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Versions: (draft-wu-pce-pcep-link-bw-utilization) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 8233

PCE Working Group                                               D. Dhody
Internet-Draft                                                     Q. Wu
Intended status: Standards Track                                  Huawei
Expires: April 8, 2016                                         V. Manral
                                                           Ionos Network
                                                                  Z. Ali
                                                           Cisco Systems
                                                               K. Kumaki
                                                        KDDI Corporation
                                                         October 6, 2015


Extensions to the Path Computation Element Communication Protocol (PCEP)
          to compute service aware Label Switched Path (LSP).
                  draft-ietf-pce-pcep-service-aware-08

Abstract

   In certain networks like financial information network (stock/
   commodity trading) and enterprises using cloud based applications,
   Latency (delay), Latency Variation (jitter) and Packet Loss are
   becoming key requirements for path computation along with other
   constraints and metrics.  These metrics are associated with the
   Service Level Agreement (SLA) between customers and service
   providers.  The Link Bandwidth Utilization (the total bandwidth of a
   link in current use for the forwarding) is another important factor
   to consider during path computation.

   IGP Traffic Engineering (TE) Metric extensions describes mechanisms
   with which network performance information is distributed via OSPF
   and IS-IS respectively.  The Path Computation Element Communication
   Protocol (PCEP) provides mechanisms for Path Computation Elements
   (PCEs) to perform path computations in response to Path Computation
   Clients (PCCs) requests.  This document describes the extension to
   PCEP to carry Latency, Latency Variation, Packet Loss, and Link
   Bandwidth Utilization as constraints for end to end path computation.

Status of This Memo

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

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





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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on April 8, 2016.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  PCEP Requirements . . . . . . . . . . . . . . . . . . . . . .   5
   4.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Extensions to METRIC Object . . . . . . . . . . . . . . .   6
       4.1.1.  Latency (Delay) Metric  . . . . . . . . . . . . . . .   6
         4.1.1.1.  Latency (Delay) Metric Value  . . . . . . . . . .   7
       4.1.2.  Latency Variation (Jitter) Metric . . . . . . . . . .   7
         4.1.2.1.  Latency Variation (Jitter) Metric Value . . . . .   8
       4.1.3.  Packet Loss Metric  . . . . . . . . . . . . . . . . .   8
         4.1.3.1.  Packet Loss Metric Value  . . . . . . . . . . . .   9
       4.1.4.  Non-Understanding / Non-Support of Service Aware Path
               Computation . . . . . . . . . . . . . . . . . . . . .   9
       4.1.5.  Mode of Operation . . . . . . . . . . . . . . . . . .   9
         4.1.5.1.  Examples  . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Bandwidth Utilization . . . . . . . . . . . . . . . . . .  11
       4.2.1.  Link Bandwidth Utilization (LBU)  . . . . . . . . . .  11
       4.2.2.  Link Reserved Bandwidth Utilization (LRBU)  . . . . .  11
       4.2.3.  BU Object . . . . . . . . . . . . . . . . . . . . . .  11
         4.2.3.1.  Elements of Procedure . . . . . . . . . . . . . .  12
     4.3.  Objective Functions . . . . . . . . . . . . . . . . . . .  13
   5.  PCEP Message Extension  . . . . . . . . . . . . . . . . . . .  14
     5.1.  The PCReq message . . . . . . . . . . . . . . . . . . . .  14



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     5.2.  The PCRep message . . . . . . . . . . . . . . . . . . . .  15
     5.3.  Stateful PCE  . . . . . . . . . . . . . . . . . . . . . .  16
       5.3.1.  The PCRpt message . . . . . . . . . . . . . . . . . .  17
   6.  Other Considerations  . . . . . . . . . . . . . . . . . . . .  17
     6.1.  Inter-domain Consideration  . . . . . . . . . . . . . . .  17
       6.1.1.  Inter-AS Link . . . . . . . . . . . . . . . . . . . .  18
       6.1.2.  Inter-Layer Consideration . . . . . . . . . . . . . .  18
     6.2.  Reoptimization Consideration  . . . . . . . . . . . . . .  18
     6.3.  Point-to-Multipoint (P2MP)  . . . . . . . . . . . . . . .  18
       6.3.1.  P2MP Latency Metric . . . . . . . . . . . . . . . . .  18
       6.3.2.  P2MP Latency Variation Metric . . . . . . . . . . . .  19
       6.3.3.  P2MP Packet Loss Metric . . . . . . . . . . . . . . .  19
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
     7.1.  METRIC types  . . . . . . . . . . . . . . . . . . . . . .  20
     7.2.  New PCEP Object . . . . . . . . . . . . . . . . . . . . .  20
     7.3.  BU Object . . . . . . . . . . . . . . . . . . . . . . . .  20
     7.4.  OF Codes  . . . . . . . . . . . . . . . . . . . . . . . .  21
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  21
     9.1.  Control of Function and Policy  . . . . . . . . . . . . .  21
     9.2.  Information and Data Models . . . . . . . . . . . . . . .  22
     9.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  22
     9.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  22
     9.5.  Requirements On Other Protocols . . . . . . . . . . . . .  22
     9.6.  Impact On Network Operations  . . . . . . . . . . . . . .  22
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  22
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     11.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   Real time network performance is becoming critical in the path
   computation in some networks.  Mechanisms to measure Latency,
   Latency-Variation, and Packet Loss in an MPLS network are described
   in [RFC6374].  Further, there exist mechanisms to measure these
   network performance metrics after the Label Switched Path (LSP) has
   been established, which is inefficient.  It is important that
   Latency, Latency Variation, and Packet Loss are considered during
   path selection process, even before the LSP is set up.

   Link bandwidth utilization based on real time traffic along the path
   is also becoming critical during path computation in some networks.
   Thus it is important that the Link bandwidth utilization is factored
   in during path computation itself.




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   Traffic Engineering Database (TED) is populated with network
   performance information like link latency, latency variation, and
   packet loss through [RFC7471] or [ISIS-TE-METRIC-EXT].
   [TE-EXPRESS-PATH] describes how a Path Computation Element (PCE)
   [RFC4655], can use that information for path selection for explicitly
   routed LSPs.

   Path Computation Client (PCC) can request PCE to provide a path
   meeting end to end network performance criteria.  This document
   extends Path Computation Element Communication Protocol (PCEP)
   [RFC5440] to handle network performance constraints.

   [RFC7471] and [ISIS-TE-METRIC-EXT] include parameters related to
   bandwidth (Residual bandwidth, Available bandwidth and Utilized
   bandwidth); this document also describes extensions to PCEP to
   consider them during path computation.

1.1.  Requirements Language

   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].

2.  Terminology

   The following terminology is used in this document.

   IGP:  Interior Gateway Protocol.  Either of the two routing
      protocols, Open Shortest Path First (OSPF) or Intermediate System
      to Intermediate System (IS-IS).

   IS-IS:  Intermediate System to Intermediate System.

   LBU:  Link Bandwidth Utilization.  (See Section 4.2.1.)

   LRBU:  Link Reserved Bandwidth Utilization.  (See Section 4.2.2.)

   MPLP:  Minimum Packet Loss Path.  (See Section 4.3.)

   MRUP:  Maximum Reserved Under-Utilized Path.  (See Section 4.3.)

   MUP:  Maximum Under-Utilized Path.  (See Section 4.3.)

   OF:  Objective Function.  A set of one or more optimization criteria
      used for the computation of a single path (e.g., path cost
      minimization) or for the synchronized computation of a set of
      paths (e.g., aggregate bandwidth consumption minimization, etc).
      (See [RFC5541].)



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   OSPF:  Open Shortest Path First.

   PCC:  Path Computation Client: any client application requesting a
      path computation to be performed by a Path Computation Element.

   PCE:  Path Computation Element.  An entity (component, application,
      or network node) that is capable of computing a network path or
      route based on a network graph and applying computational
      constraints.

   RSVP:  Resource Reservation Protocol

   TE:  Traffic Engineering.

3.  PCEP Requirements

   End-to-end service optimization based on latency, latency variation,
   packet loss, and link bandwidth utilization is a key requirement for
   service provider.  Following key requirements associated are
   identified for PCEP:

   1.  PCE supporting this draft MUST have the capability to compute
       end-to-end (E2E) path with latency, latency variation, packet
       loss, and bandwidth utilization constraints.  It MUST also
       support the combination of network performance constraint
       (latency, latency variation, loss...) with existing constraints
       (cost, hop-limit...).

   2.  PCC MUST be able to request for E2E network performance
       constraint(s) in PCReq message as the key constraint to be
       optimized or to suggest boundary condition that should not be
       crossed.

   3.  The PCC MUST be able to request for the bandwidth utilization
       constraint in PCReq message as the upper limit that should not be
       crossed for each link in the path.

   4.  The PCC MUST be able to request for these constraint in PCReq
       message as an Objective function (OF) [RFC5541] to be optimized.

   5.  PCEs are not required to support service aware path computation.
       Therefore, it MUST be possible for a PCE to reject a PCReq
       message with a reason code that indicates no support for service-
       aware path computation.

   6.  PCEP SHOULD provide a means to return end to end network
       performance information of the computed path in a PCRep message.




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   7.  PCEP SHOULD provide mechanism to compute multi-domain (e.g.,
       Inter-AS, Inter-Area or Multi-Layer) service aware paths.

   It is assumed that such constraints are only meaningful if used
   consistently: for instance, if the delay of a computed path segment
   is exchanged between two PCEs residing in different domains,
   consistent ways of defining the delay must be used.

4.  PCEP Extensions

   This section defines PCEP extensions (see [RFC5440]) for requirements
   outlined in Section 3.  The proposed solution is used to support
   network performance and service aware path computation.

4.1.  Extensions to METRIC Object

   The METRIC object is defined in section 7.8 of [RFC5440], comprising
   of metric-value, metric-type (T field) and flags.  This document
   defines the following optional types for the METRIC object.

   For explanation of these metrics, the following terminology is used
   and expanded along the way.

   - A network comprises of a set of N links {Li, (i=1...N)}.

   - A path P of a P2P LSP is a list of K links {Lpi,(i=1...K)}.

4.1.1.  Latency (Delay) Metric

   Link delay metric is defined in [RFC7471] and [ISIS-TE-METRIC-EXT] as
   "Unidirectional Link Delay".  P2P latency metric type of METRIC
   object in PCEP encodes the sum of the link delay metric of all links
   along a P2P Path.  Specifically, extending on the above mentioned
   terminology:

   - A Link delay metric of link L is denoted D(L).

   - A P2P latency metric for the Path P = Sum {D(Lpi), (i=1...K)}.

   This is as per sum of means composition function (section 4.2.5 of
   [RFC6049]).

   * Metric Type T=TBD1: Latency metric

   PCC MAY use this latency metric in PCReq message to request a path
   meeting the end to end latency requirement.  In this case B bit MUST
   be set to suggest a bound (a maximum) for the path latency metric
   that must not be exceeded for the PCC to consider the computed path



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   as acceptable.  The path metric must be less than or equal to the
   value specified in the metric-value field.

   PCC MAY also use this metric to ask PCE to optimize latency during
   path computation, in this case B flag will be cleared.

   PCE MAY use this latency metric in PCRep message along with NO-PATH
   object in case PCE cannot compute a path meeting this constraint.
   PCE MAY also use this metric to reply the computed end to end latency
   metric to PCC.

4.1.1.1.  Latency (Delay) Metric Value

   [RFC7471] and [ISIS-TE-METRIC-EXT] defines "Unidirectional Link Delay
   Sub-TLV" in a 24-bit field.  [RFC5440] defines the METRIC object with
   32-bit metric value encoded in IEEE floating point format (see
   [IEEE.754.1985]).  Consequently, encoding for Latency (Delay) Metric
   Value is quantified in units of microseconds and encoded in IEEE
   floating point format.

4.1.2.  Latency Variation (Jitter) Metric

   Link delay variation metric is defined in [RFC7471] and
   [ISIS-TE-METRIC-EXT] as "Unidirectional Delay Variation".  P2P
   latency variation metric type of METRIC object in PCEP encodes the
   sum of the link delay variation metric of all links along a P2P Path.
   Specifically, extending on the above mentioned terminology:

   - A Latency variation of link L is denoted DV(L) (average delay
   variation for link L).

   - A P2P latency variation metric for the Path P = Sum {DV(Lpi),
   (i=1...K)}.

   Note that the IGP advertisement for link attributes includes average
   latency variation over a period of time.  An implementation,
   therefore, MAY use sum of the average latency variation of links
   along a path to derive the average latency variation of the Path.  An
   implementation MAY also use some enhanced composition function for
   computing average latency variation of a Path.

   * Metric Type T=TBD2: Latency Variation metric

   PCC MAY use this latency variation metric in PCReq message to request
   a path meeting the end to end latency variation requirement.  In this
   case B bit MUST be set to suggest a bound (a maximum) for the path
   latency variation metric that must not be exceeded for the PCC to




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   consider the computed path as acceptable.  The path metric must be
   less than or equal to the value specified in the metric-value field.

   PCC MAY also use this metric to ask PCE to optimize latency variation
   during path computation, in this case B flag will be cleared.

   PCE MAY use this latency variation metric in PCRep message along with
   NO-PATH object in case PCE cannot compute a path meeting this
   constraint.  PCE MAY also use this metric to reply the computed end
   to end latency variation metric to PCC.

4.1.2.1.  Latency Variation (Jitter) Metric Value

   [RFC7471] and [ISIS-TE-METRIC-EXT] defines "Unidirectional Delay
   Variation Sub-TLV" in a 24-bit field.  [RFC5440] defines the METRIC
   object with 32-bit metric value encoded in IEEE floating point format
   (see [IEEE.754.1985]).  Consequently, encoding for Latency Variation
   (Jitter) Metric Value is quantified in units of microseconds and
   encoded in IEEE floating point format.

4.1.3.  Packet Loss Metric

   [RFC7471] and [ISIS-TE-METRIC-EXT] defines "Unidirectional Link
   Loss".  Packet Loss metric type of METRIC object in PCEP encodes a
   function of the link's unidirectional loss metric of all links along
   a P2P Path.  Specifically, extending on the above mentioned
   terminology:

   The end to end Packet Loss for the path is represented by this
   metric.

   - A Packet loss of link L is denoted PL(L) in percentage.

   - A Packet loss in fraction of link L is denoted FPL(L) = PL(L)/100.

   - A P2P packet loss metric in percentage for the Path P = (1 -
   ((1-FPL(Lp1)) * (1-FPL(Lp2)) * .. * (1-FPL(LpK))) * 100 for a path P
   with link 1 to K.

   This is as per the composition function (section 5.1.5 of [RFC6049]).

   * Metric Type T=TBD3: Packet Loss metric

   PCC MAY use this packet loss metric in PCReq message to request a
   path meeting the end to end packet loss requirement.  In this case B
   bit MUST be set to suggest a bound (a maximum) for the path packet
   loss metric that must not be exceeded for the PCC to consider the




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   computed path as acceptable.  The path metric must be less than or
   equal to the value specified in the metric-value field.

   PCC MAY also use this metric to ask PCE to optimize packet loss
   during path computation, in this case B flag will be cleared.

   PCE MAY use this packet loss metric in PCRep message along with NO-
   PATH object in case PCE cannot compute a path meeting this
   constraint.  PCE MAY also use this metric to reply the computed end
   to end packet loss metric to PCC.

4.1.3.1.  Packet Loss Metric Value

   [RFC7471] and [ISIS-TE-METRIC-EXT] defines "Unidirectional Link Loss
   Sub-TLV" in a 24-bit field.  [RFC5440] defines the METRIC object with
   32-bit metric value encoded in IEEE floating point format (see
   [IEEE.754.1985]).  Consequently, encoding for Packet Loss Metric
   Value is quantified as a percentage and encoded in IEEE floating
   point format.

4.1.4.  Non-Understanding / Non-Support of Service Aware Path
        Computation

   If the P bit is clear in the object header and PCE does not
   understand or does not support service aware path computation it
   SHOULD simply ignore this METRIC object.

   If the P Bit is set in the object header and PCE receives new METRIC
   type in path request and it understands the METRIC type, but the PCE
   is not capable of service aware path computation, the PCE MUST send a
   PCErr message with a PCEP-ERROR Object Error-Type = 4 (Not supported
   object) [RFC5440].  The path computation request MUST then be
   cancelled.

   If the PCE does not understand the new METRIC type, then the PCE MUST
   send a PCErr message with a PCEP-ERROR Object Error-Type = 3 (Unknown
   object) [RFC5440].

4.1.5.  Mode of Operation

   As explained in [RFC5440], the METRIC object is optional and can be
   used for several purposes.  In a PCReq message, a PCC MAY insert one
   or more METRIC objects:

   o  To indicate the metric that MUST be optimized by the path
      computation algorithm (Latency, Latency Variation or Loss)





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   o  To indicate a bound on the path METRIC (Latency, Latency Variation
      or Loss) that MUST NOT be exceeded for the path to be considered
      as acceptable by the PCC.

   In a PCRep message, the METRIC object MAY be inserted so as to
   provide the METRIC (Latency, Latency Variation or Loss) for the
   computed path.  It MAY also be inserted within a PCRep with the NO-
   PATH object to indicate that the metric constraint could not be
   satisfied.

   The path computation algorithmic aspects used by the PCE to optimize
   a path with respect to a specific metric are outside the scope of
   this document.

   All the rules of processing METRIC object as explained in [RFC5440]
   are applicable to the new metric types as well.

   In a PCReq message, a PCC MAY insert more than one METRIC object to
   be optimized, in such a case PCE SHOULD find the path that is optimal
   when both the metrics are considered together.

4.1.5.1.  Examples

   Example 1: If a PCC sends a path computation request to a PCE where
   two metric to optimize are the latency and the packet loss, two
   METRIC objects are inserted in the PCReq message:

   o  First METRIC object with B=0, T=TBD1, C=1, metric-value=0x0000

   o  Second METRIC object with B=0, T=TBD3, C=1, metric-value=0x0000

   PCE in such a case SHOULD try to optimize both the metrics and find a
   path with the minimum latency and packet loss, if a path can be found
   by the PCE and there is no policy that prevents the return of the
   computed metric, the PCE inserts first METRIC object with B=0,
   T=TBD1, metric-value= computed end to end latency and second METRIC
   object with B=1, T=TBD3, metric-value= computed end to end packet
   loss.

   Example 2: If a PCC sends a path computation request to a PCE where
   the metric to optimize is the latency and the packet loss must not
   exceed the value of M, two METRIC objects are inserted in the PCReq
   message:

   o  First METRIC object with B=0, T=TBD1, C=1, metric-value=0x0000

   o  Second METRIC object with B=1, T=TBD3, metric-value=M




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   If a path satisfying the set of constraints can be found by the PCE
   and there is no policy that prevents the return of the computed
   metric, the PCE inserts one METRIC object with B=0, T=TBD1, metric-
   value= computed end to end latency.  Additionally, the PCE may insert
   a second METRIC object with B=1, T=TBD3, metric-value=computed end to
   end packet loss.

4.2.  Bandwidth Utilization

4.2.1.  Link Bandwidth Utilization (LBU)

   The bandwidth utilization on a link, forwarding adjacency, or bundled
   link is populated in the TED (Utilized Bandwidth in [RFC7471] and
   [ISIS-TE-METRIC-EXT]).  For a link or forwarding adjacency, the
   bandwidth utilization represents the actual utilization of the link
   (i.e., as measured in the router).  For a bundled link, the bandwidth
   utilization is defined to be the sum of the component link bandwidth
   utilization.  This includes traffic for both RSVP and non-RSVP.

   LBU Percentage is described as the (LBU / Maximum bandwidth) * 100.

4.2.2.  Link Reserved Bandwidth Utilization (LRBU)

   The reserved bandwidth utilization on a link, forwarding adjacency,
   or bundled link can be calculated from the TED.  This includes
   traffic for only RSVP-TE LSPs.

   LRBU can be calculated by using the Residual bandwidth, the Available
   bandwidth and LBU.  The actual bandwidth by non-RSVP TE traffic can
   be calculated by subtracting the Available Bandwidth from the
   Residual Bandwidth.  Once we have the actual bandwidth for non-RSVP
   TE traffic, subtracting this from LBU would result in LRBU.

   LRBU Percentage is described as the (LRBU / (Maximum reservable
   bandwidth)) * 100.

4.2.3.  BU Object

   The BU (the Bandwidth Utilization) is used to indicate the upper
   limit of the acceptable link bandwidth utilization percentage.

   The BU object may be carried within the PCReq message and PCRep
   messages.

   BU Object-Class is TBD4.

   BU Object-Type is 1.




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   The format of the BU object body is as follows:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Reserved                         |    Type       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Bandwidth Utilization                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                           BU Object Body Format

   Reserved (24 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Type (8 bits):  Represents the bandwidth utilization type.  Link
      Bandwidth Utilization (LBU) Type is 1 and Link Reserved Bandwidth
      Utilization (LRBU) Type is 2.

   Bandwidth utilization (32 bits):  Represents the bandwidth
      utilization quantified as a percentage (as described in
      Section 4.2.1 and Section 4.2.2) and encoded in IEEE floating
      point format (see [IEEE.754.1985]).

   The BU object body has a fixed length of 8 bytes.

4.2.3.1.  Elements of Procedure

   A PCC SHOULD request the PCE to factor in the bandwidth utilization
   during path computation by including a BU object in the PCReq
   message.

   Multiple BU objects MAY be inserted in a PCReq or a PCRep message for
   a given request but there MUST be at most one instance of the BU
   object for each type.  If, for a given request, two or more instances
   of a BU object with the same type are present, only the first
   instance MUST be considered and other instances MUST be ignored.

   BU object MAY be carried in a PCRep message in case of unsuccessful
   path computation along with a NO-PATH object to indicate the
   constraints that could not be satisfied.

   If the P bit is clear in the object header and PCE does not
   understand or does not support the bandwidth utilization during path
   computation it SHOULD simply ignore BU object.





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   If the P Bit is set in the object header and PCE receives BU object
   in path request and it understands the BU object, but the PCE is not
   capable of the bandwidth utilization check during path computation,
   the PCE MUST send a PCErr message with a PCEP-ERROR Object Error-Type
   = 4 (Not supported object) [RFC5440].  The path computation request
   MUST then be cancelled.

   If the PCE does not understand the BU object, then the PCE MUST send
   a PCErr message with a PCEP-ERROR Object Error-Type = 3 (Unknown
   object) [RFC5440].

4.3.  Objective Functions

   [RFC5541] defines mechanism to specify an optimization criteria,
   referred to as objective functions.  The new metric types specified
   in this document MAY continue to use the existing objective functions
   like Minimum Cost Path (MCP).  Latency (Delay) and Latency Variation
   (Jitter) are well suited to use MCP as an optimization criteria.  For
   Packet Loss following new OF is defined -

   o  A network comprises a set of N links {Li, (i=1...N)}.

   o  A path P is a list of K links {Lpi,(i=1...K)}.

   o  Packet loss of link L is denoted PL(L) in percentage.

   o  Packet loss in fraction of link L is denoted FPL(L) = PL(L) / 100.

   o  The Packet loss of a path P (in percentage) is denoted PL(P),
      where PL(P) = (1 - ((1-FPL(Lp1)) * (1-FPL(Lp2)) * .. *
      (1-FPL(LpK))) * 100.

   Objective Function Code:  TBD5



         Name: Minimum Packet Loss Path (MPLP)

         Description: Find a path P such that PL(P) is minimized.

   Two additional objective functions -- namely, MUP (the Maximum Under-
   Utilized Path) and MRUP (the Maximum Reserved Under-Utilized Path)
   are need to optimize bandwidth utilization.  Hence two new objective
   function codes have to be defined.

   Objective functions are formulated using the following additional
   terminology:




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   o  The Bandwidth Utilization on link L is denoted u(L).

   o  The Reserved Bandwidth Utilization on link L is denoted ru(L).

   o  The Maximum bandwidth on link L is denoted M(L).

   o  The Maximum Reserved bandwidth on link L is denoted R(L).

   The description of the two new objective functions is as follows.

   Objective Function Code:  TBD6



         Name: Maximum Under-Utilized Path (MUP)

         Description: Find a path P such that (Min {(M(Lpi)- u(Lpi)) /
         M(Lpi), i=1...K } ) is maximized.

   Objective Function Code:  TBD7



         Name: Maximum Reserved Under-Utilized Path (MRUP)

         Description: Find a path P such that (Min {(R(Lpi)- ru(Lpi)) /
         R(Lpi), i=1...K } ) is maximized.

   These new objective functions are used to optimize paths based on the
   bandwidth utilization as the optimization criteria.

   If the objective function defined in this document are unknown/
   unsupported, the procedure as defined in [RFC5541] is followed.

5.  PCEP Message Extension

5.1.  The PCReq message

   The extension to PCReq message are -

   o  new metric types using existing METRIC object

   o  a new optional BU object

   o  new objective functions using existing OF object ([RFC5541])

   The format of the PCReq message (with [RFC5541] as a base) is updated
   as follows:



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      <PCReq Message> ::= <Common Header>
                           [<svec-list>]
                           <request-list>
      where:
           <svec-list> ::= <SVEC>
                           [<OF>]
                           [<metric-list>]
                           [<svec-list>]

           <request-list> ::= <request> [<request-list>]

           <request> ::= <RP>
                         <END-POINTS>
                         [<LSPA>]
                         [<BANDWIDTH>]
                         [<bu-list>]
                         [<metric-list>]
                         [<OF>]
                         [<RRO>[<BANDWIDTH>]]
                         [<IRO>]
                         [<LOAD-BALANCING>]

      and where:
           <bu-list>::=<BU>[<bu-list>]
           <metric-list> ::= <METRIC>[<metric-list>]

5.2.  The PCRep message

   The extension to PCRep message are -

   o  new metric types using existing METRIC object

   o  a new optional BU object (during unsuccessful path computation, to
      indicate the bandwidth utilization as a reason for failure)

   o  new objective functions using existing OF object ([RFC5541])

   The format of the PCRep message (with [RFC5541] as a base) is updated
   as follows:












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      <PCRep Message> ::= <Common Header>
                          [<svec-list>]
                          <response-list>

      where:

            <svec-list> ::= <SVEC>
                            [<OF>]
                            [<metric-list>]
                            [<svec-list>]

           <response-list> ::= <response> [<response-list>]

           <response> ::= <RP>
                          [<NO-PATH>]
                          [<attribute-list>]
                          [<path-list>]

           <path-list> ::= <path> [<path-list>]

           <path> ::= <ERO>
                      <attribute-list>

      and where:

           <attribute-list> ::= [<OF>]
                                [<LSPA>]
                                [<BANDWIDTH>]
                                [<bu-list>]
                                [<metric-list>]
                                [<IRO>]

           <bu-list>::=<BU>[<bu-list>]
           <metric-list> ::= <METRIC> [<metric-list>]

5.3.  Stateful PCE

   [STATEFUL-PCE] specifies a set of extensions to PCEP to enable
   stateful control of MPLS-TE and GMPLS LSPs via PCEP and maintaining
   of these LSPs at the stateful PCE.  It further distinguishes between
   an active and a passive stateful PCE.  A passive stateful PCE uses
   LSP state information learned from PCCs to optimize path computations
   but does not actively update LSP state.  In contrast, an active
   stateful PCE utilizes the LSP delegation mechanism to let PCCs
   relinquish control over some LSPs to the PCE.






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   The passive stateful PCE implementation MAY use the extension of
   PCReq and PCRep messages as defined in Section 5.1 and Section 5.2 to
   enable the use of service aware parameters.

   The additional objective functions defined in this document can also
   be used with stateful PCE.

5.3.1.  The PCRpt message

   A Path Computation LSP State Report message (also referred to as
   PCRpt message) is a PCEP message sent by a PCC to a PCE to report the
   current state or delegate control of an LSP.  The PCRpt message is
   extended to support BU object.  This optional BU object can specify
   the upper limit that should not be crossed.

   As per [STATEFUL-PCE], the format of the PCRpt message is as follows:

      <PCRpt Message> ::= <Common Header>
                          <state-report-list>

      where:

           <state-report-list> ::= <state-report> [<state-report-list>]

           <state-report> ::= [<SRP>]
                          <LSP>
                          <path>

           <path> ::= <ERO><attribute-list>[<RRO>]

   Where <attribute-list> is extended as per Section 5.2 for BU object.

   Thus a BU object can be used to specify the upper limit set at the
   PCC at the time of LSP delegation to an active stateful PCE.

6.  Other Considerations

6.1.  Inter-domain Consideration

   [RFC5441] describes the Backward-Recursive PCE-Based Computation
   (BRPC) procedure to compute end to end optimized inter-domain path by
   cooperating PCEs.  The new metric types defined in this document can
   be applied to end to end path computation, in similar manner as
   existing IGP or TE metric.  The new BU object defined in this
   document can be applied to end to end path computation, in similar
   manner as the METRIC object.





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   All domains should have the same understanding of the METRIC (Latency
   Variation etc) and BU object for end-to-end inter-domain path
   computation to make sense.  Otherwise some form of Metric
   Normalization as described in [RFC5441] MAY need to be applied.

6.1.1.  Inter-AS Link

   The IGP in each neighbour domain can advertise its inter-domain TE
   link capabilities, this has been described in [RFC5316] (ISIS) and
   [RFC5392] (OSPF).  The network performance link properties are
   described in [RFC7471] and [ISIS-TE-METRIC-EXT], the same properties
   must be advertised using the mechanism described in [RFC5392] (OSPF)
   and [RFC5316] (ISIS).

6.1.2.  Inter-Layer Consideration

   [RFC5623] provides a framework for PCE-Based inter-layer MPLS and
   GMPLS Traffic Engineering.  Lower-layer LSPs that are advertised as
   TE links into the higher-layer network form a Virtual Network
   Topology (VNT).  The advertisement in higher-layer should include the
   network performance link properties based on the end to end metric of
   lower-layer LSP.  Note that the new metric defined in this document
   are applied to end to end path computation, even though the path may
   cross multiple layers.

6.2.  Reoptimization Consideration

   PCC can monitor the setup LSPs and in case of degradation of network
   performance constraints, it MAY ask PCE for reoptimization as per
   [RFC5440].  Based on the changes in performance parameters in TED, a
   PCC MAY also issue a reoptimization request.

   Further, PCC can also monitor the link bandwidth utilization along
   the path by monitoring changes in the bandwidth utilization
   parameters of one or more links on the path in the TED.  In case of
   drastic change, it MAY ask PCE for reoptimization as per [RFC5440].

6.3.  Point-to-Multipoint (P2MP)

   This document defines the following optional types for the METRIC
   object defined in [RFC5440] for P2MP TE LSPs.  The usage of BU object
   for P2MP LSP is out of scope of this document.

6.3.1.  P2MP Latency Metric

   P2MP latency metric type of METRIC object in PCEP encodes the path
   latency metric for destination that observes the worst latency metric




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   among all destinations of the P2MP tree.  Specifically, extending on
   the above mentioned terminology:

   - A P2MP Tree T comprises of a set of M destinations {Dest_j,
   (j=1...M)}

   - P2P latency metric of the Path to destination Dest_j is denoted by
   LM(Dest_j).

   - P2MP latency metric for the P2MP tree T = Maximum {LM(Dest_j),
   (j=1...M)}.

   Value for P2MP latency metric type (T) = TBD8 is to be assigned by
   IANA.

6.3.2.  P2MP Latency Variation Metric

   P2MP latency variation metric type of METRIC object in PCEP encodes
   the path latency variation metric for destination that observes the
   worst latency variation metric among all destinations of the P2MP
   tree.  Specifically, extending on the above mentioned terminology:

   - A P2MP Tree T comprises of a set of M destinations {Dest_j,
   (j=1...M)}

   - P2P latency variation metric of the Path to destination Dest_j is
   denoted by LVM(Dest_j).

   - P2MP latency variation metric for the P2MP tree T = Maximum
   {LVM(Dest_j), (j=1...M)}.

   Value for P2MP latency variation metric type (T) = TBD9 is to be
   assigned by IANA.

6.3.3.  P2MP Packet Loss Metric

   P2MP packet loss metric type of METRIC object in PCEP encodes the
   path packet loss metric for destination that observes the worst
   packet loss metric among all destinations of the P2MP tree.
   Specifically, extending on the above mentioned terminology:

   - A P2MP Tree T comprises of a set of M destinations {Dest_j,
   (j=1...M)}

   - P2P packet loss metric of the Path to destination Dest_j is denoted
   by PLM(Dest_j).





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   - P2MP packet loss metric for the P2MP tree T = Maximum {PLM(Dest_j),
   (j=1...M)}.

   Value for P2MP packet loss metric type (T) = = TBD10 is to be
   assigned by IANA.

7.  IANA Considerations

7.1.  METRIC types

   IANA maintains the "Path Computation Element Protocol (PCEP) Numbers"
   at http://www.iana.org/assignments/pcep/pcep.xhtml.  Within this
   registry IANA maintains one sub-registrie for "METRIC object T field"
   at http://www.iana.org/assignments/pcep/pcep.xhtml#metric-object-ni-
   field.  Six new metric types are defined in this document for the
   METRIC object (specified in [RFC5440]).

   IANA is requested to make the following allocations:

        Value       Description                        Reference
        ----------------------------------------------------------
        TBD1        Latency (delay) metric             [This I.D.]
        TBD2        Latency Variation (jitter) metric  [This I.D.]
        TBD3        Packet Loss metric                 [This I.D.]
        TBD8        P2MP latency metric                [This I.D.]
        TBD9        P2MP latency variation metric      [This I.D.]
        TBD10       P2MP packet loss metric            [This I.D.]


7.2.  New PCEP Object

   IANA maintains object class in the registry of PCEP Objects at the
   sub-registry http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-
   objects.  One new allocation is requested as follows.

            Object Object     Name                  Reference
            Class  Type
            ---------------------------------------------------
            TBD4   1          BU                    [This I.D.]

7.3.  BU Object

   IANA is requested to create a new sub-registry to manage the
   codespace of the Type field of the BU Object.

   Codespace of the T field (BU Object)





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            Type     Name                           Reference
            --------------------------------------------------
            1        LBU (Link Bandwidth            [This I.D.]
                     Utilization
            2        LRBU (Link Residual            [This I.D.]
                     Bandwidth Utilization

7.4.  OF Codes

   IANA maintains registry of Objective Function (described in
   [RFC5541]) at the sub-registry http://www.iana.org/assignments/pcep/
   pcep.xhtml#of.  Three new Objective Functions have been defined in
   this document.

   IANA is requested to make the following allocations:

            Code     Name                           Reference
            Point
            --------------------------------------------------
            TBD5     Minimum Packet Loss Path       [This I.D.]
                     (MPLP)
            TBD6     Maximum Under-Utilized         [This I.D.]
                     Path (MUP)
            TBD7     Maximum Reserved               [This I.D.]
                     Under-Utilized Path (MRUP)


8.  Security Considerations

   This document defines new METRIC types, a new BU object, and OF codes
   which does not add any new security concerns beyond those discussed
   in [RFC5440] and [RFC5541] in itself.  Some deployments may find the
   service aware information like delay and packet loss as extra
   sensitive and thus should employ suitable PCEP security mechanisms
   like TCP-AO or [PCEPS].

9.  Manageability Considerations

9.1.  Control of Function and Policy

   The only configurable item is the support of the new constraints on a
   PCE which MAY be controlled by a policy module on individual basis.
   If the new constraint is not supported/allowed on a PCE, it MUST send
   a PCErr message accordingly.







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9.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB, there are no new MIB Objects for
   this document.

9.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440].

9.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440].

9.5.  Requirements On Other Protocols

   PCE requires the TED to be populated with network performance
   information like link latency, latency variation, packet loss, and
   utilized bandwidth.  This mechanism is described in [RFC7471] and
   [ISIS-TE-METRIC-EXT].

9.6.  Impact On Network Operations

   Mechanisms defined in this document do not have any impact on network
   operations in addition to those already listed in [RFC5440].

10.  Acknowledgments

   We would like to thank Alia Atlas, John E Drake, David Ward, Young
   Lee, Venugopal Reddy, Reeja Paul, Sandeep Kumar Boina, Suresh Babu,
   Quintin Zhao, Chen Huaimo and Avantika for their useful comments and
   suggestions.

   Also the authors gratefully acknowledge reviews and feedback provided
   by Qin Wu, Alfred Morton and Paul Aitken during performance
   directorate review.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.



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   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <http://www.rfc-editor.org/info/rfc5440>.

   [RFC5541]  Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
              Objective Functions in the Path Computation Element
              Communication Protocol (PCEP)", RFC 5541,
              DOI 10.17487/RFC5541, June 2009,
              <http://www.rfc-editor.org/info/rfc5541>.

   [STATEFUL-PCE]
              Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
              Extensions for Stateful PCE", draft-ietf-pce-stateful-
              pce-11 (work in progress), April 2015.

11.2.  Informative References

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <http://www.rfc-editor.org/info/rfc4655>.

   [RFC5316]  Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316,
              December 2008, <http://www.rfc-editor.org/info/rfc5316>.

   [RFC5392]  Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5392, DOI 10.17487/RFC5392,
              January 2009, <http://www.rfc-editor.org/info/rfc5392>.

   [RFC5441]  Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
              "A Backward-Recursive PCE-Based Computation (BRPC)
              Procedure to Compute Shortest Constrained Inter-Domain
              Traffic Engineering Label Switched Paths", RFC 5441,
              DOI 10.17487/RFC5441, April 2009,
              <http://www.rfc-editor.org/info/rfc5441>.

   [RFC5623]  Oki, E., Takeda, T., Le Roux, JL., and A. Farrel,
              "Framework for PCE-Based Inter-Layer MPLS and GMPLS
              Traffic Engineering", RFC 5623, DOI 10.17487/RFC5623,
              September 2009, <http://www.rfc-editor.org/info/rfc5623>.

   [RFC6049]  Morton, A. and E. Stephan, "Spatial Composition of
              Metrics", RFC 6049, DOI 10.17487/RFC6049, January 2011,
              <http://www.rfc-editor.org/info/rfc6049>.



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   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,
              <http://www.rfc-editor.org/info/rfc6374>.

   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <http://www.rfc-editor.org/info/rfc7420>.

   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
              <http://www.rfc-editor.org/info/rfc7471>.

   [ISIS-TE-METRIC-EXT]
              Previdi, S., Giacalone, S., Ward, D., Drake, J., Atlas,
              A., Filsfils, C., and W. Wu, "IS-IS Traffic Engineering
              (TE) Metric Extensions", draft-ietf-isis-te-metric-
              extensions-07 (work in progress), June 2015.

   [PCEPS]    Lopez, D., Dios, O., Wu, W., and D. Dhody, "Secure
              Transport for PCEP", draft-ietf-pce-pceps-04 (work in
              progress), May 2015.

   [TE-EXPRESS-PATH]
              Atlas, A., Drake, J., Giacalone, S., and S. Previdi,
              "Performance-based Path Selection for Explicitly Routed
              LSPs using TE Metric Extensions", draft-ietf-teas-te-
              express-path-05 (work in progress), October 2015.

   [IEEE.754.1985]
              IEEE, "Standard for Binary Floating-Point Arithmetic",
              IEEE 754, August 1985.
















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Appendix A.  Contributor Addresses

   Clarence Filsfils
   Cisco Systems
   Email: cfilsfil@cisco.com

   Siva Sivabalan
   Cisco Systems
   Email: msiva@cisco.com

   George Swallow
   Cisco Systems
   Email: swallow@cisco.com

   Stefano Previdi
   Cisco Systems, Inc
   Via Del Serafico 200
   Rome  00191
   Italy
   Email: sprevidi@cisco.com

   Udayasree Palle
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560037
   India
   Email: udayasree.palle@huawei.com

   Avantika
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560037
   India
   Email: avantika.sushilkumar@huawei.com

   Xian Zhang
   Huawei Technologies
   F3-1-B R&D Center, Huawei Base Bantian, Longgang District
   Shenzhen, Guangdong  518129
   P.R.China
   Email: zhang.xian@huawei.com


Authors' Addresses







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   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560037
   India

   EMail: dhruv.ietf@gmail.com


   Qin Wu
   Huawei Technologies
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   EMail: bill.wu@huawei.com


   Vishwas Manral
   Ionos Network
   4100 Moorpark Av
   San Jose, CA
   USA

   EMail: vishwas.ietf@gmail.com


   Zafar Ali
   Cisco Systems

   EMail: zali@cisco.com


   Kenji Kumaki
   KDDI Corporation

   EMail: ke-kumaki@kddi.com














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