Chapter 11 – Gene Expression 11.1 – 11.3 Skip 11.4 AP Biology Radjewski 2014.
Chapter 11.4
description
Transcript of Chapter 11.4
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Chapter 11.4
END-TO-END ISSUES
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Optical Internet
Optical technology Protocol translates availability of giga
bit bandwidth in user-perceived QoS
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WDM network architecture
WDM wide/metropolitan area network As an Internet backbone
Access network Ex: campus network
Domain border gateway High-speed IP router
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WDM network architecture
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Open issue
Access network Packet loss and delay due to
congestion Optical backbones
High transmission rates Extremely low bit error rates
Bridging the gap between access and backbone network is an issue
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End-to-end TCP
It is not practical, the reasons is below TCP slow-start algorithm constrains very
large bandwidth available in the lightpath until the steady state is reached
Socket buffer is not enough congestion and flow control features
needed in access network
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Split TCP connection models (1/2) It is an evolutionary approach to the TCP end-to-
end model to adapt to the specific characteristics of each of the network segment
It is not an efficient solution for optical networks due to the wavelength speed
EX: 10-Gbps wavelength bandwidth
10-ms propagation delay bandwidth delay product (BDP)=25MB File sizes in the Internet are smaller than such BDP Because of different round-trip delays, it is difficult
to optimize TCP windows to achieve transmission efficiency
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Split TCP connection models(2/2)
Most TCP features( congestion and flow control) unnecessary in optical network Extremely low loss rate in the optical
network makes retransmission unlikely to happen
The optical network can operate in a burst-switched mode in the optical layer, so there are no intermediate queues in which overflow occurs
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11.4.1 TCP for High-Speed and Split TCP Connection
First approach to solving the adaptation problem between access and backbone TCP connection can be split in the
optical backbone edges TCP extensions for high speed
a larger transmission window no slow start
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Files over lightpaths (FOL) Files are encapsulated in an optical
burst in order to be transmitted across the optical network.
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Simulation Topology
An optical channel(1Gbps) which connects several access routers located at the boundaries of optical networks
Network parameters Namely, link capacities, propagation delay,
and loss probability Performance metric
Connection throughput
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Simulation
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Simulation Result For small file sizes
The connection duration is dominated by setup time and slow start, which does not allow the window size to reach a steady-state value
For large file sizes The TCP reach steady state and the
throughput is equal to window size divided by roundtrip time.
Such behavior is expected in a large BDP network, in which connections are RTT-limited rather than bandwidth-limited
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11.4.2 Performance Evaluation of File Transfer (WWW) Services over WDM Networks(1/2)
11.4.1 is in error-free condition Ex: a first-generation WDM network (static lightp
ath between routers) second-generation WDM network suffer blo
cking probability Limited number of wavelengths Burst dropping due to limited queueing space in
photonic packet switchs Split TCP becomes inefficient
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Performance Evaluation of File Transfer (WWW) Services over WDM Networks(2/2)
In FOL, files are encapsulated in an optical bursts through the optical backbone using a simple stop-and-wait protocol for error control.
Assuming the setup of an optical burst takes RTT/2
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Simulation Result
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TCP congestion avoidance limits transfer efficiency
This serve to illustrate that the throughput penalty imposed by the TCP congestion control mechanism is rather significant
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The main difference between a simple FOL protocol and TCP is in interpreting congestion TCP considers loss is produced by queuei
ng overflow FOL is aware that loss is due to blocking