Survivable Logical Topology Design in WDM Optical Ring

Survivable Logical Topology Design in WDM Optical Ring Networks Hwajung Lee, Hongsik Choi, Suresh Subramaniam, and Hyeong-Ah Choi* The George Washington University Supported in part by DARPA under grant #N 66001 -00 -18949 (Co-funded by NSA) DISA under NSA-LUCITE Contract NSF under grant ANI-9973098

Outline ü Introduction – Network Survivability ü Motivation ü Problem Formulation ü Problem Complexity ü Heuristic Algorithm ü Numerical Results ü Concluding Remarks

Introduction Network Survivability ü To guarantee for users to use the network service without any interruption. ü Each layers have their own fault recovery functions. ü Fault propagation IP ATM IP IP SONET/ SDH ATM WDM Optical Network Physical Fiber Plant IP

Motivations Survivable Logical Topology ü Logical topology (Upper Layer) is called survivable if it remains connected in the presence of a single optical link failure. § Faulty Model : Single optical link failure.

Motivations Survivable Logical Topology Upper Layer = Logical Topology 0 Survivable 1 2 5 = Physical Topo. 2 Desirable! 5 Not Survivable Map each connection request to an optical lightpath. 3 4 1 Optical Layer 0 1 0 2 5 Electronic layer is connected even when a single optical link fails 4 3

Motivations Survivable Logical Topology ü Sometimes, there is no way to have a Survivable Logical Topology Embedding on a Physical Topology. Optical Layer = Physical Topo. Electronic Layer = Logical Topology c e 2 b … … a e 1 2 -Edge Connected d … d a … … … b c

Problem Formulation Survivable Logical Topology Design Problem (SLTDP) ü Given § a physical topology, and § a logical topology = a set of connection requests. ü Objectives § Find a route of lightpath for each connection request, such that the logical topology remains connected after a single link failure if possible. § Otherwise, determine and embed the minimum number of additional lightpaths to make the logical topology survivable.

Problem Complexity ü Survivable LT design possible § Completely connected (i. e. , (n-1)-edge connected) ü NO survivable LT design when logical topology G is § 2 -edge connected § 3 -edge connected § 4 -edged connected ü Degree Constraints § Survivable LT design possible when min. degree >= 2 n 3 n § No survivable LT design for min. degree <= ( 2 -1)

Problem Complexity Complete Graph : Survivable 1 1 2 5 3 4 5 2 3 4

Problem Complexity 3 -edge Connected Graph : not Survivable

Problem Complexity 4 -edge Connected Graph : not Survivable b 1 b 3 b 2 e 4 b 4 c 1 C 1 a 1 b 3 b 2 b 4 e 3 C 3 a 1 e 1 c 2 a 2 C 4 e 2 c 3 c 4 d 1 d 2 d 3 d 4 a 4 e 1 e 2 e 3 e 4 a 3 a 4 c 1 d 3 c 2 d 4 d 1 d 2 a 2 c 4 c 3

Problem Complexity Shortest Path Routing : Survivable if (minimum d 2 n ) 3 n n si 6 +i (L); si 6 - I + n -1(R) t: highest index in L smallest_component n n n 4 cases: t 4 -1; t 3 ; 4 t 3 -2; t= 3 -1 odes = N f o r be Num j . . n/4+1. L n/3 -1 . . . b Numb n/2 -1 n/2 . . . er of N 2 n/3 odes = . . . n-j-1 b n/4 . . 0 n-1 n/2+j R

Problem Complexity Shortest Path Routing n : not Survivable if (minimum d 2 -1 ). . : Vodd . . . : Veven 0 Kn/2 -1 Graph 0 n-1 Kn/2 -1 Graph

Heuristic Algorithm based on Shortest Path Routing ü Assign logical links to lightpaths. ü Cut each optical link and Calculate the # of Components. ü Find an optical link (x, y) with the maximum # of components. ü Add an additional lightpath without using (x, y). ü Repeat the above procedure until the logical topology being survivable.

Numerical Results # of Simulations = 1000

Concluding Remarks ü Survivable LT design in WDM ring network ü Determine if survivable design possible from G n § Degree constraint : 2 -1, 2 n 3 § Edge-connectivity constraint ü Heuristic algorithm: almost optimal ü Further Research § Tighter bounds § WDM mesh topology § Reconfiguration of Survivable Logical Topology