • NAK (Negative Acknowledgement): The receiver indicates a packet error.
  • Sender: The sender retransmits a packet if it receives a NAK.
  • Receiver: The receiver sends an ACK if the packet is received correctly and a NAK if there’s an error.

RDT2.1 - Sender FSM

  • Initial State: The sender starts with a sequence number of 0.
  • Event 1: When rdt_send is called, the sender creates a packet with data and a checksum.
  • Action 1: The packet is sent using udt_send.
  • Event 2: When an ACK or NAK arrives:
    • If corrupt, the sender retransmits.
    • If it's an ACK for sequence number 0, the sender moves to state 1.
  • Event 3: When rdt_send is called again, the sender creates a packet with data and a checksum.
  • Action 3: The packet is sent using udt_send and the sender moves to state 1.

RDT2.1 - Receiver FSM

  • Initial State: The receiver is expecting a packet with sequence number 0.
  • Event 1: When a packet arrives:
    • If corrupted or doesn’t have the correct sequence number, send a NAK.
    • If the packet is valid and has sequence number 0, extract the data and deliver it. Send an ACK for sequence number 0.
  • Event 2: When the receiver receives an ACK for sequence number 0, it moves to the state where it is expecting sequence number 1.

Handling Duplicate Packets

  • Solution: The sender adds a sequence number to each packet.
  • Receiver: The receiver discards duplicate packets.

RDT2.1 - Discussion

  • Sender: Adds a sequence number to packets.
  • Receiver: Checks the sequence number to identify duplicate packets.

Pipelined Protocols

  • Go-Back-N: Allows multiple unacknowledged packets to be in transit. The receiver only sends cumulative ACKs (acknowledging all packets up to a certain sequence number).
  • Selective Repeat: Allows multiple unacknowledged packets to be in transit. The receiver sends an individual ACK for each packet.

Go-Back-N

  • Sender:
    • Uses a k-bit sequence number in the packet header.
    • Maintains a "window" of up to N unacknowledged packets.
    • Sends packets in sequence.
    • If the timer for the oldest unacknowledged packet expires, retransmit all unacknowledged packets.
  • Receiver:
    • Only accepts packets in sequence.
    • Sends cumulative ACKs.
    • Discards out-of-order packets.

Selective Repeat

  • Sender:
    • Maintains a timer for each unacknowledged packet.
    • If the timer expires, retransmit only the corresponding packet.
  • Receiver:
    • Can buffer out-of-order packets.
    • Sends individual ACKs for each packet.

TCP Congestion Control

  • Problem: Sending too many packets can overwhelm the network and cause congestion.
  • Goal: Optimize the sending rate to avoid congestion.
  • Mechanism:
    • Congestion Window (cwnd): Limits the amount of data the sender can send at a time.
    • Slow Start: Initially starts with a small cwnd and increases it exponentially until a loss event.
    • Congestion Avoidance (CA): Increases the cwnd linearly after a loss event.
  • Loss Detection:
    • Timeout: A packet hasn't been acknowledged within a certain timeframe.
    • 3 Duplicate ACKs: Indicates packet loss.
  • Reaction to Loss:
    • Timeout: cwnd is set to 1.
    • 3 Duplicate ACKs: cwnd is cut in half.
  • AIMD (Additive Increase Multiplicative Decrease): Progressively probes for available bandwidth and adjusts the cwnd accordingly.
  • TCP Reno: A specific implementation of congestion control that uses 3 duplicate ACKs to detect loss.

TCP - Switching from Slow Start to CA

  • Condition: When cwnd reaches half its value before the timeout occurred.
  • Reason: Indicates that the network can handle a larger amount of data.

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Description

Explore the fundamentals of Reliable Data Transfer (RDT) 2.1, which addresses bit errors in communication channels. This quiz covers the concepts of acknowledgments (ACK) and negative acknowledgments (NAK), detailing how senders and receivers manage packet transmission and error correction. Test your understanding of sender and receiver mechanics in reliable data protocols.

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