Dr. Kathleen M. Kaplan's
Data Communication Networks
Baud
- Relationships!
- Bandwidth: difference (expressed in Hertz [Hz]) between limiting
frequencies of transmission on a channel. It is often expressed in
bits per second (bps) for digital systems.
- Baud Rate: signalling rate (not necessarily the same as
bps).
Given the same number of bits, the greater the baud,
the more energy needed to transmit the same
number of bits!
- Data Rate: describes a medium's capacity and is measured in
bps.
- So:
- Higher bandwidth medium is capable of a higher data rate!
- Higher baud rate (per same number of bits) is worse than
lower baud rate!
|
Token Ring: |
Baud Rate |
= 2 x Data Rate |
|
FDDI: |
Baud Rate |
= (5/4) x Data Rate |
Yet, FDDI is more efficient!
Why?
Look at Figure 2.38, page 111 of Chapter 2.
Data is divided into bit strings: b1, b2, ..., bn.
The transmitter:
- analyzes the string,
and,
- transmits a signal component
uniquely determined by the bit values.
Different signal components make up
the actual transmitted signal. If the
components are: C1, C2,..Cm,
then the transmitted signal = C1,C2,...,Cm.
The frequency with which the components
change (perhaps C1 <> C2, so there's a change!) is the
baud rate.
So, the
baud rate
is the frequency of change.
The
baud rate
then relates to the change and the more change, the more power
needed to keep up with the changes.
Thus,
FDDI
changes the signal components
less frequently
than
Token Ring.
So,
FDDI
has a lower baud rate than
Token Ring.
Therefore,
FDDI
is more efficient than
Token Ring!
More information can be found in Mischa Schwartz,
Information, Transmission, and Noise
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To:
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© Kathleen M. Kaplan 2000
Dr. Kathleen Kaplan, Howard University
Email: [email protected]