control and traffic management paper: banerjee et al.: ” generalized multiprotocol label...

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 routingo Forwarding equivalence classes (FECs)o Label hierarchy via label stacking

• One application of MPLSo 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.

• GMPLSo 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


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 simultaneouslyo Twice the control overhead


Notify messages:• Provides a mechanism for informing nonadjacent nodes

of LSP-related failures.o Inform nodes responsible for restoring connectiono Avoid processing in intermediate nodes

• Speed up o Failure detection and reaction o Re-establishment of normal operation

Overview• Introduction• Enhancements to signaling


• GMPLS protection and Restoration techniques- Protection mechanisms (Span/Path protection)- Restoration mechanisms

• Conclusions

GMPLS Protection and RestorationFault management consists of 4 primary steps:

• Detectiono 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

• Mitigationo “Repairing the failure”

GMPLS Protection and Restoration (cont.)

• The distinction between protection and restoration is centered on the different time scales in which they operateo 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.


Protection and restoration are addressed using:

• Path switching (End-to-end)o Failures addressed at path end-pointso 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

detectedo Divided into:

• Span protection – Traffic switched to an alternate parallel channel• Line restoration – Traffic switch to an alternate route


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.


• 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.


• 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 restorationo 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.


• 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


• 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

control and traffic management paper: banerjee et al.: ” generalized multiprotocol label...

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