Precision Time Protocol over MPLS

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Precision Time Protocol over MPLS

• draft-ronc-ptp-mpls-00.txt
• PWE3 WG IETF Chicago 2007
• Ron Cohen
• ronc_at_resolutenetworks.com

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Agenda

• IEEE1588/PTP in a nutshell
• Encapsulation
• PTP LSPs
• LSP Setup and Signaling
• Open issues
• Summary and Proposal

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• PTP in a nutshell

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Protocol Operation
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Protocol Operation (Cont.)
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Main PTP Entities
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Sync and Delay-Req formats
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Encapsulations

• PTP defined over
• Ethernet
• UDP/IPv4
• UDP/IPv6
• DeviceNet, ControlNet, IEC 61158
• PTP is used as part of 802.1as "Standard for
  Local and Metropolitan Area Networks - Timing and
  Synchronization for Time-Sensitive Applications
  in Bridged Local Area Networks

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• PTP over MPLS Encapsulation

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PTP MPLS Encapsulation
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PTP MPLS Encapsulation

• PTP header immediately follows PW label
• Transport Specific Field set to zero for all PTP
  messages
• Compliant with generic PW control word as
  specified in RFC4385
• A PTP Forwarding Equivalence Class (FEC) is
  associated with the PW label
• Benefits
• Bandwidth efficient
• Easy to identify PTP Event messages
• Easy to process correction field in hardware

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• Tunnel and PTP LSPs
• Scope limited to Point to Point LSP

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Tunnel and PTP LSPs

• Tunnel LSP switches MPLS tunnel labels
• Tunnel LSP connects between PTP aware LSRs
• E2E PTP LSP switches PTP/PW labels
• E2E LSP connects between PTP ordinary and
  boundary clocks

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Tunnel and PTP LSPs (Cont.)

• Peer to Peer PTP LSPs connects between PTP peers
  for Pdelay Measurements only

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Similarity to Multi-Segment PW

• Transparent clocks behave somewhat similar to PW
  stitching
• Manipulates the correction field of PTP messages
  In addition to PW label switching
• Same administrative domain and PSN on both ends

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PTP Entities
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PTP Entities over MPLS

• Communication Paths
• A set of one or more E2E LSPs
• Point to Point Communication Path or
• Each ordinary or boundary clock port must form an
  PTP LSP with all non-slave-only PTP ports.
• PTP domains
• Different Domains are sent on separate PTP LSPs
• PTP ports
• PTP port used per E2E PTP LSP or
• Single PTP port used for multiple LSPs

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MPLS Communication Path Example
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• PTP LSP Setup and Signaling

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PTP LSP Setup

• Use LDP Extensions for setup of PWs (RFC3036)
• Extended LDP discovery
• Bidirectional LSPs setup
• Downstream unsolicited label binding
• Use Forwarding Equivalence Class (FEC) to
  identify the meaning of the label and identify
  the PW type
• New FEC AII and AGI defined
• Generalized PWiD (GID) FEC used
• End-to-End or Peer-to-Peer PTP PW Types
• Port Number and Clock Identity (Port identity)
  used as Attachment Individual Identifiers (AII)
• Domain number used as Attachment Group Identifier
  

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PTP FEC
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• Open issues and Next Steps

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Open Issues

• Traffic Engineering
• Setup of symmetric LSPs
• Use of RSVP-TE for tunnel LSP
• Automatic Protection switching
• Use of P2MP and MP2MP LSPs
• FEC collision
• Discovery and Aggregation Friendly AII types
• LDP capability negotiation
• PTP management messages

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Summary and Proposal

• PTP direct mapping to MPLS is required
• PWE3 is the place to advance this work
• Non-IP encapsulation over MPLS
• Relevant experts and expertise
• Suggest to add to PWE3 agenda
• Possibly move to TICTOC if chartered
• Coordinate with other WG if required
• Suggest to adopt draft-ronc-ptp-mpls-00 as
  candidate for WG document

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Thank You

• Ron Cohen
• ronc_at_resoluteNetworks.com

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Multi-Segment PTP Scenario