1) Using normal Aloha, when is it OK for a station to transmit?




2) Using Slotted Aloha and assuming the bandwidth that can be carried on the radio waves at any time is 1000 bits per second, and assuming there are 7 stations, and assuming there are 8 bits per byte, and assuming that only one station wants to transmit, and assuming the maximum packet size is 1000 bytes, and assuming the slot width is 1000 bytes, and assuming the inter-slot gap is negligible, and assuming the electricity and all the computers are working, approximately what is the bandwidth actually broadcast?


3) Using Reservation Aloha, how many collisions are there likely to be.
   a) None.  Zero.  Not One.
   b) Normal operation will produce a few colisions.  That's expected and OK.
   c) Lots.  Heck 50% of all packets might collide.
   d) Almost all packets will collide with another packet.

4) There is an ethernet network with exactly two computers on it.  One computer is the client and the other the server.  In normal operation how many collisions will this Ethernet experience?




5) Suppose there is a collision on an Ethernet.  What's the first thing the sender should do upon collision detection?




6) Assuming no equipment failure, what's the absolute maximum latency of a correctly working token ring?
   a) Very small.  Under 1/100 of a second.
   b) Just a few seconds.
   c) A few minutes.
   d) Infinity and beyond.


7) (Yes/No) On a token bus network, must each card continue to pass the signal along even when the power is turned off?



9) Which best describes ethernet?
   a) Time Multiplexing
   b) Frequency Multiplexing
   c) Statistical Multiplexing



10) Assume that I'm playing a practical joke on Andy.  I rig things so that nine times in a row his computer broadcasts a packet, my computer sends out a jam signal.  On the tenth time I let the packet go through.  What will Andy notice?
   a) His network doesn't 90% of the time.  When he presses the 'refresh' key on his browser nine times out of ten he gets an error page.
   b) His network seems slow.  When he presses the 'refresh' key on his browser it takes a long time to reload.
   c) Nothing.  Everything seems to work just fine hunky dorry.
   d) His clothes catch on fire.

11) How many bytes is a MAC address?


12) I want more ethernet bandwidth.  I program my card so that every time it wants to broadcast it does the following:  If there is no one else talking, then my card just begins transmitting.  If someone else is talking, I send a jam, wait a very small un-random amount of time, and then transmit.  I'm the only one on my network with this special card.  What will my scheme do?




13) Does ethernet send an acknowledgment for every packet?



14) What is the return value for 'bind' if there is an error?



15) I have an ethernet and a token ring.  I want to connect them.  Which will work (chose zero or more).
   a) Bridge
   b) Repeater
   c) Router
   d) Hub

16) All of my computers want to transmit all the time.   My goal is to maximize the total amount of useful data sent per second.  Which of the Aloha's is best for this network?




17 and 18)  An ethernet frame has the components listed below.  Assume that this is a ten megabit (1.25 megabyte) ethernet.  What's the most data that can be sent per second?
       An ethernet frame consists of

19) Suppose I have a very lightly loaded network.  My one goal is to minimize the average latency of small messages.  Which is the best type of
    network.  Why?

  1. 10 megabits/sec Ethernet.  Why: _______________________________________________
  2. 10 megabits/sec Token Ring.  Why: _____________________________________________
20) What layer is Token Ring (circle all that apply)
    1. Physical
    2. Data Link
    3. Network
    4. Application
    5. None
21) What does the accept() system call do?        
    1. Gives an otherwise anonymous socket an address.         
    2. Tells the operating system how large the backlog of requests can be.         
    3. Mark the socket as ready to send data.
    4. Creates a file descriptor and connects that descriptor to a socket.         
    5. All or none of the above.


22) (Yes/No) Suppose that you call read, and the first argument is a twelve.  Will you ever receive more than 12 bytes from that read?

23) I have a CD-ROM with holds 660 megabytes.   How long will take me to send that via a 100 megabit/second ethernet?  An approximate round number will work fine.  Just be within 50%





24 and 25) A switch receives a packet and it has never seen the source or destination MAC address ever before.  To which port should it forward the packet?  What can we tell about the sending computer?








26) (Yes/No) I modify ethernet is the following way:  A card may transmit if either the wire is quiet or the address of the card that it currently using the card is lower than your own.  If there is a collision only the lower addressed card need stop transmitting.  No one sends a purposeful jam signal at any time.  Using this scheme, will higher addressed cards see higher performance than lower addressed cards?





27) (Yes/No) Using the scheme above, will any data ever get through at all?




28) Using the socket commands shown in class, how does one reserve a specific amount of bandwidth.  In other words, how can one say "I need 300 KB/sec of bandwidth for the next 17 seconds"?



29) I'm teaching some Math Ed majors for a few weeks.  Do you have any comments for the Math Ed majors.