CSC Survivability Anuj Dewangan Parinda Gandhi

Outline  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 Layer

Need 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 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 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 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 Protection 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 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 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 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 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 Protection Dedicated Path Protection

Dynamic 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

Outline  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 IP

Survivability 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

Outline  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

IP over WDM Networks

IP 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 Models  Defines interconnection between the IP and the optical network  Overlay Model: Two separate control planes The IP layer acts as a client to the Optical layer The internal topology of the optical network is not visible to the IP networks Communication between the layers is through UNIs IP router register their IP addresses with the optical network and request for lightpath creation or deletion

IP over WDM Network Interconnection Models  Peer model: There is only a single control plane Hence the optical domain is transparent to the IP routers Each OXC also need to be an IP router and be IP addressable The 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

Outline  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

Dynamic 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

Dynamic Provisioning/Protection Scheme

 F’ not directly connected to A’  Not enough bandwidth available from the logical topology  New lightpath from A’ to F’ needs to be setup

Dynamic Provisioning/Protection Scheme  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

Dynamic Provisioning/Protection Scheme

Outline  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 IP over WDM

IP 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 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  End-to-End Path Protection (Path level)  Local protection (link level)  Local loopback  Rerouting Ingress LSREgress LSR LSP 1 LSR LSP 2 LSP 1 LSP 2 LSP 1 End-to-End Path Protection

Failure 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 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

Physical failure at the WDM layer  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

Physical failure at the WDM layer  Escalation strategies for coordinating multi-layer service recovery -Bottom-up -Top-down IP/MPLS WDM Signaling IP/MPLS WDM Signaling Bottom-up Top-down

Outline  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

Restoration Scheme in IP over WDM Networks

Restoration 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 LSP 2 LSR/OXC LSP 1 IP router Optical network LSP 2

Two 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

Two layer recovery mechanism Algorithm for Optical layer recovery  Construct a graph G based on physical topology where each edge containing vertices 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

Two layer recovery mechanism  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 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

References  Dongyun Zhou and Suresh Subramaniam, “Survivability in Optical Networks”, IEEE,  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

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