Data Communications II, Spring 2001

Problem Set 4 (Tuesday 13.2.2001)

  1. Form the IP headers needed in following situations.
    1. Sending an email message of 1024 bytes from machine A to machine B.
    2. A supercomputer A sends a message of 264144 bytes to another supercomputer B. To avoid fragmentation the message has to follow the given route through routers C, D, E, and F in that order.

  2. IPv6 includes the flow label field.
    1. Give examples of situations where flow labels are useful. What kind of sendings do not benefit from flow labels? Would it be useful to use flow labels when transmitting large amounts of data in a TCP connection?
    2. What happens when a router receives an IP packet with a flow label unknown to that router so that the router does not know how to handle the packet? Can this cause problems?

  3. ARP- ja RARP-protokollat.
    1. Suppose hosts A and B have been assigned the same IP address on the same Ethernet, on which ARP is used. B starts up after A. What will happen to A's existing connections? Could RARP-protocol be useful in this situation? Or is it possible to do something else to avoid situations like this?
    2. When the IPv6 protocol is introduced, to what amount does the ARP protocol have to be changed?
    3. ARP protocol is providing services to the network layer! So, to what OSI-layer does ARP protocol belong?

  4. In Tanenbaums book, page 412 there is a picture of internet. The internet uses TCP/IP protocol suite. Now the host 1 in the LAN A in the picture sends a message to the host 2 in the LAN B. Explain how the message is routed from its source to its destination. What protocols are needed and how and where from each protocol gets the information it needs to be able to route the message to the right direction.

  5. A network connection can be secured (eg. encrypted) on different layers. What are the advantages and /or disadvantages when a connection is secured
    1. on the link layer,
    2. on network layer
    3. on application layer ( or at least above the network and transport layers)?

  6. A PC is connected to a 6 Mbps network, where token bucket method is used for congestion control. Tokens are generated at a rate of 1 Mbps. The token bucket is initially filled with to maximum capasitity of 8 megabits. How long can the computer transmit at the full 6 Mbps.