CPS 214 Written Homework 3 - Fall 1997

Due: Monday, Oct. 20, 5:30 PM

10 points

  1. Consider a sliding window protocol across a channel in which the one-way propagation delay is 270 ms. If the channel has a transmission rate of 1Mbps, is there any performance benefit in using a send window larger than 1024 frames in size? Assume frames are 10000 bits in size.
  2. Assume that there are never any transmission errors over a particular physical channel. Which protocol would you expect to have better performance across the channel: selective repeat or Go Back N?
  3. When running protocols within the x-kernel, execution begins at the label ``main'', which is supplied by the x-kernel. How then do the application routines (e.g., the asp test routines) get invoked at run time? Hint: Use gdb (or some other debugger) to single-step through the execution. Place a breakpoint at asp_init, and then follow the execution.
  4. Consider building a CSMA/CD network running at 1Gbps over a 200 meter cable. The signal speed in the cable is 200,000 km/sec. What is the minimum frame size?
  5. Even though both token ring and CSMA/CD technologies are popular in LANs, WANs never use the CSMA/CD design. Why?
  6. A 16-Mbps has a token holding time of 10 msec. What is the longest frame that can be sent on the ring?
  7. Consider an unslotted FDDI-like ring network that has a circumference of 100km long and runs at 100Mbps. After sending a frame, a station drains the frame form the ring before regenerating the token. The signal propagation speed in the fiber is 200,000 km/sec and the maximum frame size is 4000 bytes. What is the maximum efficiency of the ring? That is, what percentage of the available bandwidth can be used for sending data? You may ignore such sources of overhead as header fields.
  8. Peterson (chapter 4): 2.
  9. Consider the new Arpanet routing algorithm. If there are 50 switches in the network, each switch connects (on average) to 3 other switches, and new link metric updates are sent every 1/2 second, how many packets per second will cross each link?
  10. Tanenbaum (chapter 5): 14.
  11. Tanenbaum (chapter 5): 20.
  12. Some audio enthusiasts complain that audio CDs don't sound as good is the analog recordings recorded onto vinyl LPs. However, we know from Nyquist that CDs carry frequencies above 20kHz (CDs are sampled at 41kHz), which is beyond the range of human hearing. Are such audio enthusiasts imagining things, or is there a rational explanation for their complaints? Hint: samples are stored at 16-bit values.