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Versions: (draft-ospf-te-metric-extensions) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7471

Network Working Group                                      S. Giacalone
Internet Draft                                          Thomson Reuters
Intended status: Proposed Standard
Expires: June 2014                                              D. Ward
                                                          Cisco Systems

                                                               J. Drake
                                                       Juniper Networks

                                                                A. Atlas
                                                        Juniper Networks

                                                              S. Previdi
                                                           Cisco Systems

                                                       December 5, 2013


              OSPF Traffic Engineering (TE) Metric Extensions
                draft-ietf-ospf-te-metric-extensions-05.txt




   Abstract

   In certain networks, such as, but not limited to, financial
   information networks (e.g. stock market data providers), network
   performance criteria (e.g. latency) are becoming as critical to data
   path selection as other metrics.

   This document describes extensions to OSPF TE [RFC3630] such that
   network performance information can be distributed and collected in a
   scalable fashion. The information distributed using OSPF TE Metric
   Extensions can then be used to make path selection decisions based on
   network performance.

   Note that this document only covers the mechanisms with which network
   performance information is distributed. The mechanisms for measuring
   network performance or acting on that information, once distributed,
   are outside the scope of this document.

Status of this Memo

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





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   described in the Simplified BSD License.



Table of Contents


   1. Introduction...................................................4
   2. Conventions used in this document..............................5
   3. TE Metric Extensions to OSPF TE................................5
   4. Sub TLV Details................................................7
      4.1. Unidirectional Link Delay Sub-TLV.........................7
         4.1.1. Type.................................................7
         4.1.2. Length...............................................7


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         4.1.3. A bit................................................7
         4.1.4. Reserved.............................................7
         4.1.5. Delay Value..........................................8
      4.2. Min/Max Unidirectional Link Delay Sub-TLV.................8
         4.2.1. Type.................................................8
         4.2.2. Length...............................................8
         4.2.3. A bit................................................8
         4.2.4. Reserved.............................................9
         4.2.5. Low Delay............................................9
         4.2.6. High Delay...........................................9
         4.2.7. Reserved.............................................9
      4.3. Unidirectional Delay Variation Sub-TLV...................10
         4.3.1. Type................................................10
         4.3.2. Length..............................................10
         4.3.3. Reserved............................................10
         4.3.4. Delay Variation.....................................10
      4.4. Unidirectional Link Loss Sub-TLV.........................10
         4.4.1. Type................................................11
         4.4.2. Length..............................................11
         4.4.3. A bit...............................................11
         4.4.4. Reserved............................................11
         4.4.5. Link Loss...........................................11
      4.5. Unidirectional Residual Bandwidth Sub-TLV................12
         4.5.1. Type................................................12
         4.5.2. Length..............................................12
         4.5.3. Residual Bandwidth..................................12
      4.6. Unidirectional Available Bandwidth Sub-TLV...............13
         4.6.1. Type................................................13
         4.6.2. Length..............................................13
         4.6.3. Available Bandwidth.................................13
      4.7. Unidirectional Utilized Bandwidth Sub-TLV................13
         4.7.1. Type................................................14
         4.7.2. Length..............................................14
         4.7.3. Utilized Bandwidth..................................14
   5. Announcement Thresholds and Filters...........................14
   6. Announcement Suppression......................................15
   7. Network Stability and Announcement Periodicity................16
   8. Enabling and Disabling Sub-TLVs...............................16
   9. Static Metric Override........................................16
   10. Compatibility................................................17
   11. Security Considerations......................................17
   12. IANA Considerations..........................................17
   13. References...................................................17
      13.1. Normative References....................................17
      13.2. Informative References..................................17
   14. Acknowledgments..............................................18
   15. Author's Addresses...........................................18


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1. Introduction

   In certain networks, such as, but not limited to, financial
   information networks (e.g. stock market data providers), network
   performance information (e.g. latency) is becoming as critical to
   data path selection as other metrics.

   In these networks, extremely large amounts of money rest on the
   ability to access market data in "real time" and to predictably make
   trades faster than the competition. Because of this, using metrics
   such as hop count or cost as routing metrics is becoming only
   tangentially important. Rather, it would be beneficial to be able to
   make path selection decisions based on performance data (such as
   latency) in a cost-effective and scalable way.

   This document describes extensions to OSPF TE (hereafter called "OSPF
   TE Metric Extensions"), that can be used to distribute network
   performance information (such as link delay, delay variation, packet
   loss, residual bandwidth, and available bandwidth).

   The data distributed by OSPF TE Metric Extensions is meant to be used
   as part of the operation of the routing protocol (e.g. by replacing
   cost with latency or considering bandwidth as well as cost), by
   enhancing CSPF, or for other uses such as supplementing the data used
   by an Alto server [Alto]. With respect to CSPF, the data distributed
   by OSPF TE Metric Extensions can be used to setup, fail over, and
   fail back data paths using protocols such as RSVP-TE [RFC3209].[
   Draft-ietf-mpls-te-express-path] describes some methods for using
   this information to compute Label Switched Paths (LSPs) at the LSP
   ingress.

   Note that the mechanisms described in this document only disseminate
   performance information.  The methods for initially gathering that
   performance information, such as [RFC6375], or acting on it once it
   is distributed are outside the scope of this document.  Example
   mechanisms to measure latency, delay variation, and loss in an MPLS
   network are given in [RFC6374].  While this document does not
   specify how the performance information should be obtained, the
   measurement of delay SHOULD NOT vary significantly based upon the
   offered traffic load.  Thus, queuing delays and/or loss SHOULD NOT
   be included in any dynamic delay measurement.  For links, such as
   Forwarding Adjacencies, care must be taken that measurement of the


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   associated delay avoids significant queuing delay; that could be
   accomplished in a variety of ways, including either by measuring
   with a traffic class that experiences minimal queuing or by summing
   the measured link delays of the components of the link's path.


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 RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.



3. TE Metric Extensions to OSPF TE

   This document proposes new OSPF TE sub-TLVs that can be announced in
   OSPF TE LSAs to distribute network performance information. The
   extensions in this document build on the ones provided in OSPF TE
   [RFC3630] and GMPLS [RFC4203].

   OSPF TE LSAs [RFC3630] are opaque LSAs [RFC5250] with area flooding
   scope. Each TLV has one or more nested sub-TLVs which permit the TE
   LSA to be readily extended. There are two main types of OSPF TE LSA;
   the Router Address or Link TE LSA. Like the extensions in GMPLS
   (RFC4203), this document proposes several additional sub-TLVs for
   the Link TE LSA:

   Type  Length   Value

   TBD1  4        Unidirectional Link Delay

   TBD2  8        Low/High Unidirectional Link Delay

   TBD3  4        Unidirectional Delay Variation

   TBD4  4        Unidirectional Packet Loss

   TBD5  4        Unidirectional Residual Bandwidth

   TBD6  4        Unidirectional Available Bandwidth



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   TBD7  4        Unidirectional Utilized Bandwidth



   As can be seen in the list above, the sub-TLVs described in this
   document carry different types of network performance information.
   Many (but not all) of the sub-TLVs include a bit called the Anomalous
   (or "A") bit. When the A bit is clear (or when the sub-TLV does not
   include an A bit), the sub-TLV describes steady state link
   performance. This information could conceivably be used to construct
   a steady state performance topology for initial tunnel path
   computation, or to verify alternative failover paths.

   When network performance violates configurable link-local thresholds
   a sub-TLV with the A bit set is advertised. These sub-TLVs could be
   used by the receiving node to determine whether to fail traffic to a
   backup path, or whether to calculate an entirely new path. From an
   MPLS perspective, the intent of the A bit is to permit LSP ingress
   nodes to:

   A) Determine whether the link referenced in the sub-TLV affects any
      of the LSPs for which it is ingress. If there are, then:

   B) The node determines whether those LSPs still meet end-to-end
      performance objectives. If not, then:

   C) The node could then conceivably move affected traffic to a pre-
      established protection LSP or establish a new LSP and place the
      traffic in it.

   If link performance then improves beyond a configurable minimum
   value (reuse threshold), that sub-TLV can be re-advertised with the
   Anomalous bit cleared. In this case, a receiving node can
   conceivably do whatever re-optimization (or failback) it wishes to
   do (including nothing).

   Note that when a sub-TLV does not include the A bit, that sub-TLV
   cannot be used for failover purposes. The A bit was intentionally
   omitted from some sub-TLVs to help mitigate oscillations. See section
   7. 1. for more information.

   Consistent with existing OSPF TE specifications (RFC3630), the
   bandwidth advertisements defined in this draft MUST be encoded as
   IEEE floating point values. The delay and delay variation
   advertisements defined in this draft MUST be encoded as integer
   values. Delay values MUST be quantified in units of microseconds,
   packet loss MUST be quantified as a percentage of packets sent, and


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   bandwidth MUST be sent as bytes per second. All values (except
   residual bandwidth) MUST be calculated as rolling averages where the
   averaging period MUST be a configurable period of time. See section
   5. for more information.



4. Sub TLV Details

4.1. Unidirectional Link Delay Sub-TLV

   This sub-TLV advertises the average link delay between two directly
   connected OSPF neighbors. The delay advertised by this sub-TLV MUST
   be the delay from the local neighbor to the remote one (i.e. the
   forward path latency). The format of this sub-TLV is shown in the
   following diagram:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              TBD1             |               4               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |A|  RESERVED   |                     Delay                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.1.1. Type

   This sub-TLV has a type of TBD1.

4.1.2. Length

   The length is 4.

4.1.3. A bit

   This field represents the Anomalous (A) bit. The A bit is set when
   the measured value of this parameter exceeds its configured maximum
   threshold. The A bit is cleared when the measured value falls below
   its configured reuse threshold. If the A bit is clear, the sub-TLV
   represents steady state link performance.

4.1.4. Reserved

   This field is reserved for future use. It MUST be set to 0 when sent
   and MUST be ignored when received.



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4.1.5. Delay Value

   This 24-bit field carries the average link delay over a configurable
   interval in micro-seconds, encoded as an integer value. When set to
   the maximum value 16,777,215 (16.777215 sec), then the delay is at
   least that value and may be larger.  If there is no value to send
   (unmeasured and not statically specified), then the sub-TLV should
   not be sent or be withdrawn.



4.2. Min/Max Unidirectional Link Delay Sub-TLV

   This sub-TLV advertises the minimum and maximum delay values between
   two directly connected OSPF neighbors. The delay advertised by this
   sub-TLV MUST be the delay from the local neighbor to the remote one
   (i.e. the forward path latency). The format of this sub-TLV is shown
   in the following diagram:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              TBD2             |               8               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |A|  RESERVED   |                   Min Delay                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   RESERVED    |                   Max Delay                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



4.2.1. Type

   This sub-TLV has a type of TBD2.

4.2.2. Length

   The length is 8.

4.2.3. A bit

   This field represents the Anomalous (A) bit. The A bit is set when
   one or more measured values exceed a configured maximum threshold.
   The A bit is cleared when the measured value falls below its
   configured reuse threshold. If the A bit is clear, the sub-TLV
   represents steady state link performance.



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4.2.4. Reserved

   This field is reserved for future use. It MUST be set to 0 when sent
   and MUST be ignored when received.

4.2.5. Low Delay

   This 24-bit field carries minimum measured link delay value (in
   microseconds) over a configurable interval, encoded as an integer
   value.

   Implementations MAY also permit the configuration of a static (non
   dynamic) offset value (in microseconds) to be added to the measured
   delay value, to facilitate the communication of operator specific
   delay constraints.

   When set to the maximum value 16,777,215 (16.777215 sec), then the
   delay is at least that value and may be larger.

4.2.6. High Delay

   This 24-bit field carries the maximum measured link delay value (in
   microseconds) over a configurable interval, encoded as an integer
   value.

   Implementations MAY also permit the configuration of a static (non
   dynamic) offset value (in microseconds) to be added to the measured
   delay value, to facilitate the communication of operator specific
   delay constraints.

   It is possible for the high delay and low delay to be the same value.

   When the delay value is set to maximum value 16,777,215 (16.777215
   sec), then the delay is at least that value and may be larger.

4.2.7. Reserved

   This field is reserved for future use. It MUST be set to 0 when sent
   and MUST be ignored when received.

   When only an average delay value is sent, this field is not present
   in the TLV.







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4.3. Unidirectional Delay Variation Sub-TLV

   This sub-TLV advertises the average link delay variation between two
   directly connected OSPF neighbors. The delay variation advertised by
   this sub-TLV MUST be the delay from the local neighbor to the remote
   one (i.e. the forward path latency). The format of this sub-TLV is
   shown in the following diagram:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              TBD3             |               4               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    RESERVED   |              Delay Variation                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.3.1. Type

   This sub-TLV has a type of TBD3.

4.3.2. Length

   The length is 4.

4.3.3. Reserved

   This field is reserved for future use. It MUST be set to 0 when sent
   and MUST be ignored when received.



4.3.4. Delay Variation

   This 24-bit field carries the average link delay variation over a
   configurable interval in micro-seconds, encoded as an integer value.
   When set to 0, it has not been measured. When set to the maximum
   value 16,777,215 (16.777215 sec), then the delay is at least that
   value and may be larger.



4.4. Unidirectional Link Loss Sub-TLV

   This sub-TLV advertises the loss (as a packet percentage) between two
   directly connected OSPF neighbors. The link loss advertised by this
   sub-TLV MUST be the packet loss from the local neighbor to the remote


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   one (i.e. the forward path loss). The format of this sub-TLV is shown
   in the following diagram:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              TBD4             |               4               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |A|  RESERVED   |                 Link Loss                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.4.1. Type

   This sub-TLV has a type of TBD4

4.4.2. Length

   The length is 4.

4.4.3. A bit

   This field represents the Anomalous (A) bit. The A bit is set when
   the measured value of this parameter exceeds its configured maximum
   threshold. The A bit is cleared when the measured value falls below
   its configured reuse threshold. If the A bit is clear, the sub-TLV
   represents steady state link performance.

4.4.4. Reserved

   This field is reserved for future use. It MUST be set to 0 when sent
   and MUST be ignored when received.

4.4.5. Link Loss

   This 24-bit field carries link packet loss as a percentage of the
   total traffic sent over a configurable interval.  The basic unit is
   0.000003%, where (2^24 - 2) is 50.331642%. This value is the highest
   packet loss percentage that can be expressed (the assumption being
   that precision is more important on high speed links than the ability
   to advertise loss rates greater than this, and that high speed links
   with over 50% loss are unusable). Therefore, measured values that are
   larger than the field maximum SHOULD be encoded as the maximum value.
   When set to a value of all 1s (2^24 - 1), the link packet loss has
   not been measured.




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4.5. Unidirectional Residual Bandwidth Sub-TLV

   This sub-TLV advertises the residual bandwidth between two directly
   connected OSPF neighbors. The residual bandwidth advertised by this
   sub-TLV MUST be the residual bandwidth from the system originating
   the LSA to its neighbor.

   The format of this sub-TLV is shown in the following diagram:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              TBD5             |               4               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Residual Bandwidth                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.5.1. Type

    This sub-TLV has a type of TBD5.

4.5.2. Length

   The length is 4.

4.5.3. Residual Bandwidth

   This field carries the residual bandwidth on a link, forwarding
   adjacency [RFC4206], or bundled link in IEEE floating point format
   with units of bytes per second.  For a link or forwarding adjacency,
   residual bandwidth is defined to be Maximum Bandwidth [RFC3630] minus
   the bandwidth currently allocated to RSVP-TE LSPs.  For a bundled
   link, residual bandwidth is defined to be the sum of the component
   link residual bandwidths.

   The calculation of Residual Bandwidth is different than that of
   Unreserved Bandwidth [RFC3630]. Residual Bandwidth subtracts tunnel
   reservations from Maximum Bandwidth (i.e. the link capacity)
   [RFC3630] and provides an aggregated remainder across QoS classes.
   Unreserved Bandwidth [RFC3630], on the other hand, is subtracted from
   the Maximum Reservable Bandwidth (the bandwidth that can
   theoretically be reserved) [RFC3630] and provides per-QoS-class
   remainders. Residual Bandwidth and Unreserved Bandwidth [RFC3630] can
   be used concurrently, and each has a separate use case (e.g. the



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   former can be used for applications like Weighted ECMP while the
   latter can be used for call admission control).



4.6. Unidirectional Available Bandwidth Sub-TLV

   This TLV advertises the available bandwidth between two directly
   connected OSPF neighbors. The available bandwidth advertised by this
   sub-TLV MUST be the available bandwidth from the system originating
   the LSA to its neighbor. The format of this sub-TLV is shown in the
   following diagram:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              TBD6             |               4               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Available Bandwidth                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.6.1. Type

   This sub-TLV has a type of TBD6.

4.6.2. Length

   The length is 4.

4.6.3. Available Bandwidth

   This field carries the available bandwidth on a link, forwarding
   adjacency, or bundled link in IEEE floating point format with units
   of bytes per second.  For a link or forwarding adjacency, available
   bandwidth is defined to be residual bandwidth (see section 4.5. )
   minus the measured bandwidth used for the actual forwarding of non-
   RSVP-TE LSP packets.  For a bundled link, available bandwidth is
   defined to be the sum of the component link available bandwidths.



4.7. Unidirectional Utilized Bandwidth Sub-TLV

   This Sub-TLV advertises the bandwidth utilization between two
   directly connected OSPF neighbors. The bandwidth utilization


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   advertised by this sub-TLV MUST be the bandwidth from the system
   originating this Sub-TLV. The format of this Sub-TLV is shown in the
   following diagram:



     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              TBD7             |               4               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Utilized Bandwidth                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.7.1. Type

   This sub-TLV has a type of TBD7.

4.7.2. Length

   The length is 4.

4.7.3. Utilized Bandwidth

   This field carries the bandwidth utilization on a link, forwarding
   adjacency, or bundled link in IEEE floating point format with units
   of bytes per second. For a link or forwarding adjacency, bandwidth
   utilization represents the actual utilization of the link (i.e. as
   measured in the router). For a bundled link, bandwidth utilization is
   defined to be the sum of the component link bandwidth utilizations.



5. Announcement Thresholds and Filters

   The values advertised in all sub-TLVs (except min/max delay and
   residual bandwidth) MUST represent an average over a period or be
   obtained by a filter that is reasonably representative of an
   average. For example, a rolling average is one such filter.

   Low or high delay MAY be the lowest and/or highest measured value
   over a measurement interval or MAY make use of a filter, or other
   technique to obtain a reasonable representation of a low and high
   value representative of the interval with compensation for outliers.




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   The measurement interval, any filter coefficients, and any
   advertisement intervals MUST be configurable per sub-TLV.

   In addition to the measurement intervals governing re-advertisement,
   implementations SHOULD provide per sub-TLV configurable accelerated
   advertisement thresholds, such that:

   1. If the measured parameter falls outside a configured  upper bound
      for all but the min delay metric (or lower bound for min-delay
      metric only) and the advertised sub-TLV is not already outside
      that bound or,

   2. If the difference between the last advertised value and current
      measured value exceed a configured threshold then,

   3. The advertisement is made immediately.

   4. For sub-TLVs which include an A-bit (except low/high delay), an
      additional threshold SHOULD be included corresponding to the
      threshold for which the performance is considered anomalous (and
      sub-TLVs with the A bit are sent). The A-bit is cleared when the
      sub-TLV's performance has been below (or re-crosses) this
      threshold for an advertisement interval(s) to permit fail back.

   To prevent oscillations, only the high threshold or the low threshold
   (but not both) may be used to trigger any given sub-TLV that supports
   both.

   Additionally, once outside of the bounds of the threshold, any
   readvertisement of a measurement within the bounds would remain
   governed solely by the measurement interval for that sub-TLV.



6. Announcement Suppression

   When link performance values change by small amounts that fall under
   thresholds that would cause the announcement of a sub-TLV,
   implementations SHOULD suppress sub-TLV readvertisement and/or
   lengthen the period within which they are refreshed.

   Only the accelerated advertisement threshold mechanism described in
   section 6 may shorten the re-advertisement interval.

   All suppression and re-advertisement interval backoff timer features
   SHOULD be configurable.



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7. Network Stability and Announcement Periodicity

   Sections 6 and 7 provide configurable mechanisms to bound the number
   of re-advertisements.  Instability might occur in very large networks
   if measurement intervals are set low enough to     overwhelm the
   processing of flooded information at some of the routers in the
   topology. Therefore care SHOULD be taken in setting these values.

   Additionally, the default measurement interval for all sub-TLVs
   SHOULD be 30 seconds.

   Announcements MUST also be able to be throttled using configurable
   inter-update throttle timers. The minimum announcement periodicity is
   1 announcement per second. The default value SHOULD be set to 120
   seconds.

   Implementations SHOULD NOT permit the inter-update timer to be lower
   than the measurement interval.

   Furthermore, it is RECOMMENDED that any underlying performance
   measurement mechanisms not include any significant buffer delay, any
   significant buffer induced delay variation, or any significant
   loss due to buffer overflow or due to active queue management.



8. Enabling and Disabling Sub-TLVs

   Implementations MUST make it possible to individually enable or
   disable each sub-TLV based on configuration.



9. Static Metric Override

   Implementations SHOULD permit the static configuration and/or manual
   override of dynamic measurements data on a per sub-TLV, per metric
   basis in order to simplify migrations and to mitigate scenarios where
   measurements are not possible across an entire network.








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10. Compatibility

   As per (RFC3630), unrecognized TLVs should be silently ignored



11. Security Considerations

   This document does not introduce security issues beyond those
   discussed in [RFC3630] and [RFC5329].



12. IANA Considerations

   IANA maintains the registry for the sub-TLVs. OSPF TE Metric
   Extensions will require one new type code per sub-TLV defined in this
   document.



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.

   [RFC3630] Katz, D., Kompella, K., Yeung, D., "Traffic
             Engineering (TE) Extensions to OSPF Version 2", RFC 3630,
             September 2003.

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

13.2. Informative References

   [RFC2328] Moy, J, "OSPF Version 2", RFC 2328, April 1998

   [RFC3031] Rosen, E., Viswanathan, A., Callon, R., "Multiprotocol
             Label Switching Architecture", January 2001

   [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,



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             V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
             Tunnels", RFC 3209, December 2001.

   [RFC5250] Berger, L., Bryskin I., Zinin, A., Coltun, R., "The OSPF
             Opaque LSA Option", RFC 5250, July 2008.

   [RFC6375]  Frost, D. and S. Bryant, "A Packet Loss and Delay
              Measurement Profile for MPLS-Based Transport Networks",
              RFC 6375, September 2011.

   [Alto]    R. Alimi R. Penno Y. Yang, "ALTO Protocol"

   [Draft-ietf-mpls-te-express-path]  Atlas, A., Drake, J., Giacalone,
             S., Ward, D., Previdi, S., and C. Filsfils, "Performance-
             based Path Selection for Explicitly Routed LSPs using TE
             Metric Extensions", Draft-ietf-mpls-te-express-path (work
             in progress), October 2013



14. Acknowledgments

   The authors would like to recognize Ayman Soliman, Nabil Bitar, David
   McDysan, Edward Crabbe, and Don Fedyk for their contributions.

   The authors also recognize Curtis Villamizar for significant comments
   and direct content collaboration.


   This document was prepared using 2-Word-v2.0.template.dot.



15. Author's Addresses

   Spencer Giacalone
   Thomson Reuters
   195 Broadway
   New York, NY 10007, USA

   Email: Spencer.giacalone@thomsonreuters.com


   Dave Ward
   Cisco Systems
   170 West Tasman Dr.


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   San Jose, CA  95134, USA

   Email: dward@cisco.com


   John Drake
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089, USA

   Email: jdrake@juniper.net


   Alia Atlas
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089, USA

   Email: akatlas@juniper.net


   Stefano Previdi
   Cisco Systems
   Via Del Serafico 200
   00142 Rome
   Italy

   Email: sprevidi@cisco.com




















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