path: root/doc/rfc/rfc6777.txt

Internet Engineering Task Force (IETF)                       W. Sun, Ed.
Request for Comments: 6777                                          SJTU
Category: Standards Track                                  G. Zhang, Ed.
ISSN: 2070-1721                                                     CATR
                                                                  J. Gao
                                                                  Huawei
                                                                  G. Xie
                                                            UC Riverside
                                                              R. Papneja
                                                                  Huawei
                                                           November 2012


 Label Switched Path (LSP) Data Path Delay Metrics in Generalized MPLS
            and MPLS Traffic Engineering (MPLS-TE) Networks

Abstract

   When setting up a Label Switched Path (LSP) in Generalized MPLS
   (GMPLS) and MPLS Traffic Engineering (MPLS-TE) networks, the
   completion of the signaling process does not necessarily mean that
   the cross-connection along the LSP has been programmed accordingly
   and in a timely manner.  Meanwhile, the completion of the signaling
   process may be used by LSP users or applications that control their
   use as an indication that the data path has become usable.  The
   existence of the inconsistency between the signaling messages and
   cross-connection programming, and the possible failure of cross-
   connection programming, if not properly treated, will result in data
   loss or even application failure.  Characterization of this
   performance can thus help designers to improve the way in which LSPs
   are used and to make applications or tools that depend on and use
   LSPs more robust.  This document defines a series of performance
   metrics to evaluate the connectivity of the data path in the
   signaling process.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6777.



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Copyright Notice

   Copyright (c) 2012 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 ....................................................4
   2. Conventions Used in This Document ...............................5
   3. Overview of Performance Metrics .................................5
   4. Terms Used in This Document .....................................6
   5. A Singleton Definition for RRFD .................................7
      5.1. Motivation .................................................7
      5.2. Metric Name ................................................7
      5.3. Metric Parameters ..........................................7
      5.4. Metric Units ...............................................7
      5.5. Definition .................................................8
      5.6. Discussion .................................................8
      5.7. Methodologies ..............................................9
   6. A Singleton Definition for RSRD ................................10
      6.1. Motivation ................................................10
      6.2. Metric Name ...............................................10
      6.3. Metric Parameters .........................................10
      6.4. Metric Units ..............................................11
      6.5. Definition ................................................11
      6.6. Discussion ................................................11
      6.7. Methodologies .............................................12
   7. A Singleton Definition for PRFD ................................13
      7.1. Motivation ................................................13
      7.2. Metric Name ...............................................13
      7.3. Metric Parameters .........................................13
      7.4. Metric Units ..............................................13
      7.5. Definition ................................................14
      7.6. Discussion ................................................14
      7.7. Methodologies .............................................15






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   8. A Singleton Definition for PSFD ................................16
      8.1. Motivation ................................................16
      8.2. Metric Name ...............................................16
      8.3. Metric Parameters .........................................16
      8.4. Metric Units ..............................................16
      8.5. Definition ................................................17
      8.6. Discussion ................................................17
      8.7. Methodologies .............................................18
   9. A Singleton Definition for PSRD ................................19
      9.1. Motivation ................................................19
      9.2. Metric Name ...............................................19
      9.3. Metric Parameters .........................................19
      9.4. Metric Units ..............................................19
      9.5. Definition ................................................20
      9.6. Discussion ................................................20
      9.7. Methodologies .............................................21
   10. A Definition for Samples of Data Path Delay ...................22
      10.1. Metric Name ..............................................22
      10.2. Metric Parameters ........................................22
      10.3. Metric Units .............................................22
      10.4. Definition ...............................................22
      10.5. Discussion ...............................................23
      10.6. Methodologies ............................................23
      10.7. Typical Testing Cases ....................................23
           10.7.1. With No LSP in the Network ........................23
           10.7.2. With a Number of LSPs in the Network ..............24
   11. Some Statistics Definitions for Metrics to Report .............24
      11.1. The Minimum of the Metric ................................24
      11.2. The Median of the Metric .................................24
      11.3. The Percentile of the Metric .............................24
      11.4. Failure Probability ......................................25
           11.4.1. Failure Count .....................................25
           11.4.2. Failure Ratio .....................................25
   12. Security Considerations .......................................25
   13. References ....................................................26
      13.1. Normative References .....................................26
      13.2. Informative References ...................................26
   Appendix A. Acknowledgements ......................................27
   Appendix B. Contributors ..........................................28












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1.  Introduction

   Label Switched Paths (LSPs) are established, controlled, and
   allocated for use by management tools or directly by the components
   that use them.  In this document, we call such management tools and
   the components that use LSPs "applications".  Such applications may
   be Network Management Systems (NMSs); hardware or software components
   that forward data onto virtual links; programs or tools that use
   dedicated links; or any other user of an LSP.

   Ideally, the completion of the signaling process means that the
   signaled LSP is ready to carry traffic.  However, in actual
   implementations, vendors may choose to program the cross-connection
   in a pipelined manner, so that the overall LSP provisioning delay can
   be reduced.  In such situations, the data path may not be ready for
   use instantly after the signaling process completes.  Implementation
   deficiency may also cause inconsistency between the signaling process
   and data path provisioning.  For example, if the data plane fails to
   program the cross-connection accordingly but does not manage to
   report this to the control plane, the signaling process may complete
   successfully while the corresponding data path will never become
   functional at all.

   On the other hand, the completion of the signaling process may be
   used in many cases as an indication of data path connectivity.  For
   example, when invoking through the User-Network Interface (UNI)
   [RFC4208], a client device or an application may use the reception of
   the correct Resv message as an indication that the data path is fully
   functional and start to transmit traffic.  This will result in data
   loss or even application failure.

   Although RSVP(-TE) specifications have suggested that the cross-
   connections are programmed before signaling messages are propagated
   upstream, it is still worthwhile to verify the conformance of an
   implementation and measure the delay, when necessary.

   This document defines a series of performance metrics to evaluate the
   connectivity of the data path during the signaling process.  The
   metrics defined in this document complement the control plane metrics
   defined in [RFC5814].  These metrics can be used to verify the
   conformance of implementations against related specifications, as
   elaborated in [RFC6383].  They also can be used to build more robust
   applications.








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2.  Conventions Used in This Document

   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 [RFC2119].

3.  Overview of Performance Metrics

   In this memo, we define five performance metrics to characterize the
   performance of data path provisioning with GMPLS/MPLS-TE signaling.
   These metrics complement the metrics defined in [RFC5814], in the
   sense that the completion of the signaling process for an LSP and the
   programming of cross-connections along the LSP may not be consistent.
   The performance metrics in [RFC5814] characterize the performance of
   LSP provisioning from the pure signaling point of view, while the
   metric in this document takes into account the validity of the data
   path.

   The five metrics are:

   o  Resv Received, Forward Data (RRFD) - the delay between the point
      when the Resv message is received by the ingress node and the
      forward data path becomes ready for use.

   o  Resv Sent, Reverse Data (RSRD) - the delay between the point when
      the Resv message is sent by the egress node and the reverse data
      path becomes ready for use.

   o  PATH Received, Forward Data (PRFD) - the delay between the point
      when the PATH message is received by the egress node and the
      forward data path becomes ready for use.

   o  PATH Sent, Forward Data (PSFD) - the delay between the point when
      the PATH message is sent by the ingress node and the forward data
      path becomes ready for use.

   o  PATH Sent, Reverse Data (PSRD) - the delay between the point when
      the PATH message is sent by the ingress node and the reverse data
      path becomes ready for use.

   As in [RFC5814], we continue to use the structures and notions
   introduced and discussed in the IP Performance Metrics (IPPM)
   Framework documents [RFC2330] [RFC2679] [RFC2681].  The reader is
   assumed to be familiar with the notions in those documents.  The
   reader is also assumed to be familiar with the definitions in
   [RFC5814].





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4.  Terms Used in This Document

   o  Forward data path - the data path from the ingress node to the
      egress node.  Instances of a forward data path include the data
      path of a unidirectional LSP and a data path from the ingress node
      to the egress node in a bidirectional LSP.

   o  Reverse data path - the data path from the egress node to the
      ingress node in a bidirectional LSP.

   o  Data path delay - the time needed to complete the data path
      configuration, in relation to the signaling process.  Five types
      of data path delay are defined in this document, namely RRFD,
      RSRD, PRFD, PSFD, and PSRD.  Data path delay as used in this
      document must be distinguished from the transmission delay along
      the data path, i.e., the time needed to transmit traffic from one
      side of the data path to the other.

   o  Error-free signal - data-plane-specific indication of connectivity
      of the data path.  For example, for interfaces capable of packet
      switching, the reception of the first error-free packet from one
      side of the LSP to the other may be used as the error-free signal.
      For Synchronous Digital Hierarchy/Synchronous Optical Network
      (SDH/SONET) cross-connects, the disappearance of alarm can be used
      as the error-free signal.  Throughout this document, we will use
      "error-free signal" as a general term.  An implementation must
      choose a proper data path signal that is specific to the data path
      technology being tested.

   o  Ingress/egress node - in this memo, an ingress/egress node means a
      measurement endpoint with both control plane and data plane
      features.  Typically, the control plane part on an ingress/egress
      node interacts with the control plane of the network under test.
      The data plane part of an ingress/egress node will generate data
      path signals and send the signal to the data plane of the network
      under test, or receive data path signals from the network under
      test.














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5.  A Singleton Definition for RRFD

   This part defines a metric for forward data path delay when an LSP is
   set up.

   As described in [RFC6383], the completion of the RSVP-TE signaling
   process does not necessarily mean that the cross-connections along
   the LSP being set up are in place and ready to carry traffic.  This
   metric defines the time difference between the reception of a Resv
   message by the ingress node and the completion of the cross-
   connection programming along the forward data path.

5.1.  Motivation

   RRFD is useful for the following reasons:

   o  For the reasons described in [RFC6383], the data path may not be
      ready for use instantly after the completion of the RSVP-TE
      signaling process.  The delay itself is part of the implementation
      performance.

   o  The completion of the signaling process may be used by application
      designers as an indication of data path connectivity.  The
      existence of this delay and the potential failure of cross-
      connection programming, if not properly treated, will result in
      data loss or application failure.  The typical value of this delay
      can thus help designers to improve the application model.

5.2.  Metric Name

   RRFD = Resv Received, Forward Data path

5.3.  Metric Parameters

   o  ID0, the ingress Label Switching Router (LSR) ID

   o  ID1, the egress LSR ID

   o  T, a time when the setup is attempted

5.4.  Metric Units

   The value of RRFD is either a real number of milliseconds or
   undefined.







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5.5.  Definition

   For a real number dT,

      RRFD from ingress node ID0 to egress node ID1 at T is dT

   means that

   o  ingress node ID0 sends a PATH message to egress node ID1,

   o  the last bit of the corresponding Resv message is received by
      ingress node ID0 at T, and

   o  an error-free signal is received by egress node ID1 by using a
      data-plane-specific test pattern at T+dT.

5.6.  Discussion

   The following issues are likely to come up in practice:

   o  The accuracy of RRFD depends on the clock resolution of both the
      ingress node and egress node.  Clock synchronization between the
      ingress node and egress node is required.

   o  The accuracy of RRFD is also dependent on how the error-free
      signal is received and may differ significantly when the
      underlying data plane technology is different.  For instance, for
      an LSP between a pair of Ethernet interfaces, the ingress node may
      use a rate-based method to verify the connectivity of the data
      path and use the reception of the first error-free frame as the
      error-free signal.  In this case, the interval between two
      successive frames has a significant impact on accuracy.  It is
      RECOMMENDED that the ingress node use small intervals, under the
      condition that the injected traffic does not exceed the capacity
      of the forward data path.  The value of such intervals MUST be
      reported.

   o  The accuracy of RRFD is also dependent on the time needed to
      propagate the error-free signal from the ingress node to the
      egress node.  A typical value for propagating the error-free
      signal from the ingress node to the egress node under the same
      measurement setup MAY be reported.  The methodology to obtain such
      values is outside the scope of this document.

   o  The accuracy of this metric is also dependent on the physical-
      layer serialization/deserialization of the test signal for certain
      data path technologies.  For instance, for an LSP between a pair




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      of low-speed Ethernet interfaces, the time needed to serialize/
      deserialize a large frame may not be negligible.  In this case, it
      is RECOMMENDED that the ingress node use small frames.  The
      average length of the frame MAY be reported.

   o  It is possible that under some implementations, a node may program
      the cross-connection before it sends a PATH message further
      downstream, and the data path may be ready for use before a Resv
      message reaches the ingress node.  In such cases, RRFD can be a
      negative value.  It is RECOMMENDED that a PRFD measurement be
      carried out to further characterize the forward data path delay
      when a negative RRFD value is observed.

   o  If an error-free signal is received by the egress node before a
      PATH message is sent on the ingress node, an error MUST be
      reported and the measurement SHOULD terminate.

   o  If the corresponding Resv message is received but no error-free
      signal is received by the egress node within a reasonable period
      of time, i.e., a threshold, RRFD MUST be treated as undefined.
      The value of the threshold MUST be reported.

   o  If the LSP setup fails, this metric value MUST NOT be counted.

5.7.  Methodologies

   Generally, the methodology would proceed as follows:

   o  Make sure that the network has enough resources to set up the
      requested LSP.

   o  Start the data path measurement and/or monitoring procedures on
      the ingress node and egress node.  If an error-free signal is
      received by the egress node before a PATH message is sent, report
      an error and terminate the measurement.

   o  At the ingress node, form the PATH message according to the LSP
      requirements and send the message towards the egress node.

   o  Upon receiving the last bit of the corresponding Resv message,
      take the timestamp (T1) on the ingress node as soon as possible.

   o  When an error-free signal is observed on the egress node, take the
      timestamp (T2) as soon as possible.  An estimate of RRFD (T2 - T1)
      can be computed.






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   o  If the corresponding Resv message arrives but no error-free signal
      is received within a reasonable period of time by the ingress
      node, RRFD is deemed to be undefined.

   o  If the LSP setup fails, RRFD is not counted.

6.  A Singleton Definition for RSRD

   This part defines a metric for reverse data path delay when an LSP is
   set up.

   As described in [RFC6383], the completion of the RSVP-TE signaling
   process does not necessarily mean that the cross-connections along
   the LSP being set up are in place and ready to carry traffic.  This
   metric defines the time difference between the completion of the
   signaling process and the completion of the cross-connection
   programming along the reverse data path.  This metric MAY be used
   together with RRFD to characterize the data path delay of a
   bidirectional LSP.

6.1.  Motivation

   RSRD is useful for the following reasons:

   o  For the reasons described in [RFC6383], the data path may not be
      ready for use instantly after the completion of the RSVP-TE
      signaling process.  The delay itself is part of the implementation
      performance.

   o  The completion of the signaling process may be used by application
      designers as an indication of data path connectivity.  The
      existence of this delay and the possible failure of cross-
      connection programming, if not properly treated, will result in
      data loss or application failure.  The typical value of this delay
      can thus help designers to improve the application model.

6.2.  Metric Name

   RSRD = Resv Sent, Reverse Data path

6.3.  Metric Parameters

   o  ID0, the ingress LSR ID

   o  ID1, the egress LSR ID

   o  T, a time when the setup is attempted




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6.4.  Metric Units

   The value of RSRD is either a real number of milliseconds or
   undefined.

6.5.  Definition

   For a real number dT,

      RSRD from ingress node ID0 to egress node ID1 at T is dT

   means that

   o  ingress node ID0 sends a PATH message to egress node ID1,

   o  the last bit of the corresponding Resv message is sent by egress
      node ID1 at T, and

   o  an error-free signal is received by the ingress node ID0 using a
      data-plane-specific test pattern at T+dT.

6.6.  Discussion

   The following issues are likely to come up in practice:

   o  The accuracy of RSRD depends on the clock resolution of both the
      ingress node and egress node.  Clock synchronization between the
      ingress node and egress node is required.

   o  The accuracy of RSRD is also dependent on how the error-free
      signal is received and may differ significantly when the
      underlying data plane technology is different.  For instance, for
      an LSP between a pair of Ethernet interfaces, the egress node
      (sometimes the tester) may use a rate-based method to verify the
      connectivity of the data path and use the reception of the first
      error-free frame as the error-free signal.  In this case, the
      interval between two successive frames has a significant impact on
      accuracy.  It is RECOMMENDED in this case that the egress node use
      small intervals, under the condition that the injected traffic
      does not exceed the capacity of the reverse data path.  The value
      of the interval MUST be reported.

   o  The accuracy of RSRD is also dependent on the time needed to
      propagate the error-free signal from the egress node to the
      ingress node.  A typical value for propagating the error-free
      signal from the egress node to the ingress node under the same
      measurement setup MAY be reported.  The methodology to obtain such
      values is outside the scope of this document.



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   o  The accuracy of this metric is also dependent on the physical-
      layer serialization/deserialization of the test signal for certain
      data path technologies.  For instance, for an LSP between a pair
      of low-speed Ethernet interfaces, the time needed to serialize/
      deserialize a large frame may not be negligible.  In this case, it
      is RECOMMENDED that the egress node use small frames.  The average
      length of the frame MAY be reported.

   o  If the corresponding Resv message is sent but no error-free signal
      is received by the ingress node within a reasonable period of
      time, i.e., a threshold, RSRD MUST be treated as undefined.  The
      value of the threshold MUST be reported.

   o  If an error-free signal is received before a PATH message is sent
      on the ingress node, an error MUST be reported and the measurement
      SHOULD terminate.

   o  If the LSP setup fails, this metric value MUST NOT be counted.

6.7.  Methodologies

   Generally, the methodology would proceed as follows:

   o  Make sure that the network has enough resources to set up the
      requested LSP.

   o  Start the data path measurement and/or monitoring procedures on
      the ingress node and egress node.  If an error-free signal is
      received by the ingress node before a PATH message is sent, report
      an error and terminate the measurement.

   o  At the ingress node, form the PATH message according to the LSP
      requirements and send the message towards the egress node.

   o  Upon sending the last bit of the corresponding Resv message, take
      the timestamp (T1) on the egress node as soon as possible.

   o  When an error-free signal is observed on the ingress node, take
      the timestamp (T2) as soon as possible.  An estimate of RSRD
      (T2 - T1) can be computed.

   o  If the LSP setup fails, RSRD is not counted.

   o  If no error-free signal is received within a reasonable period of
      time by the ingress node, RSRD is deemed to be undefined.






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7.  A Singleton Definition for PRFD

   This part defines a metric for forward data path delay when an LSP is
   set up.

   In an RSVP-TE implementation, when setting up an LSP, each node may
   choose to program the cross-connection before it sends a PATH message
   further downstream.  In this case, the forward data path may become
   ready for use before the signaling process completes, i.e., before
   the Resv message reaches the ingress node.  This metric can be used
   to identify such an implementation practice and give useful
   information to application designers.

7.1.  Motivation

   PRFD is useful for the following reasons:

   o  PRFD can be used to identify an RSVP-TE implementation practice in
      which cross-connections are programmed before a PATH message is
      sent downstream.

   o  The value of PRFD may also help application designers to fine-tune
      their application model.

7.2.  Metric Name

   PRFD = PATH Received, Forward Data path

7.3.  Metric Parameters

   o  ID0, the ingress LSR ID

   o  ID1, the egress LSR ID

   o  T, a time when the setup is attempted

7.4.  Metric Units

   The value of PRFD is either a real number of milliseconds or
   undefined.











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7.5.  Definition

   For a real number dT,

      PRFD from ingress node ID0 to egress node ID1 at T is dT

   means that

   o  ingress node ID0 sends a PATH message to egress node ID1,

   o  the last bit of the PATH message is received by egress node ID1 at
      T, and

   o  an error-free signal is received by the egress node ID1 using a
      data-plane-specific test pattern at T+dT.

7.6.  Discussion

   The following issues are likely to come up in practice:

   o  The accuracy of PRFD depends on the clock resolution of the egress
      node.  Clock synchronization between the ingress node and egress
      node is not required.

   o  The accuracy of PRFD is also dependent on how the error-free
      signal is received and may differ significantly when the
      underlying data plane technology is different.  For instance, for
      an LSP between a pair of Ethernet interfaces, the egress node
      (sometimes the tester) may use a rate-based method to verify the
      connectivity of the data path and use the reception of the first
      error-free frame as the error-free signal.  In this case, the
      interval between two successive frames has a significant impact on
      accuracy.  It is RECOMMENDED in this case that the ingress node
      use small intervals, under the condition that the injected traffic
      does not exceed the capacity of the forward data path.  The value
      of the interval MUST be reported.

   o  The accuracy of PRFD is also dependent on the time needed to
      propagate the error-free signal from the ingress node to the
      egress node.  A typical value for propagating the error-free
      signal from the ingress node to the egress node under the same
      measurement setup MAY be reported.  The methodology to obtain such
      values is outside the scope of this document.

   o  The accuracy of this metric is also dependent on the physical-
      layer serialization/deserialization of the test signal for certain
      data path technologies.  For instance, for an LSP between a pair




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      of low-speed Ethernet interfaces, the time needed to serialize/
      deserialize a large frame may not be negligible.  In this case, it
      is RECOMMENDED that the ingress node use small frames.  The
      average length of the frame MAY be reported.

   o  If an error-free signal is received before a PATH message is sent,
      an error MUST be reported and the measurement SHOULD terminate.

   o  If the LSP setup fails, this metric value MUST NOT be counted.

   o  This metric SHOULD be used together with RRFD.  It is RECOMMENDED
      that a PRFD measurement be carried out after a negative RRFD value
      has already been observed.

7.7.  Methodologies

   Generally, the methodology would proceed as follows:

   o  Make sure that the network has enough resources to set up the
      requested LSP.

   o  Start the data path measurement and/or monitoring procedures on
      the ingress node and egress node.  If an error-free signal is
      received by the egress node before a PATH message is sent, report
      an error and terminate the measurement.

   o  At the ingress node, form the PATH message according to the LSP
      requirements and send the message towards the egress node.

   o  Upon receiving the last bit of the PATH message, take the
      timestamp (T1) on the egress node as soon as possible.

   o  When an error-free signal is observed on the egress node, take the
      timestamp (T2) as soon as possible.  An estimate of PRFD (T2 - T1)
      can be computed.

   o  If the LSP setup fails, PRFD is not counted.

   o  If no error-free signal is received within a reasonable period of
      time by the egress node, PRFD is deemed to be undefined.











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8.  A Singleton Definition for PSFD

   This part defines a metric for forward data path delay when an LSP is
   set up.

   As described in [RFC6383], the completion of the RSVP-TE signaling
   process does not necessarily mean that the cross-connections along
   the LSP being set up are in place and ready to carry traffic.  This
   metric defines the time difference between the point when the PATH
   message is sent by the ingress node and the completion of the cross-
   connection programming along the LSP forward data path.

8.1.  Motivation

   PSFD is useful for the following reasons:

   o  For the reasons described in [RFC6383], the data path setup delay
      may not be consistent with the control plane LSP setup delay.  The
      data path setup delay metric is more precise for LSP setup
      performance measurement.

   o  The completion of the signaling process may be used by application
      designers as an indication of data path connectivity.  The
      difference between the control plane setup delay and data path
      delay, and the potential failure of cross-connection programming,
      if not properly treated, will result in data loss or application
      failure.  This metric can thus help designers to improve the
      application model.

8.2.  Metric Name

   PSFD = PATH Sent, Forward Data path

8.3.  Metric Parameters

   o  ID0, the ingress LSR ID

   o  ID1, the egress LSR ID

   o  T, a time when the setup is attempted

8.4.  Metric Units

   The value of PSFD is either a real number of milliseconds or
   undefined.






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8.5.  Definition

   For a real number dT,

      PSFD from ingress node ID0 to egress node ID1 at T is dT

   means that

   o  ingress node ID0 sends the first bit of a PATH message to egress
      node ID1 at T, and

   o  an error-free signal is received by the egress node ID1 using a
      data-plane-specific test pattern at T+dT.

8.6.  Discussion

   The following issues are likely to come up in practice:

   o  The accuracy of PSFD depends on the clock resolution of both the
      ingress node and egress node.  Clock synchronization between the
      ingress node and egress node is required.

   o  The accuracy of PSFD is also dependent on how the error-free
      signal is received and may differ significantly when the
      underlying data plane technology is different.  For instance, for
      an LSP between a pair of Ethernet interfaces, the ingress node may
      use a rate-based method to verify the connectivity of the data
      path and use the reception of the first error-free frame as the
      error-free signal.  In this case, the interval between two
      successive frames has a significant impact on accuracy.  It is
      RECOMMENDED that the ingress node use small intervals, under the
      condition that the injected traffic does not exceed the capacity
      of the forward data path.  The value of the interval MUST be
      reported.

   o  The accuracy of PSFD is also dependent on the time needed to
      propagate the error-free signal from the ingress node to the
      egress node.  A typical value for propagating the error-free
      signal from the ingress node to the egress node under the same
      measurement setup MAY be reported.  The methodology to obtain such
      values is outside the scope of this document.

   o  The accuracy of this metric is also dependent on the physical-
      layer serialization/deserialization of the test signal for certain
      data path technologies.  For instance, for an LSP between a pair






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      of low-speed Ethernet interfaces, the time needed to serialize/
      deserialize a large frame may not be negligible.  In this case, it
      is RECOMMENDED that the ingress node use small frames.  The
      average length of the frame MAY be reported.

   o  If an error-free signal is received before a PATH message is sent,
      an error MUST be reported and the measurement SHOULD terminate.

   o  If the LSP setup fails, this metric value MUST NOT be counted.

   o  If the PATH message is sent by the ingress node but no error-free
      signal is received by the egress node within a reasonable period
      of time, i.e., a threshold, PSFD MUST be treated as undefined.
      The value of the threshold MUST be reported.

8.7.  Methodologies

   Generally, the methodology would proceed as follows:

   o  Make sure that the network has enough resources to set up the
      requested LSP.

   o  Start the data path measurement and/or monitoring procedures on
      the ingress node and egress node.  If an error-free signal is
      received by the egress node before a PATH message is sent, report
      an error and terminate the measurement.

   o  At the ingress node, form the PATH message according to the LSP
      requirements and send the message towards the egress node.  A
      timestamp (T1) may be stored locally in the ingress node when the
      PATH message packet is sent towards the egress node.

   o  When an error-free signal is observed on the egress node, take the
      timestamp (T2) as soon as possible.  An estimate of PSFD (T2 - T1)
      can be computed.

   o  If the LSP setup fails, PSFD is not counted.

   o  If no error-free signal is received within a reasonable period of
      time by the egress node, PSFD is deemed to be undefined.











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9.  A Singleton Definition for PSRD

   This part defines a metric for reverse data path delay when an LSP is
   set up.

   This metric defines the time difference between the point when the
   ingress node sends the PATH message and the completion of the cross-
   connection programming along the LSP reverse data path.  This metric
   MAY be used together with PSFD to characterize the data path delay of
   a bidirectional LSP.

9.1.  Motivation

   PSRD is useful for the following reasons:

   o  For the reasons described in [RFC6383], the data path setup delay
      may not be consistent with the control plane LSP setup delay.  The
      data path setup delay metric is more precise for LSP setup
      performance measurement.

   o  The completion of the signaling process may be used by application
      designers as an indication of data path connectivity.  The
      difference between the control plane setup delay and data path
      delay, and the potential failure of cross-connection programming,
      if not properly treated, will result in data loss or application
      failure.  This metric can thus help designers to improve the
      application model.

9.2.  Metric Name

   PSRD = PATH Sent, Reverse Data path

9.3.  Metric Parameters

   o  ID0, the ingress LSR ID

   o  ID1, the egress LSR ID

   o  T, a time when the setup is attempted

9.4.  Metric Units

   The value of PSRD is either a real number of milliseconds or
   undefined.







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9.5.  Definition

   For a real number dT,

      PSRD from ingress node ID0 to egress node ID1 at T is dT

   means that

   o  ingress node ID0 sends the first bit of a PATH message to egress
      node ID1 at T, and

   o  an error-free signal is received through the reverse data path
      by the ingress node ID0 using a data-plane-specific test pattern
      at T+dT.

9.6.  Discussion

   The following issues are likely to come up in practice:

   o  The accuracy of PSRD depends on the clock resolution of the
      ingress node.  Clock synchronization between the ingress node and
      egress node is not required.

   o  The accuracy of PSRD is also dependent on how the error-free
      signal is received and may differ significantly when the
      underlying data plane technology is different.  For instance, for
      an LSP between a pair of Ethernet interfaces, the egress node may
      use a rate-based method to verify the connectivity of the data
      path and use the reception of the first error-free frame as the
      error-free signal.  In this case, the interval between two
      successive frames has a significant impact on accuracy.  It is
      RECOMMENDED that the egress node use small intervals, under the
      condition that the injected traffic does not exceed the capacity
      of the forward data path.  The value of the interval MUST be
      reported.

   o  The accuracy of PSRD is also dependent on the time needed to
      propagate the error-free signal from the egress node to the
      ingress node.  A typical value for propagating the error-free
      signal from the egress node to the ingress node under the same
      measurement setup MAY be reported.  The methodology to obtain such
      values is outside the scope of this document.

   o  The accuracy of this metric is also dependent on the physical-
      layer serialization/deserialization of the test signal for certain
      data path technologies.  For instance, for an LSP between a pair





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      of low-speed Ethernet interfaces, the time needed to serialize/
      deserialize a large frame may not be negligible.  In this case, it
      is RECOMMENDED that the egress node use small frames.  The average
      length of the frame MAY be reported.

   o  If an error-free signal is received before a PATH message is sent,
      an error MUST be reported and the measurement SHOULD terminate.

   o  If the LSP setup fails, this metric value MUST NOT be counted.

   o  If the PATH message is sent by the ingress node but no error-free
      signal is received by the ingress node within a reasonable period
      of time, i.e., a threshold, PSRD MUST be treated as undefined.
      The value of the threshold MUST be reported.

9.7.  Methodologies

   Generally, the methodology would proceed as follows:

   o  Make sure that the network has enough resources to set up the
      requested LSP.

   o  Start the data path measurement and/or monitoring procedures on
      the ingress node and egress node.  If an error-free signal is
      received by the egress node before a PATH message is sent, report
      an error and terminate the measurement.

   o  At the ingress node, form the PATH message according to the LSP
      requirements and send the message towards the egress node.  A
      timestamp (T1) may be stored locally in the ingress node when the
      PATH message packet is sent towards the egress node.

   o  When an error-free signal is observed on the ingress node, take
      the timestamp (T2) as soon as possible.  An estimate of PSRD
      (T2 - T1) can be computed.

   o  If the LSP setup fails, PSRD is not counted.

   o  If no error-free signal is received within a reasonable period of
      time by the ingress node, PSRD is deemed to be undefined.











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10.  A Definition for Samples of Data Path Delay

   In Sections 5, 6, 7, 8, and 9, we defined the singleton metrics of
   data path delay.  Now, we define how to get one particular sample of
   such a delay.  Sampling is done to select a particular portion of
   singleton values of the given parameters.  As in [RFC2330], we use
   Poisson sampling as an example.

10.1.  Metric Name

   Type <X> data path delay sample, where X is either RRFD, RSRD, PRFD,
   PSFD, or PSRD.

10.2.  Metric Parameters

   o  ID0, the ingress LSR ID

   o  ID1, the egress LSR ID

   o  T0, a time

   o  Tf, a time

   o  Lambda, a rate in reciprocal milliseconds

   o  Th, the LSP holding time

   o  Td, the maximum waiting time for successful LSP setup

   o  Ts, the maximum waiting time for an error-free signal

10.3.  Metric Units

   A sequence of pairs; the elements of each pair are:

   o  T, a time when setup is attempted

   o  dT, either a real number of milliseconds or undefined

10.4.  Definition

   Given T0, Tf, and Lambda, compute a pseudo-random Poisson process
   beginning at or before T0, with average arrival rate Lambda, and
   ending at or after Tf.  Those time values greater than or equal to T0
   and less than or equal to Tf are then selected.  At each of the times
   in this process, we obtain the value of a data path delay sample of
   type <X> at this time.  The value of the sample is the sequence made




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   up of the resulting <time, type <X> data path delay> pairs.  If there
   are no such pairs, the sequence is of length zero and the sample is
   said to be empty.

10.5.  Discussion

   The following issues are likely to come up in practice:

   o  The parameters Lambda, Th, and Td should be carefully chosen, as
      explained in the discussions for LSP setup delay (see [RFC5814]).

   o  The parameter Ts should be carefully chosen and MUST be reported
      along with the LSP forward/reverse data path delay sample.

10.6.  Methodologies

   Generally, the methodology would proceed as follows:

   o  Select specific times, using the specified Poisson arrival
      process.

   o  Set up the LSP and obtain the value of type <X> data path delay.

   o  Release the LSP after Th, and wait for the next Poisson arrival
      process.

10.7.  Typical Testing Cases

10.7.1.  With No LSP in the Network

10.7.1.1.  Motivation

   Data path delay with no LSP in the network is important because this
   reflects the inherent delay of a device implementation.  The minimum
   value provides an indication of the delay that will likely be
   experienced when an LSP data path is configured under light traffic
   load.

10.7.1.2.  Methodologies

   Make sure that there is no LSP in the network, and proceed with the
   methodologies described in Section 10.6.









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10.7.2.  With a Number of LSPs in the Network

10.7.2.1.  Motivation

   Data path delay with a number of LSPs in the network is important
   because it reflects the performance of an operational network with
   considerable load.  This delay may vary significantly as the number
   of existing LSPs varies.  It can be used as a scalability metric of a
   device implementation.

10.7.2.2.  Methodologies

   o  Set up the required number of LSPs.

   o  Wait until the network reaches a stable state.

   o  Then proceed with the methodologies described in Section 10.6.

11.  Some Statistics Definitions for Metrics to Report

   Given the samples of the performance metric, we now offer several
   statistics of these samples to report.  From these statistics, we can
   draw some useful conclusions regarding a GMPLS network.  The value of
   these metrics is either a real number of milliseconds or undefined.
   In the following discussion, we only consider the finite values.

11.1.  The Minimum of the Metric

   The minimum of the metric is the minimum of all the dT values in the
   sample.  In computing this, undefined values SHOULD be treated as
   infinitely large.  Note that this means that the minimum could thus
   be undefined if all the dT values are undefined.  In addition, the
   metric minimum SHOULD be set to undefined if the sample is empty.

11.2.  The Median of the Metric

   The median of the metric is the median of the dT values in the given
   sample.  In computing the median, the undefined values MUST NOT be
   included.  The median SHOULD be set to undefined if all the dT values
   are undefined, or if the sample is empty.  When the number of defined
   values in the given sample is small, the metric median may not be
   typical and SHOULD be used carefully.

11.3.  The Percentile of the Metric

   The "empirical distribution function" (EDF) of a set of scalar
   measurements is a function F(x), which, for any x, gives the
   fractional proportion of the total measurements that were <= x.



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   Given a percentage X, the Xth percentile of the metric means the
   smallest value of x for which F(x) >= X.  In computing the
   percentile, undefined values MUST NOT be included.

   See [RFC2330] for further details.

11.4.  Failure Probability

   Given the samples of the performance metric, we now offer two
   statistics of failure events of these samples to report: Failure
   Count and Failure Ratio.  The two statistics can be applied to both
   the forward data path and reverse data path.  For example, when a
   sample of RRFD has been obtained, the forward data path failure
   statistics can be obtained, while a sample of RSRD can be used to
   calculate the reverse data path failure statistics.  Detailed
   definitions of Failure Count and Failure Ratio are given below.

11.4.1.  Failure Count

   Failure Count is defined as the number of the undefined value of the
   corresponding performance metric in a sample.  The value of Failure
   Count is an integer.

11.4.2.  Failure Ratio

   Failure Ratio is the percentage of the number of failure events to
   the total number of requests in a sample.  Here, a failure event
   means that the signaling completes with no error, while no error-free
   signal is observed.  The calculation for Failure Ratio is defined as
   follows:

   Failure Ratio = Number of undefined value/(Number of valid metric
   values + Number of undefined value) * 100%.

12.  Security Considerations

   In the control plane, since the measurement endpoints must be
   conformant to signaling specifications and behave as normal signaling
   endpoints, it will not incur security issues other than normal LSP
   provisioning.  However, the measurement parameters must be carefully
   selected so that the measurements inject trivial amounts of
   additional traffic into the networks they measure.  If they inject
   "too much" traffic, they can skew the results of the measurement and
   in extreme cases cause congestion and denial of service.

   In the data plane, the measurement endpoint MUST use a signal that is
   consistent with what is specified in the control plane.  For example,
   in a packet switched case, the traffic injected into the data plane



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   MUST NOT exceed the specified rate in the corresponding LSP setup
   request.  In a wavelength switched case, the measurement endpoint
   MUST use the specified or negotiated lambda with appropriate power.

   The security considerations pertaining to the original RSVP protocol
   [RFC2205] and its TE extensions [RFC3209] also remain relevant.

13.  References

13.1.  Normative References

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

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Delay Metric for IPPM", RFC 2679, September 1999.

   [RFC2681]  Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
              Delay Metric for IPPM", RFC 2681, September 1999.

   [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.

13.2.  Informative References

   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
              "Framework for IP Performance Metrics", RFC 2330,
              May 1998.

   [RFC4208]  Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
              "Generalized Multiprotocol Label Switching (GMPLS) User-
              Network Interface (UNI): Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Support for the Overlay
              Model", RFC 4208, October 2005.

   [RFC5814]  Sun, W. and G. Zhang, "Label Switched Path (LSP) Dynamic
              Provisioning Performance Metrics in Generalized MPLS
              Networks", RFC 5814, March 2010.

   [RFC6383]  Shiomoto, K. and A. Farrel, "Advice on When It Is Safe to
              Start Sending Data on Label Switched Paths Established
              Using RSVP-TE", RFC 6383, September 2011.




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Appendix A.  Acknowledgements

   We wish to thank Adrian Farrel, Lou Berger, and Al Morton for their
   comments and help.  We also wish to thank Klaas Wierenga and Alexey
   Melnikov for their reviews.

   This document contains ideas as well as text that have appeared in
   existing IETF documents.  The authors wish to thank G. Almes, S.
   Kalidindi, and M. Zekauskas.

   We also wish to thank Weisheng Hu, Yaohui Jin, and Wei Guo in the
   state key laboratory of advanced optical communication systems and
   networks for their valuable comments.  We also wish to thank the
   National Natural Science Foundation of China (NSFC) and the
   863 program of China for their support.




































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Appendix B.  Contributors

   Bin Gu
   IXIA
   Oriental Kenzo Plaza 8M, 48 Dongzhimen Wai Street
   Dongcheng District
   Beijing  200240
   China

   Phone: +86 13611590766
   EMail: BGu@ixiacom.com


   Xueqin Wei
   Fiberhome Telecommunication Technology Co., Ltd.
   Wuhan
   China

   Phone: +86 13871127882
   EMail: xqwei@fiberhome.com.cn


   Tomohiro Otani
   KDDI R&D Laboratories, Inc.
   2-1-15 Ohara Kamifukuoka Saitama
   356-8502
   Japan

   Phone: +81-49-278-7357
   EMail: tm-otani@kddi.com


   Ruiquan Jing
   China Telecom Beijing Research Institute
   118 Xizhimenwai Avenue
   Beijing  100035
   China

   Phone: +86-10-58552000
   EMail: jingrq@ctbri.com.cn











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Authors' Addresses

   Weiqiang Sun (editor)
   Shanghai Jiao Tong University
   800 Dongchuan Road
   Shanghai  200240
   China

   Phone: +86 21 3420 5359
   EMail: sun.weiqiang@gmail.com


   Guoying Zhang (editor)
   China Academy of Telecommunication Research, MIIT, China
   No. 52 Hua Yuan Bei Lu, Haidian District
   Beijing  100191
   China

   Phone: +86 1062300103
   EMail: zhangguoying@catr.cn


   Jianhua Gao
   Huawei Technologies Co., Ltd.
   China

   Phone: +86 755 28973237
   EMail: gjhhit@huawei.com


   Guowu Xie
   University of California, Riverside
   900 University Ave.
   Riverside, CA  92521
   USA

   Phone: +1 951 237 8825
   EMail: xieg@cs.ucr.edu


   Rajiv Papneja
   Huawei Technologies
   Santa Clara, CA  95050
   Reston, VA  20190
   USA

   EMail: rajiv.papneja@huawei.com




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