CS228 Midterm I

  1. How long does it take to transmit a packet (assume no failures).  You may use the variables 'latency', 'bandwidth', and 'packet_size'. _______________________________________________________________________
  2. Suppose I send a box holding 100 data tapes at 2 gigaBYTES each.  How many DAYS would a T1 line (1.54 megaBITS/second) to transmit the same data.  Show work for partial credit.  ____________________________________

    3.  

     
     
     
     

  3. What can dreams tell us
    1. That our brain gets bored when we sleep.
    2. Important insights into the subconsious
    3. Messages from the spirit world
    4. Sigmond Freud like stuff.
  4. Which OSI network layer manipulates the most bytes?

    5.          1.Physical
             2.Data Link
             3.Network
             4.Application
  5. (2 points) I just measured the time to send data between here and www.slumber.com.  It takes 215 ms to send 1000 bytes, and 265ms to send 2000 bytes.  What is the current latency and bandwidth between here and www.bike.com?  Don't forget to put units of measure.  (i.e.  don't say that the latency is 28, say its 28 bytes or seconds or gallons).

    6.       Latency: ________________________________________________________________________
          Bandwidth: ______________________________________________________________________
  6. (Two points) I notice that as more and more clients on my ethernet become busy, total network traffic successfully passed from all senders to all receivers drops, even though my clients have lots of data to transmit.

    7.       Why?________________________________________________________________________________
          _____________________________________________________________________________________
          How can I fix it? _______________________________________________________________________
          ____________________________________________________________________________________
  7. What is the maximum latency before a node can successfully transmit across the ethernet?

    8.                1.Twice the propogation delay across the cable.
                   2.Twice the propgation delay accross the cable plus the length of time needed to transmit a maximum size packet.
                   3.Infinite
                   4.28 ms.
  8. I often dream about
    1. Money
    2. Power
    3. Small yellow birds eating ice cream
    4. I never dream.  Freddy Kreuger won't let me.
  9. What does the bind() system call do?

    10.                1.Gives an otherwise anonymous socket an address.
                   2.Tells the operating system how large the backlog of requests can be.
                   3.Changes the socket to send datagrams instead of streams.
                   4.Creates a file descriptor and connects that descriptor to a socket.
                   5.All or none of the above.
  10. What does the accept() system call do?

    11.                1.Gives an otherwise anonymous socket an address.
                   2.Tells the operating system how large the backlog of requests can be.
                   3.Changes the socket to send datagrams instead of streams.
                   4.Creates a file descriptor and connects that descriptor to a socket.
                   5.All or none of the above.
  11. What's the most important feature for a dream to have
    1. Safety belt
    2. Friends and family
    3. Air bag
    4. Throttle
  12. Suppose a TCP connection is in the "slow start" phase. The current congestion window goes from (10,000-12,000). The window advertised by the receiver goes

    13.       from (10,000 - 20,000). The maximum segment size is 500 octets. Which bytes can be sent in the next segment? ___________________________________________
  13. As a sender you keep sending packets, but a high percentage of them are not acknowledged on the first sending. What should you do? (pick all that apply)

    14.       a) Reduce your congestion-window-size.
          b) Increase your time out value.
          c) Send larger packets.
  14. Calculus!! What does this expression evaluate to? ___________

    15.       lim x->2 17
  15. Suppose you are using an IP number provided by DHCP and the lease begins to expire.  What should you do to stay on the network?
    ________________________________________________________________________________________
    ________________________________________________________________________________________
  16. Right now every IP packet carries a fragment field in the header, yet most packets don't get fragemented.  This seems wasteful.  Without placeing unreasonable limits on packet size, how could this be avoided?
    ________________________________________________________________________________________
    ________________________________________________________________________________________
  17. TCP over ethernet does not explicitly handle collisions.  Why?  What happens if there is a collision?
    ________________________________________________________________________________________
    ________________________________________________________________________________________
  18. (Yes/No) Does it make sense to use both ARP and DHCP on the same Ethernet?
  19. Suppose I'm an evil hacker.  I start transmitting TCP data to www.dreamland.com with a forged source address.  Assuming they follow all the TCP/IP protocols, what will they do with this data.  WHY?
    ________________________________________________________________________________________
    ________________________________________________________________________________________
  20. My worst nightmare describes
    1. People watching me sleep
    2. Meeting my 'special someone's parents
    3. Falling Falling Falling, but never reaching the ground
    4. Taking a test