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(Slide set by Norvald Stol/Steinar Bjørnstad2013)
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Outline• 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
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Introduction• IP -> MPLS
=> Datagram to Virtual Connection (VC) (point-to-point)
• Explicitly routed label switched paths (LSPs) established before information transport – independent of actual routing paradigm
• Label swapping used as forwarding paradigm• Forwarding equivalence classes (FECs)• Label hierarchy / Label stacking
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Introduction (2)• Constraint based routing
- traffic engineering (QoS differentiation)- fast reroute (after failure)- diversity routing (disjoint alternative paths for protection)
• Routing protocols (e.g. OSPF) must exchange sufficient information for ”constraint”
• Resource reservation protocol with traffic engineering (RSVP-TE) is used to establish LSP/label forwarding states along path.(The alternative CR-LDP is not used any more)
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Introduction (3)Generalized MPLS:• Extensions to handle e.g. optical network
resources (OXC’s) (e.g. extensions of OSPF, RSVP-TE).
• Common control plane for packet and optical network
• New Link Management Protocol (LMP) for optical links.
• Support for (label) switching in time, wavelength and space domains – and a label hierarchy.
• Additional functionality to handle bidirectional links and protection/restoration.
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RSVP-TE and OSPF enhancements
• RSVP-TE (CR-LDP)– Initiate optical channel trails– For optical networks and other connection
oriented networks
• OSPF (IS-IS)– Advertise availability of resources– Bandwidth of wavelengths– Interface types– Other network attributes and constraints
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Enhancements to signaling• Control plane may be physically diverse from the
data plane.• Hierarchical LSPs
(Study the example in the article to see what establishing a new LSP may entail, start with LSP1)
• The suggested label: – An upstream node suggests an optimal label (fast)
• May be overridden by its downstream node (slower)
- In optical networks with limited wavelength conversion– Suggested wavelength (-label) to use is very useful
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Enhancements to signaling (2)Bidirectional LSP setup (New in GMPLS):• Bidirectional optical LSPs (lightpaths) are important for
network operators – Fate sharing– Protection and restoration – Same QoS in both directions, same resource demands
Problems with two independent LSPs in MPLS:• Additional delay in set-up (problem in protection)• Race conditions for scarce resources => lower probability of
success for both directions simultaneously• Twice the control overhead
In GMPLS: Single set of Path/Request and Resv/Mapping messages used to establish LSPs in both directions at once.
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Enhancements to signaling (3)Notify messages:• Added to RSVP-TE for GMPLS • Provides a mechanism for informing
nonadjacent nodes of LSP-related failures.– Inform nodes responsible for restoring
connection– Avoid processing in intermediate nodes
• Speed up – Failure detection and reaction – Re-establishment of normal operation
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GMPLS Protection and RestorationFour primary steps of fault management:• Detection
- should be handled at layer closest to failure, i.e. optical layer. E.g. ”Loss-of-light” (LOL), Bit Error Ratio, ..
• Localization- requires communication between nodes. LMP includes procedure for fault localization. – Channel fail message over separate control channel
• Notification- Notify message added to RSVP-TE signaling
• Mitigation– “Repairing the failure”
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GMPLS Protection and Restoration (2)
• Path switching (End-to-end)– Failures addressed at path end-points
• Line switching (local)– Action at intermediate transit nodes where the failure is detected
• Prot and rest. Terms not precisely defined: In practice used for fault handling in different time frames.
• ”Protection” – Fast – usually pre-allocated resources to handle failures quickly, – e.g. SDH/SONET: 50 ms – 100% extra resources and
simultaneous transmission. (1+1 protection)
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GMPLS Restoration
• When fault is handled after a failure has occurred – Dynamic resource allocation
• Usually at least one order of magnitude higher delay than protection
• Different levels of ”preparedness” – Pre-calculated routes or not; – Some resources reserved or not
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GMPLS Protection and Restoration (3)
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).• Span protection – between adjacent nodes (NB! Avoid
”fate sharing”):
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GMPLS Protection and Restoration (4)• 1+1 Path protection (disjoint paths):
• For M:N Path protection: back-up paths may be used for lower priority traffic in normal operation – preemption (Supported by GMPLS)
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GMPLS Protection and Restoration (5)• Restoration mechanisms:
• Alternative paths may be computed beforehand, but resources are seldom allocated before they are needed.
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Conclusion
• GMPLS is a good idea and do have a lot of nice functionality to handle the networks of the future!