DCN 1-5 Performance
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Transcript of DCN 1-5 Performance
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Data Communications and
NetworksNetworksChapter 1: Performance
Pham Quang Thai [email protected]
1
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Bandwidth
ThroughputBit error
rate
Performance
Latency (Delay)
Bandwidth-Delay
Product
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Bandwidth and throughput
In networking, we use the term bandwidth in
two contexts.
Bandwidth (Hz) : the range of frequencies in a
composite signal or the range of frequencies that composite signal or the range of frequencies that
a channel can pass.
Bandwidth (bps): the speed of bit transmission in
a channel or link.
Throughput: the actual speed of bit
transmission in a channel or link
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Bandwidth and throughput
Throughput
Bandwidth
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Example
An average of 12,000 frames per minute with
each frame carrying an average of 10,000 bits
is send through a channel with 10 Mbps
bandwidth. What is the throughput of this bandwidth. What is the throughput of this
network?
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Latency (delay)
Propagation time: time for the signal to travel
from one point to another
Transmission time: time for the whole
message to be sentmessage to be sent
Total latency (delay): time for the whole
message to be sent and travel through the
medium
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Example
The bandwidth of the network is 100 Mbps. The distance between the sender and the receiver is 12000 km. Signal travels at 2.4 108 m/s in copper.
1. Compare the propagation time and the transmission time for a 2.5-kbyte message (an e-mail)
2. Compare the propagation time and the transmission time for a 500-Mbyte message (a video)
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The bandwidth-delay product defines
the number of bits that can fill the link
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Bit error rate: the percentage of bits that
have errors relative to the total number of
bits received
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The Q function
mSNR
=
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Example
1. A 2-level signal is transmitted through channel with Gaussian
distributed noise. The means of lower level (bit 0) and
higher level (bit 1) are E and E, respectively. The noises
standard deviation =N0E/2. The probabilities of bit 0 and 1 are equal. Find the BER.1 are equal. Find the BER.
2. The signal in the following figure is sent through a channel
with Gaussian distributed noise. The noises standard
deviation =N0E/2. Find the BER.
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BER, eyediagram and error vector magnitude
Pb: BER, L: no. of levels, Eb/N0: SNR, M: no. of M-arys levels