1. Protection and Restoration in Optical Network
Ling Huang

2. Introduction to Network Survivability Optics in Internet
Outline
Introduction to Network Survivability
Optics in Internet
Protection and Restoration in Internet
Optical Layer Survivability
Protection in Ring Network
Protection in Mesh Network
Multi-Layer Resilience
Conclusion.

3. Network Survivability
A very important aspect of modern networks
The ever-increasing bit rate makes an unrecovered failure a significant loss for network operators.
Cable cuts (especially terrestrial) are very frequent.
No network-operator is willing to accept unprotected networks anymore.
Restoration = function of rerouting failed connections
Survivability = property of a network to be resilient to failure
Requires physical redundancy and restoration protocols.

4. Optics in the Internet Access Long Haul Metro
SONET
Data
Center
DWDM
Access
Long Haul
Metro
BPS2000, Baystack 450 & Passport 8600 (edge ethernet distribution & aggregation)
OPTera Packet Edge on OPTera Metro 3000 series & OPTera OC-48 (ethernet over metro optical/Sonet)
OPTera Metro 5000 series (ethernet over DWDM)
Preside (provisioning & management software)
Juniper & Shasta (collateral IP services & routing platforms)
Contivity (VPN/secure, encrypted tunnel services)

5. Optical Network: a Layered vision
Multi-physical layers
multi & legacy services
robustness, QOS
Thin SONET IP
Optics
MPLS
Fewer physical layers
IP service dominance
lower cost
SONET
ATM
Layer 3 2 1
Packet
Optical
Inter-
working
Smart Optical
IP/MPLS
2/3
0/1
Migration to IP on Optics
simpler, lower cost network
robustness & QOS needed for some services
2001
1999
2002

6. Protection and Restoration in Internet
A well defined set of restoration techniques already exists in the upper electronic layers:
ATM/MPLS IP
TCP
Restoration speeds in different layers:
BGP-4: 15 – 30 minutes
OSPF: 10 seconds to minutes
SONET: 50 milliseconds
Optical Mesh: currently hundred milliseconds to minutes

7. Why Optical Layer Protection
Restoration in the upper layers is slow and require intensive signaling
On contrary 50-ms range when automatic protection schemes are implement in the optical transport layer.
Purpose of performing restoration in the optical layer:
To decrease the outage time by exploiting fast rerouting of the failed connection.
Main problem in adding protection function in a new layer:
Instability due to duplication of functions.
Need the merging of DWDM and electronic transport layer control and management.

8. Why Optical Layer Protection?
Advantages.
Speed.
Efficiency.
Limitation
Detection of all faults not possible.(3R).
Protects traffic in units of light paths.
Race conditions when optical and client layer both try to protect against same failure.

9. Protection Technique Classification
Restoration techniques can protect the network against:
Link failures
Fiber-cables cuts and line devices failures (amplifers)
Equipment failures
OXCs, OADMs, eclectro-optical interface.
Protection can be implemented
In the optical channel sublayer (path protection)
In the optical multiplex sublayer (line protection)
Different protection techniques are used for
Ring networks
Mesh networks

10. Protection in Ring Network
1+1 Path Protection
Used in access rings for traffic aggregation into central office
1:1 Span and Line Protection
Used in metropolitan or long- haul rings
1:1 Line Protection
Used for interoffice rings

11. Protection in Mesh Networks
Network planning and survivability design
Disjoint path idea: service working route and its backup route are topologically diverse.
Lightpaths of a logical topology can withstand physical link failures.
Working Path
Backup Path

12. Reactive / Proactive Reactive Proactive
A search is initiated to find a new lightpath which does not use the failed components after the failure happens.
It can not guarantee successful recovery,
Longer restoration time
Proactive
Backup lightpaths are identified and resources are reserved at the time of establishing the primary lightpath itself.
100 percent restoration
Faster recovery
Taxonomy

13. Path Protection / Line Protection
Path Switching: restoration is handled by the source and the destination.
Line Switching: restoration is handled by the nodes adjacent to the failure.
Line Protection.
Normal Operation
Line Switching: restoration is handled by the nodes adjacent to the failure Span Protection: if additional fiber is available.

14. 1+1 Protection
Traffic is sent over two parallel paths, and the destination selects a better one.
In case of failure, the destination switch onto the other path.
Pros: simple for implementation and fast restoration
Cons: waste of bandwidth

15. 1:1 Protection
During normal operation, no traffic or low priority traffic is sent across the backup path.
In case failure both the source and destination switch onto the protection path.
Pros: better network utilization.
Cons: required signaling overhead, slower restoration.

16. Shared Protection
Normal Operation
1:N Protection
In Case of Failure
Backup fibers are used for protection of multiple links
Assume independent failure and handle single failure.
The capacity reserved for protection is greatly reduced.

17. Multiplexing Techniques
Primary Backup Multiplexing
Used in a dynamic traffic scenario, to further improve resource utilization.
Allows a wavelength channel to be shared by a primary and one or more backup paths.
By doing so, the blocking probability of demands decreases at the expense of reduced restoration guarantee. (An increased number of lightpaths can be established)
A lightpath loses its recoverability when a channel on its backup lightpath is used by some other primary lightpath.
It regains its recoverability when the other primary lightpath terminates.

18. Survivability Design: Joint Optimization Problem
Problem Description
Given a network in terms of nodes (WXCs) and links, and a set of point-to-point demands, find both the primary lightpath and the backup lightpath for each demand so that the total required network capacity is minimized.
Notation
N: the set of nodes;
L: the set of links;
D: the set of demands
Cij: the capacity weight for link (ij)
Wij: the capacity requirement on link (ij) in terms of # of wavelength
Objective
Minimize

19. Integer Programming Formulation
1) Objective function
2) and 3) the flow conservation constraints for demand d’s primary path and backup path, respectively.
4) Logical relationship: the backup path consumes link capacity iff the primary path is affected by the fault.
5): Restoration route independent of the failure.
6): Link capacity requirement

20. Multi-Layer Resilience

21. Multi-Layer Resilience

22. Multi-Layer Counter-Productive Behavior
Link in
Traffic
Routing table
Revision (no link)
Routing table
Revision (with link)
Link Rediscovered
ALARM
Link recovered through optical protection
Link Down
10s ms
10s seconds
10s seconds
Instant response to Level 1 alarms in high layer causes unnecessary routing activity, routing instability, and traffic congestion
Source: RHK

23. Multi-Layer Interaction

24. Multi-Layer Interaction

25. Conclusion
Different resilience schemes applicable in optical network have been discussed.
Network planning and topology design for survivability is computationally intractable and faster heuristic solutions are needed.
Multi-layer restoration is a hot point in current optical survivability research.
Joint IP/optical restoration mechanism is the trend in next generation optical network.

26. Unidirectional Path Switched Ring (UPSR)
Signal sent on both working and protected path
Best quality signal selected
Receiving Traffic
Sending Traffic N2 N1
Outside Ring = Working
Inside Ring = Protection N3 N4
N1 send data to N2

27. Unidirectional Path Switched Ring (UPSR)
Signal sent on both working and protected path
Best quality signal selected
Reply Traffic
Receiving Traffic N2 N1
Outside Ring = Working
Inside Ring = Protection N3 N4
N2 replies back to N1

28. Bidirectional Line Switched Ring (2-Fiber BLSRs)
Sending/Receiving
Traffic
Sending/Receiving
Traffic N2 N1
Both Rings = Working & Protection N3 N4
N1 send data to N2 & N2 replies to N1

29. Bidirectional Line Switched Ring (4-Fiber BLSRs)
Sending/Receiving
Traffic
Sending/Receiving
Traffic N2 N1
OC-48
2 Outside Rings = Working
2 Inside Rings = Protection N3 N4
N1 send data to N2 & N2 replies to N1