Data Communications II, Autumn 2003

Problem set 6 (29.10.2003)

1. How is a V.90 standard modem functioning? How is it possible to achieve 56 kbps rates, though the theoretical maximum for telephone network is only 35 kbps? And why is it only 56 kbps and not 64 kbp

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. The network below uses RSVP protocol and multicast trees to transmit video flows to the receivers. Hosts 1 and 2 function as senders and 3,4 and 5as receivers. The host 3 request a 2 MBps channel from the sender 1 and a 1 MBps channel from the sender 2 because it wants watch both Formula Racing and Football Game. The host 4 requests a 2 MBps channel from the sender 1 and host 5 requests a 1 MBps channel from the sender 2. How do these requests move in the network and how much channel capasity is reserved in the routers a, ...f?
   
   
5. There are proposals for two different ways to add quality of service to Internet. Explain the most important features of these proposals. In your opinion which of these ways seems to be the better way to add quality of service to Internet? Is it really necessary to add any Quality of Service at all to Internet? Wouldn't it be enough just to put enough capacity and bandwidh into the lines?

6. Your opinions about this course.
   1. What subjects were, in your opinion, the most interesting and important ones? What subjects were dull and unnecessary?
   2. How should the course be changed in the future? What should be more and what less? What missing subjects should be included? What items could be dropped from the course?
   3. Fill the teaching evalution form for this course (http://ilmo.cs.helsinki.fi/kurssit/servlet/Valinta).