Protection and Restoration in Optical Network

advertisement
Protection and Restoration in
Optical Network
UCB
Ling Huang
Hling@cs.berkeley.edu
Outline
UCB




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

A very important aspect of modern networks





Network Survivability
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
Data
Center
Optics in the Internet
SONET
SONET
DWD
M
DWD
M
SONET
SONET
Access
Metro
Long Haul
Metro
Access
UCB
Optical Network: a Layered vision
Layer
3
2
1
0
Layer
IP
ATM
IP
SONET
Optics
MPLS
Thin SONET
Opti
cs
Multi-physical layers
• multi & legacy services
• robustness, QOS
1999
Interworking
Packet
Optical
Packet
IP/MPLS
Smart
Optical
2/3
0/1
Fewer physical layers
• IP service dominance
• lower cost
2001
2002
UCB

A well defined set of restoration techniques already
exists in the upper electronic layers:




Protection and Restoration in Internet
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

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:


Why Optical Layer Protection
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.
Why Optical Layer Protection?
UCB

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

Restoration techniques can protect the network
against:

Link failures


OXCs, OADMs, eclectro-optical interface.
Protection can be implemented



Fiber-cables cuts and line devices failures (amplifers)
Equipment failures


Protection Technique Classification
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 Span and Line Protection 1:1 Line Protection
Used in metropolitan or longhaul rings
Used for interoffice
rings
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:
restoration is handled
by the source and the
destination.
Line Switching: restoration is
handled by is
restoration
thehandled
nodes by
adjacent
the
nodestoadjacent
the failure.
to the
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
Routing table
Revision (no link)
Routing table
Revision (with link)
Link in
Traffic
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
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
UCB
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
UCB Bidirectional
Line Switched Ring (2-Fiber BLSRs)
Sending/Receiving
Traffic
N2
Sending/Receiving
Traffic
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
Traffic
N2
Sending/Receiving
Traffic
N1
OC-48
2 Outside Rings = Working
2 Inside Rings = Protection
N3
N4
N1 send data to N2 & N2 replies to N1
Download