Data Communications II, Autumn 2002

Problem set 5 (22.-24.10.2002)

1. 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 reseacher, send email using his own PC?

   2. The members of his research group in Helsinki are sending him the results of a test series and want his opinion on a recent problem in tests. How are these messages between Helsinki and university B routed in Internet?

   3. How does the communication and the routing change if Mobile IP is used?

   4. How does GSM network route messages to the mobile phone of Etevä, providing that his phone can also be used in USA?

2. Token bucket

   1. A token bucket scheme is used for traffic shaping. A new token is put into the bucket every 5 microsecond and one token allows the sending of one packet. What is the maximum sending rate, when the maximum size of the packet is 1000 bits?

   2. A computer on a 6-Mbps network is regulated by a token bucket. The token bucket is filled at a rate of 1 Mbps. It is initially filled to capacity with 8 megabits. How long can the computer transmit at the full 6 Mbps?

3. Token bucket + leaky bucket
   New tokens are generated at the rate of 1000 tokens per second and each token allows the sending of a packet. The maximum size of the packet sent is 1000 bytes. The capacity of the token bucket is 2000 tokens. The maximum data rate of the line is 10 MBps (B = byte). Anyhow a peak sending rate of 5 MBps has been agreed. What kind of leaky bucket is needed between the token bucket and the network so that the agreed maximum sending rate is not exceeded and all the data from the application can be sent and nothing is lost in a buffer overflow?

4. Token ring

   1. The token can get lost, because the station holding the token is disconnected from the network. How does a token ring handle the situation?

   2. Assume that in a token ring there is a fixed number, n, stations. Under what circumstances can be guaranteed that a station will get its turn to send after a limited maximum time? Under what circumstances no such maximum time exists? Does the token ring, in this respect, actually differ much from the the Ethernet LAN?

   3. In a token ring the sender removes the data frame. Would the token ring be more efficient if the receiver would remove the data frame and send a short acknowledgement to the sender?

5. FDDI

   1. How does a FDDI LAN differ from a token ring?

   2. A large FDDI ring has 100 stations and a token rotation time of 40 msec. The token holding time is 10 msec. What is the maximum achievable efficiency of the ring?

6. Find out about Bluetooth. What is Bluetooth? Where is it used? How is it related to other wireless standards? What OSI layer protocols does it standardise? How does it in principal function?