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EE450-U1-PerformanceMeasures-Nazarian-Summer11

# EE450-U1-PerformanceMeasures-Nazarian-Summer11 - University...

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EE450 Computer Networks Network Performance and Latency Measures University of Southern California Viterbi School of Engineering Shahin Nazarian Summer 2011

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Shahin Nazarian/EE450/Summer 2011 2 Network Performance Measures Two most important measures are delay or _______ (in seconds) and throughput (in _____ or packets per sec) A systems with lower delay and _______ throughput has a ________ performance
Shahin Nazarian/EE450/Summer 2011 3 Four Sources of Packet Delay 1. Nodal processing delay (___) To check bit errors To determine output link A B propagation transmission nodal processing queueing 2. Queuing delay (____) Time waiting at output link for transmission Depends on congestion level of router Both d proc and d queue are ______ parameters There is no deterministic equation for them, therefore they are studied statistically

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Shahin Nazarian/EE450/Summer 2011 4 Delay in packet-switched networks 3. Transmission delay (____) R = link ________ (bps) L = packet length (____) time to send bits into link = d trans = _____ 4. Propagation delay (_____) d = length of physical link s = propagation speed in medium (2 10 8 to 3 10 8 ___ ) propagation delay = d prop = ___ A B propagation transmission nodal processing queueing Note: s and R are very different quantities! Both d trans and d proc are _________ parameters
Shahin Nazarian/EE450/Summer 2011 5 How Do Loss and Delay Occur? Packets queue in router buffers If packet arrival rate to link _________ the output link capacity, packets queue, and wait for turn A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets are ______ ( loss ) if no free buffers

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Shahin Nazarian/EE450/Summer 2011 6 Transmission Delay, d trans ____________ delay , denoted by d trans , is the time it takes to push into the link (transmit) all the message bits: d trans = ______ where L (bits) is the message length and R (bps) is the bit rate d trans can be significant for low-speed links Note: d trans is only about transmitting the message (send the message to the link.) It does not include the time it takes for message to propagate and be received by the other end of the link) A B Time (sec) 0 message d trans
Shahin Nazarian/EE450/Summer 2011 7 Transmission Delay (Cont.) Example: What is the bit rate, R? R = ___bits/____sec = ____ bps What is the transmission delay for a message of length 128bits? d trans = ____bits/____bps = 21.33 sec What is the transmission delay for one bit? d trans-1bit = 1/6bps = 0.167 sec Note the transmission delay for one bit, is also referred to as the ____________. Bit duration is desired to be low 1 0 1 1 0 0 Time (sec) Logic level 1 ___________ = 1/R

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Shahin Nazarian/EE450/Summer 2011 Transmission Delay (Cont.) Example: Host H1, is downloading the season finale of “_________” from its peer, H2. Is the download time the same as the transmission delay of H2?
Shahin Nazarian/EE450/Summer 2011 9 Propagation Delay, d prop _________ delay , denoted by d prop , is the difference between the time one bit is transmitted and the time, that one bit is received. Another words, the time for one bit to propagate from source to destination d prop = _____

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• Summer '06
• Zahid
• Channel capacity, Measuring network throughput, Network performance, Shahin Nazarian, Shahin Nazarian/EE450/Summer

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EE450-U1-PerformanceMeasures-Nazarian-Summer11 - University...

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