Control and Traffic Management Paper: Banerjee et al.: ” Generalized multiprotocol label switching: an overview of signaling enhancements and recovery techniques” Alfredo Reyes

Overview Introduction Enhancements to signaling GMPLS protection and restoration techniques Conclusions

Introduction IP (connectionless network)=> Packet forwarding performed at each router (independently), based on destination address. (Multipoint-to-point path) Multiprotocol Label Switching (MPLS) => Connectivity abstraction (Point-to-point path)

Introduction (cont.) MPLS key concepts: o Explicitly routed label switched paths (LSPs) o Label swapping used to support multiple routing o Forwarding equivalence classes (FECs) o Label hierarchy via label stacking One application of MPLS o Constraint-based routing -> Compute paths that satisfy various requirements subject to a set of constraints.

Introduction (cont.) Constraint based routing purposes: - traffic engineering (QoS differentiation) - fast reroute (after failure) - diversity routing (disjoint alternative paths for protection) With MPLS constraint based routing the extensions to Open Shortest Path First (OSPF) and Intermediate system to Intermediate System (IS-IS) allows nodes to exchange information about network topology, resource availability and administrative constraints. This is used to compute an appropriate path.

Introduction (cont.) Resource reservation protocol with traffic engineering (RSVP-TE) or Constraint-Based Routing Label Distribution Protocol is used to establish LSP/label forwarding states along path. Some enhancements are required to address the characteristics of optical transport networks.

Introduction (cont.) Protocol extensions to MPLS => Generalized MPLS (GMPLS): Extensions to handle optical network resources (OXC’s) (e.g. extensions of OSPF, RSVP-TE). New Link Management Protocol (LMP) for optical networks. Additional functionality to handle bidirectional connections and protection bandwidth for lower- priority traffic.

Introduction (cont.) Using MPLS o A link or node failure along the routes of established service connections could only be handled locally, or along the nodes of the path. GMPLS o Failures can be reported to a centralized management system. The devices detect a failure, report it and determine spare capacity available on other routes. Then restore the service connection circumventing the point of failure.

Overview Introduction Enhancements to signaling - Hierarchical LSP setup - The suggested label - Bidirectional LSP setup - Notify messages GMPLS protection and Restoration techniques Conclusions

Enhancements to signaling GMPLS requires that an LSP start and end on similar types of devices to terminate signaling requests. The control plane is not only separate from the data plane but may be physically diverse from it too. Enhancements - Hierarchical LSP setup - The suggested label - Bidirectional LSP setup - Notify messages

Enhancements to signaling (cont.) Hierarchical LSPs o Occurs when a new LSP is tunneled inside an existing higher-order LSP so that the preexisting LSP serves as a link along the path of the new LSP. Low order LSPs trigger the formation of higher order LSPs The suggested label: o GMPLS signaling allows a label to be suggested by an upstream node May be overridden by a downstream node (slower) –Useful in optical networks with limited wavelength conversion capability –It permits an upstream node along a service path to start configuring its hardware with the suggested label before the downstream node communicates a label to it.

Enhancements to signaling (cont.)

Bidirectional LSP setup Bidirectional optical LSPs (lightpaths) are a requirement for many optical networking service providers. o Traffic engineering requirements: Fate sharing Protection and restoration Resource requirements (latency and jitter) Problems establishing a bidirectional LSP using two independent LSPs in MPLS: o Additional delay in set-up (problem in protection) o Race conditions for scarce resources => lower probability of success for both directions simultaneously o Twice the control overhead

Enhancements to signaling (cont.) Notify messages: Provides a mechanism for informing nonadjacent nodes of LSP-related failures. o Inform nodes responsible for restoring connection o Avoid processing in intermediate nodes Speed up o Failure detection and reaction o Re-establishment of normal operation

Overview Introduction Enhancements to signaling - Hierarchical LSP setup - The suggested label - Bidirectional LSP setup - Notify messages GMPLS protection and Restoration techniques - Protection mechanisms (Span/Path protection) - Restoration mechanisms Conclusions

GMPLS Protection and Restoration Fault management consists of 4 primary steps: Detection o Should be handled at layer closest to failure, i.e. optical layer. E.g. ”Loss-of-light” (LOL), signal to noise ratio optically measured bit error rate, dispersion, crosstalk and alternation. Localization o Requires communication between nodes to determine where the failure has occurred. LMP includes a fault localization procedure (in optical and optoelectrical networks). ChannelFail message over a control channel separate from data channel Notification - Notify message added to RSVP-TE signaling Mitigation o “Repairing the failure”

GMPLS Protection and Restoration (cont.) The distinction between protection and restoration is centered on the different time scales in which they operate o Protection requires preallocated resources and is designed to react to failures rapidly. (< 200 ms) Typically requires 100 percent resource redundancy o Restoration relies on dynamic resource establishment Can be computationally expensive if the backup paths are not precalculated.

GMPLS Protection and Restoration (cont.) Protection and restoration are addressed using: Path switching (End-to-end) o Failures addressed at path end-points o Divided into: Path protection – Secondary paths are preallocated Path restoration – Connections are rerouted (dynamically or using precalculated paths Line switching (local) o Action at intermediate transit nodes where the failure is detected o Divided into: Span protection – Traffic switched to an alternate parallel channel Line restoration – Traffic switch to an alternate route

GMPLS Protection and Restoration (cont.) Nomenclature for protection mechanisms: 1+1 protection: simultaneous transmission of data on two different paths. M:N protection: M preallocated back-up paths shared by N connections. (1:N is most usual; 1:1 also relevant).

GMPLS Protection and Restoration (cont.) Span protection o Carried out between two adjacent nodes and involves switching to a backup channel when a failure occurs. In GMPLS the link protection type (LPT) is advertised so that span protection can be used in route calculation. o 1+1 Requires twice the connection bandwidth to replicate the data on both channels. o M:N Failures must be first localized before the switchover can occur, then RSVP Path refresh message to refresh LSP state. Minimizes the potential backup channel (label) conflict when protection switching

GMPLS Protection and Restoration (cont.) Path protection o Addressed at the end nodes and requires switching to an alternate path when a failure occurs. o 1:1 The connection is transmitted simultaneously over two disjoint paths and the terminator node choose the best signal based on the integrity of the signal. o M:N Back-up paths may be used for lower priority traffic in normal operation. Preemption if there is a failure on the primary path.

GMPLS Protection and Restoration (cont.) Restoration mechanisms: o Designed to react to failures quickly and use bandwidth efficiently. Involves dynamic resource establishment and route calculation. (Requires more time to switch than protection techniques) o Restoration can be implemented at the source or an intermediate node.

GMPLS Protection and Restoration (cont.) Line restoration o Traffic is switched via an alternate route around a failure, a new path is selected at an intermediate node. o Beneficial for connections that span multiple hops and/or large distances (latency is reduced). o The constraints used for routing the connection must be forwarded so that an intermediate node (doing restoration) calculates an appropriate alternate route. Path restoration o Switches traffic to an alternate route around a failure, where the new path is selected at the source node. o Precomputed and preallocated resources enables a faster restoration process unless are claimed by higher priority connections.

GMPLS Protection and Restoration (cont.) Path restoration: o On receipt of a failure notification, the source node computes the path to be used dynamically and signals for a new connection to be set up.

Overview Introduction Enhancements to signaling - Hierarchical LSP setup - The suggested label - Bidirectional LSP setup - Notify messages GMPLS protection and Restoration techniques - Protection mechanisms (Span/Path protection) - Restoration mechanisms Conclusions

Conclusions The functionality delivered by GMPLS allows network operators to scale their networks well beyond current limitations implicitly created by the segregation of the transport network. The signaling capabilities allow the use of high capacity infrastructures that support fast provisioning of connection services. The flexible M:N protection and restoration capabilities allow efficient addressing of network survivability, while accepting new types of services.

References Banerjee, A.; Drake, L.; Lang, L.; Turner, B.; Awduche, D.; Berger, L.; Kompella, K.; Rekhter, Y.; “Generalized multiprotocol label switching: an overview of signalling enhancements and recovery techniques”, Communications Magazine, IEEE, Volume: 39, Issue: 7, July 2001, Pages:144 – 151