Data Communications II, Autumn 2004

Problem set 4 (25.10.2004) 0n Monday 12-14 in room C220

    1. Consider one sender and 32 receivers. Suppose the sender is connected to the receivers through a binary tree of routers. The sender is the root and the receivers are the leaves in the tree and in each node between has a router. The sender sends a packet first to the next router, that sends it to the router below etc until the packet reaches the the receiver.

      1. How many sendings alltogether are needed if a separate packet is sent to each receiver?
      2. How many sendings are needed, if the packet is sent as a multicast packet to each receiver?
    2. In what kind of network topology is the cost difference between sending a message using multicast and sending the same message separate to its receivers
      1. smallest.
      2. biggest?

  2. Suppose node C is chosen as the center in a center-based multicast routing algorithm. Assuming that each attached router in the multicast group (= A, B, E and F) uses its least-cost path to node C, show the resulting center-based multicast routing tree. Is the resulting tree a minimum-cost spanning tree? 

                   1             1
       B ------------ D ------------ E
       | .                          .|
       |  .                       .  |
       |   .                    .    |
       |    . 2             2 .      |
     4 |     .              .        | 1
       |      .           .          |
       |       .        .            |
       |        .     .              |
       |         .  .                |
       A -------- C ---------------  F
            3             2

  3. Consider the network below. Supposing that the link costs are equal on all links, what kind of "reverse path forwarding" -tree would you make for node F? How is this tree actually formed? When node F sends a broadcast packet, how many packets are really sent in the subnetwork? 

                 B --------------------------------------------- C
             |                                               |
      E -----|---------------------------- A                 |
      |      |                             |                 |
      |      |                             |                 |
      H -----|------------ I ------------- F --------------- D
      |      |             | .                               |
      |      L             |  .                              |
      |     .              |   .                             |
      |    .               |    .                            |
      |   .                |     .                           |
      |  .                 |      .                          |
      | .                  |       .                         |
      |.                   |        .                        |
      K -------- M ------- N -- O -- J --------------------- G
  4. The researcher Eri Etevä from the University of Helsinki is visiting universities and research institutes in USA that are of importance to his field of research. He stays a couple of days in one place and then moves along to another place. He carries with him his personal PC to store all the important and necessary information.
    1. How can he, when staying a few days in the university B as a visiting researcher, send email in Internet to his colleagues in Helsinki how are his colleagues able to send him information using normal Internet protocols?
    2. How does the communication and the routing change if Mobile IP is used?
    3. How does GSM network route messages to the mobile phone of Etevä, providing that his phone can also be used in USA?

  5. Suppose that mobile user Eri Etevä moves his PC first from foreign network A to foreign network B and finally to foreign network C and a colleague from the University of Oulu started a connection with Etevä's PC when it was in the network A. Can the connection be held intact during the changes from network to network? Is it possible that messages are lost? What kind of messages and in what order do the different foreign agents change with each other and with the home agent of Eri Etevä?

  6. How fast are the Ethernet adapters nowadays? What estimates are given for the Ethernet to reach terabit speeds? What factors, in your opinion, have most helped the Ethernet technology to gain the dominant position in LANs?
    Information about fast Ethernet can be found, among others, in the pages below: http://www.intel.com/network/connectivity/solutions/gigabit.htm?ssi_ppc_lad1 http://www.intel.com/network/connectivity/resources/doc_library/tech_brief/gigabit_ethernet.htm http://www.directionsmag.com/article_372/ http://encyclopedia.thefreedictionary.com/Ethernet