CprE 489 Assignment 2

Distributed: Sept. 04, 1997.
Due: Sept. 11, 1997.

Exercises:

  1. (Theoretical, Single Bit Transmission Time) (2.5 pts) Signals travel at about 200 meters per microsecond in most LAN media. How long is the transmission time of a single bit on a 10Mbps Ethernet type of LAN?

  2. ( Theoretical, Signal Propagation Delay) (7.5 pts) An important parameter associated with a data link is the round-trip delay associated with the link; that is, the time delay between the first bit of a block being transmitted by the sender and the last bit of its associated acknowledgement being received. Clearly, this will be a function not only of the time taken to transmit the frame at the link bit rate but also on the propagation delay of the link. The relative weighting of the two times will vary for different types of data link and hence the two times are often expressed as a ratio a such that:

    a = Tp / Tx

    where

    Tp = propagation delay = physical separation S in meters / velocity of propagation V in meters per second.

    and:

    Tx = transmission delay = number of bits to be transmitted N / link bit rate R in bits per second.

    Question:

    A 1000-bit block of data is to be transmitted between the two nodes. Determine the ratio of the propagation delay to the transmission delay a for the following types of data link.

    (a) 100 m of twisted pair wire and a transmission rate of 10 kbps.
    (b) 10 km of coaxial cable and a transmission rate of 1 Mbps.
    (c) 50 000 km of free space (satellite link) and a transmission rate of 10 Mbps.

    Assume (and note!) the velocity of propagation of an electrical signal within each type of medium is 2x108 m/s.

    What can you conclude from the results?

    Why is the case (c) interesting?

    How many bits will be in transit between the two points of the satellite link (between the source and the destination), providing blocks are transmitted contiguously? What are the implications of this last result, in light of the functions of the Data link layer?

  3. (Theoretical, Data Transmission Theory)(5pt) Problem 2, Tanenbaum Chapter 2, pg 171.

  4. (Theoretical, Data Transmission Theory)(5pt) Problem 4, Tanenbaum Chapter 2, pg 171.