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Versions: (draft-wu-alto-te-metrics) 00 01 02 03 04 05 06 07 08 09

ALTO Working Group                                                 Q. Wu
Internet-Draft                                                    Huawei
Intended status: Standards Track                                 Y. Yang
Expires: September 10, 2020                              Yale University
                                                                D. Dhody
                                                                  Huawei
                                                          S. Randriamasy
                                                         Nokia Bell Labs
                                                            L. Contreras
                                                              Telefonica
                                                          March 09, 2020


                     ALTO Performance Cost Metrics
                 draft-ietf-alto-performance-metrics-09

Abstract

   Cost metric is a basic concept in Application-Layer Traffic
   Optimization (ALTO), and is used in basic ALTO services including
   both the cost map service and the endpoint cost service.

   Different applications may use different cost metrics, but the ALTO
   base protocol [RFC7285] documents only one single cost metric, i.e.,
   the generic "routingcost" metric; see Sec. 14.2 of [RFC7285].  Hence,
   if the resource consumer of an application prefers a resource
   provider that offers low-delay delivery to the resource consumer, the
   base protocol does not define the cost metric to be used.

   ALTO cost metrics can be generic metrics and this document focuses on
   network performance metrics, including network delay, jitter, packet
   loss, hop count, and bandwidth.

   When using an ALTO performance metric, an application may need
   additional contextual information beyond the metric value.  For
   example, whether the metric is an estimation based on measurements or
   a service-level agreement (SLA) can define the meaning of a
   performance metric.  Hence, this document introduces an additional
   "cost-context" field to the ALTO "cost-type" field to convey such
   information.  To report an estimated value of a performance metric,
   the ALTO server may derive and aggregate from routing protocols with
   different granularity and scope, such as BGP-LS, OSPF-TE and ISIS-TE,
   or from end-to-end traffic management tools.  These metrics may then
   be exposed by an ALTO Server to allow applications to determine
   "where" to connect based on network performance criteria.

   Requirements Language The key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",



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   and "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

Status of This Memo

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

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

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

   This Internet-Draft will expire on September 10, 2020.

Copyright Notice

   Copyright (c) 2020 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.  Performance Metric Context: cost-context  . . . . . . . . . .   5
   3.  Network Performance Cost Metrics  . . . . . . . . . . . . . .   7
     3.1.  Cost Metric: One Way Delay (owdelay)  . . . . . . . . . .   7
       3.1.1.  Identifier  . . . . . . . . . . . . . . . . . . . . .   7
       3.1.2.  Value Representation  . . . . . . . . . . . . . . . .   7
       3.1.3.  Intended Semantics and Use  . . . . . . . . . . . . .   7
       3.1.4.  Measurement Considerations and Parameters . . . . . .   8
     3.2.  Cost Metric: RoundTrip Time (rtt) . . . . . . . . . . . .   9
       3.2.1.  Identifier  . . . . . . . . . . . . . . . . . . . . .   9
       3.2.2.  Value Representation  . . . . . . . . . . . . . . . .   9



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       3.2.3.  Intended Semantics and Use  . . . . . . . . . . . . .   9
       3.2.4.  Measurement Considerations and Parameters . . . . . .  10
     3.3.  Cost Metric: Packet Delay Variation (pdv) . . . . . . . .  11
       3.3.1.  Identifier  . . . . . . . . . . . . . . . . . . . . .  11
       3.3.2.  Value Representation  . . . . . . . . . . . . . . . .  11
       3.3.3.  Intended Semantics and Use  . . . . . . . . . . . . .  11
       3.3.4.  Measurement Considerations and Parameters . . . . . .  12
     3.4.  Cost Metric: Hop Count  . . . . . . . . . . . . . . . . .  13
       3.4.1.  Identifier  . . . . . . . . . . . . . . . . . . . . .  13
       3.4.2.  Value Representation  . . . . . . . . . . . . . . . .  13
       3.4.3.  Intended Semantics and Use  . . . . . . . . . . . . .  13
       3.4.4.  Measurement Considerations and Parameters . . . . . .  14
     3.5.  Cost Metric: Packet Loss  . . . . . . . . . . . . . . . .  15
       3.5.1.  Identifier  . . . . . . . . . . . . . . . . . . . . .  15
       3.5.2.  Value Representation  . . . . . . . . . . . . . . . .  15
       3.5.3.  Intended Semantics and Use  . . . . . . . . . . . . .  15
       3.5.4.  Measurement Considerations and Parameters . . . . . .  16
     3.6.  Cost Metric: Throughput . . . . . . . . . . . . . . . . .  16
       3.6.1.  Identifier  . . . . . . . . . . . . . . . . . . . . .  16
       3.6.2.  Value Representation  . . . . . . . . . . . . . . . .  16
       3.6.3.  Intended Semantics and Use  . . . . . . . . . . . . .  16
       3.6.4.  Measurement Considerations and Parameters . . . . . .  17
   4.  Traffic Engineering Performance Cost Metrics  . . . . . . . .  18
     4.1.  Cost Metric: Link Maximum Reservable Bandwidth  . . . . .  18
       4.1.1.  Identifier  . . . . . . . . . . . . . . . . . . . . .  18
       4.1.2.  Value Representation  . . . . . . . . . . . . . . . .  18
       4.1.3.  Intended Semantics and Use  . . . . . . . . . . . . .  18
       4.1.4.  Measurement Considerations and Parameters . . . . . .  19
     4.2.  Cost Metric: Link Residue Bandwidth . . . . . . . . . . .  20
       4.2.1.  Identifier  . . . . . . . . . . . . . . . . . . . . .  20
       4.2.2.  Value Representation  . . . . . . . . . . . . . . . .  20
       4.2.3.  Intended Semantics and Use  . . . . . . . . . . . . .  20
       4.2.4.  Measurement Considerations and Parameters . . . . . .  21
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .  22
     5.1.  Source Considerations . . . . . . . . . . . . . . . . . .  22
     5.2.  Backward Compatibility Considerations . . . . . . . . . .  23
     5.3.  Computation Considerations  . . . . . . . . . . . . . . .  23
       5.3.1.  Configuration Parameters Considerations . . . . . . .  23
       5.3.2.  Availability Considerations . . . . . . . . . . . . .  23
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  25
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  25
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26





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1.  Introduction

   Cost Metric is a basic concept in Application-Layer Traffic
   Optimization (ALTO).  It is used in both the ALTO cost map service
   and the ALTO endpoint cost service, to allow applications to request
   network cost metrics.

   Different applications may use different cost metrics.  Hence, the
   ALTO base protocol [RFC7285] introduces an ALTO Cost Metric Registry
   (Section 14.2 of [RFC7285]), as a systematic mechanism to allow
   different metrics to be specified.  For example, a delay-sensitive
   application may want to use latency related metrics, and a bandwidth-
   sensitive application may want to use bandwidth related metrics.  The
   ALTO base protocol [RFC7285], however, has registered only one single
   cost metric, i.e., the generic "routingcost" metric; no latency or
   bandwidth related metrics are defined.

   This document registers a set of new cost metrics specified in
   Table 1, to support the aforementioned applications, to allow them to
   better determine "where" to connect based on network performance
   criteria.  This document follows the guideline (Section 14.2 of
   [RFC7285]) of the ALTO base protocol on registering ALTO cost
   metrics.  Hence it specifies the identifier, the intended semantics,
   and the security considerations of each one of the metrics defined in
   Table 1.

   +--------------------------+-------------+-------------+
   | Metric                   | Definition  |  Origin     |
   +--------------------------+-------------+-------------+
   | One Way Delay            | Section 2.1 | [RFC7679]   |
   | Round Trip Delay         | Section 2.2 | [RFC2681]   |
   | Packet Delay Variation   | Section 2.3 | [RFC3393]   |
   | Hop Count                | Section 2.4 | [RFC7285]   |
   | Packet Loss              | Section 2.5 | [RFC7680]   |
   | Throughput               | Section 2.6 | [RFC6349]   |
   | Max Reservable Bandwidth | Section 3.1 | [RFC5305]   |
   | Residue Bandwidth        | Section 3.2 | [RFC7810]   |
   +------------+-----------------------------------------+
      Table 1. Cost Metrics Defined in this Document.

   The purpose of this document is to ensure proper usage of the metrics
   by ALTO clients.  It does not claim novelty of the metrics; see
   Table 1 for the source definition of each metric.

   An ALTO server may provide only a subset of the cost metrics
   described in this document.  Hence, all cost metrics defined in this
   document are optional and not all of them need to be exposed to a




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   given application.  For example, those that are subject to privacy
   concerns should not be provided to unauthorized ALTO clients.

   When an ALTO server supports a cost metric defined in this document,
   it MUST announce this metric in its information resource directory
   (IRD).

   An ALTO server introducing these metrics should also consider
   security issues.  As a generic security consideration on the
   reliability and trust in the exposed metric values, applications
   SHOULD rapidly give up using ALTO-based guidance if they detect that
   the exposed information does not preserve their performance level or
   even degrades it.  We discuss security considerations in more details
   in Section 6.

   Following the ALTO base protocol, this document uses JSON to specify
   the value type of each defined metric.  See [RFC8259] for JSON data
   type specification.

2.  Performance Metric Context: cost-context

   The semantics of a performance metric depends on the context.
   Specifically, this document defines three sources when defining
   performance metrics: "estimation", "nominal", and "sla".

   Even given the source, precise interpretation of a performance metric
   value, if needed, depends on an additional set of measurement and
   computation parameters.  For example, see Section 3.8 of [RFC7679] on
   items which a more complete measurement-based report should include.

   To make it possible to specify both the source and the additional
   parameters, this document introduces an optional "cost-context" field
   to the "cost-type" field defined by the ALTO base protocol
   (Section 10.7 of [RFC7285]) as the following:

















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       object {
         CostMetric   cost-metric;
         CostMode     cost-mode;
         [CostContext cost-context;]
         [JSONString  description;]
       } CostType;

       object {
         JSONString    cost-source;
         [JSONValue    parameters;]
       } CostContext;



   The "cost-source" MUST be one of only three values: "estimation",
   "nominal", and "sla".  If a "cost-type" does not include the optional
   "cost-context" field which includes the "cost-source" field, the
   application MUST assume that the value of "cost-source" is
   "estimation".

   An ALTO server may compute "estimation" values by retrieving and/or
   aggregating information from routing protocols or other traffic
   measurement management tools, with corresponding operational issues.
   A potential architecture on estimating these metrics is shown in
   Figure 1 below.  In Section 5, we discuss in more detail the
   operational issues and how a network may address them.

     +--------+   +--------+  +--------+
     | Client |   | Client |  | Client |
     +----^---+   +---^----+  +---^----+
          |           |           |
          +-----------|-----------+
                NBI   |ALTO protocol
                      |
                      |
                   +--+-----+  retrieval      +---------+
                   |  ALTO  |<----------------| Routing |
                   | Server |  and aggregation|         |
                   |        |<-------------+  | Protocol|
                   +--------+              |  +---------+
                                           |
                                           |  +---------+
                                           |  |Management
                                           ---|         |
                                              |  Tool   |
                                              +---------+
   Figure 1. Potential framework to compute performance cost metrics




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3.  Network Performance Cost Metrics

   This section introduces generic ALTO network performance metrics such
   as one way delay, round trip delay, hop count, packet loss, and
   throughput.

3.1.  Cost Metric: One Way Delay (owdelay)

3.1.1.  Identifier

   The identifier for this performance metric is "owdelay".

3.1.2.  Value Representation

   The metric value type is a single 'JSONNumber' type value conforming
   to the number specification of [RFC8259] Section 6.  The number MUST
   be non-negative.  The unit is expressed in milliseconds.

3.1.3.  Intended Semantics and Use

   Intended Semantics: To specify spatial and temporal aggregated delay
   of a stream of packets exchanged between the specified source and
   destination or the time that the packet spends to travel from source
   to destination.  The spatial aggregation level is specified in the
   query context (e.g., PID to PID, or endpoint to endpoint).

   Use: This metric could be used as a cost metric constraint attribute
   used either together with cost metric attribute 'routingcost' or on
   its own or as a returned cost metric in the response.






















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   Example 1: Delay value on source-destination endpoint pairs

   POST /endpointcost/lookup HTTP/1.1
   Host: alto.example.com
   Content-Length: TBA
   Content-Type: application/alto-endpointcostparams+json
   Accept:
     application/alto-endpointcost+json,application/alto-error+json

   {
     "cost-type": {"cost-mode" : "numerical",
                   "cost-metric" : "owdelay"},
     "endpoints" : {
       "srcs": [ "ipv4:192.0.2.2" ],
       "dsts": [
         "ipv4:192.0.2.89",
         "ipv4:198.51.100.34",
         "ipv6:2000::1:2345:6789:abcd"
       ]
     }
   }

   HTTP/1.1 200 OK
   Content-Length: TBA
   Content-Type: application/alto-endpointcost+json
   {
     "meta" :{
       "cost-type": {"cost-mode" : "numerical",
                     "cost-metric" : "owdelay"
        }
      },
       "endpoint-cost-map" : {
         "ipv4:192.0.2.2": {
           "ipv4:192.0.2.89"    : 10,
           "ipv4:198.51.100.34" : 20,
           "ipv6:2000::1:2345:6789:abcd"  : 30,
       }
     }
   }

   Comment: Since the "cost-type" does not include the "cost-source"
   field, the values are based on "estimation".

3.1.4.  Measurement Considerations and Parameters

   See Section 4 of [I-D.ietf-ippm-initial-registry] for measurement
   considerations and parameters which may be specified in "parameters".




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   Note that the "parameters" field is an optional field providing non-
   normative information.

3.2.  Cost Metric: RoundTrip Time (rtt)

3.2.1.  Identifier

   The identifier for this performance metric is "rtt".

3.2.2.  Value Representation

   The metric value type is a single 'JSONNumber' type value conforming
   to the number specification of [RFC8259] Section 6.  The number MUST
   be non-negative.  The unit is expressed in milliseconds.

3.2.3.  Intended Semantics and Use

   Intended Semantics: To specify spatial and temporal aggregated round
   trip delay between the specified source and destination or the time
   that the packet spends to travel from source to destination and then
   from destination to source.  The spatial aggregation level is
   specified in the query context (e.g., PID to PID, or endpoint to
   endpoint).

   Use: This metric could be used as a cost metric constraint attribute
   used either together with cost metric attribute 'routingcost' or on
   its own or as a returned cost metric in the response.
























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   Example 2: Roundtrip Delay value on source-destination endpoint pairs

   POST /endpointcost/lookup HTTP/1.1
   Host: alto.example.com
   Content-Length: TBA
   Content-Type: application/alto-endpointcostparams+json
   Accept:
     application/alto-endpointcost+json,application/alto-error+json

   {
    "cost-type": {"cost-mode" : "numerical",
                  "cost-metric" : "rtt"},
     "endpoints" : {
        "srcs": [ "ipv4:192.0.2.2" ],
        "dsts": [
          "ipv4:192.0.2.89",
          "ipv4:198.51.100.34",
          "ipv6:2000::1:2345:6789:abcd"
        ]
      }
   }

    HTTP/1.1 200 OK
    Content-Length: TBA
    Content-Type: application/alto-endpointcost+json
    {
      "meta" :{
        "cost-type": {"cost-mode" : "numerical",
                      "cost-metric" : "rtt"
         }
       },
        "endpoint-cost-map" : {
          "ipv4:192.0.2.2": {
            "ipv4:192.0.2.89"    : 4,
            "ipv4:198.51.100.34" : 3,
            "ipv6:2000::1:2345:6789:abcd"  : 2,
        }
      }
    }


3.2.4.  Measurement Considerations and Parameters

   See Section 4 of [I-D.ietf-ippm-initial-registry] for measurement
   considerations and parameters which may be specified in "parameters".
   Note that the "parameters" field is an optional field providing non-
   normative information.




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3.3.  Cost Metric: Packet Delay Variation (pdv)

3.3.1.  Identifier

   The identifier for this performance metric is "pdv".

3.3.2.  Value Representation

   The metric value type is a single 'JSONNumber' type value conforming
   to the number specification of [RFC8259] Section 6.  The number MUST
   be non-negative.  The unit is expressed in milliseconds.

3.3.3.  Intended Semantics and Use

   Intended Semantics: To specify spatial and temporal aggregated jitter
   (packet delay variation) with respect to the minimum delay observed
   on the stream over the specified source and destination.  The spatial
   aggregation level is specified in the query context (e.g., PID to
   PID, or endpoint to endpoint).

   Use: This metric could be used as a cost metric constraint attribute
   used either together with cost metric attribute 'routingcost' or on
   its own or as a returned cost metric in the response.




























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   Example 3: PDV value on source-destination endpoint pairs

   POST /endpointcost/lookup HTTP/1.1
   Host: alto.example.com
   Content-Length: TBA
   Content-Type: application/alto-endpointcostparams+json
   Accept:
      application/alto-endpointcost+json,application/alto-error+json

   {
     "cost-type": {"cost-mode" : "numerical",
      "cost-metric" : "pdv"},
     "endpoints" : {
       "srcs": [ "ipv4:192.0.2.2" ],
       "dsts": [
         "ipv4:192.0.2.89",
         "ipv4:198.51.100.34",
         "ipv6:2000::1:2345:6789:abcd"
       ]
     }
   }
   HTTP/1.1 200 OK
    Content-Length: TBA
    Content-Type: application/alto-endpointcost+json
   {
     "meta": {
              "cost type": {
              "cost-mode": "numerical",
              "cost-metric":"delayjitter"
       }
      },
     "endpoint-cost-map": {
              "ipv4:192.0.2.2": {
              "ipv4:192.0.2.89"    : 0
              "ipv4:198.51.100.34" : 1
              "ipv6:2000::1:2345:6789:abcd"  : 5
            }
         }
      }

3.3.4.  Measurement Considerations and Parameters

   See Section 5 of [I-D.ietf-ippm-initial-registry] for measurement
   considerations and parameters which may be specified in "parameters".
   Note that the "parameters" field is an optional field providing non-
   normative information.





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3.4.  Cost Metric: Hop Count

   The metric hopcount is mentioned in [RFC7285] Section 9.2.3 as an
   example.  This section further clarifies its properties.

3.4.1.  Identifier

   The identifier for this performance metric is "hopcount".

3.4.2.  Value Representation

   The metric value type is a single 'JSONNumber' type value conforming
   to the number specification of [RFC8259] Section 6.  The number MUST
   be an integer and non-negative.  The value represents the number of
   hops.

3.4.3.  Intended Semantics and Use

   Intended Semantics: To specify the number of hops in the path between
   the source endpoint and the destination endpoint.  The hop count is a
   basic measurement of distance in a network and can be exposed as
   Router Hops, in direct relation to the routing protocols originating
   this information.

   Use: This metric could be used as a cost metric constraint attribute
   used either together with cost metric attribute 'routingcost' or on
   its own or as a returned cost metric in the response.
























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   Example 4: hopcount value on source-destination endpoint pairs

   POST /endpointcost/lookup HTTP/1.1
   Host: alto.example.com
   Content-Length: TBA
   Content-Type: application/alto-endpointcostparams+json
   Accept:
     application/alto-endpointcost+json,application/alto-error+json

     {
       "cost-type": {"cost-mode" : "numerical",
        "cost-metric" : "hopcount"},
       "endpoints" : {
         "srcs": [ "ipv4:192.0.2.2" ],
         "dsts": [
           "ipv4:192.0.2.89",
           "ipv4:198.51.100.34",
           "ipv6:2000::1:2345:6789:abcd"
         ]
       }
     }

   HTTP/1.1 200 OK
   Content-Length: TBA
   Content-Type: application/alto-endpointcost+json
   {
       "meta": {
                  "cost type": {
                "cost-mode": "numerical",
                "cost-metric":"hopcount"}
          }
       },
      "endpoint-cost-map": {
              "ipv4:192.0.2.2": {
              "ipv4:192.0.2.89"   : 5,
              "ipv4:198.51.100.34": 3,
              "ipv6:2000::1:2345:6789:abcd" : 2,
                                }
                }
    }

3.4.4.  Measurement Considerations and Parameters

   The hop count can be calculated based on the number of routers from
   the source endpoint through which data must pass to reach the
   destination endpoint.  This count can be measured at the source
   endpoint by traceroute.




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   Upon need, the traceroute can use UDP probe message or other
   implementations that use ICMP and TCP to discover the hop counts
   along the path from source endpoint to destination endpoint.

3.5.  Cost Metric: Packet Loss

3.5.1.  Identifier

   The identifier for this performance metric is "pktloss".

3.5.2.  Value Representation

   The metric value type is a single 'JSONNumber' type value conforming
   to the number specification of [RFC8259] Section 6.  The number MUST
   be non-negative.  The value represents the percentage of packet loss.

3.5.3.  Intended Semantics and Use

   Intended Semantics: To specify spatial and temporal aggregated packet
   loss over the specified source and destination.  The spatial
   aggregation level is specified in the query context (e.g., PID to
   PID, or endpoint to endpoint).

   Use: This metric could be used as a cost metric constraint attribute
   used either together with cost metric attribute 'routingcost' or on
   its own or as a returned cost metric in the response.

   Example 5: pktloss value on source-destination endpoint pairs

   POST /endpointcost/lookup HTTP/1.1
   Host: alto.example.com
   Content-Length: TBA
   Content-Type: application/alto-endpointcostparams+json
   Accept:
     application/alto-endpointcost+json,application/alto-error+json

     {
       "cost-type": {"cost-mode" : "numerical",
        "cost-metric" : "pktloss"},
       "endpoints" : {
         "srcs": [ "ipv4:192.0.2.2" ],
         "dsts": [
           "ipv4:192.0.2.89",
           "ipv4:198.51.100.34",
           "ipv6:2000::1:2345:6789:abcd"
         ]
       }
     }



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   HTTP/1.1 200 OK
   Content-Length: TBA
   Content-Type: application/alto-endpointcost+json
   {
       "meta": {
                  "cost type": {
                "cost-mode": "numerical",
                "cost-metric":"pktloss"}
          }
       },
      "endpoint-cost-map": {
              "ipv4:192.0.2.2": {
              "ipv4:192.0.2.89"   : 0,
              "ipv4:198.51.100.34": 0,
              "ipv6:2000::1:2345:6789:abcd" : 0,
                                }
                }
    }

3.5.4.  Measurement Considerations and Parameters

   See Section 4 of [I-D.ietf-ippm-initial-registry] for measurement
   considerations and parameters which may be specified in "parameters".
   Note that the "parameters" field is an optional field providing non-
   normative information.

3.6.  Cost Metric: Throughput

3.6.1.  Identifier

   The identifier for this performance metric is "throughput".

3.6.2.  Value Representation

   The metric value type is a single 'JSONNumber' type value conforming
   to the number specification of [RFC8259] Section 6.  The number MUST
   be non-negative.  The unit is Mbps.

3.6.3.  Intended Semantics and Use

   Intended Semantics: To specify spatial and temporal throughput over
   the specified source and destination.  The spatial aggregation level
   is specified in the query context (e.g., PID to PID, or endpoint to
   endpoint).

   Use: This metric could be used as a cost metric constraint attribute
   used either together with cost metric attribute 'routingcost' or on
   its own or as a returned cost metric in the response.



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   Example 5: throughtput value on source-destination endpoint pairs

   POST /endpointcost/lookup HTTP/1.1
   Host: alto.example.com
   Content-Length: TBA
   Content-Type: application/alto-endpointcostparams+json
   Accept:
     application/alto-endpointcost+json,application/alto-error+json

   {
     "cost-type": {"cost-mode" : "numerical",
                   "cost-metric" : "throughput"},
     "endpoints" : {
       "srcs": [ "ipv4:192.0.2.2" ],
       "dsts": [
          "ipv4:192.0.2.89",
          "ipv4:198.51.100.34",
          "ipv6:2000::1:2345:6789:abcd"
       ]
     }
   }

   HTTP/1.1 200 OK
   Content-Length: TBA
   Content-Type: application/alto-endpointcost+json
   {
     "meta": {
        "cost type": {
           "cost-mode": "numerical",
           "cost-metric":"throughput"
       }
     }
     "endpoint-cost-map": {
       "ipv4:192.0.2.2": {
         "ipv4:192.0.2.89"   : 25.6,
         "ipv4:198.51.100.34": 12.8,
         "ipv6:2000::1:2345:6789:abcd" : 42.8,
     }
   }

3.6.4.  Measurement Considerations and Parameters

   See Section 3.3 of [RFC6349] for measurement method and parameters
   which may be specified in "parameters".  Note that the "parameters"
   field is an optional field providing non-normative information.






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4.  Traffic Engineering Performance Cost Metrics

   This section introduces ALTO network performance metrics that may be
   aggregated from network metrics measured on links and specified in
   other documents.  In particular, the bandwidth related metrics
   specified in this section are only available through link level
   measurements.  For some of these metrics, the ALTO Server may further
   expose aggregated values while specifying the aggregation laws.

4.1.  Cost Metric: Link Maximum Reservable Bandwidth

4.1.1.  Identifier

   The identifier for this performance metric is "maxresbw".

4.1.2.  Value Representation

   The metric value type is a single 'JSONNumber' type value that is
   non-negative.  The unit of measurement is Mbps.

4.1.3.  Intended Semantics and Use

   Intended Semantics: To specify spatial and temporal maximum
   reservable bandwidth over the specified source and destination.  The
   value is corresponding to the maximum bandwidth that can be reserved
   (motivated from RFC 3630 Sec. 2.5.7.).  The spatial aggregation unit
   is specified in the query context (e.g., PID to PID, or endpoint to
   endpoint).

   Use: This metric could be used as a cost metric constraint attribute
   used either together with cost metric attribute 'routingcost' or on
   its own or as a returned cost metric in the response.



















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     Example 6: maxresbw value on source-destination endpoint pairs

   POST/ endpointcost/lookup HTTP/1.1
   Host: alto.example.com
   Content-Length: TBA
   Content-Type: application/alto-endpointcostparams+json
   Accept:
     application/alto-endpointcost+json,application/alto-error+json

     {
       "cost-type" { "cost-mode":  "numerical",
                     "cost-metric":  "maxresbw"},
       "endpoints":  {
         "srcs": [ "ipv4 : 192.0.2.2" ],
         "dsts": [
           "ipv4:192.0.2.89",
           "ipv4:198.51.100.34",
           "ipv6:2000::1:2345:6789:abcd"
         ]
       }
     }

   HTTP/1.1 200 OK
   Content-Length: TBA
   Content-Type: application/alto-endpointcost+json
   {
       "meta": {
              "cost-type": {
              "cost-mode": "numerical",
              "cost-metric": "maxresbw"
              }
       },
     " endpoint-cost-map": {
             "ipv4:192.0.2.2" {
             "ipv4:192.0.2.89" :    0,
             "ipv4:198.51.100.34": 2000,
             "ipv6:2000::1:2345:6789:abcd":  5000,
                               }
              }
   }

4.1.4.  Measurement Considerations and Parameters

   Method of Measurement or Calculation:

      Maximum Reservable Bandwidth is the bandwidth measured between two
      directly connected IS-IS neighbors or OSPF neighbors.  See
      Section 3.5 of [RFC5305] for Measurement Method.



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   Measurement Point(s) with Potential Measurement Domain:

      See Section 4.1 this document for discussions.


   Measurement Timing:

      See Section 3.5 of [RFC5305] and Section 5 of [RFC7810] for
      Measurement Timing.


4.2.  Cost Metric: Link Residue Bandwidth

4.2.1.  Identifier

   The identifier for this performance metric is "residuebw".

4.2.2.  Value Representation

   The metric value type is a single 'JSONNumber' type value that is
   non-negative.  The unit of measurement is Mbps.

4.2.3.  Intended Semantics and Use

   Intended Semantics: To specify spatial and temporal residual
   bandwidth over the specified source and destination.  The value is
   calculated by subtracting tunnel reservations from Maximum Bandwidth
   (motivated from [RFC7810], Section 4.5.).  The spatial aggregation
   unit is specified in the query context (e.g., PID to PID, or endpoint
   to endpoint).

   Use: This metric could be used as a cost metric constraint attribute
   used either together with cost metric attribute 'routingcost' or on
   its own or as a returned cost metric in the response.

















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   Example 7: residuebw value on source-destination endpoint pairs

   POST/ endpointcost/lookup HTTP/1.1
   Host: alto.example.com
   Content-Length: TBA
   Content-Type: application/alto-endpointcostparams+json
   Accept:
     application/alto-endpointcost+json,application/alto-error+json

     {
      "cost-type": { "cost-mode":  "numerical",
                     "cost-metric":  "residuebw"},
      "endpoints":  {
        "srcs": [ "ipv4 : 192.0.2.2" ],
        "dsts": [
          "ipv4:192.0.2.89",
          "ipv4:198.51.100.34",
          "ipv6:2000::1:2345:6789:abcd"
        ]
      }
     }

   HTTP/1.1 200 OK
   Content-Length: TBA
   Content-Type: application/alto-endpointcost+json
   {
      "meta": {
             "cost-type" {
             "cost-mode": "numerical",
             "cost-metric": "residuebw"
           }
       },
   "endpoint-cost-map" {
            "ipv4:192.0.2.2" {
            "ipv4:192.0.2.89" :    0,
            "ipv4:198.51.100.34": 2000,
            "ipv6:2000::1:2345:6789:abcd":  5000,
                          }
           }
   }

4.2.4.  Measurement Considerations and Parameters

   Method of Measurement or Calculation:

      Residue Bandwidth is the Unidirectional Residue bandwidth measured
      between two directly connected IS-IS neighbors or OSPF neighbors.
      See Section 4.5 of [RFC7810] for Measurement Method.



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   Measurement Point(s) with Potential Measurement Domain:

      See Section 4.1 of this document.


   Measurement Timing:

      See Section 5 of [RFC7810] for Measurement Timing.


5.  Operational Considerations

   The exact measurement infrastructure, measurement condition and
   computation algorithms can vary from different networks, and are
   outside the scope of this document.  Both the ALTO server and the
   ALTO clients, however, need to be cognizant of the operational issues
   discussed below.

   Also, the performance metrics specified in this document are similar,
   in that they may use similar data sources and have similar issues in
   their calculation.  Hence, we specify common issues unless one metric
   has its unique challenges.

5.1.  Source Considerations

   The addition of the "cost-source" field is to solve a key issue: An
   ALTO server needs data sources to compute the cost metrics described
   in this document and an ALTO client needs to know the data sources to
   better interpret the values.

   To avoid too fine-grained information, this document introduces
   "cost-source" to indicate only the high-level type of data sources:
   "estimation" or "sla", where "estimation" is a type of measurement
   data source and "sla" is a type that is more based on policy.

   For estimation, for example, the ALTO server may use log servers or
   the OAM system as its data source [RFC7971].  In particular, the cost
   metrics defined in this document can be computed using routing
   systems as the data sources.  Mechanisms defined in [RFC2681],
   [RFC3393], [RFC7679], [RFC7680], [RFC3630], [RFC3784], [RFC7471],
   [RFC7810], [RFC7752] and [I-D.ietf-idr-te-pm-bgp] that allow an ALTO
   Server to retrieve and derive the necessary information to compute
   the metrics that we describe in this document.








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5.2.  Backward Compatibility Considerations

   One potential issue introduced by the optional "cost-source" field is
   backward compatibility.  Consider that an IRD which defines two cost-
   types with the same "cost-mode" and "cost-metric", but one with
   "cost-source" being "estimation" and the other being "sla".  Then an
   ALTO client that is not aware of the extension will not be able to
   distinguish between these two types.  A similar issue can arise even
   with a single cost-type which has "cost-source" being "sla", but the
   backward client will ignore this field and consider the metric
   estimation.

   To address this issue, the only defined "routingcost" metric can be
   ONLY "estimation".

5.3.  Computation Considerations

   The metric values exposed by an ALTO server may result from
   additional processing on measurements from data sources to compute
   exposed metrics.  This may involve data processing tasks such as
   aggregating the results across multiple systems, removing outliers,
   and creating additional statistics.  There are two challenges on the
   computation of ALTO performance metrics.

5.3.1.  Configuration Parameters Considerations

   Performance metrics often depend on configuration parameters.  For
   example, the value of packet loss rate depends on the measurement
   interval and varies over time.  To handle this issue, an ALTO server
   may collect data on time periods covering the previous and current
   time or only collect data on present time.  The ALTO server may
   further aggregate these data to provide an abstract and unified view
   that can be more useful to applications.  To make the ALTO client
   better understand how to use these performance data, the ALTO server
   may provide the client with the validity period of the exposed metric
   values.

5.3.2.  Availability Considerations

   Applications value information relating to bandwidth availability
   whereas bandwidth related metrics can often be only measured at the
   link level.  This document specifies a set of link-level bandwidth
   related values that may be exposed as such by an ALTO server.  The
   server may also expose other metrics derived from their aggregation
   and having different levels of endpoint granularity, e.g., link
   endpoints or session endpoints.  The metric specifications may also
   expose the utilized aggregation laws.




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6.  Security Considerations

   The properties defined in this document present no security
   considerations beyond those in Section 15 of the base ALTO
   specification [RFC7285].

   However concerns addressed in Sections "15.1 Authenticity and
   Integrity of ALTO Information", "15.2 Potential Undesirable Guidance
   from Authenticated ALTO Information" and "15.3 Confidentiality of
   ALTO Information" remain of utmost importance.  Indeed, TE
   performance is a highly sensitive ISP information, therefore, sharing
   TE metric values in numerical mode requires full mutual confidence
   between the entities managing the ALTO Server and Client.  Numerical
   TE performance information will most likely be distributed by ALTO
   Servers to Clients under strict and formal mutual trust agreements.
   On the other hand, ALTO Clients must be cognizant on the risks
   attached to such information that they would have acquired outside
   formal conditions of mutual trust.

7.  IANA Considerations

   IANA has created and now maintains the "ALTO Cost Metric Registry",
   listed in Section 14.2, Table 3 of [RFC7285].  This registry is
   located at <http://www.iana.org/assignments/alto-protocol/alto-
   protocol.xhtml#cost-metrics>.  This document requests to add the
   following entries to "ALTO Cost Metric Registry".

   +------------+--------------------+
   | Identifier | Intended Semantics |
   +------------+--------------------+
   | owdelay    | See Section 2.1    |
   | rtt        | See Section 2.2    |
   | pdv        | See Section 2.3    |
   | hopcount   | See Section 2.4    |
   | pktloss    | See Section 2.5    |
   | throughput | See Section 2.6    |
   | maxresbw   | See Section 3.1    |
   | residuebw  | See Section 3.2    |
   +------------+--------------------+

   This document requests the creation of the "ALTO Cost Source
   Registry" with the following currently defined values:









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   +------------+---------------------------+
   | Identifier | Intended Semantics        |
   +------------+---------------------------+
   | estimation | Values by estimation      |
   | nominal    | Values in nominal cases   |
   | sla        | Values reflecting service |
   |            | level agreement           |
   +------------+---------------------------+

8.  Acknowledgments

   The authors of this document would also like to thank Brian Trammell,
   Haizhou Du, Kai Gao, Lili Liu, Li, Geng, Danny Alex Lachos Perez for
   the reviews and comments.  Young Lee is an author of an earlier
   version of the document.

9.  References

9.1.  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, <https://www.rfc-editor.org/info/
              rfc2119>.

   [RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Delay Metric for IPPM", RFC 2679, DOI 10.17487/RFC2679,
              September 1999, <https://www.rfc-editor.org/info/rfc2679>.

   [RFC2681]  Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
              Delay Metric for IPPM", RFC 2681, DOI 10.17487/RFC2681,
              September 1999, <https://www.rfc-editor.org/info/rfc2681>.

   [RFC3393]  Demichelis, C. and P. Chimento, "IP Packet Delay Variation
              Metric for IP Performance Metrics (IPPM)", RFC 3393, DOI
              10.17487/RFC3393, November 2002, <https://www.rfc-
              editor.org/info/rfc3393>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

   [RFC6349]  Constantine, B., Forget, G., Geib, R., and R. Schrage,
              "Framework for TCP Throughput Testing", RFC 6349, DOI
              10.17487/RFC6349, August 2011, <https://www.rfc-
              editor.org/info/rfc6349>.





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   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.

   [RFC7810]  Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and
              Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions",
              RFC 7810, DOI 10.17487/RFC7810, May 2016,
              <https://www.rfc-editor.org/info/rfc7810>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259, DOI 10.17487/
              RFC8259, December 2017, <https://www.rfc-editor.org/info/
              rfc8259>.

9.2.  Informative References

   [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
              Performance Metric Development", BCP 170, RFC 6390, DOI
              10.17487/RFC6390, October 2011, <https://www.rfc-
              editor.org/info/rfc6390>.

   [RFC7971]  Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and
              S. Previdi, "Application-Layer Traffic Optimization (ALTO)
              Deployment Considerations", RFC 7971, DOI 10.17487/
              RFC7971, October 2016, <https://www.rfc-editor.org/info/
              rfc7971>.

Authors' Addresses

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

   Email: bill.wu@huawei.com


   Y. Richard Yang
   Yale University
   51 Prospect St
   New Haven, CT  06520
   USA

   Email: yry@cs.yale.edu




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   Dhruv Dhody
   Huawei
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   Email: dhruv.ietf@gmail.com


   Sabine Randriamasy
   Nokia Bell Labs
   Route de Villejust
   Nozay  91460
   FRANCE

   Email: sabine.randriamasy@nokia-bell-labs.com


   Luis Miguel Contreras Murillo
   Telefonica

   Email: luismiguel.contrerasmurillo@telefonica.com





























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