Network Working Group
 Internet Draft
 Expires: January 2008
 Intended Status: Informational

                                               S. Poretsky
                                               Reef Point Systems

                                               R. Papneja
                                               Isocore

                                               J. Karthik
                                               S.Vapiwala
                                               Cisco Systems

                                               July 2007

         Benchmarking Terminology for Protection Performance
             <draft-ietf-bmwg-protection-term-02.txt >

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Abstract
  This document provides common terminology and metrics for benchmarking
  the performance of sub-IP layer protection mechanisms. The performance
  benchmarks are measured at the IP-Layer, so avoid dependence on
  specific sub-IP protection mechanisms. The benchmarks and terminology
  can be applied in methodology documents for different sub-IP layer
  protection mechanisms such as Automatic Protection Switching (APS),
  Virtual Router Redundancy Protocol (VRRP), Stateful High Availability
  (HA), and Multi-Protocol Label Switching Fast Reroute (MPLS-FRR).

Table of Contents
        1. Introduction..............................................3
        2. Existing definitions......................................4
        3. Test Considerations.......................................4
           3.1. Path.................................................5
              3.1.1. Path............................................5
              3.1.2. Tunnel..........................................6
              3.1.3. Working Path....................................6
              3.1.4. Primary Path....................................7
              3.1.5. Protected Primary Path..........................7
              3.1.6. Backup Path.....................................8
              3.1.7. Standby Backup Path.............................8
              3.1.8. Dynamic Backup Path.............................9
              3.1.9. Disjoint Paths..................................9
              3.1.10. Shared Risk Link Group (SRLG)..................10
           3.2. Protection...........................................10
              3.2.1. Protection Switching System.....................10
              3.2.2. Link Protection.................................11
              3.2.3. Node Protection.................................11
              3.2.4. Path Protection.................................12
              3.2.5. Backup Span.....................................12
              3.2.6  Protected Interface.............................12
           3.3. Failure..............................................13
              3.3.1. Failover Event..................................13
              3.3.2. Failure Detection...............................13
              3.3.3. Failover........................................14
              3.3.4. Restoration (Failover recovery).................14
              3.3.5. Reversion.......................................15
           3.4. Nodes................................................15
              3.4.1. Protection-Switching Node.......................15
              3.4.2. Non-Protection Switching Node...................15
              3.4.3. Failover Node...................................16
              3.4.4. Merge Node......................................16

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              3.4.5. Point of Local repair (PLR).....................17
              3.4.6. Head-end Failover Node..........................17
           3.5. Metrics..............................................18
              3.5.1. Failover Packet Loss............................18
              3.5.2. Reversion Packet Loss...........................18
              3.5.3. Primary Path Latency............................19
              3.5.4. Backup Path Latency.............................19
           3.6. Benchmarks...........................................20
              3.6.1. Failover Time...................................20
              3.6.2. Additive Backup Latency.........................21
              3.6.3. Reversion Time..................................21
           3.7 Failover Calculation Method...........................22
              3.7.1 Time-Based Loss Method...........................22
              3.7.2 Packet-Based Loss Method.........................22
              3.7.3 Timestamp-Based Method...........................23
        4. Acknowledgments...........................................24
        5. IANA Considerations.......................................24
        6. Security Considerations...................................24
        7. References................................................24
           7.1. Normative References.................................24
           7.2. Informative References...............................24
        8. Author's Address..........................................25

1. Introduction

   The IP network layer provides route convergence to protect data
   traffic against planned and unplanned failures in the internet.
   Fast convergence times are critical to maintain reliable network
   connectivity and performance.  Technologies that function at sub-IP
   layers can be enabled to provide further protection of IP
   traffic by providing the failure recovery at the sub-IP layers so
   that the outage is not observed at the IP-layer.  Such technologies
   includes High Availability (HA) stateful failover.  Virtual Router
   Redundancy Protocol (VRRP), Automatic Link Protection (APS) for
   SONET/SDH, Resilient Packet Ring (RPR) for Ethernet, and Fast
   Reroute for Multi-Protocol Label Switching (MPLS).

   Benchmarking terminology have been defined for IP-layer route
   convergence [7].  New terminology and methodologies specific
   to benchmarking sub-IP layer protection mechanisms are required.
   This will enable different implementations of the same
   protection mechanisms to be benchmarked and evaluated. In
   addition, different protection mechanisms can be benchmarked and
   evaluated.  The metrics for benchmarking the performance of sub-IP
   protection mechanisms are measured at the IP layer, so that the
   results are always measured in reference to IP and independent of

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   the specific protection mechanism being used. The purpose of this
   document is to provide a single terminology for benchmarking sub-IP
   protection mechanisms.  It is intended that there can exist unique
   methodology documents for each sub-IP protection mechanism.

   Figure 1 shows the fundamental model that is to be used in
   benchmarking sub-IP protection mechanisms.  The sequence of
   events is Failover Event, Failure Detection, Failover, Restoration
   (Failover recovery), and optionally Reversion.  Protection
   Switching consists of a minimum of two Protection-Switching Nodes
   with a  Primary Path and a Backup Path.  A Failover Event occurs
   along the Primary Path.  A tester is set outside the two nodes as
   it sends and receives IP traffic along the Working Path.  The
   Working Path is the Primary Path prior to the Failover Event and
   the Backup Path following the Failover Event.  If Reversion is
   supported then the Working Path is the Primary Path after Failure
   Recovery.  The tester MUST record the IP packet sequence numbers,
   departure time, and arrival time so that the metrics of Failover
   Time, Additive Latency, and Reversion Time can be measured.  The
   Tester may be a single device or a test system.

                                  +-----------+
             +--------------------|  Tester   |<-------------------+
             |                    +-----------+                    |
             | IP Traffic               | Failover      IP Traffic |
             |                          | Event                    |
             |              Primary     |                          |
             |    +--------+  Path      v            +--------+    |
             |    |        |------------------------>|        |    |
             +--->| Node 1 |                         | Node 2 |----+
                  |        |- - - - - - - - - - - - >|        |
                  +--------+      Backup Path        +--------+
                  |                                           |
                  |            IP-Layer Forwarding            |
                  +-------------------------------------------+

   Figure 1.  System Under Test (SUT) for Sub-IP Protection Mechanisms

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2. Existing definitions
   This document uses existing terminology defined in other BMWG
   work.  Examples include, but are not limited to:

             Latency                   [Ref.[2], section 3.8]
             Frame Loss Rate           [Ref.[2], section 3.6]
             Throughput                [Ref.[2], section 3.17]
             Device Under Test (DUT)   [Ref.[3], section 3.1.1]
             System Under Test (SUT)   [Ref.[3], section 3.1.2]
             Out-of-order Packet       [Ref.[4], section 3.3.2]
             Duplicate Packet          [Ref.[4], section 3.3.3]
             Packet Loss               [Ref.[7], Section 3.5]
             Packet Reordering         [Ref.[10] section 3.3]

   This document adopts the definition format in Section 2 of RFC 1242
   [2].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119 [5].
   RFC 2119 defines the use of these key words to help make the
   intent of standards track documents as clear as possible.  While this
   document uses these keywords, this document is not a standards track
   document.

3. Test Considerations

  3.1. Path

    3.1.1 Path

    Definition:
       A sequence of nodes, <R1, ..., Rn>, with the following
       properties:
       - R1 is the ingress node and forwards IP packets, which input
       into DUT/SUT, to R2 as sub-IP frames.
       - Ri is a node which forwards data frames to R[i+1] for all i,
       1<i<n, based on information in the sub-IP layer.
       - Rn is the egress node and it outputs sub-IP frames from
       DUT/SUT as IP packets.

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    Discussion:
       The path is defined in the sub-IP layer in this document, unlike
       an IP path in RFC 2026 [1].  For example, the SONET/SDH path,
       the label switched path for MPLS, and optical path.  One path
       may be regarded as being equivalent to one IP link between two
       IP nodes, i.e., R1 and Rn.  The two IP nodes may have multiple
       paths for protection.  A packet will travel on only one path
       between the nodes.  Packets belonging to a microflow [9]
       will transverse one or more paths.  The path is unidirectional.

    Measurement units:
       n/a

    Issues:
       "A bidirectional path", which transmits traffic in both
       directions along the same nodes, consists of two unidirectional
       paths.  Therefore, the two unidirectional paths belonging to
       "one bidirectional path" will be treated independently when
       benchmarking for "a bidirectional path".

       See Also:

    3.1.2. Tunnel

    Definition:
       Tunnel is a collection of related Paths.

    Discussion:
       A Tunnel is used to carry a specific flow of traffic which
       is generally large aggregation of microflows, but may be any
       flow defined by a classifier at the ingress. A Tunnel may
       include two primary paths during the MPLS make-before-break
       reroute.

    Measurement units: n/a

    Issues: None

    See Also:
       Path
       Primary Path
       Backup Path

    3.1.3. Working Path

    Definition:
       The path that the DUT/SUT is currently using to forward
       packets.

    Discussion:
       A Primary Path is a Working Path before occurrence of a
       Failover Event.  A Backup Path becomes the Working Path after
       a Failover Event.

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    Measurement units:
       n/a

    Issues:

    See Also:
       Path
       Primary Path
       Backup Path

    3.1.4.  Primary Path

    Definition:
       The preferred path for forwarding traffic between two or
       more nodes.

    Discussion:

    Measurement units:
       n/a

    Issues:

    See Also:
       Path

    3.1.5.  Protected Primary Path

       Definition:
       The Primary Path that is protected with a Backup Path.

       Discussion:

       Measurement units:
          n/a

       Issues:

       See Also:
          Path
          Primary Path

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    3.1.6.  Backup Path

       Definition:
       A path that exists to carry data traffic only if a Failover
       Event occurs.

       Discussion:
       The Backup Path is the Working Path upon a Failover Event.
       There are various types of Backup Paths: a dedicated recovery
       path (1+1), which has 100% redundancy for a specific ordinary
       path, a shared Backup Path (1:N), which is dedicated to the
       protection for more than one specific Primary Path, and an
       associated shared Backup Path (M:N) for which a specific set
       of Backup Paths protects a specific set of more than one
       Primary Path. Backup path is always computed before the
       failover event. A new path computed after the failover event
       is simply reroute of the primary path. A backup may be
       signaled or unsignaled.

       Measurement units:
          n/a

       Issues:

       See Also:
          Path
          Working Path
          Primary Path

     3.1.7.  Standby Backup Path

        Definition:
        A Backup Path that is established prior to a Failover Event
        to protect a Primary Path.



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         Discussion:

         Measurement units:
             n/a

         Issues:

         See Also:
             Path
             Working Path
             Primary Path
             Failover Event

     3.1.8. Dynamic Backup Path

         Definition:
         A Backup Path that is established upon occurrence of a
         Failover Event.

         Discussion:

         Measurement units:
             n/a

         Issues:

         See Also:
             Path
             Working Path
             Primary Path
             Failover Event


     3.1.9. Disjoint Paths

        Definition:
        A pair of paths is considered disjoint if they do not
        share a common link.


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        Discussions:
        Paths that protect a segment of a path may merge beyond the
        segment being protected and are considered disjoint if they
        do not use a link from the set of links in the protected
        segment. A path is node disjoint if it does not share a
        common node other than the ingress and egress.

        Measurement units:
           n/a

        Issues:

        See Also:
           Path
           Primary Path
           SRLG

     3.1.10. Shared Risk Link Group (SRLG)

         Definition:
          SRLG is a set of links which are likely to fail
          concurrently due to sharing a physical resource.

         Discussion:
          SRLG are considered the set of links to be avoided when
          the primary and secondary paths are considered disjoint.

         Measurement units:
             n/a

         Issues:

         See Also:
             Path
             Primary Path
             Disjoint Path

   3.2. Protection

     3.2.1.  Protection Switching System

        Definition:
          A SUT that is capable of Failover from a Primary to a
          Backup Path.

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        Discussion:
          The Protection Switching System MUST have a Primary Path
          and a Backup Path.  The Backup Path MAY be a Standby
          Backup Path or a dynamic Backup Path.  The Protection
          Switching System includes the mechanisms for both Failure
          Detection and Failover.

        Measurement units: n/a

        Issues: None

        See Also:
             Primary Path
             Backup Path
             Failure Detection
             Failover

     3.2.2.  Link Protection

         Definition:
           A backup path is signal to next node avoiding protected
           interface that provide protection for link failure

         Discussion:
           Link Protection may or may not protect the entire Primary
           Path.

         Measurement units: n/a

         Issues: None

         See Also:
             Primary Path
             Backup Path

     3.2.3.  Node Protection

         Definition:
           A backup path is signal to next to next node avoiding
           protected node that provide protection failure of link or
           node.

         Discussion:
           Node Protection may or may not protect the entire Primary
           Path.  Node Protection also provides Link Protection.

         Measurement units: n/a

         Issues: None

         See Also:
             Link Protection

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     3.2.4.   Path Protection

        Definition:
        A Backup Path that provides protection for the entire
        Primary Path.

        Discussion:
        Path Protection provides Node Protection and Link Protection
        for every node and link along the Primary Path.  A Backup
        Path providing Path Protection MUST have the same ingress
        node as the Primary Path.

        Measurement units: n/a

        Issues: None

        See Also:
             Primary Path
             Backup Path
             Node Protection
             Link protection

     3.2.5. Backup Span

        Definition:
        The numbers of hop used by backup tunnel to protected link or
        node.

        Discussion:

        Measurement units: number of nodes

        Issues: None

        See Also:
             Primary Path
             Backup Path

     3.2.6 Protected Interface

        Definition:
        A interface which primary path is signaled over and protected by
        backup tunnel

        Discussion:

        Measurement units: None

        Issues: None

        See Also:

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   3.3. Failure

     3.3.1.  Failover Event

       Definition:
       The occurrence of a planned or unplanned action in the network
       that results in a change in the Path that data traffic traverses.

       Discussion:
       Failover Events include, but are not limited to, link failure
       and router failure.  Routing changes are considered Convergence
       Events [7] and are not Failover Events.  This restricts
       Failover Events to sub-IP layers. Failover may be at the PLR or
       at the ingress. If the failover is at the ingress it is
       generally on a disjoint path from the ingress to egress.


       Measurement units:
          n/a

       Issues:

       See Also:
          Path
          Failure Detection
          Disjoint Path

     3.3.2.  Failure Detection

       Definition:
       To identify a Primary Path failure at a sub-IP layer.

       Discussion:
       Failure Detection occurs at the ingress node of the Primary
       Path.  Failure Detection occurs via a sub-IP mechanism such
       as detection of a link down event or timeout for receipt
       of a control packet. A failure may be completely isolated. A
       failure may affect a set of links which share a single SRLG
       (e.g. port with many sub-interfaces). A failure may affect
       multiple links that are not part of SRLG.

       Measurement units:
         n/a

       Issues:

       See Also:
         Primary Path

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     3.3.3.  Failover

        Definition:
        To switch data traffic from the Primary Path to the Backup
        Path upon a Failover Event.

        Discussion:
        Failover to a Backup Path provides Link Protection, Node
        Protection, or Path Protection.  Failover is complete when
        Lost Packets, Out-of-Order Packets, and Duplicate Packets
        are no longer observed.

        Measurement units:
            n/a

        Issues:

        See Also:
             Primary Path
             Backup Path
             Failover Event

     3.3.4.  Restoration

        Definition:
        The act of Failover Recovery in which the Primary Path is
        restored following a Failover Event.

        Discussion:
        Restoration MUST occur while the Backup Path is the
        Working Path.  The Backup Path is maintained as the
        Working Path during Failure Recovery. This implies that
        the service is either restored fully or partially.
        Restoration can cause congestion, but primary paths
        rerouting avoid restoration. An unavoidable problem in any
        restoration is the discontinuity in end to end delay when
        the primary and backup path delays differ significantly. If
        the backup path has a shorter delay out of order delivery
        may occur if restoration is fast.  If the backup path is
        longer then a sudden increase in delay will occur which can
        affect real time applications which use playback buffers to
        remove limited jitter.

        Measurement units:

        Issues:

        See Also:
             Primary Path
             Failover Event
             Failure Recovery
             Working Path
             Backup Path

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     3.3.5.  Reversion

         Definition:
         The act of restoring the Primary Path as the Working Path.

         Discussion:
         Protection Switching Systems may or may not support Reversion.
         Reversion, if supported, MUST occur after Failure Recovery.

         Measurement units:
             n/a

         Issues:

         See Also:
             Protection Switching System
             Working Path
             Primary Path

   3.4. Nodes

     3.4.1.  Protection-Switching Node

         Definition:
         A node that is capable to participate in a Protection Switching
         System.

         Discussion:
         The Protection Switching Node MAY be an ingress or egress for
         a Primary Path or Backup Path.

         Measurement units:
             n/a

         Issues:

         See Also:
             Protection Switching System
             Primary Path
             Backup Path

     3.4.2.  Non-Protection Switching Node

         Definition:
             A node that not capable of participating in a Protection
             Switching System, however it MAY exist along the Primary
             Path or Backup Path.

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         Discussion:

         Measurement units:
             n/a

         Issues:

         See Also:
             Protection Switching System
             Primary Path
             Backup Path

     3.4.3.  Failover Node

         Definition:
             A node along the Primary Path that is capable of Failover.

         Discussion:
             The Failover Node can be any node along the Primary Path
             except the egress node of the Primary Path.  There can be
             multiple Failover Nodes along a Primary Path.  The Failover
             Node MUST be the ingress to the Backup Path.  The Failover
             Node MAY also be the ingress of the Primary Path.

         Measurement units:
             n/a

         Issues:

         See Also:
             Primary Path
             Backup Path
             Failover

     3.4.4.  Merge Node

         Definition:
             A Node along the primary path where backup path terminates
.

         Discussion:
             The Merge Node can be any node along the Primary Path
             except the ingress node of the Primary Path.  There can be
             multiple Merge Nodes along a Primary Path.  A Merge Node
             can be the egress node for a single or multiple Backup
             Paths.  The Merge Node MUST be the egress to the Backup
             Path.  The Merge Node MAY also be the egress of the
             Primary Path or point of local repair (PLR).

         Measurement units:
             n/a

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         Issues:

         See Also:
             Primary Path
             Backup Path
             PLR
             Failover

     3.4.5. Point of Local repair (PLR)

         Definition:
         A node that uses a Backup Path to protect another
         node or link.

         Discussion:
         Based on the functionality of the PLR, its role is defined
         based on the type of method used.  If the one-to-one backup
         method is used, the PLR is responsible for computing a
         separate Backup Path for each Primary Path.  In the case
         the facility backup method is used, the PLR creates a
         single Backup Path that can be used to protect multiple
         Primary Paths.

         Measurement units: n/a

         Issues:

         See Also:
             Primary Path
             Backup Path
             Failover

     3.4.6.  Head-end Failover Node

        Definition:
        A node that is ingress to the Primary Path that is capable
        of Failover.

        Discussion:
        Based on the functionality of the Head-end, its role is
        defined to be as the ingress of the signaled LSP. It could
        also occur, that this node happens to be a PLR. In this
        scenario the term head-end failover node is defined.

        Measurement units: n/a

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        Issues:

        See Also:
             Primary Path
             Backup Path
             Failover

   3.5. Metrics

      3.5.1.  Failover Packet Loss

        Definition:
        The amount of packet loss produced by a Failover Event
        until Failover completes.

        Discussion:
        Packet loss can be observed as a reduction of forwarded
        traffic from the maximum forwarding rate.  Failover Packet
        Loss includes packets that were lost and packets that were
        delayed due to buffering.  Failover Packet Loss MAY reach
        100% of the offered load.

        Measurement units:
          Number of Packets

        Issues:  None

        See Also:
           Failover Event
           Failover

      3.5.2.   Reversion Packet Loss

        Definition:
        The amount of packet loss produced by Reversion.

        Discussion:
        Packet loss can be observed as a reduction of forwarded
        traffic from the maximum forwarding rate.  Reversion Packet
        Loss includes packets that were lost and packets that were
        delayed due to buffering.  Reversion Packet Loss MAY reach
        100% of the offered load.

         Measurement units: Number of Packets

         Issues:  None

         See Also:
           Reversion

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      3.5.3.    Primary Path Latency

        Definition:
             Latency [2] measured along the Primary Path.

         Discussion:

         Measurement units:
           seconds

         Issues:  None

         See Also:
           Primary Path


      3.5.4.    Backup Path Latency

        Definition:
             Latency [2] measured along the Backup Path.

         Discussion:

         Measurement units:
             seconds

         Issues:  None

         See Also:
             Backup Path

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     3.6.  Benchmarks

        3.6.1. Failover Time

         Definition:
          The amount of time it takes for Failover to complete so
          that the Backup Path is the Working Path.

         Discussion:
           Failover Time can be calculated using the Time-Based Loss
           Method (TBLM), Packet-Based Loss Method (PBLM), or
           Timestamp-Based Method (TBM).  It is RECOMMENDED that the
           TBM is used.

         Measurement units:
           Seconds

         Issues: None

         See Also:
           Failover
           Failover Time
           Working Path
           Backup Path
           Time-Based Loss Method (TBLM)
           Packet-Based Loss Method (PBLM)
           Timestamp-Based Method (TBM)

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      3.6.2.  Additive Backup Latency

        Definition:
        The amount of increased latency resulting from data traffic
        traversing the Backup Path instead of the Primary Path.

        Discussion:
        Additive Backup Latency is calculated using Equation 1 as
        shown below:

          (Equation 1) Additive Backup Latency =
                    Backup Path Latency - Primary Path Latency.

         Measurement units:
             Seconds

         Issues:
         Additive Backup Latency MAY be a negative result.
         This is theoretically possible, but could be indicative
         of a sub-optimum network configuration .

         See Also:
             Primary Path
             Backup Path
             Primary Path Latency
             Backup Path Latency

      3.6.3.  Reversion Time

        Definition:
        The amount of time it takes for Reversion to complete so
        that the Primary Path is restored as the Working Path.

        Discussion:
        Reversion Time can be calculated using the Time-Based Loss
        Method (TBLM), Packet-Based Loss Method (PBLM), or
        Timestamp-Based Method (TBM).  It is RECOMMENDED that the
        TBM is used.

        Measurement units:
           Seconds

        Issues: None

        See Also:
           Reversion
           Primary Path
           Working Path
           Reversion Packet Loss
           Time-Based Loss Method (TBLM)
           Packet-Based Loss Method (PBLM)
           Timestamp-Based Method (TBM)

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     3.7 Failover Calculation Method

     3.7.1 Time-Based Loss Method (TBLM)

      Definition:
      The method to calculate Failover Time (or Reversion Time) using a
      time scale to measure duration of packet loss.

      Discussion:
      Traffic generators provide statistics which show the duration of
      failure on a time scale to granularity of milliseconds based on
      occurrence of packet loss on a time scale.  This is indicated by
      the duration of non-zero packet loss.  The TBLM includes failure
      detection time and time for data traffic to begin traversing the
      Backup Path.

      Measurement units:
             Milliseconds

      Issues: None

      See Also:
             Failover
             Packet-Based Loss Method

     3.7.2 Packet-Based Loss Method (PBLM)

         Definition:
          The method used to calculate Failover Time (or Reversion Time)
          from the amount of Packet Loss.

         Discussion:
           Failover Time can be calculated using PBLM is from Failover
           Packet Loss that occurs due to a Failover Event and Failover
           as shown below in Equation 2:

           (Equation 2) Failover (or Reversion) Time =
            Number of packets drop/(rate per
            second * 1000) milliseconds


           Packet based loss method includes failure detection time and
           time for data traffic to begin traversing the Backup Path.

         Measurement units:
             milliseconds

         Issues:

         See Also:
             Failover
             Time-Based Loss Method

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     3.7.3 Timestamp-Based Method (TBM)

      Definition:
      The method to calculate Failover Time (or Reversion Time)
      using a time scale to quantify the interval between
      unimpaired packets arriving in the test stream.

      Discussion:
      The purpose of this method is to quantify the duration of
      failure or reversion on a time scale with granularity of
      milliseconds based on the observation of unimpaired packets,
      using Equation 3.

        (Equation 3)
        Failover (or Reversion) Time = Time2 - Time1

      where
      Time1 is the arrival time of the last unimpaired packet before
      the effects of Failover (or Reversion) are observed in the packet
      stream.

      Time2 is the arrival time of the first unimpaired packet
      following the observation of impaired packets due to Failover
      (or Reversion) in the packet stream.

      Unimpaired packets are normal packets that are not lost,
      reordered, or duplicated.  A reordered packet is defined in
      [10, section 3.3].  A duplicate packet is defined in
      [4, section 3.3.3].  A lost packet is defined in
      [7, Section 3.5].  Unimpaired packets may be detected by checking
      a sequence number in the payload, where the sequence number equals
      the next expected number for an unimpaired packet.  A sequence gap
      or sequence reversal may indicate impaired packets.

      For calculating Failover Time, the TBM includes failure
      detection time and time for data traffic to begin traversing the
      Backup Path.  For calculating Reversion Time, the TBM includes
      Reversion Time and time for data traffic to begin traversing the
      Primary Path.

      Measurement units:
         milliseconds

      Issues: None

      See Also:
         Failover
         Failover Time
         Reversion
         Reversion Time

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4. Acknowledgements
     We would like thank the BMWG and particularly Al Morton and Curtis
     Villamizar for their reviews, comments, and contributions to this
     work.

5. IANA Considerations
     This document requires no IANA considerations.

6. Security Considerations
     This document only addresses terminology for the performance
     benchmarking of protection systems, and the information contained
     in this document has no effect on the security of the Internet.

7. References
7.1. Normative References
     [1] Bradner, S., "The Internet Standards Process -- Revision 3",
         RFC 2026, October 1996.

     [2] Bradner, S., Editor, "Benchmarking Terminology for
         Network Interconnection Devices", RFC 1242, July 1991.

     [3] Mandeville, R., "Benchmarking Terminology for LAN
         Switching Devices", RFC 2285, February 1998.

     [4] Poretsky, S., et al., "Terminology for Benchmarking
         Network-layer Traffic Control Mechanisms", RFC 4689,
         November 2006.

     [5] Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Levels", RFC 2119, July 1997.

     [6] Paxson, V., et al., "Framework for IP Performance Metrics",
         RFC 2330, May 1998.

     [7] Poretsky, S., Imhoff, B., "Benchmarking Terminology for IGP
         Convergence", draft-ietf-bmwg-igp-dataplane-conv-term-13,
         work in progress, July 2007.

     [8] Pan., P. et al, "Fast Reroute Extensions to RSVP-TE for LSP
         Tunnels", RFC 4090, May 2005.

     [9] Nichols, K., et al, "Definition of the Differentiated
         Services Field (DS Field) in the IPv4 and IPv6 Headers",
         RFC 2474, December 1998.

     [10] Morton, A., et al, "Packet Reordering Metrics", RFC 4737,
          November 2006.

7.2. Informative References

     None

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8.  Author's Address

   Scott Poretsky
   Reef Point Systems
   8 New England Executive Park
   Burlington, MA 01803
   USA
   Phone: + 1 508 439 9008
   EMail: sporetsky@reefpoint.com

   Rajiv Papneja
   Isocore
   12359 Sunrise Valley Drive
   Reston, VA 22102
   USA
   Phone: 1 703 860 9273
   Email: rpapneja@isocore.com

   Jay Karthik
   Cisco Systems
   300 Beaver Brook Road
   Boxborough, MA 01719
   USA
   Phone: +1 978 936 0533
   Email: jkarthik@cisco.com

   Samir Vapiwala
   Cisco System
   300 Beaver Brook Road
   Boxborough, MA 01719
   USA
   Phone: +1 978 936 1484
   Email: vapiwala@cisco.com


Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
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   This document and the information contained herein are provided
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   ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
   FOR A PARTICULAR PURPOSE.

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Acknowledgement
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