ALTO Working Group                                                 Q. Wu
Internet-Draft                                                    Huawei
Intended status: Standards Track                                 Y. Yang
Expires: January 9, May 7, 2020                                     Yale University
                                                                  Y. Lee
                                                                D. Dhody
                                                                  Huawei
                                                          S. Randriamasy
                                                         Nokia Bell Labs
                                                           July 08,
                                                       November 04, 2019

                     ALTO Performance Cost Metrics
                 draft-ietf-alto-performance-metrics-07
                 draft-ietf-alto-performance-metrics-08

Abstract

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

   Different applications may use different cost metrics, but the ALTO
   base protocol documents only one single cost metric, i.e., the
   generic "routingcost" metric; see Sec. 14.2 of ALTO base
   specification [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.  These  Additional cost metrics can may be derived
   documented in other documents.

   When using an ALTO performance metric, applications need additional
   information beyond the metric.  In particular, its "cost-source",
   such as it being an estimation or an SLA, is key to define the
   meaning of a performance metric.  Hence, each ALTO performance metric
   should include the "cost-source" of the metric.  To report an
   estimated value of a performance metric, the ALTO server may derive
   and
   aggregated 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.  Additional cost metrics may
   be documented in other documents.

   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
   RFC 2119 [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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 9, May 7, 2020.

Copyright Notice

   Copyright (c) 2019 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
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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
   2.  Network Performance Cost Metrics  . . . . . . . . . . . . . .   5   6
     2.1.  Cost Metric: One Way Delay (owdelay)  . . . . . . . . . .   5   6
       2.1.1.  Intended Semantics  . . . . . . . . . . . . . . . . .   6
       2.1.2.  Use and Example . . . . . . . . . . . . . . . . . . .   6
       2.1.3.  Measurement Considerations  . . . . . . . . . . . . .   7
     2.2.  Cost Metric: RoundTrip Time (rtt) . . . . . . . . . . . .   7   8
       2.2.1.  Intended Semantics  . . . . . . . . . . . . . . . . .   8
       2.2.2.  Use and Example . . . . . . . . . . . . . . . . . . .   8
       2.2.3.  Measurement Considerations  . . . . . . . . . . . . .   9
     2.3.  Cost Metric: Packet Delay Variation (pdv) . . . . . . . .   9  10
       2.3.1.  Intended Semantics  . . . . . . . . . . . . . . . . .  10
       2.3.2.  Use and Example . . . . . . . . . . . . . . . . . . .  10
       2.3.3.  Measurement Considerations  . . . . . . . . . . . . .  11
     2.4.  Cost Metric: Hop Count  . . . . . . . . . . . . . . . . .  12
       2.4.1.  Intended Semantics  . . . . . . . . . . . . . . . . .  12
       2.4.2.  Use and Example . . . . . . . . . . . . . . . . . . .  13
       2.4.3.  Measurement Considerations  . . . . . . . . . . . . .  14
     2.5.  Cost Metric: Packet Loss  . . . . . . . . . . . . . . . .  14
       2.5.1.  Intended Semantics  . . . . . . . . . . . . . . . . .  14
       2.5.2.  Use and Example . . . . . . . . . . . . . . . . . . .  15
       2.5.3.  Measurement Considerations  . . . . . . . . . . . . .  16
     2.6.  Cost Metric: Throughput . . . . . . . . . . . . . . . . .  16
       2.6.1.  Intended Semantics  . . . . . . . . . . . . . . . . .  17
       2.6.2.  Use and Example . . . . . . . . . . . . . . . . . . .  17
       2.6.3.  Measurement Considerations  . . . . . . . . . . . . .  18
   3.  Traffic Engineering Performance Cost Metrics  . . . . . . . .  18
     3.1.  Cost Metric: Link Maximum Reservable Bandwidth  . . . . .  19
       3.1.1.  Intended Semantics  . . . . . . . . . . . . . . . . .  19
       3.1.2.  Use and Example . . . . . . . . . . . . . . . . . . .  19
       3.1.3.  Measurement Considerations  . . . . . . . . . . . . .  20
     3.2.  Cost Metric: Link Residue Bandwidth . . . . . . . . . . .  21
       3.2.1.  Intended Semantics  . . . . . . . . . . . . . . . . .  21
       3.2.2.  Use and Example . . . . . . . . . . . . . . . . . . .  21
       3.2.3.  Measurement Considerations  . . . . . . . . . . . . .  22
   4.  Operational Considerations  . . . . . . . . . . . . . . . . .  23
     4.1.  Data  Source Considerations . . . . . . . . . . . . . . . . . .  23
     4.2.  Backward Compatibility Considerations . . . . . . . . . .  24
     4.3.  Computation Considerations  . . . . . . . . . . . . . . .  24
       4.2.1.
       4.3.1.  Configuration Parameters Considerations . . . . . . .  24
       4.2.2.
       4.3.2.  Availability Considerations . . . . . . . . . . . . .  24
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  24  25
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  25  26
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  25  26
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  25  26
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  27  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27  28

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 more delay-
   sensitive application may want to use latency related metrics, and a
   more 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
   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 | [RFC2679] Section 3.6 |
   | Round Trip Delay         | Section 2.2 | [RFC2681] Section 2.6 |
   | Packet Delay Variation   | Section 2.3 | [RFC3393] Section 2.6 |
   | Hop Count                | Section 2.4 | [RFC7285]             |
   | Packet Loss              | Section 2.5 | [RFC7680] Section 2.6 |
   | Throughput               | Section 2.6 | [RFC6349] Section 3.3 |
   | Max Reservable Bandwidth | Section 3.1 | [RFC5305] Section 3.5 |
   | Residue Bandwidth        | Section 3.2 | [RFC7810] Section 4.5 |
   +------------+---------------------------------------------------+
      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.  Some of
   these metrics are already specified by standards such as IPPM; some
   are ISP dependent such as those registered in ISIS or OSPF-TE.  This
   document will refer to the relevant specifications.

   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 them need to be exposed to
   applications.  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).

   The cost metrics defined in

   To make clear how the value of an ALTO performance metric is derived,
   this document defines an optional field named "cost-source" to extend
   the ALTO "cost-type".  The "cost-source" indicates how the metric is
   derived, and currently it can be retrieved and
   aggregated either "estimation" or "sla".  If a
   "cost-type" does not include the optional "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 computing estimating these metrics is shown in
   Figure 1 below.  In Section 4, we discuss in more detail the
   operations issues and how to 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

   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 feel the
   exposed information does not preserve their performance level or even
   degrades it.  We discuss security considerations in more details in
   Section 5.

   Following the ALTO base protocol, this document uses JSON to specify
   the value type of each defined metric.  See [RFC4627] for JSON data
   type specification.

2.  Network Performance Cost Metrics

   This section introduces generic ALTO network performance metrics such
   as one way delay,round delay, round trip delay,hop count,packet loss,throughput
   derived delay, hop count, packet loss, and aggregated from routing protocols or from end to end
   traffic management tools.
   throughput.

2.1.  Cost Metric: One Way Delay (owdelay)

   Metric name:

      One Way Delay

   Metric Identifier:

      owdelay

2.1.1.  Intended Semantics

   Metric Description: 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).

   Metric Representation: The metric value type is a single 'JSONNumber'
   type value containing a non-negative integer component that may be
   followed by an exponent part.  See section 8.4.3 conforming to the number specification of [I-D.ietf-ippm-
   initial-registry] for metric unit. [RFC8259]
   Section 6.  The number MUST be non-negative.  The unit is expressed
   in milliseconds in this document.

2.1.2.  Use and Example

   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 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".

2.1.3.  Measurement Considerations

   Method of Measurement or Calculation:

      See section 8.3 of [I-D.ietf-ippm-initial-registry] for potential
      measurement method.

   Measurement Point(s) with Potential Measurement Domain:

      See Section 4.1, Data sources for potential data sources.

   Measurement Timing:

      See section 8.3.5 of [I-D.ietf-ippm-initial-registry] for
      potential measurement timing considerations.

2.2.  Cost Metric: RoundTrip Time (rtt)

   Metric name:

      Round Trip Time

   Metric Identifier:

      rtt

2.2.1.  Intended Semantics

   Metric Description: 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).

   Metric Representation: The metric value type is a single 'JSONNumber'
   type value containing a non-negative integer component that may be
   followed by an exponent part.  See section 4.4.3 conforming to the number specification of [I-D.ietf-ippm-
   initial-registry] for Measurement Unit. [RFC8259]
   Section 6.  The number MUST be non-negative.  The unit is expressed
   in milliseconds in this document.

2.2.2.  Use and Example

   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 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,
        }
      }
    }

2.2.3.  Measurement Considerations

   Method of Measurement or Calculation:

      See section 4.3 of [I-D.ietf-ippm-initial-registry] for potential
      measurement method.

   Measurement Point(s) with Potential Measurement Domain:

      See section 4.1, Data sources.

   Measurement Timing:

      See section 4.3.5 of [I-D.ietf-ippm-initial-registry] for
      Measurement Timing.

2.3.  Cost Metric: Packet Delay Variation (pdv)

   Metric name:

      Packet Delay Variation

   Metric Identifier:

      pdv

2.3.1.  Intended Semantics

   Metric Description: 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).

   Metric Representation: The metric value type is a single 'JSONNumber'
   type value containing a non-negative integer component that may be
   followed by an exponent part.  See section 5.4.4 conforming to the number specification of [I-D.ietf-ippm-
   initial-registry] for Measurement Unit. [RFC8259]
   Section 6.  The number MUST be non-negative.  The unit is expressed
   in milliseconds in this document.

2.3.2.  Use and Example

   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 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
            }
         }
      }

2.3.3.  Measurement Considerations

   Method of Measurement or Calculation:

      See Section 5.3 of [I-D.ietf-ippm-initial-registry] for potential
      measurement method.

   Measurement Point(s) with Potential Measurement Domain:

      See Section 4.1, Data sources for potential data sources.

   Measurement Timing:

      See Section 5.3.5 of [I-D.ietf-ippm-initial-registry] for
      Measurement Timing.

2.4.  Cost Metric: Hop Count

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

   Metric name:

      Hop count

   Metric Identifier:

      hopcount

2.4.1.  Intended Semantics

   Metric Description:

      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.

   Metric Representation:

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

2.4.2.  Use and Example

   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 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,
                                }
                }
    }

2.4.3.  Measurement Considerations

   Method of Measurement or Calculation:

      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.

   Measurement Point(s) with Potential Measurement Domain:

      The hop count can be measured at the source endpoint by
      traceroute.

   Measurement Timing:

      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.

2.5.  Cost Metric: Packet Loss

   Metric name:

      Packet loss

   Metric Identifier:

      pktloss

2.5.1.  Intended Semantics

   Metric Description:

      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).

   Metric Representation:

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

2.5.2.  Use and Example

   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"
         ]
       }
     }

   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,
                                }
                }
    }

2.5.3.  Measurement Considerations

   Method of Measurement or Calculation:

      See Section 2.6 of [RFC7680] for Measurement Method.

   Measurement Point(s) with Potential Measurement Domain:

      See Section 4.1 this document, Data sources.

   Measurement Timing:

      See Section 2 and Section 3 of [RFC7680] for Measurement Timing.

2.6.  Cost Metric: Throughput

   Metric name:

      Throughput

   Metric Identifier:

      throughput

2.6.1.  Intended Semantics

   Metric Description:

      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).

   Metric 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.

2.6.2.  Use and Example

   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: 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,
     }
   }

2.6.3.  Measurement Considerations

   Method of Measurement or Calculation:

      See Section 3.3 of [RFC6349] for Measurement Method.

   Measurement Point(s) with Potential Measurement Domain:

      See Section 4.1 of this document.

   Measurement Timing:

      Similar to RTT.  See Section 4.3.5 of [I-D.ietf-ippm-initial-
      registry] for Measurement Timing.

3.  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.

3.1.  Cost Metric: Link Maximum Reservable Bandwidth

   Metric name:

      Maximum Reservable Bandwidth

   Metric Identifier:

      maxresbw

3.1.1.  Intended Semantics

   Metric Description:

      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).

   Metric Representation:

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

3.1.2.  Use and Example

   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 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,
                               }
              }
   }

3.1.3.  Measurement Considerations

   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.

   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.

3.2.  Cost Metric: Link Residue Bandwidth

   Metric name:

      Residue Bandwidth

   Metric Identifier:

      residuebw

3.2.1.  Intended Semantics

   Metric Description:

      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).

   Metric Representation:

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

3.2.2.  Use and Example

   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 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,
                          }
           }
   }

3.2.3.  Measurement Considerations

   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.

   Measurement Point(s) with Potential Measurement Domain:

      See Section 4.1 of this document.

   Measurement Timing:

      See Section 5 of [RFC7810] for Measurement Timing.

4.  Operational Considerations

   It can be non-trivial for an ALTO server to derive the metrics.
   Also, the

   The exact infrastructure measurement infrastructure, measurement condition and
   computation algorithms can vary from different networks, and are
   outside the scope of this document.  However, since
   they present challenges, we discuss these common challenges.  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.

4.1.  Data  Source Considerations

   The additiona 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.  This document does not define and an ALTO client needs to know the exact data sources. 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.

4.2.  Backward Compatibility Considerations

   One challenge lies in the data sources originating potential issue introduced by the ALTO metric
   values.  The very important purpose of ALTO optional "cost-source" field is to guide application
   traffic
   backward compatibility.  Consider that an IRD which defines two cost-
   types with provider network centric information the same "cost-mode" and "cost-metric", but one with
   "cost-source" being "estimation" and the other being "sla".  Then an
   ALTO client that may is not aware of the extension will not be exposed able to ALTO Clients in
   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 form of network performance metric values.
   Not all of these metrics have values produced by standardized
   measurement methods or routing protocols.  Some of them involve
   provider-centric policy considerations.  Some of them may describe
   wireless or cellular networks.
   estimation.  [RFC7285]

   To reliably guide users and
   applications while preserving provider privacy, ALTO performance address this issue, the only defined "routingcost" metric values may also add abstraction to measurements or provide
   unitless performance scores.

4.2. can be
   ONLY "estimation".

4.3.  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.

4.2.1.

4.3.1.  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.

4.2.2.

4.3.2.  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.

5.  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.

6.  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:

   +------------+------------------------+
   | Identifier | Intended Semantics     |
   +------------+------------------------+
   | estimation | Values by estimation   |
   | sla        | Values reflect service |
   |            | level agreement        |
   +------------+------------------------+

7.  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.

8.  References

8.1.  Normative References

   [I-D.ietf-idr-te-pm-bgp]
              Ginsberg, L., Previdi, S., Wu, Q., Tantsura, J., and C.
              Filsfils, "BGP-LS Advertisement of IGP Traffic Engineering
              Performance Metric Extensions", draft-ietf-idr-te-pm-
              bgp-18 (work in progress), December 2018.

   [I-D.ietf-ippm-initial-registry]
              Morton, A., Bagnulo, M., Eardley, P., and K. D'Souza,
              "Initial Performance Metrics Registry Entries", draft-
              ietf-ippm-initial-registry-11
              ietf-ippm-initial-registry-12 (work in progress), March
              September 2019.

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

   [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>.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, DOI
              10.17487/RFC4627, July 2006, <https://www.rfc-
              editor.org/info/rfc4627>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/
              RFC5234, January 2008, <https://www.rfc-editor.org/info/
              rfc5234>.

   [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>.

   [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>.

   [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,
              <https://www.rfc-editor.org/info/rfc7471>.

   [RFC7679]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Delay Metric for IP Performance Metrics
              (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
              2016, <https://www.rfc-editor.org/info/rfc7679>.

   [RFC7680]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Loss Metric for IP Performance Metrics
              (IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
              2016, <https://www.rfc-editor.org/info/rfc7680>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016, <https://www.rfc-
              editor.org/info/rfc7752>.

   [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>.

8.2.  Informative References

   [RFC6390]  Clark, A. and B. Claise, "Framework for Performance Metric
              Development", RFC 6390, July 2011.

   [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

   Young Lee
   Huawei
   1700 Alma Drive, Suite 500
   Plano, TX  75075
   USA

   Email: leeyoung@huawei.com
   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