Chapter 11.4

1. Chapter 11.4 END-TO-END ISSUES

2. Optical Internet • Optical technology • Protocol translates availability of gigabit bandwidth in user-perceived QoS

3. WDM network architecture • WDM wide/metropolitan area network • As an Internet backbone • Access network • Ex: campus network • Domain border gateway • High-speed IP router

4. WDM network architecture

5. 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

6. 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

7. 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

8. 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

9. 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

10. Files over lightpaths (FOL) • Files are encapsulated in an optical burst in order to be transmitted across the optical network.

11. 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

12. Simulation

14. 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

15. 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

16. 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

17. Simulation Result

18. TCP congestion avoidance limits transfer efficiency • This serve to illustrate that the throughput penalty imposed by the TCP congestion control mechanism is rather significant

19. 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