Download Control and Traffic Management

Control and Traffic
Management
Alfredo Reyes
Paper: Banerjee et al.: ” Generalized multiprotocol
label switching: an overview of signaling
enhancements and recovery techniques”
Overview
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•
•
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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
o
o
o
Explicitly routed label switched paths (LSPs)
Label swapping used to support multiple routing
Forwarding equivalence classes (FECs)
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 lowerpriority 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.)
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