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Chapter 11.4. END-TO-END ISSUES. Optical Internet. Optical technology Protocol translates availability of gigabit bandwidth in user-perceived QoS. WDM network architecture. WDM wide/metropolitan area network As an Internet backbone Access network Ex: campus network Domain border gateway

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chapter 11 4

Chapter 11.4

END-TO-END ISSUES

optical internet
Optical Internet
  • Optical technology
  • Protocol translates availability of gigabit bandwidth in user-perceived QoS
wdm network architecture
WDM network architecture
  • WDM wide/metropolitan area network
    • As an Internet backbone
  • Access network
    • Ex: campus network
  • Domain border gateway
    • High-speed IP router
open issue
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
end to end tcp
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
split tcp connection models 1 2
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
split tcp connection models 2 2
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
11 4 1 tcp for high speed and split tcp connection
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
files over lightpaths fol
Files over lightpaths (FOL)
  • Files are encapsulated in an optical burst in order to be transmitted across the optical network.
simulation
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
simulation result
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
11 4 2 performance evaluation of file transfer www services over wdm networks 1 2
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 lightpath between routers)
  • second-generation WDM network suffer blocking probability
    • Limited number of wavelengths
    • Burst dropping due to limited queueing space in photonic packet switchs
  • Split TCP becomes inefficient
performance evaluation of file transfer www services over wdm networks 2 2
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
slide18
TCP congestion avoidance limits transfer efficiency
  • This serve to illustrate that the throughput penalty imposed by the TCP congestion control mechanism is rather significant
slide19
The main difference between a simple FOL protocol and TCP is in interpreting congestion
    • TCP considers loss is produced by queueing overflow
    • FOL is aware that loss is due to blocking