Data Communications II Autumn 2004

Problem set 2. (11.10.2004)

  1. Suppose that the partial acknowlegdements of NewReno are in use. How does the TCP handle the situation where after a succesfull transmit of one segment, three following segments will get lost? After that there are no problems in the transmission. The congestion window is 8 MSS. The round-trip-time is 100 ms and the retransmission timer is set to 200 ms. Only the congestion window limits the sending.

  2. RED buffer and ECN
    1. How does a RED buffer work? What are its benefits?
    2. A TCP implementation wants to use ECN (Explicit Congestion Notification). What extra functionalities are needed in TCP and IP protocols? How is the ECN usage negociated? Suppose a segment on a TCP connection using ECN ends up into congestion. How does the information about this reach the sender and how does the sender behave after that.

  3. IP protocol and large packets
    1. How large amounts of data can be sent using IP protocols? What factors constrain the size of an IP datagram? What is the maximum size of the IP datagram?
    2. The supercomputer A wants to send messages of 262144 bytes to another supercomputer B using IPv4 protocol. How is it done? What happens if a datagram sent has to pass a network that cannot transfer so big datagrams?
    3. Is it possible for IPv6 to handle datagrams of 264 144 bytes? How is it done? What happens if a network on its way to the destination cannot handle so large datagrams?
  1. Show the format of the IPv6 message when
    1. the IP datagram carrying a TCP segment is using the authentication header AH,
    2. the IP datagram has to travel from the machine H1 to machine H2 strictly just through the routers A, B, C and D. How do the routers between handle this IP datagram?

  2. What is the status of IPv6 now? To what extend is it deployed and used? What is 6Bone? Look for information in WWW or otherwhere.

  3. What are the network addresses and host addresses of the IP address 192.31.63.18
    1. when using class addresses,
    2. when using classless addressing (CIDR) 192.31.63.8/20,
    3. when using classless addressing and a subnet mask, with 28 ones in the beginning and rest of the mask zeroes?
    4. How is the IPv4 address 192.31.63.18 given as an IPv6 address.
    5. When an organization is using both classless addresssing and subnetting, what kind information is stored in the routing tables of the routers belonging to that organization? How do these routers route packets?