Controllers in MPLS-TE networks

MPLS uses Label Switched Paths (LSPs), a type of lightweight virtual circuit. The IP Traffic Engineering (TE) capability of MPLS uses special LSPs to finely adjust IP traffic flows. MPLS thus extends existing IP protocols and makes use of MPLS forwarding capabilities to provide a sort of native TE. MPLS-TE applications or controllers as required per RFC 2702 reduce the impact of network failures and increase service availability of the MPLS forwarding. They solve:

Explicit routing

MPLS-TE brings explicit routing capabilities to MPLS networks. An originating Label Switching Route (LSR) can setup/tear down a TE Label Switched Path (LSP) to a terminating LSR through an explicitly defined path containing a list of intermediate LSRs. An offline tool or a Path Computation Element can perform path computation independently and leaves TE LSP signaling to the LSRs. Computation might be partial with loose routing mechanisms that lets the intermediate or boundary LSR to complete the path.

Constraint-based routing

MPLS-TE also extends the MPLS routing capabilities with support for constraint-based routing. Instead using a single metric as Interior Gateway Protocol (IGP) typically computes, constraint-based routing can take into account more detailed information about network constraints and policy resources. MPLS-TE extends link-state protocols (IS-IS and OSPF) to distribute such information. Constraint-based routing and explicit routing allow an originating LSR to compute a path that meets some requirements to a terminating LSR and setup a TE LSP through that path.

Fast ReRoute

MPLS-TE supports also local repair of TE LSPs using Fast ReRoute (FRR) mechanism. The node immediately next to the failure is responsible for rerouting the traffic and is the headend of the backup TE LSP. FRR can reroute traffic in tens of milliseconds as per RFC 4090 defines. This mechanism can be used in link failure and even node protection.

Make-Before-Break

The capability to reroute an established TE LSP is critical in case of administrative maintenance for preplanned intervention or bandwidth modification or also in case of failure or disruptions. Of course in such case, it is desirable not to disrupt traffic, or adversely impact network operations while LSP tunnels rerouting is in progress. This adaptive and smooth rerouting requirement necessitates establishing a new LSP tunnel and transferring traffic from the old LSP tunnel onto it before tearing down the old LSP tunnel. Because the old and new LSP tunnels might compete with each other for resources on network segments which they have in common, this competition can result the new LSP tunnel from being established. As defined in RFC 3209, using RSVP to establish LSP tunnels solves this problem "very elegantly" by using such so called Make-Before-Break mechanism.

MARBEN MPLS-TE Controllers

Marben provides a ready made controller that interacts between the protocols needed MARBEN RSVP-TE, MARBEN OSPF-TE or MARBEN ISIS-TE, the MPLS cross-connect fabric and the management protocols of the nodes.

overview
MARBEN MPLS Controllers architecture

MARBEN MPLS controllers solve:

  • the Setup - teardown of LSP tunnels through a simple and high level API. It hides the complexity of the manipulation of RSVP-TE objects,
  • the computation of the tunnel using the Constrained-SPF algorithms,
  • the Make-Before-Break mechanism for bandwidth modification and route changing,
  • the Protection through Fast Reroute mechanism for link and node protection in both mode, one-to-one and facility backup,
  • the graceful restart mechanism on both IGPs and RSVP-TE for recovering gracefully from an interruption in service,
  • the full read/write/create access to the MPLS-TE and Tunnel MIB.

As an extension of the MPLS-TE framework and as a consequence of the Marben' GMPLS expertise, Marben does supply also the End-to-End protection as per RFC 4873 as a ready made features into such controllers:

  • Full LSP rerouting (full or preplanned with extra traffic)
  • Shared mesh restoration
  • 1:N protection with extra traffic
  • 1+1 unidirectional and bidirectional protection

The controllers may also interact with MARBEN PCE depending the policy applied to the path computation, locally or through the help of a Path Computation Element.

MARBEN MPLS controllers have been used also with third party offer for the routing, and thus demonstrating its modularity in the field.

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