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Versions: 00 01 02 03 04 05 06 07 draft-ietf-mpls-residence-time

MPLS Working Group                                             G. Mirsky
Internet-Draft                                                S. Ruffini
Intended status: Standards Track                                 E. Gray
Expires: January 4, 2016                                        Ericsson
                                                                J. Drake
                                                        Juniper Networks
                                                               S. Bryant
                                                           Cisco Systems
                                                           A. Vainshtein
                                                             ECI Telecom
                                                            July 3, 2015


               Residence Time Measurement in MPLS network
                  draft-mirsky-mpls-residence-time-07

Abstract

   This document specifies G-ACh based Residence Time Measurement and
   how it can be used by time synchronization protocols being
   transported over MPLS domain.

   Residence time is the variable part of propagation delay of timing
   and synchronization messages and knowing what this delay is for each
   message allows for a more accurate determination of the delay to be
   taken into account in applying the value included in a PTP event
   message.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 4, 2016.







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Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Conventions used in this document . . . . . . . . . . . .   3
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   4
   2.  Residence Time Measurement  . . . . . . . . . . . . . . . . .   4
   3.  G-ACh for Residence Time Measurement  . . . . . . . . . . . .   4
     3.1.  PTP Packet Sub-TLV  . . . . . . . . . . . . . . . . . . .   6
   4.  Control Plane Theory of Operation . . . . . . . . . . . . . .   7
     4.1.  RTM Capability  . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  RTM Capability Sub-TLV  . . . . . . . . . . . . . . . . .   8
     4.3.  RTM Capability Advertisement in OSPFv2  . . . . . . . . .   9
     4.4.  RTM Capability Advertisement in OSPFv3  . . . . . . . . .   9
     4.5.  RTM Capability Advertisement in IS-IS . . . . . . . . . .   9
     4.6.  RSVP-TE Control Plane Operation to Support RTM  . . . . .  10
     4.7.  RTM_SET Object  . . . . . . . . . . . . . . . . . . . . .  11
       4.7.1.  RSO Sub-objects . . . . . . . . . . . . . . . . . . .  12
   5.  Data Plane Theory of Operation  . . . . . . . . . . . . . . .  14
   6.  Applicable PTP Scenarios  . . . . . . . . . . . . . . . . . .  15
   7.  One-step Clock and Two-step Clock Modes . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     8.1.  New RTM G-ACh . . . . . . . . . . . . . . . . . . . . . .  17
     8.2.  New RTM TLV Registry  . . . . . . . . . . . . . . . . . .  18
     8.3.  New RTM Sub-TLV Registry  . . . . . . . . . . . . . . . .  18
     8.4.  RTM Capability sub-TLV  . . . . . . . . . . . . . . . . .  19
     8.5.  IS-IS RTM Application ID  . . . . . . . . . . . . . . . .  19
     8.6.  RTM_SET Object RSVP Class Number, Class Type and Sub-
           object Types  . . . . . . . . . . . . . . . . . . . . . .  19
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  21



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     11.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   Time synchronization protocols, Network Time Protocol version 4
   (NTPv4) [RFC5905] and Precision Time Protocol (PTP) Version 2
   [IEEE.1588.2008] can be used to synchronize clocks across network
   domain.  Measurement of the time a PTP event message spends
   traversing a node (using precise times of receipt at an ingress
   interface and transmission at an egress interface), called Residence
   Time, can be used to improve the accuracy of clock synchronization.
   This document defines new Generalized Associated Channel (G-ACh) that
   can be used in Multi-Protocol Label Switching (MPLS) network to
   measure Residence Time over Label Switched Path (LSP).  Mechanisms
   for transport of time synchronization protocol packets over MPLS are
   out of scope in this document.

   Though it is possible to use RTM over LSPs instantiated using LDP
   such scenarios are outside the scope of this document.  The scope of
   this document is on LSPs instantiated using RSVP-TE [RFC3209] because
   the LSP's path can be determined.

1.1.  Conventions used in this document

1.1.1.  Terminology

   MPLS: Multi-Protocol Label Switching

   ACH: Associated Channel

   TTL: Time-to-Live

   G-ACh: Generic Associated Channel

   GAL: Generic Associated Channel Label

   NTP: Network Time Protocol

   ppm: parts per million

   PTP: Precision Time Protocol

   LSP: Label Switched Path

   LSR: Label Switching Router

   OAM: Operations, Administration, and Maintenance



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   RRO: Record Route Object

   RSO: RTM Set Object

   RTM: Residence Time Measurement

   IGP: Internal Gateway Protocol

1.1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

2.  Residence Time Measurement

   Packet Loss and Delay Measurement for MPLS Networks [RFC6374] can be
   used to measure one-way or two-way end-to-end propagation delay over
   LSP or PW.  But these metrics are insufficient for use in some
   applications, for example, time synchronization across a network as
   defined in the Precision Time Protocol (PTP).  PTPv2 [IEEE.1588.2008]
   uses "residence time", the time it takes for a PTPv2 event packet to
   transit a node.  Residence times are accumulated in the
   correctionField of the PTP event messages, as defined in
   [IEEE.1588.2008], or of the associated follow-up messages (or
   Delay_Resp message associated with the Delay_Req message) in case of
   two-step clocks (detailed discussion in Section 7).  The residence
   time values are specific to each output PTP port and message.

   IEEE 1588 uses this residence time to correct the propagated time,
   effectively making these nodes transparent.

   This document proposes mechanism to accumulate packet residence time
   from all LSRs that support the mechanism across a particular LSP.
   The values accumulated in scratchpad fields of MPLS RTM messages can
   be used by the last RTM-capable LSR on an LSP to update the
   correctionField of the corresponding PTP event packet prior to
   performing the usual PTP processing.

3.  G-ACh for Residence Time Measurement

   RFC 5586 [RFC5586] and RFC 6423 [RFC6423] extended applicability of
   PW Associated Channel (ACH) [RFC5085] to LSPs.  G-ACh provides a
   mechanism to transport OAM and other control messages.  Processing by
   arbitrary transit LSRs can be triggered through controlled use of the
   Time-to-Live (TTL) value.  In a way that is analogous to PTP




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   operations, the packet residence time can be handled by the RTM
   capable node either as "one-step clock" or as a "two-step clock".

   The packet format for Residence Time Measurement (RTM) is presented
   in Figure 1

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version|   Reserved    |          RTM Channel          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                     Scratch Pad                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Type               |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             Value                             |
    ~                                                               ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 1: RTM G-ACh packet format for Residence Time Measurement

   o  First four octets are defined as G-ACh Header in [RFC5586]

   o  The Version field is set to 0, as defined in RFC 4385 [RFC4385].

   o  The Reserved field MUST be set to 0 on transmit and ignored on
      receipt.

   o  The RTM G-ACh field, value to be allocated by IANA, identifies the
      packet as such.

   o  The Scratch Pad field is 8 octets in length.  The first RTM-
      capable LSR MUST initialize the Scratch Pad field, it SHOULD set
      it to zero value.  The Scratch Pad is used to accumulate the
      residence time spent in each RTM capable LSR transited by the
      packet on its path from ingress LSR to egress LSR.  Its format is
      IEEE double precision and its units are nanoseconds.  Note:
      depending on one-step or two-step operation (Section 7), the
      residence time might be related to the same packet carried in the
      Value field or to a packet carried in a different RTM packet.

   o  The Type field identifies the type of Value that the TLV carries.
      IANA will be asked to create a sub-registry in Generic Associated
      Channel (G-ACh) Parameters Registry called "MPLS RTM TLV
      Registry".




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   o  The Length field contains the number of octets of the Value field.

   o  The optional Value field may be used to carry a packet of a given
      time synchronization protocol.  If packet data is carried in the
      RTM message, then this is identified by Type accordingly.  The
      data MAY be NTP [RFC5905] or PTP [IEEE.1588.2008].  It is
      important to note that the packet may be authenticated or
      encrypted and carried over MPLS LSP edge to edge unchanged while
      residence time being accumulated in the Scratch Pad field.  Sub-
      TLVs MAY be included in the Value field.

   o  The TLV MUST be included in the RTM message, even if the length of
      the Value field is zero.

3.1.  PTP Packet Sub-TLV

   Figure 2 presents format of a PTP sub-TLV that MUST be precede every
   PTP packet carried in RTM TLV.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             Type              |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Flags                         |PTPType|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            Port ID                            |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |           Sequence ID         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2: PTP Sub-TLV format

   where Flags field has format

     0                   1                   2
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |S|                      Reserved                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 3: Flags field format of PTP Packet Sub-TLV

   o  The Type field identifies PTP sub-TLV defined in the Table 19
      Values of messageType field in [IEEE.1588.2008].





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   o  The Length field of the PTP sub-TLV contains the number of octets
      of the Value field and MUST be 20.

   o  The Flags field currently defines one bit, the S-bit, that defines
      whether or not the current message has been processed by a 2-step
      node, where the flag is cleared if the message has been handled
      exclusively by 1-step nodes and there is no follow-up message, and
      set if there has been at least one 2-step node and a follow-up
      message is forthcoming.

   o  The PTPType indicates the type of PTP packet carried in the TLV.
      PTPType is the messageType field of the PTPv2 packet whose values
      are defined in the Table 19 [IEEE.1588.2008].

   o  The 10 octets long Port ID field contains the identity of the
      source port.

   o  The Sequence ID is the sequence ID of the PTP message carried in
      the Value field of the message.

4.  Control Plane Theory of Operation

   The operation of RTM depends upon TTL expiry to deliver an RTM packet
   from one RTM capable interface to the next along the path from
   ingress LSR to egress LSR.  This means that an LSR with RTM capable
   interfaces MUST be able to compute a TTL which will cause the expiry
   of an RTM packet at the next LSR with RTM capable interfaces.

4.1.  RTM Capability

   Note that RTM capability of a node is with respect to the pair of
   interfaces that will be used to forward an RTM packet.  In general,
   the ingress interface of this pair must be able to capture the
   arrival time of the packet and encode it in some way such that this
   information will be available to the egress interface.

   The supported modes (1-step verses 2-step) of any pair of interfaces
   is then determined by the capability of the egress interface.  In
   both cases, the egress interface implementation MUST be able to
   determine the precise departure time of the same packet and determine
   from this, and the arrival time information from the corresponding
   ingress interface, the difference representing the residence time for
   the packet.

   An interface with the ability to do this and update the associated
   ScratchPad in real-time (i.e. while the packet is being forwarded) is
   said to be 1-step capable.




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   Hence while both ingress and egress interfaces are required to
   support RTM, for the pair to be RTM-capable, it is the egress
   interface that determines whether or not the node is 1-step or 2-step
   capable with respect to the interface-pair.

   The RTM capability used in the sub-TLV shown in Figure 4 is thus
   associated with the egress port of the node making the advertisement,
   while the ability of any pair of interfaces that includes this egress
   interface to support any mode of RTM depends on the ability of that
   interface to record packet arrival time in some way that can be
   conveyed to and used by that egress interface.

   When an LSR uses an IGP to carry the RTM capability sub-TLV, the sub-
   TLV MUST reflect the RTM capability (1-step or 2-step) associated
   with egress interfaces and MUST NOT propagate this sub-TLV in IGP
   LSAs sent from a router which describe a particular interface that
   does not support the same capability for RTM messages it receives.

4.2.  RTM Capability Sub-TLV

   The format for the RTM Capabilities sub-TLV is presented in Figure 4

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Type(TBA5)          |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | RTM |                       Reserved                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 4: RTM Capability sub-TLV

   o  Type value will be assigned by IANA from appropriate registries.

   o  Length MUST be set to 4.

   o  RTM (capability) - is a three-bit long bit-map field with values
      defined as follows:

      *  0b001 - one-step RTM supported;

      *  0b010 - two-step RTM supported;

      *  0b100 - reserved.

   o  Reserved field must be set to all zeroes on transmit and ignored
      on receipt.




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   [RFC4202] explains that the Interface Switching Capability Descriptor
   describes switching capability of an interface.  For bi-directional
   links, the switching capabilities of an interface are defined to be
   the same in either direction.  I.e., for data entering the node
   through that interface and for data leaving the node through that
   interface".  That principle SHOULD be applied when a node advertises
   RTM Capability.

   A node that supports RTM MUST be able to act in two-step mode and MAY
   also support one-step RTM mode.  Detailed discussion of one-step and
   two-step RTM modes in Section 7.

4.3.  RTM Capability Advertisement in OSPFv2

   The capability to support RTM on a particular link advertised in the
   OSPFv2 Extended Link Opaque LSA [I-D.ietf-ospf-prefix-link-attr] as
   RTM Capability sub-TLV, presented in Figure 4, of the OSPFv2 Extended
   Link TLV.

   Type value will be assigned by IANA from the OSPF Extended Link TLV
   Sub-TLVs registry that will be created per
   [I-D.ietf-ospf-prefix-link-attr] request.

4.4.  RTM Capability Advertisement in OSPFv3

   The capability to support RTM on a particular link in OSPFv3 can be
   advertised by including an RTM Capability sub-TLV defined in
   Section 4.3 in the following TLVs defined in
   [I-D.ietf-ospf-ospfv3-lsa-extend] Intra-Area-Prefix TLV, IPv6 Link-
   Local Address TLV, or IPv4 Link-Local Address TLV when these are
   included in E-Link-LSA.

4.5.  RTM Capability Advertisement in IS-IS

   The RTM capability logically belongs to a group of parameters
   characterized as "generic information not directly related to the
   operation of the IS-IS protocol" [RFC6823].  Hence the capability to
   process RTM messages can be advertised by including RTM Capability
   sub-TLV in GENINFO TLV [RFC6823].

   With respect to the Flags field of the GENINFO TLV:

   o  The S bit MUST be cleared to prevent the RTM Capability sub-TLV
      from leaking between levels.

   o  The D bit of the Flags field MUST be cleared as required by
      [RFC6823].




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   o  The I bit and the V bit MUST be set accordingly depending on
      whether RTM capability being advertised for IPv4 or IPv6 interface
      of the node.

   Application ID (TBA6) will be assigned from the Application
   Identifiers for TLV 251 IANA registry.  The RTM Capability sub-TLV,
   presented in Figure 4, MUST be included in GENINFO TLV in Application
   Specific Information.

4.6.  RSVP-TE Control Plane Operation to Support RTM

   Throughout this document we refer to an LSR as RTM capable LSR when
   at least one of its interfaces is RTM capable.  Figure 5 provides an
   example of relationship between roles a network element may have in
   PTP over MPLS scenario and RTM capability:

    -----     -----     -----     -----     -----     -----     -----
    | A |-----| B |-----| C |-----| D |-----| E |-----| F |-----| G |
    -----     -----     -----     -----     -----     -----     -----

                        Figure 5: RTM capable roles

   o  A is a Boundary Clock with its egress port in Master state.  Node
      A transmits PTP messages;

   o  B is the ingress LER for the MPLS LSP and is not RTM capable;

   o  C is the first RTM capable LSR; it initializes the RTM Scratch Pad
      field and encapsulates PTP messages in the RTM ACH; the
      transmitted Scratch Pad information includes the residence time
      measured by C;

   o  D is a transit LSR that is not RTM capable; it passes along the
      RTM ACH encapsulated PTP message unmodified;

   o  E is the last RTM capable LSR; it updates the Correction field of
      the PTP message with the value in the Scratch Pad field of the RTM
      ACH, and removes the RTM ACH encapsulation;

   o  F is the egress LER for the MPLS LSP and is not RTM capable;

   o  G is a Boundary Clock with its ingress port in Slave state.  Node
      G receives PTP messages.

   An ingress LSR that is configured to perform RTM along a path through
   an MPLS network to an egress LSR verifies that the selected egress
   LSR has an interface that supports RTM via the egress LSR's
   advertisement of the RTM Capability sub-TLV.  In the Path message



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   that the ingress LSR uses to instantiate the LSP to that egress LSR
   it places initialized Record Route Object (RRO) [RFC3209] and RTM Set
   Object (RSO) [Section 4.7], which tell the egress LSR that RTM is
   requested for this LSP.

   In the Resv message that the egress LSR sends in response to the
   received Path message, it includes initialized RRO and RSO.  The RSO
   contains an ordered list, from egress LSR to ingress LSR, of the RTM
   capable LSRs along the LSP's path.  Each such LSR will use the ID of
   the first LSR in the RSO in conjunction with the RRO to compute the
   hop count to its downstream LSR with reachable RTM capable interface.
   It will also insert its ID at the beginning of the RTM Set Object
   before forwarding the Resv upstream.

   After the ingress LSR receives the Resv, it MAY begin sending RTM
   packets to the first RTM capable LSR on the LSP's path.  Each RTM
   packet has its Scratch Pad field initialized and its TTL set to
   expire on that first subsequent RTM capable LSR.

   It should be noted that RTM can also be used for LSPs instantiated
   using [RFC3209] in an environment in which all interfaces in an IGP
   support RTM.  In this case the RSO MAY be omitted.

4.7.  RTM_SET Object

   RTM capable interfaces can be recorded via RTM_SET object (RSO).  The
   RTM Set Class is TBA7.  This document defines one C_Type, Type TBA8
   RTM Set. The RTM_SET object format presented in Figure 6

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                             |
    ~                        Sub-objects                          ~
    |                                                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 6: RTM Set object format

   The contents of a RTM_SET object are a series of variable-length data
   items called sub-objects.  The sub-objects are defined in
   Section 4.7.1 below.

   The RSO can be present in both RSVP Path and Resv messages.  If a
   Path message contains multiple RSOs, only the first RSO is
   meaningful.  Subsequent RSOs SHOULD be ignored and SHOULD NOT be
   propagated.  Similarly, if in a Resv message multiple RSOs are
   encountered following a FILTER_SPEC before another FILTER_SPEC is



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   encountered, only the first RSO is meaningful.  Subsequent RSOs
   SHOULD be ignored and SHOULD NOT be propagated.

4.7.1.  RSO Sub-objects

   The RTM Set object contains an ordered list, from egress LSR to
   ingress LSR, of the RTM capable LSRs along the LSP's path.

   The contents of a RTM_SET object are a series of variable-length data
   items called sub-objects.  Each sub-object has its own Length field.
   The length contains the total length of the sub-object in bytes,
   including the Type and Length fields.  The length MUST always be a
   multiple of 4, and at least 8 (smallest IPv4 sub-object).

   Sub-objects are organized as a last-in-first-out stack.  The first
   -out sub-object relative to the beginning of RSO is considered the
   top.  The last-out sub-object is considered the bottom.  When a new
   sub-object is added, it is always added to the top.

   Three kinds of sub-objects for RSO are currently defined.

4.7.1.1.  IPv4 Sub-object

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Type     |     Length    |             Flags             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       IPv4 address                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 7: IPv4 sub-object format

   Type

      0x01 IPv4 address

   Length

      The Length contains the total length of the sub-object in bytes,
      including the Type and Length fields.  The Length is always 8.

   IPv4 address

      A 32-bit unicast host address.

   Flags




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      TBD

4.7.1.2.  IPv6 Sub-object

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Type     |     Length    |             Flags             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                             |
    |                         IPv6 address                        |
    |                                                             |
    |                                                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 8: IPv6 sub-object format

   Type

      0x02 IPv6 address

   Length

      The Length contains the total length of the sub-object in bytes,
      including the Type and Length fields.  The Length is always 20.

   IPv6 address

      A 128-bit unicast host address.

   Flags

      TBD

4.7.1.3.  Unnumbered Interface Sub-object

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Type     |     Length    |             Flags             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Router ID                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Interface ID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 9: IPv4 sub-object format




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   Type

      0x03 Unnumbered interface

   Length

      The Length contains the total length of the sub-object in bytes,
      including the Type and Length fields.  The Length is always 12.

   Router ID

      The Router ID interpreted as discussed in the Section 2 of RFC
      3447 [RFC3477].

   Interface ID

      The identifier assigned to the link by the LSR specified by the
      Router ID.

   Flags

      TBD

5.  Data Plane Theory of Operation

   After instantiating an LSP for a path using RSVP-TE [RFC3209] as
   described in Section 4.6 or as described in the second paragraph of
   Section 4 and in Section 4.6, ingress LSR MAY begin sending RTM
   packets to the first downstream RTM capable LSR on that path.  Each
   RTM packet has its Scratch Pad field initialized and its TTL set to
   expire on the next downstream RTM-capable LSR.  Each RTM-capable LSR
   on the explicit path receives an RTM packet and records the time at
   which it receives that packet at its ingress interface as well as the
   time at which it transmits that packet from its egress interface;
   this should be done as close to the physical layer as possible to
   ensure precise accuracy in time determination.  The RTM-capable LSR
   determines the difference between those two times; for 1-step
   operation, this difference is determined just prior to or while
   sending the packet, and the RTM-capable egress interface adds it to
   the value in the Scratch Pad field of the message in progress.  Note,
   for the purpose of calculating a residence time, a common free
   running clock synchronizing all the involved interfaces may be
   sufficient, as, for example, 4.6 ppm accuracy leads to 4.6 nanosecond
   error for residence time on the order of 1 millisecond.

   For 2-step operation, the difference between packet arrival time (at
   an ingress interface) and subsequent departure time (from an egress
   interface) is determined at some later time prior to sending a



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   subsequent follow-up message, so that this value can be used to
   update the correctionField in the follow-up message.

   See Section 7 for further details on the difference between 1-step
   and 2-step operation.

   The last RTM-capable LSR on the LSP MAY then use the value in the
   Scratch Pad field to perform time correction, if there is no follow-
   up message.  For example, the egress LSR may be a PTP Boundary Clock
   synchronized to a Master Clock and will use the value in the Scratch
   Pad field to update PTP's correctionField.

6.  Applicable PTP Scenarios

   The proposed approach can be directly integrated in a PTP network
   based on the IEEE 1588 delay reqest-response mechanism.  The RTM
   capable LSR nodes act as end-to-end transparent clocks, and typically
   boundary clocks, at the edges of the MPLS network, use the value in
   the Scratch Pad field to update the correctionField of the
   corresponding PTP event packet prior to performing the usual PTP
   processing.

7.  One-step Clock and Two-step Clock Modes

   One-step mode refers to the mode of operation where an egress
   interface updates the correctionField value of an original event
   message.  Two-step mode refers to the mode of operation where this
   update is made in a subsequent follow-up message.

   Processing of the follow-up message, if present, requires the
   downstream end-point to wait for the arrival of the follow-up message
   in order to combine correctionField values from both the original
   (event) message and the subsequent (follow-up) message.  In a similar
   fashion, each 2-step node needs to wait for the related follow-up
   message, if there is one, in order to update that follow-up message
   (as opposed to creating a new one.  Hence the first node that uses
   2-step mode MUST do two things:

   1.  Mark the original event message to indicate that a follow-up
       message will be forthcoming (this is necessary in order to

          Let any subsequent 2-step node know that there is already a
          follow-up message, and

          Let the end-point know to wait for a follow-up message;

   2.  Create a follow-up message in which to put the RTM determined as
       an initial correctionField value.



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   IEEE 1588v2 [IEEE.1588.2008] defines this behaviour for PTP messages.

   Thus, for example, with reference to the PTP protocol, the PTPType
   field identifies whether the message is a Sync message, Follow_up
   message, Delay_Req message, or Delay_Resp message.  The 10 octet long
   Port ID field contains the identity of the source port, that is, the
   specific PTP port of the boundary clock connected to the MPLS
   network.  The Sequence ID is the sequence ID of the PTP message
   carried in the Value field of the message.

   PTP messages also include a bit that indicates whether or not a
   follow-up message will be coming.  This bit, once it is set by a
   2-step mode device, MUST stay set accordingly until the original and
   follow-up messages are combined by an end-point (such as a Boundary
   Clock).

   Thus, an RTM packet, containing residence time information relating
   to an earlier packet, also contains information identifying that
   earlier packet.

   For compatibility with PTP, RTM (when used for PTP packets) must
   behave in a similar fashion.  To do this, a 2-step RTM capable egress
   interface will need to examine the S-bit in the Flags field of the
   PTP sub-TLV (for RTM messages that indicate they are for PTP) and -
   if it is clear (set to zero), it MUST set it and create a follow-up
   PTP Type RTM message.  If the S bit is already set, then the RTM
   capable node MUST wait for the RTM message with the PTP type of
   follow-up and matching originator and sequence number to make the
   corresponding residence time update to the Scratch Pad field.

   In practice an RTM operating according to two-step clock behaves like
   a two-steps transparent clock.

   A 1-step capable RTM node MAY elect to operate in either 1-step mode
   (by making an update to the Scratch Pad field of the RTM message
   containing the PTP even message), or in 2-step mode (by making an
   update to the Scratch Pad of a follow-up message when its presence is
   indicated), but MUST NOT do both.

   Two main subcases can be identified for an RTM node operating as a
   two-step clock:

   A) If any of the previous RTM capable node or the previous PTP clock
   (e.g. the BC connected to the first LSR), is a two-step clock, the
   residence time is added to the RTM packet that has been created to
   include the associated PTP packet (i.e. follow-up message in the
   downstream direction), if the local RTM-capable LSR is also operating
   as a two-step clock.  This RTM packet carries the related accumulated



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   residence time and the appropriate values of the Sequence Id and Port
   Id (the same identifiers carried in the packet processed) and the
   Two-step Flag set to 1.

   Note that the fact that an upstream RTM-capable node operating in the
   two-step mode has created a follow-up message does not require any
   subsequent RTM capable LSR to also operate in the 2-step mode, as
   long as that RTM-capable LSR forwards the follow-up message on the
   same LSP on which it forwards the corresponding previous message.

   A one-step capable RTM node MAY elect to update the RTM follow-up
   message as if it were operating in two-step mode, however, it MUST
   NOT update both messages.

   A PTP event packet (sync) is carried in the RTM packet in order for
   an RTM node to identify that residence time measurement must be
   performed on that specific packet.

   To handle the residence time of the Delay request message on the
   upstream direction, an RTM packet must be created to carry the
   residence time on the associated downstream Delay Resp message.

   The last RTM node of the MPLS network in addition to update the
   correctionField of the associated PTP packet, must also properly
   handle the two-step flag of the PTP packets.

   B) When the PTP network connected to the MPLS and RTM node, operates
   in one-step clock mode, the associated RTM packet must be created by
   the RTM node itself.  The associated RTM packet including the PTP
   event packet needs now to indicate that a follow up message will be
   coming.

   The last RTM node of the LSP, modeif it receives an RTM message with
   a PTP payload indicating a follow-up message will be forthcoming,
   must generate a follow-up message and properly set the two-step flag
   of the PTP packets.

8.  IANA Considerations

8.1.  New RTM G-ACh

   IANA is requested to reserve a new G-ACh as follows:









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          +-------+----------------------------+---------------+
          | Value |        Description         | Reference     |
          +-------+----------------------------+---------------+
          | TBA1  | Residence Time Measurement | This document |
          +-------+----------------------------+---------------+

                  Table 1: New Residence Time Measurement

8.2.  New RTM TLV Registry

   IANA is requested to create sub-registry in Generic Associated
   Channel (G-ACh) Parameters Registry called "MPLS RTM TLV Registry".
   All code points in the range 0 through 127 in this registry shall be
   allocated according to the "IETF Review" procedure as specified in
   [RFC5226] .  Remaining code points are allocated according to the
   table below.  This document defines the following new values RTM TLV
   type s:

           +-----------+-------------+-------------------------+
           | Value     | Description | Reference               |
           +-----------+-------------+-------------------------+
           | 0         |   Reserved  | This document           |
           | 1         |  No payload | This document           |
           | 2         |    PTPv2    | This document           |
           | 3         |     NTP     | This document           |
           | 4-127     |   Reserved  | IETF Consensus          |
           | 128 - 191 |   Reserved  | First Come First Served |
           | 192 - 255 |   Reserved  | Private Use             |
           +-----------+-------------+-------------------------+

                           Table 2: RTM TLV Type

8.3.  New RTM Sub-TLV Registry

   IANA is requested to create sub-registry in MPLS RTM TLV Registry,
   requested in Section 8.2, called "MPLS RTM Sub-TLV Registry".  All
   code points in the range 0 through 127 in this registry shall be
   allocated according to the "IETF Review" procedure as specified in
   [RFC5226] .  Remaining code points are allocated according to the
   table below.  This document defines the following new values RTM sub-
   TLV types:










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           +-----------+-------------+-------------------------+
           | Value     | Description | Reference               |
           +-----------+-------------+-------------------------+
           | 0         |   Reserved  | This document           |
           | 1         |  PTP 2-step | This document           |
           | 2-127     |   Reserved  | IETF Consensus          |
           | 128 - 191 |   Reserved  | First Come First Served |
           | 192 - 255 |   Reserved  | Private Use             |
           +-----------+-------------+-------------------------+

                         Table 3: RTM Sub-TLV Type

8.4.  RTM Capability sub-TLV

   IANA is requested to assign a new type for RTM Capability sub-TLV
   from future OSPF Extended Link TLV Sub-TLVs registry as follows:

                +-------+----------------+---------------+
                | Value |  Description   | Reference     |
                +-------+----------------+---------------+
                | TBA2  | RTM Capability | This document |
                +-------+----------------+---------------+

                      Table 4: RTM Capability sub-TLV

8.5.  IS-IS RTM Application ID

   IANA is requested to assign a new Application ID for RTM from the
   Application Identifiers for TLV 251 registry as follows:

                  +-------+-------------+---------------+
                  | Value | Description | Reference     |
                  +-------+-------------+---------------+
                  | TBA3  |     RTM     | This document |
                  +-------+-------------+---------------+

                     Table 5: IS-IS RTM Application ID

8.6.  RTM_SET Object RSVP Class Number, Class Type and Sub-object Types

   IANA is requested to assign a new Class Number for RTM_SET object as
   follows:









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                +-------+----------------+---------------+
                | Value |  Description   | Reference     |
                +-------+----------------+---------------+
                | TBA4  | RTM_SET object | This document |
                +-------+----------------+---------------+

                       Table 6: RTM_SET object Class

   IANA is requested to assign a new Class Type for RTM_SET object as
   follows:

                  +-------+-------------+---------------+
                  | Value | Description | Reference     |
                  +-------+-------------+---------------+
                  | TBA5  |   RTM Set   | This document |
                  +-------+-------------+---------------+

                    Table 7: RTM_SET object Class Type

   IANA requested to create new sub-registry for sub-object types of
   RTM_SET object as follows:

      +-----------+----------------------+-------------------------+
      | Value     |     Description      | Reference               |
      +-----------+----------------------+-------------------------+
      | 0         |       Reserved       |                         |
      | 1         |     IPv4 address     | This document           |
      | 2         |     IPv6 address     | This document           |
      | 3         | Unnumbered interface | This document           |
      | 4-127     |       Reserved       | IETF Consensus          |
      | 128 - 191 |       Reserved       | First Come First Served |
      | 192 - 255 |       Reserved       | Private Use             |
      +-----------+----------------------+-------------------------+

                 Table 8: RTM_SET object sub-object types

9.  Security Considerations

   Routers that support Residence Time Measurement are subject to the
   same security considerations as defined in [RFC5586] .

   In addition - particularly as applied to use related to PTP - there
   is a presumed trust model that depends on the existence of a trusted
   relationship of at least all PTP-aware nodes on the path traversed by
   PTP messages.  This is necessary as these nodes are expected to
   correctly modify specific content of the data in PTP messages and
   proper operation of the protocol depends on this ability.




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   As a result, the content of the PTP-related data in RTM messages that
   will be modified by intermediate nodes cannot be authenticated, and
   the additional information that must be accessible for proper
   operation of PTP 1-step and 2-step modes MUST be accessible to
   intermediate nodes (i.e. - MUST NOT be encrypted in a manner that
   makes this data inaccessible).

   While it is possible for a supposed compromised LSR to intercept and
   modify the G-ACh content, this is an issue that exists for LSRs in
   general - for any and all data that may be carried over an LSP - and
   is therefore the basis for an additional presumed trust model
   associated with existing LSPs and LSRs.

   The ability for potentially authenticating and/or encrypting RTM and
   PTP data that is not needed by intermediate RTM/PTP-capable nodes is
   for further study.

   Security requirements of time protocols are provided in RFC 7384
   [RFC7384].

10.  Acknowledgements

   Authors want to thank Loa Andersson for his thorough review and
   thoghtful comments.

11.  References

11.1.  Normative References

   [I-D.ietf-ospf-ospfv3-lsa-extend]
              Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
              LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-06
              (work in progress), February 2015.

   [I-D.ietf-ospf-prefix-link-attr]
              Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", draft-ietf-ospf-prefix-link-attr-06 (work
              in progress), June 2015.

   [IEEE.1588.2008]
              "Standard for a Precision Clock Synchronization Protocol
              for Networked Measurement and Control Systems", IEEE
              Standard 1588, March 2008.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.




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   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC3477]  Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
              in Resource ReSerVation Protocol - Traffic Engineering
              (RSVP-TE)", RFC 3477, January 2003.

   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, February 2006.

   [RFC5085]  Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
              Connectivity Verification (VCCV): A Control Channel for
              Pseudowires", RFC 5085, December 2007.

   [RFC5586]  Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
              Associated Channel", RFC 5586, June 2009.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

   [RFC6423]  Li, H., Martini, L., He, J., and F. Huang, "Using the
              Generic Associated Channel Label for Pseudowire in the
              MPLS Transport Profile (MPLS-TP)", RFC 6423, November
              2011.

   [RFC6823]  Ginsberg, L., Previdi, S., and M. Shand, "Advertising
              Generic Information in IS-IS", RFC 6823, December 2012.

11.2.  Informative References

   [RFC4202]  Kompella, K. and Y. Rekhter, "Routing Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4202, October 2005.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374, September 2011.

   [RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in
              Packet Switched Networks", RFC 7384, October 2014.





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Authors' Addresses

   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com


   Stefano Ruffini
   Ericsson

   Email: stefano.ruffini@ericsson.com


   Eric Gray
   Ericsson

   Email: eric.gray@ericsson.com


   John Drake
   Juniper Networks

   Email: jdrake@juniper.net


   Stewart Bryant
   Cisco Systems

   Email: stbryant@cisco.com


   Alexander Vainshtein
   ECI Telecom

   Email: Alexander.Vainshtein@ecitele.com















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