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 (C)</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 (C)</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 (A)</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 (D)</p> Signup and view all the answers

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

<p>Base 4 (B)</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 (C)</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 (C)</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 (B)</p> Signup and view all the answers

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

<p>To sequence packets (A)</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 (D)</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 (A)</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. (B)</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. (A)</p> Signup and view all the answers

What triggers a TCP fast retransmit?

<p>Receipt of three duplicate ACKs. (B)</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. (A)</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. (C)</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. (C)</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. (B)</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. (D)</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. (A)</p> Signup and view all the answers

What is the purpose of the ACK in TCP?

<p>To acknowledge the receipt of a segment. (B)</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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