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CS 635 Fall 1998

Homework 1 (W. Stallings Lan&Wan)

1.3  What are the key factors that determine the response time and throughput of a local area network such as that of Figure 1.2 (bus)? Of a centralized system such as that of Problem 1.2 (point-to-point links to the central server)?
A. For a LAN, performance depends primarily on how efficiently the communications medium is used. For a centralized system, performance depends primarily on the ability of the central system to keep up with the load imposed on it.

2.4 For the bit stream 0101110, sketch the waveforms for NRZ, NRZI, Manchester, and Differential Manchester as well as for Miller coding and E-NRZ.

Nonreturn-to-Zero-Level (NRZ-L)
0 = high level
1 = low level
Nonreturn-to-Zero Inversted (NRZI)
0 = no transition at beginning of interval (one bit time)
1 = transition at beginning of interval
Manchester
0 = transition from high to low in middle of interval
1 = transition from low to high in middle of interval
Differential Manchester
Always a transition in middle of interval
0 = transition at beginning of interval
1 = no transition at beginning of interval
Enhanced Nonreturn-to-Zero (E-NRZ)
Separate NRZ-L into 7-bit words
Invert bits 2,3,6,7
Add one parity bit to each word to make the total number of 1's in the 8-bit word and odd count
Miller coding
0 = transition at the end of the bit period if the next bit is 0, no transition if the next bit is 1
1 = transition in the middle of the interval