Protection and Restoration in
Optical Network
UCB
Ling Huang
Hling@cs.berkeley.edu
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
Data
SONET
Center
SONET
DWD
M DWD
M
SONET
SONET
Metro Long Haul Metro
Access
Access
UCB Optical Network: a Layered vision
Layer
3 Layer
IP
2
ATM
1 IP
2/3
MPLS
0 Packet
SONET Packet
Thin SONET
Inter- IP/MPLS
Opti working Smart
Optics
cs Optical Optical 0/1
Multi-physical layers Fewer physical layers
• multi & legacy services • IP service dominance
• robustness, QOS • lower cost
1999 2001 2002
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 1:1 Span and Line Protection 1:1 Line Protection
Used in access rings for Used in metropolitan or long- Used for interoffice
traffic aggregation into haul rings rings
central office
UCB 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
UCB Reactive / Proactive
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.
Taxonomy
100 percent restoration
Faster recovery
UCB Path Protection / Line Protection
Normal Operation
Path Switching: Line Switching: restoration is
restoration is handled handled by is
restoration thehandled
nodes by
by the source and the adjacent
the nodestoadjacent
the failure.
to the
destination. Span Protection: if additional
failure.
fiber is available.
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
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.
UCB 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.
UCB 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
UCB 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
UCB Multi-Layer Resilience
UCB Multi-Layer Resilience
UCB Multi-Layer Counter-Productive Behavior
Link in
Routing table Traffic
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
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 Best quality
both working and signal selected
protected path
Receiving Traffic
Sending Traffic
N2
N1
Outside Ring = Working
Inside Ring = Protection
N3
N4
N1 send data to N2
UCB Unidirectional Path Switched Ring (UPSR)
Signal sent on
Best quality both working and
signal selected protected path
Reply Traffic
Receiving Traffic N2
N1
Outside Ring = Working
Inside Ring = Protection
N3
N4
N2 replies back to N1
UCB Bidirectional Line Switched Ring (2-Fiber BLSRs)
Sending/Receiving Sending/Receiving
Traffic Traffic
N2
N1
Both Rings = Working & Protection
N3
N4
N1 send data to N2 & N2 replies to N1
UCB Bidirectional Line Switched Ring (4-Fiber BLSRs)
Sending/Receiving Sending/Receiving
Traffic Traffic
N2
N1
OC-48
2 Outside Rings = Working
2 Inside Rings = Protection
N3
N4
N1 send data to N2 & N2 replies to N1
