Transport Layer : Flow & Congestion control PYQ QUIZ GATE CS

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Question 1

Consider the sliding window flow-control protocol operating between a sender and a receiver over a full-duplex error-free link. Assume the following:

  • The time taken for processing the data frame by the receiver is negligible.
  • The time taken for processing the acknowledgement frame by the sender is negligible.
  • The sender has infinite number of frames available for transmission.
  • The size of the data frame is 2,000 bits and the size of the acknowledgement frame is 10 bits.
  • The link data rate in each direction is 1 Mbps (= 106 bits per second).
  • One way propagation delay of the link is 100 milliseconds.

The minimum value of the sender's window size in terms of the number of frames, (rounded to the nearest integer) needed to achieve a link utilization of 50% is_____________.

  • 51

  • 50

  • 25

  • 52

Question 2

Every host in an IPv4 network has a 1-second resolution real-time clock with battery backup. Each host needs to generate up to 1000 unique identifiers per second. Assume that each host has a globally unique IPv4 address. Design a 50-bit globally unique ID for this purpose. After what period (in seconds) will the identifiers generated by a host wrap around?

  • 128

  • 64

  • 256

  • 512

Question 3

Consider the three-way handshake mechanism followed during TCP connection establishment between hosts P and Q. Let X and Y be two random 32-bit starting sequence numbers chosen by P and Q respectively.

Suppose P sends a TCP connection request message to Q with a TCP segment having SYN bit =1, SEQ number =X, and ACK bit =0. Suppose Q accepts the connection request.

Which one of the following choices represents the information present in the TCP segment header that is sent by Q to P?

  • SYN bit =1, SEQ number =X+1, ACK bit =0, ACK number =Y, FIN bit =0

  • SYN bit =0, SEQ number =X+1, ACK bit =0, ACK number =Y, FIN bit =1

  • SYN bit =1, SEQ number =Y, ACK bit =1, ACK number =X+1, FIN bit =0

  • SYN bit =1, SEQ number =Y, ACK bit =1, ACK number =X, FIN bit =0

Question 4

Consider a TCP connection between a client and a server with the following specifications; the round trip time is 6 ms, the size of the receiver advertised window is 50 KB, slow-start threshold at the client is 32 KB, and the maximum segment size is 2 KB. The connection is established at time t=0. Assume that there are no timeouts and errors during transmission. Then the size of the congestion window (in KB) at time t+60 ms after all acknowledgements are processed is _________ . 

  • 33

  • 44

  • 55

  • 50

Question 5

Consider the following statements regarding the slow start phase of the TCP congestion control algorithm. Note that

cwnd

stands for the TCP congestion window and MSS denotes the Maximum Segment Size.

  1. The cwnd increase by 2 MSS on every successful acknowledgement.
  2. The cwnd approximately doubles on every successful acknowledgedment.
  3. The cwnd increase by 1 MSS every round trip time.
  4. The cwnd approximately doubles every round trip time.

Which one of the following is correct?

  • Only (ii) and (iii) are true

  • Only (i) and (iii) are true

  • Only (iv) is true

  • Only (i) and (iv) are true

Question 6

The three way handshake for TCP connection establishment is shown below. 

 


Which of the following statements are TRUE?
(S1) Loss of SYN + ACK from the server will not establish a connection
(S2) Loss of ACK from the client cannot establish the connection
(S3) The server moves LISTEN → SYN_RCVD → SYN_SENT → ESTABLISHED in the state machine on no packet loss 
(S4) The server moves LISTEN → SYN_RCVD → ESTABLISHED in the state machine on no packet loss.

  • S2 and S3 only

  • S1 and S4

  • S1 and S3

  • S2 and S4

Question 7

Consider a network connecting two systems located 8000 kilometers apart. The bandwidth of the network is 500 × 106 bits per second. The propagation speed of the media is 4 × 106 meters per second. It is needed to design a Go-Back-N sliding window protocol for this network. The average packet size is 107 bits. The network is to be used to its full capacity. Assume that processing delays at nodes are negligible. Then, the minimum size in bits of he sequence number field has to be ________.

  • 2

  • 4

  • 8

  • 16

Question 8

Consider the following statements. 

I. TCP connections are full duplex.
II. TCP has no option for selective acknowledgment
III. TCP connections are message streams.

  • Only I is correct

  • Only I and II are correct

  • Only II and III are correct

  • All of I, II and III are correct

Question 9

Identify the correct order in which a server process must invoke the function calls accept, bind, listen, and recv according to UNIX socket API.

  • listen, accept, bind recv

  • bind, listen, accept, recv

  • bind, accept, listen, recv

  • accept, listen, bind, recv

Question 10

A client process P needs to make a TCP connection to a server process S. Consider the following situation: the server process S executes a socket(), a bind() and a listen() system call in that order, following which it is preempted. Subsequently, the client process P executes a socket() system call followed by connect() system call to connect to the server process S. The server process has not executed any accept() system call. Which one of the following events could take place?

  • connect () system call returns successfully

  • connect () system call blocks

  • connect () system call returns an error

  • connect () system call results in a core dump

There are 15 questions to complete.

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