PCE Communication Protocol Generic Requirements (draft-ietf-pce-comm-protocol-gen-reqs-01.txt)

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PCE Communication ProtocolGeneric
Requirements(draft-ietf-pce-comm-protocol-gen-req
s-01.txt)
Design Team Jerry Ash (ATT) Alia Atlas
(Avici) Arthi Ayyangar (Juniper) Nabil Bitar
(Verizon) Igor Bryskin (Independent
Consultant) Dean Cheng (Cisco) Durga Gangisetti
(MCI) Kenji Kumaki (KDDI) Jean-Louis Le Roux
(France Telecom) Eiji Oki (NTT) Raymond Zhang (BT
Infonet)
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PCE Communication ProtocolGeneric
Requirements(draft-ietf-pce-comm-protocol-gen-req
s-01.txt)

• lists generic requirements for PCE communication
  protocol
• application-specific requirements to be addressed
  in separate requirements documents
• possible PCE-based applications include
• intra-area path computation
• inter-area path computation
• inter-AS intra provider inter-AS inter-provider
  path computation
• multi-layer path computation virtual network
  topology computation/reconfiguration

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Open Issues

• requirements for less constrained path
  requests/response
• currently no consensus for less-constrained path
• concerns expressed over complexity
• need more WG feedback
• requirements for responsiveness session
  maintenance
• more detailed requirements on throttling messages
  under overload
• specify boundary numbers on scalability ( of
  PCCs, PCEs, domains, path requests, etc.)
• need to clearly state supported policy models
  corresponding requirements/implications
• avoid feature creep
• suggest less featured PCE more robust protocol
  construction
• need to progress application-specific
  requirements
• Inter-area
• Inter-AS Inter-SP
• MRN VNT
• PCE protocol proposal needs to identify how
  generic application-specific requirements are
  met
• once consensus reached on major issues, propose
  moving I-D to WG last call

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Backup Slides
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PCE Communication Protocol ApplicationExternal
PCE Node
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PCE Communication Protocol ApplicationMultiple
PCE Path Computation
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PCE Communication Protocol ApplicationMultiple
PCE Path Computationwith Inter-PCE Communication
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PCE Communication Protocol (PCECP)Generic
Requirements

• commonality of PCC-PCE PCE-PCE communication
• MUST use one protocol for both cases
• client-server communication
• MUST support PCC/PCE request message to request
  path computation
• MUST support PCE response message with computed
  path
• SHOULD support unsolicited communication PCE-PCC
• NON-REQUIREMENT to maintain PCC-PCE session
• request/response exchange defines limited
  association between requester responder
• transport
• MAY use existing transport protocol or operate
  directly over IP
• transport protocol MAY satisfy reliability
  security requirements
• transport protocol MUST NOT limit size of messages

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PCE Communication Protocol (PCECP)Generic
Requirements

• Path Computation Requests PCECP MUST
• include source destination
• support path constraints (e.g., bandwidth, hops,
  affinities to include/exclude)
• e.g., exclude points of failure in new path if
  LSP setup fails
• support path reoptimization inclusion of a
  previously computed path
• allow to select/prefer from advertised list of
  standard objective functions/options
• SHOULD be able to select vendor-specific/experimen
  tal objective function/option
• allow to customize objective function/options
• i.e., set parameters for individual objective
  functions
• specification of objective functions parameters
  required in protocol extensibility
• PCE response negative if objective function not
  supported
• PCE MAY execute objective functions not
  advertised to PCC
• e.g. policy based path computation for load
  balancing instructed by management plane

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PCE Communication Protocol (PCECP)Generic
Requirements

• Path Computation Requests PCECP
• MAY request a less-constrained path
• SHOULD support inclusion of request for
  less-constrained path, including one or more
  constraint-relaxation policys
• Path Computation Responses PCECP MUST
• return computed path(s) other elements
• return any explicit path acceptable for
  MPLS/GMPLS LSP specified as RSVP-TE ERO
• path(s) may be consist of strict or loose hops
• hop may be non-simple abstract node
• PCE response negative if constraints cannot be
  satisfied
• MAY include reasons for failure constraints to
  relax to achieve positive result
• MAY provide less-constrained path
• SHOULD support inclusion of reasons for failure
  less-constrained path reflecting
  constraint-relaxation policys

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PCE Communication Protocol (PCECP)Generic
Requirements

• Cancellation of Pending Requests
• PCC/PCE MUST be able to cancel pending request
• Multiple Requests Responses PCECP MUST
• support multiple path computation requests in
  request message
• limit by configuration number of requests within
  a message
• support multiple computed paths in response
  message
• corresponding to same request (e.g. load
  balancing) or distinct requests
• support continuation correlation where related
  requests or computed paths cannot fit within one
  message
• maximum message size maximum number of requests
  per message
• MAY be exchanged through PCE messages to PCC
• MAY be indicated in the request message
• MAY form part of PCE capabilities advertisement
  PCE-DISC-REQ
• implementation MAY limit message size to avoid
  big message from delaying small message

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PCE Communication Protocol (PCECP)Generic
Requirements

• Reliable Message Exchange PCECP MUST
• include reliability
• achieved by PCECP itself or transport protocol
• allow detection recovery of lost messages to
  occur quickly not impede operation of
  communication protocol
• handle overload situations without significant
  decrease in performance
• e.g., through throttling of requests
• provide
• acknowledged message delivery with retransmission
• in order message delivery or facility (e.g.,
  message numbering) to restore order
• message corruption detection
• flow control back-pressure to throttle requests
• rapid partner failure detection
• informed rapidly of failure of PCE-PCC connection
• functionality SHOULD NOT be added to PCECP if
  transport protocol provides it

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PCE Communication Protocol (PCECP)Generic
Requirements

• Secure Message Exchange PCECP MUST
• be secure
• provided by PCECP or transport protocol
• support mechanisms to prevent
• spoofing (e.g., authentication)
• snooping (e.g., encryption)
• DOS attacks
• Request Prioritization PCECP MUST
• allow PCC to specify priority of a request
• priority used by PCE to service high priority
  requests before lower priority requests
• Unsolicited Notifications PCECP SHOULD
• support unsolicited notifications PCE-PCC,
  PCE-PCE, or PCC-PCE
• facilitates communication of updated paths,
  alerts, etc.

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PCE Communication Protocol (PCECP)Generic
Requirements

• Asynchronous Communication PCECP MUST
• allow asynchronous communication
• PCC MUST NOT have to wait for response before
  making another request
• allow order of responses differ from order of
  requests
• e.g., when path request messages have different
  priorities
• Communication Overhead Minimization PCECP SHOULD
• minimize communication overhead
• give particular attention to message size
• other considerations include
• number of messages exchanged to arrive at answer
• amount of background messages used by PCECP or
  transport protocol to keep alive any session or
  PCE-PCC association
• processing cost associated with PCECP messages
  (as distinct from path computation)

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PCE Communication Protocol (PCECP)Generic
Requirements

• Extensibility PCECP MUST
• allow introduction of new path computation
  constraints, diversity types, objective
  functions, optimization methods, parameters, etc.
• without requiring modifications to the protocol
• be easily extensible to support applications
  including
• intra-area path computation
• inter-area path computation
• inter-AS intra provider inter-AS inter-provider
  path computation
• multi-layer path virtual network topology
  computation/reconfiguration
• SHOULD be easily extensible to support future
  applications not currently in scope of PCE
  working group
• e.g., P2MP path computations, etc.
• application specific requirements will be
  addressed in separate requirements documents

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PCE Communication Protocol (PCECP)Generic
Requirements

• Scalability PCECP MUST
• scale at least linearly with increase in number
  of
• PCCs
• PCEs
• PCCs communicating with a single PCE
• PCEs communicated to by a single PCC
• PCEs communicated to by another PCE
• domains
• path requests
• handling bursts of requests

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PCE Communication Protocol (PCECP)Generic
Requirements

• Constraints PCECP MUST support
• MPLS-TE and GMPLS generic constraints
• Bandwidth
• Affinities inclusion/exclusion
• Link, Node, SRLG inclusion/exclusion
• Maximum end-to-end Delay metrics
• Hop Count
• MPLS-TE specific constraints
• Class-Type
• GMPLS specific constraints
• Switching Type, Encoding Type
• Protection type
• TBD constraints

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PCE Communication Protocol (PCECP)Generic
Requirements

• Support for Different Service Provider
  Environments PCECP MUST
• operate in various SP environments, such as
• MPLS-TE and GMPLS networks
• centralized distributed PCE path computation
• single multiple PCE path computation
• Policy Support PCECP MUST
• allow for policies to accept/reject requests
• allow PCC to determine reason for rejection
• e.g. filtering intra-AS requests reject requests
  from another AS
• allow for notification of policy violation
• policy details left to application-specific PCECP
  requirements
• policies, configuration, applicability out of
  scope

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PCE Communication Protocol (PCECP)Generic
Requirements

• Aliveness Detection PCECP MUST
• allow PCC to check liveliness of PCEs PCE to
  check liveliness of PCCs
• provide partner failure detection
• MAY be met by PCECP or transport protocol design
• PCC/PCE Failure Response
• procedures MUST be defined for PCE/PCC failures
• PCC MUST be able to clear any pending request to
  a PCE
• RECOMMENDED that PCC select another PCE upon
  detection of PCE failure
• PCE MUST be able to clear pending requests from a
  PCC
• e.g. when it detects PCC failure or request
  buffer is full

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PCE Communication Protocol (PCECP)Generic
Requirements

• Protocol Recovery PCECP
• MUST support resynchronization of information
  requests between sender receiver
• SHOULD minimize repeat data transfer
• SHOULD allow PCE to respond to computation
  requests issued before failure without requests
  being re-issued
• stateful PCE SHOULD be able to resynchronize/recov
  er states (e.g., LSP status, paths) after restart