Local Recovery In Multiple Link Failures

1
Distributed Local Recovery from Multiple Link
Failures in MPLS-TE Networks Andrea Fumagalli,
Marco Tacca, Kai Wu, Sudheer Vinukonda, Priti
Mahale Optical Networks Advanced Research
(OpNeAR) Lab
Finding an RLS
Local Recovery
Risk Level and Risk Link Set (RLS)

• Local Recovery Fast ReRoute (FRR)
• Restoration performed as close to point of
  failure as possible
• Backup path pre-computed and pre-signaled
• Global or local revert, make-before-break
• 10s of ms recovery
• Single failure assumption
• Fast failure detection
• Layer 2 (Sonet LOS etc.)
• RSVP Hello

• Risk Failure Probability (Unavailability or
  Frequency of failure)
• Risk level is a range of risk
• RLS is a set of link associated with a risk level
• Every failure scenario is represented by an RLS
• Aggregation of SRLGs
• Defined at the IP/MPLS layer
• Distributed by IGP extensions
• Static or dynamic

• Bottom up
• From IP-to-optical mapping
• Reliability information of all components
• Network layer
• IGP listener
• Combined

Fault Independent Approach
Hybrid Approach
Fault Dependent Approach

• Step 1 For each local failure pattern, there is
  a list of suspect RLSs
• Ex PLRA, Failed LinkA-B (A-F and A-D work)
• LRLS0,RLS2,RLS3,RLS4,RLS5,RLS7
• Step 2 Identify the most possible RLS or set of
  RLSs (logical RLS)
• Step 3 Find the facilities belonging to the
  (logical) RLS, and select bypass tunnel for the
  facility against the (logical) RLS

Local Recovery Procedure

• Divide the suspect RLS list into logical RLSs
  according to some rules
• Shorten the (RLS) detection time by reducing the
  requirement on remote failure information
• Increase the chance of finding a bypass tunnel by
  reducing the size of logical RLS

• Identify the exact RLS that fails
• (extra time)
• Select bypass tunnels for all facilities
• in the RLS

• No need to identify exact RLS
• Select bypass tunnels for all facilities in the
  RLS
• There is no bypass tunnel to protect facility A-B
  that avoids all the links contained in the list
  of suspected RLS L for any Risk Level.
• If the required Risk level is reduced to 2,
  PathA-F-G-H-I-C-E-B (cost6). With RL1
  PathA-D-B (the longer path A-I-G-H-I-C-B also
  works)

Simulation Setup
Bypass tunnel selection Monitoring time vs.
Correct RLS Selection, Fault Dependent
Bypass tunnel selection Monitoring time vs.
Correct RLS Selection, Hybrid Approach
Summary

• European Network
• Random RLS generation

• Proposed an RLS information model to incorporate
  multiple failures
• Extended FRR to support fast local recovery
  against multiple failures
• Investigated three approaches, fault dependent,
  fault independent and hybrid
• Traded recovery time with recovery ratio