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SET 1


  Question 1

Suppose two hosts use a TCP connection to transfer a large file. Which of the following statements is/are FALSE with respect to the TCP connection?
I. If the sequence number of a segment is m, then the sequence number of the subsequent segment is always m+1.
II. If the estimated round trip time at any given point of time is t sec, the value of the retransmission timeout is always set to greater than or equal to t sec.
III. The size of the advertised window never changes during the course of the TCP connection.
IV. The number of unacknowledged bytes at the sender is always less than or equal to the advertised window


A : III only
B : I and III only
C : I and IV only
D : II and IV only


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     Correct answer is :B

     Solution :
      S1: FALSE
    The sequence number of the subsequent segment depends on the number of 8-byte characters in the current segment
    S2: TRUE
    Depending on the value of ? or Estimated RTT it may or may not be greater than 1.
    S3: FALSE
    It is the size of the receiver's buffer that's never changed. Receive Window is the part of the receiver's buffer that's changing all the time depending on the processing capability at the receiver's side and the network traffic.
    S4: TRUE
    The number

  •   Question 2

    Which one of the following fields of an IP header is NOT modified by a typical IP router?

    A : Checksum
    B : Source address
    C : Time to live (TTL)
    D : Length


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     Correct answer is :B

     Solution :
      Option C (TTL) is decremented by each visited router. When it reaches to Zero, then Packet will be discarded.
    Option A (Checksum) needs to be updated by each visited Router since TTL Value is modified.
    Option D (Length) also modified whenever there is a need of performing the fragmentation process.
    Option B (Source Address) can't be modified by an IP router. Only NAT can modify it.

  •   Question 3

    In one of the pairs of protocols given below, both the protocols can use multiple TCP connections between the same client and the server. Which one is that?

    A : HTTP, FTP
    B : HTTP, TELNET
    C : FTP, SMTP
    D : HTTP, SMTP


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     Correct answer is :D

     Solution :
      HTTP & SMTP protocols can use multiple TCP connections b/w the same client and the server.

  •   Question 4

    Consider a LAN with four nodes S1, S2, S3 and S4. Time is divided into fixed-size slots, and a node can begin its transmission only at the beginning of a slot. A collision is said to have occurred if more than one node transmit in the same slot. The probabilities of generation of a frame in a time slot by S1, S2, S3 and S4 are 0.1, 0.2, 0.3 and 0.4, respectively. The probability of sending a frame in the first slot without any collision by any of these four stations is _________.



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     Correct answer is :0.462


  •   Question 5

    Suppose that the stop-and-wait protocol is used on a link with a bit rate of 64 kilobits per second and 20 milliseconds propagation delay. Assume that the transmission time for the acknowledgment and the processing time at nodes are negligible. Then the minimum frame size in bytes to achieve a link utilization of at least 50% is _________.



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     Correct answer is :320

     Solution :
      Given B = 64 kbps
    Tp = 20 ms n ? 50%
    For n>= 50% => L >= BR
    => L=64 * 103 * 2 * 20 * 10-3
    =2560bits= 320bytes

  •   Question 6

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

    A : listen, accept, bind recv
    B : bind, listen, accept, recv
    C : bind, accept, listen, recv
    D : accept, listen, bind recv


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     Correct answer is :B

     Solution :
      The correct order in which a server process must invoke the function calls is bind, listen, accept and recv. First three are used in connection establishment phase and recv is used in data transfer phase.

  •   Question 7

    Which one of the following statements is NOT correct about HTTP cookies?

    A : A cookie is a piece of code that has the potential to compromise the security of an internet user
    B : A cookie gains entry to the user?s work area through an HTTP header
    C : A cookie has an expiry date and time
    D : Cookies can be used to track the browsing pattern of a user at a particular site


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     Correct answer is :B

     Solution :
      (A) is correct
    (B) Option B is false
    (C) Option C is correct
    (D) Option D is correct


  •   Question 8

    A link has a transmission speed of 106 bits/sec. It uses data packets of size 1000 bytes each. Assume that the acknowledgement has negligible transmission delay, and that its propagation delay is the same as the data propagation delay. Also assume that the processing delays at the nodes are negligible. The efficiency of the stop-and-wait protocol in this setup is exactly 25%. The value of the one-way propagation delay (in milliseconds) is __________



  •  
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     Correct answer is :12

     Solution :
      Given, B =106 bps
    L=1000 bytes
    n=25%
    Tp = ?
    In stop-and-wait, efficiency = 1/(1+2a)
    => 1/4 = 1/(1+2a) => 1+2a =4
    2a=3; a=3/2
    Tx = L/B = (8*103)/106=8ms
    Tp/tx = 3/2 ; 2Tp = 3Tx
    2Tp=24ms
    Tp =12ms

  •   Question 9

    Host A sends a UDP datagram containing 8880 bytes of user data to host B over an Ethernet LAN. Ethernet frames may carry data up to 1500 bytes (i.e. MTU = 1500 bytes). Size of UDP header is 8 bytes and size of IP heard is 20 bytes.There is no option field in IP header How many total number of IP fragments will be transmitted and what will be the contents of offset field in the last fragment?

    A : 6 and 95
    B : 6 and 7400
    C : 7 and 1110
    D : 7 and 8880


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     Correct answer is :C


  •   Question 10

    Consider the following routing table at an IP router:
      Network No.     Net Mask      Next hop   
      128.96.170.0    255.255.254.0     Interface 0   
       128.96.168.0         255.255.254.0        Interface 1       
       128.96.166.0   255.255.254.0   R2
       128.96.164.0    255.255.252.0    R3
       0.0.0.0   Default    R4

    For each IP address in Group I identify the correct choice of the next hop from Group II using the entries from the routing table above.
    <
          Group 1                   Group 2            
       128.96.171.92   Interface 0
       128.96.167.151   Interface 1
       128.96.163.151   R2
       128.96.165.121    R3
       R4


    A : i-a , ii-c , iii-e , iv-d
    B : i-a , ii-d , iii-b , iv-e
    C : i-b , ii-c , iii-d , iv-3
    D : i-b , ii-c , iii-e , iv-d


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    .

     Correct answer is :A


  •   Question 11

    Assume that the bandwidth for a TCP connection is 1048560 bits/sec. Let Α be the value of RTT in milliseconds. (rounded off to the nearest integer) after which the TCP window scale option is needed. Let Β be the maximum possible window size the window scale option. Then the values of Α and Β are



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     Correct answer is :


  •   Question 12

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


    A : Only I is correct
    B : Only I and III are correct
    C : Only II and III are correct
    D : All of I, II and III are correct


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     Correct answer is :A

     Solution :
      S1: TCP allows full duplex communication. This is TRUE statement. TCP is a full-duplex protocol; it allows both parties to send and receive data within the context of the single TCP connection..
    S2: TCP has no option for selective acknowledgments. This is FALSE statement TCP may experience poor performance when multiple packets are lost from one window of data. With the limited information available from cumulative acknowledgments, a TCP sender can only learn about a single lost packet per

  •   Question 13

    Consider a CSMA/CD network that transmits data at a rate of 100 Mbps (108 bits second) over a 1 km(kilometer) cable with no repeaters. If the minimum frame size required for this network is 1250 bytes, what is the signal speed (km/sec) in the cable?

    A : 8000
    B : 10000
    C : 16000
    D : 20000


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     Correct answer is :D

     Solution :
      Given L=1250 Bytes
    B= 100 mbps d= 1km
    V=?
    In CSMA/CD, L=2*d*B/v
    V= 2dB /L = (2*103*108)/ 104 = V= 20,000 km/sec

  •   Question 14

    Consider a network connected 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 the sequence number field has to be ___________.



  •  
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     Correct answer is :8


  •   Question 15

    In the network 200.20.11.144/27, the fourth octet (in decimal) of the last IP address of the network which can be assigned to a host is ________.



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     Correct answer is :158

     Solution :
      Given IP address 200.20.11.144/27
    To find out the loss address in a block, we have to set (32-n) no. of right most bits to 1.
    n=27
    32 - n = 32 - 27 = 5
    200.20.11.10010000
    200.20.11.10011111
    200.20.11.159
    CIDR Address range is 200.20.11.128/27-200.20.11.159/27
    But w.r.t the question, the value of the last octet of last host in this network is 200.10.11.158.

  •   Question 16

    Two hosts are connected via a packet switch with 107 bits per second links. Each link has a propagation. Delay of 20 microseconds. The switch begins forwarding a packet 35 microseconds after it receives the same. If 1000 bits of data are to be transmitted between the two hosts using a packet size of 5000 bits, the time elapsed between the transmission of the first bit of data and the reception of the last of the data in microsecond is _________.



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     Correct answer is :1575


  • MY REPORT
    TOTAL = 16
    ANSWERED =
    CORRECT / TOTAL = /16
    POSITIVE SCORE =
    NEGATIVE SCORE =
    FINAL SCORE =