Dr. Meir Herzberg AVP Network-Planning Tools, Optical Networks

2. Strategiesfor Survivable Telecommunication Networks Dr. Meir Herzberg AVP Network-Planning Tools, Optical Networks December 2003

3. Outline • Introduction • Network Architectures • Classification and strategies • Mesh Survivable networks • Ring Survivable networks • Future trends and concluding remarks

4. Motivation • Higher bit rate of transmission systems (2.5, 10, 40 Gb/s, due to economy of scale advantages) • Evolvement of the DWDM technology • Fiber-optic infrastructure expensive ($50 per meter length, bill of land) and vulnerable • Introduction of real-time services (time critical) • Competition –available new alternatives • The establishment of re-configurable networks following the development of advanced NEs, e.g. DCSs / ODCSs and ADMs / OADMs • Selfhealing networks (W.Grover – Uni. of Alberta)

5. Issues of concern • Assignment of redundant resources in the network (well before network failures) • Following network re-arrangement events • During provisioning • Recovery mechanisms immediately after failures occur • Protocols • Outage times • Equipment dependent

6. Addressing Survivability • At the network infrastructure layer • Improved network capabilities • Closer to the underlying physical layer • Service differentiation • At the service layer • More service oriented • Own re-routing capabilities • Complementary service aspects • Telephony experience

7. Outline • Introduction • Network Architectures • Classification and strategies • Mesh Survivable networks • Ring Survivable networks • Future trend, concluding remarks

8. Network Applications and Services Service Aspects: Quality, Assurance, Activation Layers 4+ Network Architecture Traffic Patterns, Routing, Capacities Layer 3 Underlying Net. Infrastructure Nodes, Cables, Distances, Nodal NEs Layers 1-2 Environment of NetArch and its Interaction Factors Layering Management OSI Business Service Network Net. Element

9. Hierarchical Network Architecture l 4/4 4/4 Long Haul Network Part 4/4 l 4/4 4/4 4/4 4/4 l 4/4 4/3/1 l Regional, Metro Network Part OC48/ STM16 4/3/1 l OC12/ STM4 l 4/3/1 - Static DWDM TM - Digital Cross-connect OC3/ STM1 - Add Drop Multiplexer 3/1 - Terminal Multiplexer 1/0 - User Terminal - Inter-level connection

10. Single Architecture (SA) Approach l l l l l l l l l (c) (a) Multi ADM Multi ADM + DCS SA-NE (b) (d) (e) (f) Multi ADM + Optics DCS + Optics Multi ADM + DCS + Optics Ring Mesh Ear Ring (h) (g)

11. Outline • Introduction • Network Architectures • Clasification and strategies • Mesh Survivable networks • Ring Survivable networks • Future trends, concluding remarks

12. Classification ofSurvivable Networks ITU-T Restoration Protection Reconfigurable Network (rerouting protocol) Self-healing Network (on-demand protocol) Protection Switching - Dedicated, - Distributed (1+1, 1:1, 1:N) Resources - Shared, Mechanism - Distributed - Shared, - Centralized

13. Survivable Networks – Strategies and Policies Resource Redundancy Recovery View Surveillance Mechanism Policy Network Segment (fiber, MS line, node) Distributed/Surveillance Mode Distributed with Centralized pre-planning Path Level (end-to-end) Centralized Management System Shared Restoration Semi- Dedicated Dedicated Protection

14. Survivability – Tradeoff Resources Allocated Policy A Policy B Policy C Recovery Time msecs Secs 10XSecs

15. Survivable Planning Phases • Selecting a suitable network architecture – geography, fiber infrastructure and traffic aspects • Establishing a suitable survivable network policy • Pre-planning of working and redundancy resources • During failure - alarming, real-time surveillance • Following failure - service outage, resource management • After failure is fixed -’revert to normal’ (not always)

16. Outline • Introduction • Network Architecture • Classification and strategies • Mesh Survivable networks • Ring Survivable networks • Future trends, concluding remarks

17. Network segment Line Recovery End to end Path Recovery Recovery View - Line vs Path

18. Recovery View - Line vs Path Loop Haul Line Recovery may be associated with Loop Hauls * Usually less efficient in resource utilization (loop hauls) * Simple updates (total usage) * Potentially faster as recovery activities (single node-pair considerations compared to many origin-destination node-pairs considerations in Path Recovery)

19. Working trail (shortest path) Protection trail (longer) Redundancy – Shared vs Dedicated • Dedicated protection resources - very demanding. Total protection resources can even be more then total working resources • Shared restoration may save dedundant resources Question - how much can be saved?

20. Redundant Shared Resources • Saving following shared resources is network dependent. The higher the network connectivity the more diverse routes are available and the less redundant resources required • We can prove that the lower bound of shared resources is derived by the simple relationship 1 Network Connectivity - 1 Shared Resources Working Resources >= Average number of physical fibers per site can be explained

21. 35 (25) 25 (35) 20 (10) 15 (15) 25 (5) 20 (0) 15 (5) 12 (8) 13 (7) Redundancy - Shared • Network connectivity = 2 • Network connectivity = 3 • Network connectivity = 4 (60) 60 1 2 - 1 = (30) 60 1 3 - 1 = (20) 60 1 4 - 1 = Intuitive explenation

22. Redundant Resources Dedicated, Semi-dedicated and Fully Shared • Dedicated - both routes and their associated resources are pre-calculated and assigned • Semi-dedicated – restoration routes are dedicated, failure independent, resources are shared and be used differently for different failure scenarios (named also “Fast Mesh”) • Fully Shared - both restoration routes and shared resources are failure dependent

23. 2+3 2+3 C 2+3 3 2 3 3 A B 2 2 2 C,A B Working Paths (disjoint) B C,A Protecting/Restoration Paths Redundancy - Dedicated vs Semi dedicated The Semi-dedicated approach, developed first for ATM networks for restoration of Virtual Paths (VPs) can also be applied to other networks.

24. 1 1 1 1 1 1 1 1 1 Mechanism - Distributed vs Centralised • Centralized mode has a global view of the network • Requires a demending Data Communication Network (DCN) between the NMS and the NEs • Reaching highest utilization of network resources • Distributed mode leads to faster recovery times but may face “Trap Situations” • Distributed mode leads to faster recovery times B A Two Capacity Units are Required to be Restored between A-B

25. Outline • Introduction • Network Architecture • Classification and strategies • Mesh Survivable networks • Ring Survivable networks • Future trends, concluding remarks

26. Main Ring Types • UPSR (unidirectional path-switched ring) • Both main and protection trails consume resources along the ring • Dedicated redundancy resources - Time Slot Assignment (TSA) • BPSR (bi-directional path-switched ring - Syncom) • Protection trails consume resources along the ring, complies with SNCP for inter-ring trails • Dedicated redundancy resources - TSA • BLSR (bi-directional line-switched ring) or MS-Spring (MS shared protection ring) • Reuse of time slots along the ring • Shared redundancy resources - Time Slot Interchange (TSI)

27. BPSR vs UPSR • For protected trails, there is no difference as both uses resources along the entire rin • For unprotected trails BPSR is usually superior • Superiority is achieved by the use of OD shortest paths • Unprotect traffic between adjacent sites consume resources only from a single secion of the ring

28. W P TSI F F W P B B D C D C Ring Survivable Networks BLSR (Mspring) vs BPSR Unprotected Trail Protected Trail

29. MS-Spring vs BPSR • For unprotected trails, there is no difference as both have the same routing flexibility. • For protected trails MS-Spring is usually superior • Superiority is achieved by the use of shared resources through TSI mode of operation • Restoration time in MS-Spring is fast, despite using shared redundant resources, as routing decisions are simple • There are two types of MS-Spring: 2, 4 fibers (2F), (4F) • 4F-MS-Spring has twice the capacity of 2F-MS-Spring and uses double ADMs at ring sites (less then double the cost, extra redundancy)

30. Outline • Introduction • Network Architecture • Classification and strategies • Mesh Survivable networks • Ring Survivable networks • Future Trends, concluding remarks

31. Summary • Using Multi-Service Provisiong Platforms (MSPPs) following the development of compound NEs • Employing Multi-Technology Network Management (MTNM) systems • Tied relationship between NE capabilities and Network Architecture • Creating multi-service networks (Survivable Networks) • Offering a set of survivability policies • Network planning and network operation aspects

32. Thank You !