Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit

CS 462 Computer Networks – Final Exam

Note:  Show all work. No points will be awarded if work is not shown even if the answer is correct. Please put your name on every sheet.

1. Suppose a network uses distance-vector routing.  Provide the routing tables for router C for every round until it converges.

 

Series of rounds:

      Dest    NxtNode    Cost    Dest  NxtNode    Cost     

         A            A  

         B                   B  

Round 1          D                  D   Round 2

         E            E  

         F             F  

         G            G  

         H            H  

      Dest    NxtNode    Cost    Dest   NxtNode    Cost     

         A           A

         B          B  

         D               D  

Round 3          E             E Round 4

         F          F  

         G          G  

         H          H  

2. A channel has a data rate of R bps and a propagation delay of t seconds per kilometer. The distance between the sending and receiving nodes is L kilometers. Nodes exchange fixed-sized frames of B bits. Find a formula that gives the minimum sequence numbers field size of the frame as a function of R, t, B, and L (considering maximum utilization). Assume the processing at the nodes is instantaneous and all frames are negligible in size.

3. For the LAN segments shown below, apply the Bridge Spanning Tree algorithm to obtain a set of optimal ports. (Draw the corresponding tree with each node and LAN along with their corresponding cost). Show all work!

L1

     1      1 L2

      2         1       

   2   L3     3        

     1         2 1        

        2         2       L6       

  2         1 3       

L4   1

   L5   2

Draw connections that are in the final spanning tree below:

L1

            L2

               

      L3     

    

                        L6  

L4   

   L5   

4. Consider a Go-Back-N protocol with a sender window size of N and a sequence number range of 1024. Suppose that at time t the next packet that the receiver is expecting has a sequence number of k. Assume that the medium does not re-order messages. Answer the following:

(a) Assume the receiver has received packet k-1 and has ACKed that and all other preceding

packets and the ACKs have been received at the sender. The sender’s window is

[              ,              ].   Justify your answer in terms of k and N

(a) Suppose that none of the ACKs have been received at the sender, the sender’s window is

[               ,             ]

(b) What are all possible values of the ACK field in all possible messages currently propagating back to the sender at time t?  

5. For the netID below:

NetID    Subnets required

190.176.0.0 122

Determine the

(a) subnet mask (show work)

(b) first available host address of subnet one (NOT subnet zero)

 (c) the maximum number of hosts per subnet for the network ID below?