Bi-Link-Failure-Free Routing and Wavelength Assignment for Torus-Based Avionic WDM LANs

1. Bi-Link-Failure-Free Routing and Wavelength Assignment for Torus-Based Avionic WDM LANs Dexiang Wang and Janise McNair Department of Electrical and Computer Engineering University of Florida

2. Outline • Introduction • Mission-Critical Communications/Design Requirements • Applied Network Topology/Architecture • Related Work and Contributions • Working Lightpaths Routing and Wavelength Assignment (WRWA) • Spare Lightpaths Routing and Wavelength Assignment (SRWA) • Enhanced 4-Way Protection • Fault Tolerance Performance Evaluation • Conclusions and Future Work

3. Introduction • Mission-Critical Communications • Avionic onboard communication system • Optical backbone LAN • High bandwidth provision, light weight, and electric-magneto interference resistance (compared with traditional copper wire based design) • Fast (Time-critical date delivery) • Reliable (Tolerate communication link failures) • Solution • All-optical LAN • Fault-tolerant routing and resource allocation

4. Network Topology/Architecture • 2D-Torus-based architecture • Easy for deployment into aircraft physical structure • Rich connectivity (four possible link/node-disjoint routes connecting any S-D pair) • Each link is bidirectional (Bilink) 4×4 torus • Traffic configuration model • All-terminal communication • For a N×N torus, there exist N2(N2-1)/2 bidirectional communication pairs

5. Related Works on Torus-Based Optical LANs • Single-lightpath routing and wavelength assignment (RWA) problem has been studied by B. Beauquier (for even N) and by H. Schroder et al. (for odd N). • The results reach optimality in terms of wavelength utilization • N3/8 wavelengths needed for N being even • N(N2-1)/8 wavelengths needed for N being odd • Four-lightpath fault-tolerant routing scheme was proposed in our previous work and the scheme reaches optimality in link utilization. • We also developed a wavelength allocation and reuse (WAR) scheme for all four dedicated lightpaths for all-terminal communication

6. Approaches/Achievements in this Work • Approaches • Aimed to develop a low resource-intensive RWA solution for all-terminal communication model while still being able to tolerate an arbitrary bilink failure • Working paths routing and wavelength assignment is achieved by applying single-lightpath RWA solution developed by B. Beauquier and H. Schroder • Spare paths routing and wavelength assignment is based on routing analysis of working paths on a specific bilink • Achievements • Started study with a 4×4 torus • Resulting protective wavelength assignment is at cost of 25% of that for working lightpaths • In addition, a 4-way protection scheme is introduced to enhance fault tolerance capacity beyond the first bilink failure

7. Bilink-Failure-Free RWA • Apply B. Beauquier’s single-lightpath RWA solution on working lightpaths • However, there exist multiple RWA ways to achieve optimal wavelength utilization • Decide the RWA based on (1) whether it can provide uniform patterns that working paths pass through bilinks and (2) whether the passing-through patterns favors deriving a low spare resource demanding solution for bilink-failure tolerance

8. Working Lightpaths RWA (WRWA) • WRWA for 4×4 torus, demanding 43/8 = 8 wavelengths (in different colors below) Lightpaths (Group I) corresponding to type-M moves Lightpaths (Group II) corresponding to type-H and type-K moves

9. Spare Lightpaths RWA (SRWA) • Bundling bilink • Bilink that “bundles” a group of lightpaths passing through it • Design constraint • Spare lightpaths protecting working lightpaths on a bundling bilink must avoid being routed through the bundling bilink • Spare paths of bundled working paths cannot share wavelength resource • Spare routing and wavelength assignment for Group I working lightpaths SRWA for horizontal bundling bilink SRWA for vertical bundling bilink

10. Spare Lightpaths RWA (SRWA) (Cont.) • Spare routing and wavelength assignment for Group II working lightpaths SRWA for horizontal bundling bilink SRWA for horizontal bundling bilink • Finally, 2 spare wavelengths are allocated (optimal), at cost 25% of that for working paths (8 wavelengths)

11. Enhanced 4-Way Protection • Observe that there are still wavelength/link resources on 2 spare wavelengths after SRWA • Further protection (beyond the first bilink failure) can potentially be achieved by exploring 4-way disjoint routing on those resources • Above four lightpaths may experience state transition

12. Performance Evaluation • Metrics • Connection Unreliability • Two-Terminal Unreliability (TTUR) and One-to-All-others Unreliability (ATUR) • Conditional TTUR and OAUR on a given number (n) of bilink failures • Conditional Average Network Capacity

13. Performance Evaluation (Cont.) • Two-terminal unreliability (TTUR) 11→23 11 12 13 14 21 22 23 24 31 32 33 34 41 42 43 44 • Conditional TTUR 11→23 • TTUR distribution from 11

14. Performance Evaluation (Cont.) • Conditional OAUR • Conditional average throughput • Conditional switch blocking rate • Conditional distribution on # of disconnected S-D pairs

15. By carefully choosing WRWA scheme for working lightpaths, certain common passing-through patterns can be extracted and SRWA scheme can be developed. • The WRWA+SRWA scheme (possibly with enhanced 4-way protection) is proved to help improve fault-tolerance capacity. • In the future, we plan to extend the 4×4 torus study to general N×N torus and we expect 1/N of working wavelength resources are needed for SRWA based on our current progress. Conclusions and Future Work