Contents:

• Do Exercise 2 of Lab 15 of the Meyer text, answer all of the given questions along the way.
  
• Do Exercise 4 of Lab 15 of the Meyer text, answer all of the given questions along the way. 
• Suppose a network has the following connections and routing.  For simplicity assume all IP addresses start 8.8.8. and only the last digits differ.  As shorthand, just this last digit is used to identify nodes.
  

    1
   / \
  2 - 4 - 5 - 6
   \ /
    3    

  Node	Neighbors	Routing table
  1	2, 4	* 2
  2	1, 3, 4	* 3
  3	2, 4	* 4
  4	1, 2, 3, 5	* 1
  5	4, 6	* 4
  6	5	* 5

  In parts a - f, give the nodes in order that deal with a message from the given sender to the receiver. 

  1. Sender: 1  Receiver:  4
  2. Sender: 1  Receiver:  3
  3. Sender: 1  Receiver:  5
  4. Sender: 2  Receiver:  4
  5. Sender: 6  Receiver:  3
  6. Sender: 3  Receiver:  6
  7. At which one node could you add to the routing information so the message in part f. would be delivered correctly?  Show this new routing table with the one necessary addition.

1. (5 points)
   Do Exercise 1 of Lab 15 of the Meyer text, answer all of the given questions along the way.  One ambiguity:  part of the length of a header is the sequence number.  These change.  For consistency you may assume all the sequence numbers are 2 digits.
   
2. (5 points)
   Do Exercise 5 of Lab 15 of the Meyer text, answer all of the given questions along the way.
   
3. Suppose a network has the following connections and routing.  For simplicity assume all IP addresses start 8.8.8. and only the last digits differ.  As shorthand, just this last digit is used to identify nodes.
   

   2         5
   | \     / |
   |  3 - 4  |
   | /     \ |
   1         6

   Node	Neighbors	Routing table
   1	2, 3	* 2
   2	1, 3	* 3
   3	1, 2, 4	* 1
   4	3, 5, 6	* 5
   5	4, 6	* 6
   6	4, 5	* 4

   In parts a - b, give the nodes in order that deal with a message from the given sender to the receiver. 

   1. (2 points) Sender: 5  Receiver:  4
   2. (2 points) Sender: 5  Receiver:  3
   3. (2 points) What is an example of a sender and receiver where communication would fail?
   4. (4 points) Keep all the default routings above, but insert minimal extra instructions in whatever routing tables need it, so all senders can communicate with all receivers.
      

Practice Problem Solutons

----------

4) If you delete the re-transmitted packet, the sender will again wait
   for a timeout, at which point it will yet again resend the same
   packet.  Thus, the protocol for a re-transmitted packet is really
   identical as to the protocol used for the originally transmitted packet.

5) Deleting the ACK or NAK packets has the same effect as deleting the
   originally transmitted packets.  Consider things from 0's point of
   view.  Whether the original packet got deleted, or the ACK got deleted, 
   0 has not heard anything in response to the packet it originally sent.
   Since it is not sure that the packet was received, it will resend the packet.
   0 simply has no way to differentiate between a lost packet and a lost ACK.

Lab 15, Exercise 4
----------

3) 159.121.2.13 will send messages to 138.92.0.5.
   However these nodes are not directly connected.

4) If not connected, 159.121.66.98 sends outgoing (or forwarded) messages 
   to its neighbor, 37.61.25.46

5) Will vary somewhat.  In this applet, the "forwarded" count actually
   includes those messages which originate with that node.  For this
   particular node, you will find that it receives zero packets, and
   the forwarded count is roughly twice that of the number it sends.
   No packets should be dropped.

6) Packets are sent from 128.92.6.17  to 159.121.66.98
   Packets are sent from 159.121.2.13 to 138.92.0.5

7) Node 37.61.25.46 does not send or receive messages.  It will have
   only forwarded messages.

1. 1 4
2. 1 2 3
3. 1 2 3 4 5
4. 2 4
5. 6 5 4 3
6. 3 4 1 2 ... continuous loop
7. node 4
      6  5
      *  1