Requirements for Ring Protection in MPLS-TP

1
Requirements for Ring Protectionin MPLS-TP

• John Drake (John.E.Drake2_at_boeing.com)
• Adrian Farrel (adrian_at_olddog.co.uk)

2
What do service providers say?

• Service providers give us two fundamental
  requirements
• We want to deploy MPLS-TP in rings.
• We want to protect our traffic
• That means we need to provide ring protection
  (i.e., protection in rings)
• But what is a ring?

3
There is a base requirement

• draft-jenkins-mpls-mpls-tp-requirements-01
• req-47 If protection is supported then
• MPLS-TP MAY support mechanisms that are optimized
  for specific network topologies (e.g. ring).
  These mechanisms MUST be interoperable with the
  mechanisms defined for arbitrary topology (mesh)
  networks.
• If optimized mechanisms for ring topologies are
  supported then they MUST support switching times
  within 50 ms (depending on CV rate configuration)
  assuming a reference network of a 16 node ring
  with less than 1200 Km of fiber, as defined by
  ITU SG15, Question 9.
• This has caused some confusion.
• In order to define optimized mechanisms, we must
  define what we are trying to optimize, and how we
  will judge the solution. That means we need
  specific requirements written down.

4
What is a ring?Deployment Scenarios

• The network is the ring
• Deploy routers to replace TDM equipment
• Ring as a layer network
• The virtual rings imposed on a mesh network to
  provide connectivity

5
Physical rings

• Physical topology is easy
• An arrangement of two or more nodes each with
  exactly two line-side interfaces

• Each node may have multiple
  customer-facing interfaces
• That means that the full extent of the
  MPLS-TP network is the ring
• The ring can be used to support
  connectivity as a layer network
• We can extend this idea to allow ring-
  interconnect to make larger networks

6
Layered Network

• A ring in the server layer can provide a set of
  TE links in the client layer
• The TE links are protected by the protection
  within the ring

7
Virtual Rings

• We can super-impose a ring onto a mesh
• This creates a virtual or logical ring
• We can apply ring properties (whatever they are)
  to this ring
• This ring could be operated as a layer (scenario
  2) or as if a real ring (scenario 1)

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Detailed Requirements

• Supplied by ITU based on draft version of G.8132
• T-MPLS Shared Protection Ring
• Summarised and clarified a little
• A packet transport ring protection scheme shall
• Be applicable at a packet transport layer, for
  both logical and physical ring topologies
• Operate in the data plane, i.e., be independent
  of a control plane or a management plane
• Have the capability to coordinate protection
  switching actions with resiliency mechanisms
  possibly operating at the server layer
• Support switching time within 50 ms
• Protect pt-to-pt and pt-to-mp connections
• Have the capability to disable ring protection on
  selected links (depending on operators need)
• Maximize the recovery of all possible traffic,
  both in case of single and multiple failures
  (including link and/or node failure)
• Allow administrative protection switching
• Support priority logic to negotiate and
  accommodate simultaneous requests
• Support bidirectional switching (unidirectional
  protection switching is not required)
• Support revertive switching (non-revertive is not
  required)
• Prevent protection switch thrashing
• Support the sharing of ring protection bandwidth
  for best-effort traffic and prioritised
  protection
• Support inter-ring connectivity with single and
  dual node connectivity
• Support vendor interoperability in a single ring
  or at the shared node/link of interconnected
  rings

9
Recent Additional Requirements

• Know/control where my traffic is in the network
• Obviously a bit more simple in a ring

10
Requirements are not solutions

• Important not to drive requirements by statements
  of existing solutions in other technologies
• Requirements should be stated clearly in abstract
  terms
• Requirements should not be unnecessarily limited
  to rings
• Where-ever possible applicable to general mesh
  networks
• Even optimization requirements might be met by
  general solutions
• We will attempt to meet requirements using
  existing techniques (this is a JWT requirement)
• MPLS data plane techniques (label stacking, etc.)
• Must operate without using a control plane
• MPLS control plane (fast reroute)
• GMPLS control plane
• Link level protection
• End-to-end protection
• Segment protection
• New solutions if and only if necessary to meet
  requirements

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What next?

• Do we really need an I-D to describe ring
  protection requirements?
• Which of the requirements listed would not be
  applicable in generic mesh networks?
• But maybe there are other requirements (e.g.,
  optimization requirements)
• It will be valuable to have applicability
  statements
• How to use existing mechanisms to provide
  protection in ring deployments
• Show how all ring protection requirements are
  solved
• Include scenarios for optimization cases
• This could all be included in the Protection and
  Survivability Framework I-D
• draft-sprecher-mpls-tp-survive-fwk-00.txt