Precision Time Protocol
over MPLS
draft-ronc-ptp-mpls-00.txt
PWE3 WG IETF Chicago 2007
Ron Cohen
[email protected]
Agenda
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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
Align Master to Slave Time/Frequency
• Sync and Follow-Up messages downstream
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Measure Master to Slave Delay
• Delay-Request and Delay-Response exchange
• End to End (E2E) measurement
Measure per-link Delay (Optional)
• Pdelay-Request, Pdelay-Response and PdelayResponse-Follow-Up
• Peer to Peer (P2P) measurement
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Protocol Operation (Cont.)
Master-Slave Hierarchy Setup and
Maintenance
• Announce messages sent from master to slaves
• Used to relay synchronization status and build hierarchy
Signaling
• Signaling messages exchanged between clock for
negotiation, setup etc.
Clock Management
• Management messages sent between manager and clocks
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Main PTP Entities
Ordinary clock
• Grand Master is the source of time/frequency
• Ordinary slave clocks are the synchronization clients
Boundary Clock
• Connects between different networks or administrative
domains
• Does not forward PTP messages
• Slave on one port and Master/Passive on others
Transparent Clock
• Forwards PTP messages
• Measures and Corrects PTP messages to compensate for
queuing processing and propagation delays
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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
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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
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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
Identity
Port
Communication
Path
Domain
• Each clock has a globally unique clock identity
• Based either on EUI-64 / MAC address / Private ID
networks
• A logical access point of a PTP clock for PTP
communications to the communications network.
• A segment of a network enabling direct
communication between two PTP ordinary or
boundary clocks.
• A logical grouping of PTP clocks that synchronize to
each other using the PTP protocol, but that are not
necessarily synchronized to PTP clocks in another
PTP domain.
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PTP Entities over MPLS
• Communication Paths
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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
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Different Domains are sent on separate PTP LSPs
• PTP ports
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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)
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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
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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
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Setup of symmetric LSPs
 Use of RSVP-TE for tunnel LSP
 Automatic Protection switching
• Use of P2MP and MP2MP LSPs
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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
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Non-IP encapsulation over MPLS
Relevant experts and expertise
• Suggest to add to PWE3 agenda
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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
[email protected]
Multi-Segment PTP Scenario
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