csc 778 - survivability anuj dewangan parinda gandhi

CSC 778 - SurvivabilityCSC 778 - Survivability

Anuj Dewangan

Parinda Gandhi

OutlineOutline

Survivability in Optical Layer

Survivability in IP

IP over WDM

Dynamic Provisioning/Protection Scheme

Survivability in IP over WDM

Restoration Scheme for IP over WDM

Networks

Survivability in Optical LayerSurvivability in Optical Layer

Need for Optical Layer SurvivabilityNeed for Optical Layer Survivability

Optical fibers in WDM networks carry a

large amount of data

The optical layer can provide faster

service recovery than the higher layers

The optical layer survivability can

provide protection and restoration with

significant cost savings.

Cons:

Because protocol transparent, it is

unable to detect increased Bit Error Rates

(BER)

Failures and Optical Layer SurvivabilityFailures and Optical Layer Survivability

Link failure, node and channel failures

Link failure much more likely

Single failure and multiple failure

Survivability against multiple failures

is prohibitively costly and unlikely.

Our discussion is restricted to single

link failures only

Optical Layer Survivability ParadigmsOptical Layer Survivability Paradigms

Static Protection

Spare network resources are reserved during

network design or at the time of connection

establishment for protection against network

failures.

Faster but inefficient in resource utilization

Dynamic Restoration

The network searches dynamically for spare

network services after network failures occurs

Better in resource utilization but slower and

has no guarantees

Static ProtectionStatic Protection

Two ways to classify

Dedicated protection and shared

protection

Dedicated Protection: 1:1 and 1+1

Shared Protection: 1 : N

Link protection and path protection

Link protection: Dedicated and shared

link protection

Path protection: Dedicated and shared

path protection

Static Protection – Dedicated ProtectionStatic Protection – Dedicated Protection

1 + 1 Protection

If the working link fails, the receiver only needs to simply switch over to the protection link The advantage of 1+1 protection is that it can provide very fast service recovery.

Static Protection – Dedicated ProtectionStatic Protection – Dedicated Protection

1 :1 Protection

If the working link fails, the receiver and sender both need to switch over to the protection link In absence of failure, the protection link can be used to transmit a signal that carries low priority traffic Because only the receiving end can detect the failure, the receiving end must use a signaling protocol to notify the transmitting end of the failed link so that the transmitter can switch over to the protection link

Static Protection – Shared ProtectionStatic Protection – Shared Protection

1:N Protection

It can handle the failure of any single working link only. It increases link utilization of the protection link.

Line Protection

Static Protection – Link ProtectionStatic Protection – Link Protection

Span Protection A backup path or protection path is reserved for each link of the primary path during the establishment of the connection The recovery is handled at the end nodes of the failed link The source and destination nodes are unconscious of the link failure The wavelength used for the backup path should be the same as that used for the primary path

Static Protection – Path ProtectionStatic Protection – Path Protection

A back up path is reserved for the primary path on an end-to-end basis during the establishment of a connection The backup path should be link disjoint This requires the end nodes of the failed link to inform the source and destination nodes of the link failure Longer service recovery time Backup path wavelength need not be the same

Shared Path Protection

Static Protection – Path ProtectionStatic Protection – Path Protection

Dedicated Path Protection

Dynamic RestorationDynamic Restoration

Two ways to classify

Link Restoration End nodes of a failed link dynamically search for

a backup path for each connection that traverses

the failed link

If no backup path found, the connection is

blocked

Path Restoration Source and Destination nodes of each connection

dynamically search for a backup path on an end-to-

end basis in event of a link failure

If no backup path found, the connection is

blocked

OutlineOutline


Survivability in IP

IP over WDM




Networks

Survivability in IPSurvivability in IP

Survivability in IP layerSurvivability in IP layer

Achieved by rerouting through the

convergence of routing information after

the detection of a failure

Best effort in nature

Advantages:

Ability to find optimal routes through the

network

Ability to provide a finer granularity of

protection

Slow in nature

OutlineOutline


Survivability in IP

IP over WDM




Networks

IP over WDM NetworksIP over WDM Networks

IP over WDM Network ArchitectureIP over WDM Network Architecture

IP packets are directly carried over WDM networks Hence flexible bandwidth allocation has to be handled at the WDM layer: Dynamic provisioning

IP over WDM Network Interconnection ModelsIP over WDM Network Interconnection Models

Defines interconnection between the IP and the optical network Overlay Model:

Two separate control planesThe IP layer acts as a client to the

Optical layerThe internal topology of the optical

network is not visible to the IP networksCommunication between the layers is

through UNIsIP router register their IP addresses

with the optical network and request for lightpath creation or deletion

IP over WDM Network Interconnection ModelsIP over WDM Network Interconnection Models

Peer model:There is only a single control planeHence the optical domain is transparent

to the IP routersEach OXC also need to be an IP router

and be IP addressableThe routers in the IP network and

Optical network can run routing protocols like OSPF or IS-IS with appropriate extensions

Now, an edge router can create an end-to-end connection using MPLS based signaling

OutlineOutline


Survivability in IP

IP over WDM




Networks

Dynamic Provisioning/Protection Dynamic Provisioning/Protection SchemeScheme

Dynamic Provisioning/Protection SchemeDynamic Provisioning/Protection Scheme

Focuses on service reliability for Border LSRs It is a protection scheme It dynamically computes a primary lightpath and a backup path, when LSRs request a lightpath The flow is blocked if either the primary or the backup path fails to establish Initially, based on aggregated traffic demands, a virtual topology is designed by using optimization approach. A backup path is also reserved


F’ not directly connected to A’

Not enough bandwidth available from the logical topology

New lightpath from A’ to F’ needs to be setup


Need for a backup path Since bandwidth of backup path is α f(k) < f(k), logical topology A’-E’ and E’-F’ can be selected

OutlineOutline


Survivability in IP

IP over WDM




Networks

Survivability in IP over WDMSurvivability in IP over WDM

IP over WDMIP over WDM

WDM technologies with high bandwidth

capacity are going to play a dominant role

in future networks

In WDM, lightpaths are set up to provide

end-to-end connections between Optical

cross connects

IP/WDM is a simple example of multilayer

network where IP layer resides above an

optical network

Multilayer Survivability in IP over WDMMultilayer Survivability in IP over WDM

Protection/Restoration capability at IP

and WDM layer

IP layer provides a finer granularity of

protection

Example: Packet level or LSP level

WDM layer provides protection at a coarse

granularity

Example: Fiber or Wavelength level

Service Recovery at IP is slower than WDM

layer

MPLS based IP networks provide fast

restoration/protection capabilities

compared to IP layer

Mechanisms for MPLS recovery Mechanisms for MPLS recovery

End-to-End Path Protection (Path level)

Local protection (link level)

Local loopback

Rerouting

Ingress LSR Egress LSR

LSP 1

LSR

LSR LSR

LSR

LSP 2

LSP 1

LSP 2

LSP 2

LSP 1

End-to-End Path Protection

Failure detection in IP over WDMFailure detection in IP over WDM

Failure at IP/MPLS layer cannot be cannot

be detected at the WDM layer and vice

versa

Failure at IP/MPLS layer can only be

recovered by itself while failure at WDM

layer can be recovered by both layers

Important to coordinate service recovery

at IP/MPLS and WDM layer in an effective

manner

Physical failure at the WDM layerPhysical failure at the WDM layer

Strategies for service recovery at IP/MPLS

and WDM layers

- Parallel and Sequential Strategies

In parallel strategy service recovery is

initiated in IP/MPLS and WDM layers

simultaneously

Problems:

- Service recovery at WDM layer is faster

than IP

- Difficult to coordinate resulting in

insufficient resource utilization or even

failure in service recovery


In sequential strategy service recovery is

activated at the WDM and the IP/MPLS

layers in a sequential manner

Problem:

Escalate failure detected at the WDM layer

to IP/MPLS layer

Coordination can be implemented using

hold-off timer method or recovery token

method


Escalation strategies for coordinating

multi-layer service recovery

- Bottom-up

- Top-down

IP/MPLS

WDM

Signaling

Signaling

IP/MPLS

WDM

Signaling

Signaling

Bottom-up Top-down

OutlineOutline


Survivability in IP

IP over WDM




Networks

Restoration Scheme in IP over WDM Restoration Scheme in IP over WDM NetworksNetworks

Restoration scheme in IP/WDMRestoration scheme in IP/WDM

In which layer should one provide network

survivability ?

Survivability at each layer has its own

pros and cons

Solution: Two layer recovery mechanism

LSP 1

LSR/OXC LSR/OXC

LSR/OXC

LSP 2

LSP 2

LSR/OXC LSR/OXC

LSR/OXCLSP 1

LSP 1

IP router IP router

Optical network

LSP 2

LSP 2

Two layer recovery mechanismTwo layer recovery mechanism

Bottom-up approach

Restoration used instead of protection

Path switching used due to limited

wavelength resources around failed link

Full wavelength conversion is assumed at

every node in the network


Algorithm for Optical layer recovery

Construct a graph G based on physical

topology where each edge containing

vertices <s , d> represents there are

spare wavelengths in the link

On receiving failure notification for a

light path, at the source OXC Dijkstra’s

algorithm is used to compute a new light

path with minimum hops from source to

destination implying minimum number of

wavelengths are used to reroute the light

path


If the light path cannot be restored at

the Optical layer the IP layer has to take

care of rerouting the LSPs carried by the

affected light path.

Existing light paths with spare bandwidths

or new lightpaths can be can be

established to reroute the affected LSPs

Various algorithms have been proposed

Simulation resultsSimulation results

Topology

Performance of two layer restoration with recovery token is compared with single IP/MPLS restoration

Comparison of hold-off timer versus Recovery Token mechanism

ReferencesReferences

Dongyun Zhou and Suresh Subramaniam, “Survivability in Optical Networks”, IEEE, 2000.

Jun Zheng and Hussein T. Mouftah, “Optical WDM Networks-

Concepts and Design Principles”, Wiley, 2004

Arun K. Somani, “Survivability and Traffic Grooming in

WDM Optical Networks”, Cambridge University, 2006

Yinghua Ye, Chadi Assi, Sudhir Dixit, Mohammed A. Ali,

“A Simple Dynamic Integrated Provisioning/Protection

Scheme in IP over WDM Networks”, IEEE, 2001

Yang Qin, Lorne Mason, Ke Jia, “ Study on a Joint

Multiple Layer Restoration Scheme for IP over WDM

Networks”, IEEE, 2003

http://cufagradforum.files.wordpress.com/2007/05/questions.gif

Thank You

csc 778 - survivability anuj dewangan parinda gandhi

Documents

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failed link

single working link

outline survivability

network failures occursbetter

absence of failure

likely single failure

network design