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MPLS Traffic Engineering: RSVP-TE, FRR, Bandwidth Constraints

Segment Routing reduced the need for state in the dataplane, but RSVP-TE remains the gold-standard for bandwidth-reserved, fast-rerouting LSPs in service provider transport. OcNOS implements the full RSVP-TE stack (CSPF, FRR link/node protection, DS-TE class-types, and auto-bandwidth) alongside SR-MPLS, on the same chassis.

RSVP-TE LSP with FRR Backup

A four-router ring carrying a primary RSVP-TE LSP from PE-1 to PE-3. The primary path (solid) is the CSPF-computed shortest path that meets the 1G bandwidth constraint; the FRR backup (dashed) protects the primary against a P-A link or node failure.

MPLS-TE topology: four-router ring with a primary RSVP-TE LSP and a Fast Reroute backup path with bandwidth labels
MPLS-TE: four-router ring with a primary RSVP-TE LSP, an FRR backup path, and bandwidth reservations.

Where MPLS-TE still wins

Segment Routing handles most modern transport elegantly, but there are still two things RSVP-TE does better: strict bandwidth admission control across the network, and Fast Reroute backups that pre-program a detour LSP at every PLR. For carriers with strict SLA contracts, capacity-managed wholesale services, or per-class-type DiffServ guarantees, OcNOS delivers a complete RSVP-TE stack that runs alongside (or instead of) SR-MPLS on the same hardware.

The OcNOS MPLS-TE implementation

RSVP-TE

Path / Resv signalling

Full RSVP-TE signalling with explicit-route (ERO), record-route (RRO), graceful restart, hello-based detection, and refresh reduction.

CSPF

Constraint-based path

CSPF using IGP-TE extensions (OSPF-TE / IS-IS-TE): bandwidth, affinity, hop-count, SRLG-disjoint, and admin-group constraints.

FRR

Link / node protection

Facility-mode FRR with bypass tunnels at every PLR. Sub-50 ms repair on link, node, or SRLG failure with bandwidth-aware backup selection.

DS-TE

Class-types & bandwidth pools

Russian-doll and maximum-allocation bandwidth constraint models; per-class-type (CT0-CT7) reservations with strict admission control.

Auto-Bandwidth

Adaptive reservation

Auto-bandwidth resizing based on observed utilization with configurable adjust-interval and overflow / underflow thresholds.

Inter-AS TE

Per-domain expansion

Inter-AS TE LSPs with per-domain ERO expansion and PCE-based stitching for multi-AS service provider deployments.

What you get with OcNOS MPLS-TE

  • Coexists with SR-MPLS. Run RSVP-TE for legacy services and SR-MPLS for new ones on the same router: same IGP, same forwarding plane.
  • Carrier-grade scale. Tested with thousands of LSPs per node, including auto-bandwidth resize churn and large FRR backup meshes.
  • Operational tooling. CLI and gNMI streaming for LSP state, RSVP neighbour status, and bandwidth-pool utilization per class-type.
  • PCE-ready. PCEP support for stateful PCE deployments, including PCInitiate for controller-driven LSP placement.
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FAQ

Frequently asked questions

What is MPLS Traffic Engineering?
MPLS-TE forwards traffic along bandwidth-reserved, explicitly routed label-switched paths rather than the IGP shortest path. RSVP-TE signals each LSP and CSPF computes a path that meets bandwidth, affinity, hop-count, and SRLG-disjoint constraints, giving carriers strict admission control across the network.
What is RSVP-TE Fast Reroute (FRR)?
Fast Reroute pre-programs a backup bypass tunnel at every point of local repair, so traffic switches to a detour in under 50 ms when a protected link or node fails. OcNOS supports facility-mode FRR with bandwidth-aware backup selection for link, node, and SRLG protection.
When should I use MPLS-TE instead of Segment Routing?
Segment Routing handles most modern transport with less dataplane state, but RSVP-TE still does two things better: strict network-wide bandwidth admission control and pre-programmed FRR backups. It suits carriers with strict SLAs, capacity-managed wholesale services, or per-class DiffServ guarantees.
Can OcNOS run MPLS-TE and SR-MPLS together?
Yes. OcNOS runs the full RSVP-TE stack alongside SR-MPLS on the same router, sharing the same IGP and forwarding plane. Operators can keep RSVP-TE for legacy bandwidth-reserved services while moving new services to SR-MPLS, with no separate hardware.
What is DS-TE in OcNOS?
DS-TE (Diffserv-aware MPLS-TE, RFC 4124) extends traffic engineering with per-class-type bandwidth pools. OcNOS supports Russian-doll and maximum-allocation constraint models with per-class-type CT0 through CT7 reservations and strict admission control.
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