Physical Layer Impairment Aware Wavelength Routing Algorithms

1. Vasilis Anagnostopoulos1, Christina (T.) Politi1,2, Chris Matrakidis1,2, Alexandros Stavdas2 1 National Technical University of Athens (NTUA), 9 Heroon Polytechniou Street, Zografou, 15773, Athens, Greece 2 Department of Telecommunications Science and Technology, University of Peloponnese Terma Karaiskaki, 22100, Tripolis, Greece Physical Layer Impairment Aware Wavelength Routing Algorithms

2. Outline Motivation Main assumptions Evaluation of existing solutions First approach. PLI awareness into the WRA Virtual test-bench Equations for impairments Results related to Q factor Tests with SWP algorithm Dynamic Network Simulation Remarks Conclusion

3. Motivation Network planning for PLI insensitivity gives expensive networks. We have to relax our assumptions. Transparent Optical Networks do not offer inherent regeneration, so impairments (noise, nonlinearities etc) are accumulated across the selected paths inducing errors A request for a connection should be dropped (blocking) even when traditional resources are available (lambdas) but the BER of the signal is expected to be insufficient. We have to find an online scheme that overcomes the above problems

4. Main assumptions The routing is centrally controlled by a Routing Computation Module (RCM) Wavelength Continuity Constraint. Impairments are local and additive in links but non-local in wavelengths. A reservation in lambda i affects all other lambdas. Signal attenuation, Noise, Four-Wave Mixing and Cross Phase Modulation are treated. No, SPM !!! (In this work only!!!) All links carry the same number of wavelengths, no multi-fiber routing. Requests are dynamic, requesting 1 wavelength.

5. Evaluation of existing solutions Bounds on hops. (Very small paths) Routing using a standard algorithm (CSPF, SWPF, MinHop) (Q factor must be evaluated at the end) Network planning. (expensive networks) Routing using Q factor minimization ( a reservation can affect pre-established paths) Note : For Q factor minimization, and established paths probing, we need analytical models, otherwise we have too much computational complexity.

6. First approach (1)

7. First Approach (2) Our first approach serves as a basis for future work. It is a motivation for development of a JAVA based simulator. Why JAVA > RAD (Rapid Application Development), well suited for Networking, JDOM is very good for configuration We got our first qualitative and quantitative results. We used the analytical models and made necessary adjustments for efficient calculations.

8. Virtual test-bench The Pan-European Network] is used here as a reference network with K=16 nodes and N=23 links. It is assumed to be uniform with each fiber link carrying L=40 wavelengths. Blocking probability (BP) is used as a means of network performance evaluation. We use a PLI SP (in distance) algorithm combined with FF (First-Fit), BF (Best-Fit) and RF (Random-Fit) wavelength assignment. We ‘measure’ Q-factors of the light-paths as the traffic load grows from 5 to 30 (exponential inter-arrival and life-times, to all nodes). A PLI blind SP has high failure rate if we require Q ≥ 10)

9. Equations for impairments (1)

10. Equations for impairments (2) The equations are very complicated. However the analytical model in the case at hand can be simplified to a couple of simple tractable equations. (Future Publication) -> achieved 5 fold computation reduction by simplifying the calculation of FWM and XPM interactions in a chain of fibres and amplifiers, modified to include both DCF and SMF fibres. Equations used taken from the publications : A.V.T. Cartaxo, "Cross-Phase Modulation in Intensity Modulation-Direct Detection WDM Systems with Multiple Optical Amplifiers and Dispersion Compensators", Journal of Lightwave Technology, Vol 17. No.2, pp178-190, February 1999. W. Zeiler et all, “Modeling of four-wave mixing and gain peaking in amplified WDM optical communication systems and networks”, Journal of Lightwave Technology, Vol. 14, No. 9 pp. 1933-1942, 1996.

11. Results related to Q factors (PLI unaware)

12. Results related to Q factors (PLI unaware)

13. Results related to Q factors (PLI unaware)

14. Tests with SWP algorithm We continued the tests with an approximate version of the SWP algorithm since it gives better load-balancing. In this context, SWP means that the algorithm finds the path with the maximal number of continuous wavelengths. NP hard -> simple iterative heuristic inspired by Bellman-Ford. This h We put different thresholds for acceptable Q factor in order to control the blocking probability. We check the affected light-paths for establishing a new one. (Affected light-paths) ≤ (nodes-1) × (number of wavelengths)

15. Dynamic network simulation

16. Remarks Plotting is done versus traffic load offered, not resource availability of the network. Available resource <> Useful resource (in view of PLIs) SWP and SP have similar performance. (we need more tests in different networks) . FF, BF , RF are almost the same. PLIs cause increase in BP ( we expected that) We need PLI aware algorithms. We need an RCM, no distributed computations can be done.

17. Conclusion This was a first attempt to evaluate the impact of PLIs on routing in Transparent Optical Networks. More tests are necessary. An ideal algorithm must be aware of usefulness of resources, not only feasibility. An ideal algorithm must keep track of affected established light-paths. We must find a way to reduce computational complexity.