Optical Networks (3-4)-Network Survivability
Instructor: Xiaohong JiangSchool of Information Science
大学院情報科学研究科姜 暁鴻 助教授
Lecture 3: Network Survivability
SurvivabilityProtectionOptical Networks EvolutionProtection for Point-to-Point LinksProtection for Ring NetworksProtection for Mesh Networks
3
4
Outline
SurvivabilityProtectionOptical Networks EvolutionProtection for Point-to-Point LinksProtection for Ring NetworksProtection for Mesh Networks
Survivability
DefinitionWhy Survivable Optical Networks
Survivability DefinitionSurvivability of a network can be defined as its ability to continue providing service in the presence of failure(s). A network is survivable if it has a certain degree of survivability.
A survivable network A non-survivable network
A
IPRouter
OADMB
SONET Terminal
C D
IPRouter
SONET Terminal
E
IPRouter F IP
Router
OLT
OXC
Lightpath λ1
λ1
λ2 λ2
λ2
λ1
A
IPRouter
OADMB
SONET Terminal
C D
IPRouter
SONET Terminal
E
IPRouter F IP
Router
OLT
OXC
Lightpath λ1
λ1
λ2 λ2
λ2
λ1
Why Survivable Optical Networks
Potential bandwidth of one optical fiber exceeds several tens Tbps (note that the bandwidth of copper cable is only a few Mbps). A single failure can disrupt millions of users and result in millions of dollars of lost revenue to users and operators of a network.Note: The most likely failure event is fiber cut (link failure) and the protection is the key technique used to ensure survivability.
Link failure(fiber cut)Switch
failure
Outline
SurvivabilityProtectionOptical Networks EvolutionProtection for Point-to-Point LinksProtection for Ring NetworksProtection for Mesh Networks
ProtectionProtection DefinitionWorking and Protection PathsDedicated and Shared ProtectionRevertive and Nonrevertive ProtectionUnidirectional and Bidirectional Protection SwitchingPath Switching, Span Switching, and Ring Switching
Protection DefinitionProtection is to provide some redundant capacity within a network and automatically reroute traffic around the failure using this redundant capacity.
ProtectionProtection DefinitionWorking and Protection PathsDedicated and Shared ProtectionRevertive and Nonrevertive ProtectionUnidirectional and Bidirectional Protection SwitchingPath Switching, Span Switching, and Ring Switching
Working and Protection PathsWorking paths carry traffic under normal operation;Protection paths provide alternate paths to carry the traffic in case of failure.
Working and protection paths are usually diversely routed (link-disjoint) so that both path are not lost in the case of a single failure.
Working path
Protect path
ProtectionProtection DefinitionWorking and Protection PathsDedicated and Shared ProtectionRevertive and Nonrevertive ProtectionUnidirectional and Bidirectional Protection SwitchingPath Switching, Span Switching, and Ring Switching
Dedicated and Shared ProtectionDedicated protection provides each working path its own dedicated protection path;Shared protection allows bandwidth sharing among the protection paths of connections if the working paths of these connections will not fail simultaneously (usually link-disjoint).
Working path
Protect path
Working path
Protect path
Working path
Protect path
Working path
Protect path
Dedicated protection Shared protection
ProtectionProtection DefinitionWorking and Protection PathsDedicated and Shared ProtectionRevertive and Nonrevertive ProtectionUnidirectional and Bidirectional Protection SwitchingPath Switching, Span Switching, and Ring Switching
Revertive and NonrevertiveProtection
Revertive protection automatically switch the traffic back from protection path onto the working path once the working path is repaired.Nonrevertive protection allows the traffic remains on the the protection path after the working path is repaired.
Working path
Protect path
Working path
Protect path
Working path
Protect path
Working path
Protect path
Dedicated protection(revertive or non revertive)
Shared protection(revertive )
ProtectionProtection DefinitionWorking and Protection PathsDedicated and Shared ProtectionRevertive and Nonrevertive ProtectionUnidirectional and Bidirectional Protection SwitchingPath Switching, Span Switching, and Ring Switching
Unidirectional and Bidirectional Protection Switching
Working
Protection
Protection switching can be unidirectional or bidirectional.Unidirectional protection switching: In the event of a single fiber cut, only one direction of traffic is switched over to the protection fiber and the other direction remains on the original working fiber. (Suitable for dedicated protection schemes)Bidirectional protection switching: In the event of a single fiber cut, both directions are switched over to the protection fibers(Suitable for shared protection schemes)
(a) Normal operation (b) Unidirectional protectionswitching
(c) Bidirectional protectionswitching
Working
Protection
×
Protection
Working
×
ProtectionProtection DefinitionWorking and Protection PathsDedicated and Shared ProtectionRevertive and Nonrevertive ProtectionUnidirectional and Bidirectional Protection SwitchingPath Switching, Span Switching, and Ring Switching
Path Switching, Span Switching, and Ring Switching
Path Switching, Span Switching, and Ring Switching involve how and where the traffic is rerouted in the event of a failure.Path switching: connection is rerouted end to end from its source to its destination along an alternate path.Span switching: connection is rerouted on a spare link between the nodes adjacent to the failure.Ring switching: connection is rerouted on a ring between the nodes adjacent to the failure.
Working path(a) Normal operation (b) Path switching (c) Span switching (d) Ring switching
Outline
SurvivabilityProtectionOptical Networks EvolutionProtection for Point-to-Point LinksProtection for Ring NetworksProtection for Mesh Networks
Optical Networks Evolution
::
λ3
λ2λ1
λ3λ1
λ2
λ3λ3
λ2λ1 λ2λ1
λ3λ1
λ2
Opt
ical
Pat
h C
ontr
olla
bilit
y
Stat
ic C
ontr
olD
ynam
ic C
ontr
ol
1990’s 2010’s
Point-to-point WDM transmission
OADM-based WDM Ring Network
OXC-based WDM Mesh Network
OADM
OXC
Time
Network Autonomously Controlled by IndividualPhotonic MPLS Routers
MPLS: Multi-Protocol Label SwitchingOADM:Optical Add/Drop Multiplexer OXC: Optical Cross-connect
Photonic MPLS Routers
Fast Optical Burst Data Switching Network
Outline
SurvivabilityProtectionOptical Networks EvolutionProtection for Point-to-Point LinksProtection for Ring NetworksProtection for Mesh Networks
Protection for Point-to-Point Links (Automatic Protection Switching )
1+1 protection 1:1 protection 1:N protection
1+1 Protection
SwitchSplitter
Source Destination
In 1+1 protection, traffic is transmitted simultaneously on two separate fibers (usually over disjoint routes) from source to the destination, and the destination simply selects one of the two fibers for reception. If that fiber is cut, the destination simply switches over to the other fiber and continues to receive data.1+1 protection is fast but requires high bandwidth redundancy.
1:1 Protection In 1:1 protection, there are still two fibers from source to the destination. However, traffic is transmitted over only one fiber at a time (working fiber). If that fiber is cut, the source and the destination both switch over to the other protection fiber.1:1 protection is not as quick as 1+1 protection in restoring traffic, but results in a better bandwidth utilization.
SwitchSwitch
Source Destination
Working fiber
Protection fiber
1:N Protection 1:N protection is a generalization of 1:1 protection, in which N working fibers share s single protection fiber. This scheme can handle the failure of any single working fiber. 1:N protection is very efficient in terms of bandwidth utilization.
SwitchSwitch
Source Destination
Protection fiber
SwitchSwitch
SwitchSwitch
Switch Switch
1
2
N
::
Low-priority data
Outline
SurvivabilityProtectionOptical Networks EvolutionProtection for Point-to-Point LinksProtection for Ring NetworksProtection for Mesh Networks
Protection for Ring Networks (Self-Healing Rings)
Ring networksUnidirectional Path-Switched RingBidirectional Line-Switched Ring (BLSR)BLSR-Span SwitchingBLSR-Ring SwitchingRing Interconnection-a simple wayRing Interconnection-dual homing
Ring Networks
2
1
4
3
fiber
A ring is the simplest topology that is 2-connected, that is, provide two separate paths between any pair of nodes. Ring networks are popular for carrier as well as enterprise networks.
Ring networksUnidirectional Path-Switched RingBidirectional Line-Switched Ring (BLSR)BLSR-Span SwitchingBLSR-Ring SwitchingRing Interconnection-a simple wayRing Interconnection-dual homing
Protection for Ring Networks
Unidirectional Path-Switched Ring (UPSR)In a UPSR, one fiber (a path) is used as working fiber and the other as the protection fiber. Traffic is transmitted simultaneously on the working fiber in the clockwise directionand on the protection fiber in the counterclockwise direction. A UPSR is essentially 1+1 protection.
Ring networksUnidirectional Path-Switched RingBidirectional Line-Switched Ring (BLSR)BLSR-Span SwitchingBLSR-Ring SwitchingRing Interconnection-a simple wayRing Interconnection-dual homing
Protection for Ring Networks
Bidirectional Line-Switched Rings (BLSR)In a four-fiber BLSR, two fibers (a line) are used as working fibers and, two are used for protection. Unlike a UPSR, working traffic in a BLSR can be carried on both directionsalong the ring (usually along shortest path between two nodes). A BLSR is essentially 1:1 protection. The BLSR employs two protection mechanisms: span switching and ring Switching.
Ring networksUnidirectional Path-Switched RingBidirectional Line-Switched Ring (BLSR)BLSR-Span SwitchingBLSR-Ring SwitchingRing Interconnection-a simple wayRing Interconnection-dual homing
Protection for Ring Networks
BLSR-Span SwitchingIn span switching, if a transmitter or receiver on a working fiber fails, the traffic is routed onto the protection fiber in the same span (Span switching can also be used to restore traffic in the event of fiber cut,provided the protection fibers on thatspan are routed separately from the working fibers. However, this is usually not the case. So ring switching is usually used to restore traffic in case of fiber or cable cut.)
Span switching
Ring networksUnidirectional Path-Switched RingBidirectional Line-Switched Ring (BLSR)BLSR-Span SwitchingBLSR-Ring SwitchingRing Interconnection-a simple wayRing Interconnection-dual homing
Protection for Ring Networks
BLSR-Ring SwitchingIn the ring switching, the traffic on the failed link is rerouted around the ring on the protection fibers between the nodes adjacent to the failure.Note: BLSRs (1:1 protection) are more efficient than UPSRs(1+1 protection), because BLSRs provide spatial reuse capabilities by allowing protection bandwidth to be shared between spatially separated connections.
Ring switching
Ring networksUnidirectional Path-Switched RingBidirectional Line-Switched Ring (BLSR)BLSR-Span SwitchingBLSR-Ring SwitchingRing Interconnection-a simple wayRing Interconnection-dual homing
Protection for Ring Networks
Ring Interconnection-a simple wayThe entire network typically consists of multiple rings interconnected with each other, and a connection may have to be routed through multiple rings to get t its destination.
The simplest way for rings interconnection is to connect the drop sides of two AMDs on different rings back to back. Note this interconnection is broken if one of the AMDs fails or there is a problem with the cabling between the two ADMs.
Ring networksUnidirectional Path-Switched RingBidirectional Line-Switched Ring (BLSR)BLSR-Span SwitchingBLSR-Ring SwitchingRing Interconnection-a simple wayRing Interconnection-dual homing
Protection for Ring Networks
Ring Interconnection-Dual homingDual homing makes use of two hub nodes to perform the interconnection.
In dual homing, each end node is connected to two hub nodes so as to be able to recover from the failure of a hub node or the failure of any interconnection between the hub nodes.
Outline
SurvivabilityProtectionOptical Networks EvolutionProtection for Point-to-Point LinksProtection for Ring NetworksProtection for Mesh Networks
Protection for Mesh NetworksThere are two main pre-designed protection techniques against single-link failure in WDM Mesh networks:•Link-based protection•Path-based protection
5
6
3
4
1
2
Working path
Link-based protection
Path-based protection
Link-based Protection for Mesh Networks
In link-based protection, a protection path is reserved for each link based on ring switching.
Dedicated link protection:A protection lightpath is dedicated to a particular link. If the protection paths of two links are overlapped, then different wavelengths must be used in the overlapped links.
Shared link protection : It allows different backup paths to share a wavelength on the overlapping links, if the corresponding working channels are on different links. It utilizes capacity more efficient than dedicated link protection
5
6
3
4
1
2
5
6
3
4
1
2
λ1 λ2
λ1
Path-based Protection for Mesh Networks
In path-based protection, a protection path is reserved for each working path.
Dedicated path protection: It provides each working path its own dedicated protection path;
Shared path protection: Itallows bandwidth sharing among the protection paths of connections if the working paths of these connections will not fail simultaneously (usually link-disjoint).
Working path
Protect path
Working path
Protect path
Working path
Protect path
Working path
Protect path