ucb protection and restoration in optical network ling huang [email protected]
TRANSCRIPT
UCB 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.
UCB 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.
UCB Optics in the Internet
SONET
DataCenter SONET
SONET
SONET
DWDM DWD
M
Access
Long HaulAccess
MetroMetro
UCB 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
IP
Optics
ATM
LayeLayerr33
22
11
00Packet
Optical
Inter-working Smart
Optical Smart Optical
PacketIP/MPLSPacket
IP/MPLS
LayeLayerr
2/32/3
0/10/1
1999 20022001
UCB
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
UCB 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.
UCB 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.
UCB
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
UCB Protection in Ring Network
1+1 Path Protection
Used in access rings for traffic aggregation
into central office
1:1 Line Protection
Used for interoffice rings
1:1 Span and Line Protection
Used in metropolitan or long- haul rings
UCB Protection in Mesh Networks
Working Path
Backup Path
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.
UCB
Reactive 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
Reactive / Proactive
Taxonomy
UCB
Path Switching: restoration is handled by the source and the destination.
Normal Operation
Line Switching: restoration is handled by the nodes adjacent to the failure. Span Protection: if additional fiber is available.
Line Switching: restoration is handled by the nodes adjacent to the failure.
Line Protection.
Path Protection / Line Protection
UCB 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
UCB 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.
UCB Shared Protection
1:N Protection
Backup fibers are used for protection of multiple links Assume independent failure and handle single failure. The capacity reserved for protection is greatly reduced.
Normal Operation
In Case of Failure
UCB
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.
Multiplexing Techniques
UCB
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
Survivability Design: Joint Optimization Problem
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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
Integer Programming Formulation
UCB Multi-Layer Resilience
UCB Multi-Layer Resilience
UCB
Multi-Layer Counter-Productive Behavior
Instant response to Level 1 alarms in high layer causes unnecessary routing activity, routing instability, and traffic congestion
Link Down
Link recovered through optical protection
Routing tableRevision (no link) Routing table
Revision (with link)
Link Rediscovered
10s ms 10s seconds 10s seconds
ALARM
Link inTraffic
Source: RHK
UCB Multi-Layer Interaction
UCB Multi-Layer Interaction
UCB 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.
UCB
Unidirectional Path Switched Ring (UPSR)
Signal sent on both working and
protected path
Best quality signal selected
Receiving Traffic
N1 send data to N2
N1N2
Outside Ring = WorkingInside Ring = Protection
Sending Traffic
N4
N3
UCBUnidirectional Path Switched Ring (UPSR)
Reply Traffic
N2 replies back to N1
Receiving Traffic
N1N2
Outside Ring = WorkingInside Ring = Protection
N4
N3
Signal sent on both working and
protected pathBest quality
signal selected
UCB
Bidirectional Line Switched Ring (2-Fiber BLSRs)
Sending/ReceivingTraffic
Sending/ReceivingTraffic
N1 send data to N2 & N2 replies to N1
Both Rings = Working & Protection
N1N2
N4
N3
UCB
Bidirectional Line Switched Ring (4-Fiber BLSRs)
Sending/ReceivingTraffic
Sending/ReceivingTraffic
OC-48
N1 send data to N2 & N2 replies to N1
2 Outside Rings = Working2 Inside Rings = Protection
N1N2
N4
N3