Introduction to Protection &
Restoration for OBS
Presented by
Zaoyang Guo & Dahai Xu
Copyright, 2000, SUNY, Univ. at Buffalo
Outline
• Basic Concepts of Protection & Restoration
• Review of OBS
• Protection & Restoration for OBS
Basic Concepts of Protection &
Restoration
• What is protection & Restoration?
• Why we need Protection/Restoration?
• Protection
• Restoration
• Comparison between Protection & Restoration
• Protection/Restoration for Optical Network
What is protection &
Restoration?
• Network is unreliable somehow
• Protection & Restoration are the
mechanisms to recover from network failure
• Their difference will be discussed in the
following parts
Why we need
Protection/Restoration?
• To Recover from network failure
• To prevent a lot of data loss
• To provide reliable communication service
Protection
• Path Protection
• Link Protection
• Advantages & Disadvantages
Path Protection
• Use more than one path to guarantee the
data be sent successfully
Path Protection (Continued)
• Dedicated Path Protection
• Shared Path Protection
Dedicated Path Protection
• 1+1 Protection
• Point-to-Point Protection & Mesh Network
Protection
1+1 Protection
Mesh Network Protection
Shared Path Protection
• 1:1 Protection
• 1:N Protection
1:1 Protection
1:N Protection
Link Protection
• Use an alternate path if the link failed
Link Protection (Continued)
• Dedicated Link Protection: not practical
• Shared Link Protection: practical
• It may fail when a node fails
Dedicated Link Protection
Advantages & Disadvantages of
Protection
• Simple
• Quick: Do not require much extra process
time
• Usually can only recover from single link
fault
• Inefficient usage of resource
Restoration
• Path Restoration
• Link Restoration
• Advantages & Disadvantages
Path Restoration
• The route can be computed after failure
• The resource is reserved and then used
Link Restoration
• The path is discovered at the end nodes of
the failed link
• More practical than path restoration
Advantages & Disadvantages of
Restoration
• Usually can recover from multiplex
element faults
• More efficient usage of resource
• Complex
• Slow: require extra process time to setup
path and reserve resource
Comparison between Protection
& Restoration
• Characteristic: Protection -- the resource are
reserved before the failure, they may be not
used; Restoration -- the resource are
reserved and used after the failure
• route: Protection -- predetermined;
Restoration -- can be dynamically computed
• Resource Efficiency: Protection -- Low;
Restoration -- High
Comparison between Protection
& Restoration (Continued)
• Time used: Protection -- Short; Restoration
-- Long
• Reliability: Protection -- mainly for single
fault; Restoration -- can survive under
multiplex faults
• Implementation: Protection -- Simple;
Restoration -- Complex
Protection/Restoration for
Optical Network
• Wavelength Path (WP) & Virtual
Wavelength Path (VWP)
• FDL: to delay data
• Routing: central controlled or distributed
controlled
• Resource Reservation: forward reservation /
backward reservation
Wavelength Path (WP) & Virtual
Wavelength Path (VWP)
• Wavelength Path (WP) / Lightpath (LP) :
a wavelength and a physical path, no
wavelength translation is used
• Virtual Wavelength Path (VWP) :
wavelength translation may be employed
• Optical cross-connection
WP & VWP (Continued)
• Three types of network: no wavelength
translation at all nodes; wavelength
translation at all nodes; wavelength
translation at some nodes
Review of OBS
• Main Advantages of OBS
• Requirement & Assumption
Main Advantages of OBS
• No buffer capacity is required at
•
intermediate
nodes: A lightpath/wavelength
Path (WP) or Virtual Wavelength Path
(VWP) must be setup
• Quick Setup: No acknowledgement from
receiver (destination)
Main Advantages of OBS
(Continued)
• Low Overhead: A control packet is sent and
processed before the busty data
transmission
• High efficient utilization of bandwidth: No
acknowledgement from destination, low
overhead
Requirement & Assumption
• Reliable Network: No ack.
• OBS is mainly used in backbone networks
• Every node knows sufficient information
about the route or the topology of the whole
network
Requirement & Assumption
(Continued)
• If one element in the network fails, all the
nodes will be notified in a short time
• Assume there will be only one element fail:
If one element fails, the others will work
correctly
• Generally only single link failure is
considered
Protection & Restoration for
OBS
• Protection/Restoration At The Source Node
• Protection/Restoration At Intermediate
Node
Protection/Restoration At The
Source Node
• Dedicated Path Protection: Send burst data
to each path
• Shared Path Protection: Set a delay time to
backup path
• Disadvantage: Not efficient usage of
bandwidth
Protection/Restoration At
Intermediate Node
• Assumption: The intermediate node found
the next link is failed when it processes the
control packet
• Method: Use alternate backup path to
destination node or only to next node
• Use longer offset time: Need more
intermediate nodes
Protection/Restoration At
Intermediate Node (Continued)
• May need FDL to delay the data
• The route should be predetermined: No
extra time to dynamically compute route
• VWP preferred: Easy to reserve resource
(wavelength) successfully
MPLS Protection
• Overview
• MPLS Protection Principles
• An MPLS path Protection mechanism
Overview of MPLS Protection
• To deliver reliable service
– LSP need protection
– LSR provide protection
Motivation for MPLS Protection
• Layer 3 or IP rerouting is too slow
• Layer 0 or Layer 1 may be limited
• Layer 0 or Layer 1 mechanisms can not see
higher layer operations
• Interoperability of protection mechanisms
between multi-vendor LSRs in core MPLS
networks.
MPLS Protection Principles
• MPLS protection switching
• Fast MPLS layer protection
• No assumptions about the underlying layer
1 or layer 2 transport mechanisms or their
protection mechanism.
Objectives of MPLS Protection
• Fast recovery of the working traffic
• Should be specified for an LSP,
PMTP(Protected MPLS Traffic Portion), or
PMTG (Protected MPLS Traffic Group).
• Specified for traffic on an end-to- end LSP
or for a segment of an LSP.
Objectives of MPLS Protection
(Cont’)
• Not adversely effect other network
operations.
• No interference among protection domains.
• Compatible with lower layers.
• Avoid Network layer violations.
Protection Configuration
• Dynamic
• Pre-negotiate
Protection Activation
• Global (end-to-end or centralized)
• Local (distributed)
Protection Span
• Link protection
• Path protection
Protection Modes
• Revertive
• Non-revertive
Protection Switching Options
• 1+1 Protection
• 1:1, 1:n, and n:m Protection
Failure Detection
• Loss of Signal: A signal is not detected at
an interface
• Link Failure: Link probing mechanism
fails
• Loss of Packets:Excessive discarding of
packets at an LSR interface
An MPLS path recovery
mechanism
• Liveness message to detect faults
• Special tree structure to distribute fault
and/or recovery information
• Permit recovery mechanisms at different
layers to coexist
• Lightweight notification mechanism
• Minimize delays of a recovery cycle
Core MPLS Path Protection
Components
•
•
•
•
•
Working Path
Recovery Path
Path Switch LSR (PSL)
Path Merge LSR (PML)
Intermediate LSR
Reverse Notification Tree (RNT)
• Can be established in association with the
working path
• Only one RNT is required for all the
working paths that merge
• Can be implemented either at Layer 3 or at
Layer 2
Illustration of MPLS protection
configuration
Protection Domain
• Definition:
the set of LSRs which the
working path and its corresponding
recovery path are routed over
• LSPs merge
Relationship between protection
domains
• with different RNTs
– Independent
– Overlap
• with the same RNT
Multiple Faults
Configuration
• Establishing a Recovery/Protection Path
• Creating the RNT
• Engineering a Protection Domain
Establishing a
Recovery/Protection Path
• working path and its corresponding
recovery path would be specified during
LSP setup
– Path selection algorithm (running at a
centralized location or at an ingress LSR)
– Administrative configuration
• Inverse cross-connect table
Fault Detection
• Unidirectional Link Fault
– Downlink Fault
– Uplink Fault
• Bi-directional Link Fault or Node Fault
Fault Processing
•
•
•
•
Fault Notification
Switch Over
Switch Back
----Finished----
Domains With different RNTs
(Independent)
Domains With different RNTs
(Overlap)
Domains With same RNT
Graph of Switch Over
Inverse cross-connect table
Reference
•
•
•
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"Survivable WDM Mesh Networks, Part I -Protection", S.Ramamurthy and B.
Mukherjeee, IEEE INFOCOM'99, 1999
"Survivable WDM Mesh Networks, Part I -Restoration", S.Ramamurthy and B.
Mukherjeee, IEEE INFOCOM'99, 1999
"Wavelength Requirements and Survivability in WDM Cross-Connected Networks", N.
Wauters, ECOC'94
"Dynamic Routing of Bandwidth Guaranteed Tunnels with Restoration", Murali
Kodialam (Bell Labs, Lucent Technologies), T. V. Lakshman (Bell Labs, Lucent
Technologies) IEEE INFOCOM 2000
"Wavelength conversion in WDM networking", B. Ramamurthy and B. Mukherjee,
IEEE Journal on Selected Areas in Communications, Sept. 1998, vol.16, (no.7):1061-73.
"Optical Burst Switching (OBS) - A New Paradigm for an Optical Internet", C.Qiao, in a
special issue of J. High Speed Networks (JHSN) on WDM Networks, Vol. 8, No. 1, pp.
69-84
Reference (Cont’)
•
•
•
•
•
•
•
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"Choices, Features and Issues in Optical Burst Switching", C.Qiao, to appear in Optical
Networks .
"MPLS Traffic Engineering : A Choice of Signaling Protocols "- White paper comparing
RSVP and CR-LDP for label path distribution. By Data Connection
"A Unified Approach to Network Survivability for Teletraffic Networks: Models,
Algorithms and Analysis",D. Medhi, IEEE Trans. on Communications, Vol. 42, pp. 534548, 1994.
"Multiprotocol Label Switching Architecture", <draft-ietf-mpls-arch-06.txt>
"A Framework for Multiprotocol Label Switching", <draft-ietf-mpls-framework-05.txt>
"Framework for MPLS Based Recovery", <draft-makam-mpls-recovery-frmwrk-00.txt>
"Protection/Restoration of MPLS Networks", <draft-makam-mpls-protection-00.txt>
"A Path Protection/Restoration Mechanism for MPLS Networks", <draft-chang-mplspath-protection-00.txt>