CS 535, Telecommunications

Quiz 5, 17 November 2004

  1. Both papers for this section mentioned Kleinrock's paper titled The Latency/Bandwidth Tradeoff in Gigabit Networks. What is the relevance of Kleinrock's paper to these papers?

    In both cases the essential point is that the speed of light may be the fastest thing in nature, it is still finite, and that can cause problems. Vetters points out that the speed of light plus gigabit output rates, small packets (cells), and long fibers leads to high delay-bandwidth products. High delay-bandwidth products leads to high momentum traffic in which many packets can be sent into the network before the first packet reaches its destination. Chatterjee and Pawlowski make the more fundamental point that there'll always be delay because nothing's faster than the speed of light and the speed of light is finite.

  2. Chatterjee and Pawlowski describe three architectures for optical networks: point-to-point (pp), broadcast and select (passive-star coupled, bs), and wavelength routed (wr). For each pair (pp-bs, pp-wr, and bs-wr) of architectures give a one sentence description of a single, essential difference between the two architectures.

    1. PP-BS: PP is point-to-point while BS is broadcast.

    2. PP-WR: PP does wavelength transformations at the end-points while WR does them in the network.

    3. BS-WR: BS does one-in-many-out routing (multicast) while WR does selective point-to-point routing between input and output ports.
    There were many many answers of the form "pp does point-to-point connections and bs does broadcast-and-select connections." These answers, while not wrong, weren't particularly right either, because they didn't show any great insight into the essential differences between architectures.

This page last modified on 2 December 2004.