Data Communications I, Autumn 2001

Exercise 5 (16.-19.10.2001)

1. A TCP machine is sending windows of 65 535 bytes over a 1-Gbps channel that has a 10-msec one-way delay. What is the maximum throughput achievable? What is the line efficiency?

2. Dijkstra's shortest path algorithm in routing

   1. Find using Dijkstra's algorithm the shortest (lowest cost) routes from node A to all other nodes in the network below.

                                  3
                          B . . . . . . .F
                        .  .            .  . 
                     .      .          .    .
                3  .       1 .      4 .      . 2
                 .            .      .        .
                .     3        .   .     3     .
      network  A . . . . . . .  D . . . . . . . .E
                 .             .  .             .
                  .           .    .           .
                   .         . 2    . 2       .
                 2  .       .        .       .  1
                     .     .          .     .
                      .   .            .  .
                       C . . . . . . .  G
       
                                2

   2. Give, based on the routes found, the routing table for node A. In the routing table there is, for each node the outlink to be used and the cost of the route. The outlinks are numbered so that the link from A to be is number 1, from A to D number 2 and from A to C number 3.

3. For routing the distance vector algorithm is used. Supposing each node in the network below, first knows only the distances to its neighbors. What is the content of routing table of the node E after the node E has changed routing information with its neighbors?

                 1
        A --------------- B
        |               / |
        |              /  |
        |           5 /   |
        |            /    | 
        |           /     |
        |2         /      |15
        |        E        |
        |      /   \      |
        |     /     \     |
        |    /       \    |
        |   / 2    10 \   |
        |  /           \  |
        | /             \ |
        C --------------- D
                1
    

4. How do distance vector routing and link state routing differ from each other? Go through all the states of link state routing.

5. The network layer of host A gets from its transport layer 3000 bytes of data to be sent to the host B. A and B are situated in different networks that are connected by one router. A's LAN can carry at most 1500 bytes of data in one packet and the maximum size of data in B's LAN is only 1000 bytes. Suppose that the next sequence number for A's IP packet is 100.

           A - XXXXXXXXX  -  router  -  XXXXXXXXXXXX - B
   
                LAN  a                     LAN b 
         max. 1500 bytes data        max. 1000 bytes  data

   What kind of IP packets does A send? What does the router do to these packets? What kind of IP packets does B receive? Give the contents of the IP header fields involved in fragmentation in the sent and received IP packets.

6. In the SMTP connection the first message sent is the HELO message.

   1. What kind of TCP segment carries the HELO message in the TCP connection? What information is included in the header fields of this TCP segment? What TCP segments have already been sent before this TCP segment carrying the HELO message?

   2. How are these TCP segments transferred in IP packets? What information do the header fields of these IP packets contain?