Generalized Multiprotocol Label Switching: An Overview of Signaling Enhancements and Recovery Techniques IEEE Communications Magazine July 2001

Outline Introduction Enhancements to Signaling GMPLS Protection & Restoration Techniques Conclusions

Introduction (1/3) MPLS is based on Separation of forwarding information (label) from the content of the IP header Use of a single forwarding paradigm at data plane to support multiple routing paradigms at control plane Use of different technologies and link layer mechanisms to realize label swapping forwarding paradigm Flexibility in the formation of forwarding equivalence classes (FECs) The concept of a forwarding hierarchy via label stacking

Introduction (2/3) Recent work: extend MPLS control plane, specifically MPLS constraint-based routing, from routers/ATM switches to optical crossconnects Using MPLS as the foundation for connection establishment and a common control plane Simplify network operations and management Provide a wide range of deployment scenarios, ranging from overlay to peer Reuse and extend existing routing and signaling protocols thus minimizing risks and reducing time to market for advanced optical switching equipment

Introduction (3/3) GMPLS: extensions to MPLS Enhancements to RSVP-TE and CR-LDP signaling protocols for optical transport networks Enhancements to OSPF and IS-IS IGPs to advertise availability of optical resources in the network A new link management protocol for optical networks Ability to establish bidirectional connections in a single request Ability of fault isolation, fault localization, fault notification and fault mitigation

Enhancements to Signaling Enhancements to the label distribution protocols, RSVP-TE and CR-LDP Hierarchical LSP Setup The Suggested Label Bidirectional LSP Setup Notify Messages

Hierarchical LSP Setup (1/2)

Hierarchical LSP Setup (2/2)

The Suggested Label GMPLS allows a label to be suggested by an upstream node Valuable when set up a bidirectional LSP using paired Tx and Rx interfaces to the same physical port Useful in optical subnetworks with limited wavelength conversion capability Permit an upstream node along a service path to start hardware configuration before the downstream node communicates a label to it Downstream node may reject the suggested label and pass a different label upstream, the upstream node must accept the label

Bidirectional LSP Setup LSPs in basic MPLS architecture are unidirectional, a bidirectional LSP uses two unidirectional LSP in opposite directions Increased setup latency for LSP establishment Twice the control overhead Complicated route selection Difficult to provide a clean interface for SONET equipment which may rely on bidirectional hop-by-hop paths for protection switching Use of a single set of Path/Request and Resv/ Mapping messages to establish bidirectional LSPs

Notify Messages A node passing transit connections should be able to notify the node responsible for restoring the connections when failures occur The Notify message has been added to RSVP-TE for GMPLS to provide a mechanism for informing nonadjacent nodes of LSP-related failures Application: to notify when the control plane of a link fails but the data plane (LSP) is still functional, such link is referred to as degraded link

GMPLS Protection and Restoration Techniques Features Technique ProtectionRestoration Require preallocated resources, react to failures rapidly Rely on dynamic resource establishment, longer restore time Path Switching Path ProtectionPath Restoration Line Switching Span ProtectionLine Restoration

Protection Mechanisms (1/3) Nomenclature 1+1 protection: payload data transmitted over two disjoint path and a selector at receiving node M:N protection: M preallocated backup paths shared between N primary paths 1:N protection 1:1 pretection Mechanisms Span Protection Path Protection

Protection Mechanisms (2/3)

Protection Mechanisms (3/3)

Restoration Mechanisms (1/2) Line restoration A new path is selected at an intermediate node Beneficial for connections spanning multiple hops and/or large distances May break TE requirements Path restoration The new path is selected at the source node Alternate routes may be precomputed by the head-end of the connection and cached for future use May reuse nodes in the original path

Restoration Mechanisms (2/2)

Conclusions GMPLS will constitute an integral part of next- generation data and optical networks. The functionality delivered by GMPLS allows network operators to scale their network well beyond current limitations. The signaling capabilities of GMPLS will allow service providers to quickly build out high- capacity agile infrastructures. Flexible M:N protection and restoration capabilities of GMPLS allow efficient addressing of network survivability.