Introduction to Protection & Restoration for OBS

Copyright, 2000, SUNY, Univ. at Buffalo

Presented by

Zaoyang Guo & Dahai Xu

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

• 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

• Time used: Protection -- Short; Restoration -- Long

• Reliability: Protection -- mainly for single fault; Restoration -- can survive under multiplex faults

• Implementation: Protection -- Simple; Restoration -- Complex

Comparison between Protection & Restoration (Continued)

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

• "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’)

• "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. 534-548, 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-mpls-path-protection-00.txt>