Transport Layer Selective Repeat Protocol
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Questions and Answers

What is the primary function of the sender window in selective repeat protocol?

  • To store received packets out of order
  • To regulate the transmission rate
  • To detect packet errors
  • To buffer packets before transmission (correct)

    • What happens when the receiver's window size is equal to 3 in selective repeat protocol?

  • The receiver can accept packets with sequence numbers 0, 1, and 2 (correct)
  • The receiver can accept packets with errors
  • The receiver can accept packets out of order
  • The receiver can accept only three packets at a time

    • What is the consequence of a packet loss in selective repeat protocol?

  • The sender will retransmit the lost packet (correct)
  • The receiver will request retransmission of the lost packet
  • The connection will be terminated
  • The packet will be discarded

    • What is the purpose of sequence numbers in selective repeat protocol?

    <p>To ensure packet ordering</p> Signup and view all the answers

    What is the primary function of the sender window in selective repeat protocol?

    <p>To buffer out-of-order packets</p> Signup and view all the answers

    What is the consequence of a timeout in selective repeat protocol?

    <p>The sender will retransmit the packet</p> Signup and view all the answers

    What is the primary advantage of selective repeat protocol over other protocols?

    <p>Out-of-order packet delivery</p> Signup and view all the answers

    What is the base counting system used for sequencing packets in the example?

    <p>Base 4</p> Signup and view all the answers

    What is the role of the receiver window in selective repeat protocol?

    <p>To store received packets in order</p> Signup and view all the answers

    Why does the receiver window play a crucial role in selective repeat protocol?

    <p>To reassemble packets in the correct order</p> Signup and view all the answers

    What is the implication of the receiver's behavior in both cases?

    <p>The receiver's behavior is identical in both cases</p> Signup and view all the answers

    What is the purpose of base 4 counting in selective repeat protocol?

    <p>To sequence packets</p> Signup and view all the answers

    What is the purpose of sequence numbers in packet transmission?

    <p>To ensure packets are received in the correct order</p> Signup and view all the answers

    What is the relationship needed between the sender and receiver windows?

    <p>The sender and receiver windows must be identical</p> Signup and view all the answers

    What happens when a TCP receiver gets an in-order segment with a sequence number that is expected?

    <p>It sends a single cumulative ACK.</p> Signup and view all the answers

    What is the purpose of a duplicate ACK in TCP?

    <p>To indicate a gap in the sequence of received segments.</p> Signup and view all the answers

    What triggers a TCP fast retransmit?

    <p>Receipt of three duplicate ACKs.</p> Signup and view all the answers

    What is the purpose of the SendBase in TCP?

    <p>To keep track of the sequence number of the next expected byte.</p> Signup and view all the answers

    What happens when a TCP receiver gets an out-of-order segment with a higher sequence number?

    <p>It immediately sends a duplicate ACK.</p> Signup and view all the answers

    What is the purpose of a cumulative ACK in TCP?

    <p>To acknowledge the receipt of multiple segments.</p> Signup and view all the answers

    What happens when a TCP sender receives three duplicate ACKs?

    <p>It retransmits the unACKed segment with the smallest sequence number.</p> Signup and view all the answers

    What is the purpose of the sequence number in TCP?

    <p>To keep track of the order of received packets.</p> Signup and view all the answers

    What happens when a TCP receiver gets a segment that partially or completely fills a gap?

    <p>It immediately sends a single cumulative ACK.</p> Signup and view all the answers

    What is the purpose of the ACK in TCP?

    <p>To acknowledge the receipt of a segment.</p> Signup and view all the answers

    Study Notes

    Selective Repeat

    • Selective repeat has a sender window and receiver window
    • Sequence numbers (seq #s) are used, with base 4 counting (0, 1, 2, 3)
    • Window size determines how many packets can be sent before waiting for acknowledgement

    Dilemma Example

    • If packet 0 is lost, the receiver will accept packet 0 with sequence number 0
    • If packet 0 is retransmitted, the receiver will also accept it with sequence number 0
    • The receiver's behavior is identical in both cases, leading to a dilemma

    Receiver Behavior

    • If a packet with an expected sequence number arrives, the receiver sends an ACK
    • If a packet with a higher-than-expected sequence number arrives, the receiver sends a duplicate ACK
    • If a packet fills a gap, the receiver sends an ACK
    • If no packet arrives within a certain time (e.g. 500ms), the receiver sends an ACK for the next expected segment

    TCP Retransmission Scenarios

    • If a segment is lost, the sender retransmits the segment after a timeout
    • If an ACK is lost, the sender retransmits the segment after a timeout
    • A cumulative ACK can be sent to cover earlier lost ACKs

    TCP Fast Retransmit

    • If the sender receives three duplicate ACKs for the same data, it resends the unACKed segment with the smallest sequence number
    • This is likely due to the unACKed segment being lost, so the sender doesn't wait for a timeout

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    Description

    This quiz is about the Selective Repeat protocol in the Transport Layer of computer networks, focusing on sender and receiver windows.

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