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Versions: (draft-randriamasy-alto-cost-calendar) 00 01 02 03 04 05 06 07

Network Working Group                                     S. Randriamasy
Internet-Draft                                           Nokia Bell Labs
Intended status: Standards Track                                 R. Yang
Expires: January 3, 2019                                 Yale University
                                                                   Q. Wu
                                                                  Huawei
                                                                 L. Deng
                                                            China Mobile
                                                               N. Schwan
                                                      Thales Deutschland
                                                           July 02, 2018


                           ALTO Cost Calendar
                    draft-ietf-alto-cost-calendar-07

Abstract

   The goal of Application-Layer Traffic Optimization (ALTO) is to
   bridge the gap between network and applications by provisioning
   network related information in order to allow applications to make
   network informed decisions.  The present draft extends the ALTO cost
   information so as to broaden the decision possibilities of
   applications to not only decide 'where' to connect to, but also
   'when'.  This is useful to applications that need to schedule their
   data transfers and connections and have a degree of freedom to do so.
   ALTO guidance to schedule application traffic can also efficiently
   help for load balancing and resources efficiency.  Besides, the ALTO
   Cost Calendar allows to schedule the ALTO requests themselves and
   thus to save a number of ALTO transactions.

   This draft proposes new capabilities and attributes on filtered cost
   maps and endpoint cost maps enabling an ALTO Server to provide "Cost
   Calendars".  These capabilities are applicable to ALTO metrics with
   time-varying values.  With ALTO Cost Calendars, an ALTO Server
   exposes ALTO cost values in JSON arrays where each value corresponds
   to a given time interval.  The time intervals as well as other
   Calendar attributes are specified in the IRD and ALTO Server
   responses.

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].






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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 https://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 January 3, 2019.

Copyright Notice

   Copyright (c) 2018 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
   (https://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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Overview of ALTO Cost Calendars . . . . . . . . . . . . . . .   4
     2.1.  ALTO Cost Calendar information features . . . . . . . . .   5
     2.2.  ALTO Calendar design characteristics  . . . . . . . . . .   6
       2.2.1.  ALTO Cost Calendar for all cost modes . . . . . . . .   6
       2.2.2.  Compatibility with legacy ALTO Clients  . . . . . . .   7
   3.  ALTO Calendar specification: IRD extensions . . . . . . . . .   7
     3.1.  Calendar attributes in the IRD resources capabilities . .   7
     3.2.  Calendars in a delegate IRD . . . . . . . . . . . . . . .   9
     3.3.  Example IRD with ALTO Cost Calendars  . . . . . . . . . .   9
   4.  ALTO Calendar specification: Service Information Resources  .  12
     4.1.  Calendar extensions for filtered cost maps  . . . . . . .  13
       4.1.1.  Calendar extensions in Filtered Cost Map requests . .  13
       4.1.2.  Calendar extensions in Filtered Cost Map responses  .  14



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       4.1.3.  Use case and example: FCM with a bandwidth Calendar .  16
     4.2.  Calendar extensions in the Endpoint Cost Service  . . . .  18
       4.2.1.  Calendar specific input in  Endpoint Cost requests  .  18
       4.2.2.  Calendar attributes in the Endpoint Cost response . .  18
       4.2.3.  Use case and example: ECS with a routingcost Calendar  19
       4.2.4.  Use case and example: ECS with a multi-cost calendar
               for routingcost and latency . . . . . . . . . . . . .  22
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
   7.  Operational Considerations  . . . . . . . . . . . . . . . . .  25
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  25
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  25
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   IETF is currently standardizing the ALTO protocol which aims at
   providing guidance to overlay applications needing to select one or
   several hosts from a set of candidates able to provide a desired
   resource.  This guidance is based on parameters that affect
   performance and efficiency of the data transmission between the hosts
   such as the topological distance.  The goal of ALTO is to improve the
   Quality of Experience (QoE) in the application while optimizing
   resource usage in the underlying network infrastructure.

   The ALTO protocol in [RFC7285] specifies a network map which defines
   groupings of endpoints in provider-defined network regions (called
   PIDs).  The Cost Map Service, Endpoint Cost Service (ECS) and
   Endpoint Ranking Service then provide ISP-defined costs and rankings
   for connections among the specified endpoints and PIDs and thus
   incentives for application clients to connect to ISP preferred
   locations, e.g. to reduce their costs.  ALTO intentionally avoids
   provisioning realtime information as explained in the ALTO Problem
   Statement [RFC5693] and ALTO Requirements [RFC5693].Thus the current
   Cost Map and Endpoint Cost Service are providing, for a given Cost
   Type, exactly one path cost value.  Applications have to query one of
   these two services to retrieve the currently valid cost values.  They
   therefore need to plan their ALTO information requests according to
   their own estimation of the frequency of cost value change.

   With [RFC7285], an ALTO client should interpret the returned costs as
   those at the query moment.  However, Network costs can fluctuate,
   e.g. due to diurnal patterns of traffic demand or planned events such
   as network maintenance, holidays or highly publicized events.
   Providing network costs for only the current time thus may not be
   sufficient, in particular for applications that can schedule their



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   traffic in a span of time, for example by deferring backup to night
   during traffic trough.

   In case the ALTO Cost value changes are predictable over a certain
   period of time and the application does not require immediate data
   transfer, it can save time to get the whole set of cost values over
   this period in one single ALTO response.  Using this set to schedule
   data transfers allows optimizing the network resources usage and QoE.
   ALTO Clients and Servers can also minimize their workload by reducing
   and accordingly scheduling their data exchanges.

   This document extends RFC7285 to allow an ALTO server to provide
   network costs for a given duration of time.  A sequence of network
   costs across a time span for a given pair of network locations is
   named an "ALTO Cost Calendar".  The Filtered Cost Map Service and
   Endpoint Cost Service are extended to provide Cost Calendars.  In
   addition to this functional ALTO enhancement, we expect to further
   gain on storage and on the wire data exchange by gathering multiple
   Cost Values for one Cost Type into one single ALTO Server response.

   In this draft an "ALTO Cost Calendar" is specified by information
   resources capabilities that are applicable to time-sensitive ALTO
   metrics.  An ALTO Cost Calendar exposes ALTO Cost Values in JSON
   arrays where each value corresponds to a given time interval.  The
   time intervals as well as other Calendar attributes are specified in
   the IRD and in the Server response to allow the ALTO Client to
   interpret the received ALTO values.  Last, the proposed extensions
   for ALTO Calendars are applicable to any Cost Mode and they ensure
   backwards compatibility with legacy ALTO clients.

   In the rest of this document, Section 2 provides the design
   characteristics.  Sections 3 and 4 define the formal specifications
   for the IRD and the information resources.  Section 5 provides non-
   normative use cases to illustrate the usage of cost calendars.  IANA
   considerations and security considerations will be completed in
   further versions.

2.  Overview of ALTO Cost Calendars

   An ALTO Cost calendar provided by the ALTO Server provides 2
   information items:

   o  an array of values for a given metric, where each value
      corresponds to a time interval, where the value array can
      sometimes be a cyclic pattern that repeats a certain number of
      times.





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   o  attributes describing the time scope of the calendar such as the
      size and number of the intervals and the date of the starting
      point of the calendar, allowing an ALTO Client to properly
      interpret the values.

   An ALTO Cost Calendar can be used like a "time table" to figure out
   the best time to schedule data transfers and also to proactively
   manage application traffic given predictable events such as flash
   crowds, traffic intensive holidays and network maintenance.  It may
   be viewed as a synthetic abstraction of real measurements that can be
   historic or be a prediction for upcoming time periods.

   Most likely, the ALTO Cost Calendar would be used for the Endpoint
   Cost Service, assuming that a limited set of feasible Endpoints for a
   non-real time application is already identified, that they do not
   need to be accessed immediately and that their access can be
   scheduled within a given time period.  The Filtered Cost Map Service
   is also applicable as long as the size of the Map allows it.

2.1.  ALTO Cost Calendar information features

   The Calendar attributes are provided in the IRD and in ALTO Server
   responses.  The IRD announces attributes with dateless values in its
   information resources capabilities, where as attributes with time
   dependent values are provided in the "meta" of Server responses.  The
   ALTO Cost Calendar attributes provide the following information:

   o  attributes to interpret the time scope of the Calendar value
      array:

      *  generic time zone,

      *  applicable time interval size for each calendar value:
         combining a number and a time unit to reflect for example: 1
         hour, 2 minutes, 10 seconds, 1 week, 1 month,

      *  duration of the Calendar: e.g. the number of intervals provided
         in the calendar.

   o  "calendar-start-date": specifying when the calendar starts, that
      is to which date the first value of the cost calendar is
      applicable.

   o  "repeated": an optional attribute indicating for how many
      iterations the provided calendar will have the same values.  The
      server may use it to allow the client to schedule its next request
      and thus save its own workload by avoiding to process useless
      requests.



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2.2.  ALTO Calendar design characteristics

   The protocol extension placeholders for an ALTO Calendar are: the
   IRD, the ALTO requests and responses for Cost calendars.

   Extensions are designed to be light and ensure backwards
   compatibility with base protocol ALTO Clients and with other
   extensions.  It uses section 8.3.7 "Parsing of Unknown Fields" of
   RFC7285 that writes: "Extensions may include additional fields within
   JSON objects defined in this document.  ALTO implementations MUST
   ignore unknown fields when processing ALTO messages."

   The calendar-specific capabilities are integrated in the information
   resources of the IRD and in the "meta" member of ALTO responses to
   Cost Calendars requests.  A calendar and its capabilities are
   associated with a given information resource and within this
   information resource with a given cost type.  This design has several
   advantages:

   o  it does not introduce a new mode,

   o  it does not introduce new media types,

   o  it allows an ALTO Server to offer calendar capabilities on a cost
      type, with attributes values adapted to each information resource.

   The Applicable Calendared information resources are:

   o  the Filtered Cost Map,

   o  the Endpoint Cost Map.

   The ALTO Server can choose in which frequency it provides cost
   Calendars to ALTO Clients.  It may either provide calendar updates
   starting at the request date, or carefully schedule its updates so as
   to take profit from a potential repetition/periodicity of calendar
   values.

2.2.1.  ALTO Cost Calendar for all cost modes

   ALTO Calendars are well-suited for values encoded in the "numerical"
   mode.  Actually, Calendars can also represent metrics in other modes
   and having considered as time-varying values.  For example, types of
   Cost values such as JSONBool can also be expressed as calendars, as
   their value may be 'true' or 'false' depending on given time periods
   or likewise, values represented by strings, such as "medium", "high",
   "low", "blue", "open" .




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   Note also that a Calendar is suitable as well for time-varying
   metrics provided in the "ordinal" mode, if these values are time-
   varying and their update is carefully managed by the ALTO Server.

2.2.2.  Compatibility with legacy ALTO Clients

   The ALTO protocol extensions for Cost Calendars have been defined so
   as to ensure that Calendar capable ALTO Servers can provide legacy
   ALTO Clients with legacy information resources as well.  That is a
   legacy ALTO Client can request resources and receive responses as
   specified in RFC7285.

   A Calendar-aware ALTO Server MUST implement the base protocol
   specified in RFC7285.

   When a metric is available as a calendar, it MUST be available as a
   single value as well.

   For compatibility with legacy ALTO Clients specified in RFC7285,
   calendared information resources are not applicable for full cost
   maps for the following reason: a legacy ALTO client would receive a
   calendared cost map via an HTTP 'GET' command.  As specified in
   section 8.3.7 of RFC7285, it will ignore the Calendar Attributes
   indicated in the "meta" of the responses.  Therefore, lacking
   information on calendar attributes, it will not be able to correctly
   interpret and process the values of the received array of calendar
   cost values.

   Therefore, calendared information resources MUST be requested via the
   Filtered Cost Map Service or the Endpoint Cost Service, using a POST
   method.

3.  ALTO Calendar specification: IRD extensions

   The Calendar attributes in the IRD information resources capabilities
   carry constant dateless values.  A calendar is associated with an
   information resource rather than a cost type.  For example, a Server
   can provide a "routingcost" calendar for the Filtered Cost Map
   Service at a granularity of one day and a "routingcost" calendar for
   the Endpoint Cost service at a finer granularity but for a limited
   number of endpoints.

3.1.  Calendar attributes in the IRD resources capabilities

   When for an applicable resource, an ALTO Server provides a Cost
   Calendar for a given Cost Type, it MUST indicate this in the IRD
   capabilities of this resource, by an object of type




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   'CalendarAttributes', associated with this Cost Type and specified
   below.

   The capabilities of a Calendar-aware information resource entry have
   a member named "calendar-attributes" which is an array of objects of
   type CalendarAttributes.  It is necessary to use an array because of
   resources such as Filtered Cost Map and Endpoint Cost Map, for which
   the member "cost-type-names" is an array of 1 or more values.

   A member "calendar-attributes" MUST appear only once for each
   applicable cost type name of a resource entry.  If "calendar-
   attributes" are specified several times for a same "cost-type-name"
   in the capabilities of a resource entry, the ALTO client SHOULD
   ignore any additional occurrence of "calendar-attributes", for this
   cost type name.

   An ALTO Client should assume that the time interval size specified in
   the IRD is the smallest possible one that the ALTO Server can
   provide.  The Client can aggregate cost values on its own if it needs
   a larger granularity.

   CalendarAttributes calendar-attributes <1..*>;

   object{
     JSONString cost-type-names <1..*>;
     JSONString time-interval-size;
     JSONNumber number-of-intervals;
   } CalendarAttributes;

   o  "cost-type-names":

      *  An array of one or more elements indicating the cost-type-names
         in the IRD entry to which the capabilities apply.

   o  "time-interval-size":

      *  is the duration of an ALTO calendar time interval.  A "time-
         interval-size" value contains 2 entities separated by exactly
         one whitespace: a JSONNumber and a string representing a time
         unit and taking values in {second, minute, hour, day, week,
         month, year}.  Example values are: "5 minute" , "2 hour",
         meaning that each calendar value applies on a time interval
         that lasts respectively 5 minutes and 2 hours.

   o  "number-of-intervals":

      *  the integer number of values of the cost calendar array, at
         least equal to 1.



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   - Attribute "cost-type-name" , if used, provides a better readability
   to the calendar attributes specified in the IRD and avoids confusion
   with calendar attributes of other cost-types.

   - Multiplying Attributes 'time-interval-size' and 'number-of-
   intervals' provides the duration of the provided calendar.  For
   example an ALTO Server may provide a calendar for ALTO values
   changing every 'time-interval-size' equal to 5 minutes.  If 'number-
   of-intervals' has the value 12, then the duration of the provided
   calendar is "1 hour".

3.2.  Calendars in a delegate IRD

   One option to clarify IRD resources is that a "root" ALTO Server
   implementing base protocol resources delegates "specialized"
   information resources such as the ones providing Cost Calendars to
   another ALTO Server running in a subdomain specified with its URI in
   the "root" ALTO Server.  This option is described in Section 9.2.4
   "Delegation using IRDs" of RFC7285.

   This document provides an example, where a "root" ALTO Server runs in
   a domain called "alto.example.com".  It delegates the announcement of
   Calendars capabilities to an ALTO Server running in a subdomain
   called "custom.alto.example.com".  The location of the "delegate
   Calendar IRD" is assumed to be indicated in the "root" IRD by the
   resource entry: "custom-calendared-resources".

   Another advantage is that some Cost Types for some resources may be
   more advantageous as Cost Calendars and it makes few sense to get
   them as a single value.  For example, Cost Types with predictable and
   frequently changing values, calendared in short time intervals such
   as a minute.

3.3.  Example IRD with ALTO Cost Calendars

   The cost types in this example are either specified in the base ALTO
   protocol or may be specified in other drafts see
   [draft-ietf-alto-performance-metrics] or defined in this draft for
   illustrative purposes.  In this example, the available cost metrics
   are indicated in the "meta" field by cost type names "num-
   routingcost", "num-latency", "num-pathbandwidth" and "string-quality-
   status".  Metrics "routingcost", "latency" and "bandwidthscore" are
   available in the "numerical" Cost Mode.  Metric "quality-status" is
   available in the "string" Cost Mode.

   The example IRD includes 2 particular URIs providing calendars:





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   o  "http://custom.alto.example.com/calendar/costmap/filtered": a
      filtered cost map in which calendar capabilities are indicated for
      cost type names: "num-routingcost", "num-pathbandwidth" and
      "string-service-status",

   o  "http://custom.alto.example.com/calendar/endpointcost/lookup": an
      endpoint cost map in which calendar capabilities are indicated for
      cost type names: "num-routingcost", "num-latency", "num-
      pathbandwidth", "string-service-status".

   The design of the Calendar capabilities allows that some calendars on
   a cost type name are available in several information resources with
   different Calendar Attributes.  This is the case for calendars on
   "num-routingcost", "num-pathbandwidth" and "string-service-status" ,
   available in both the Filtered Cost map and Endpoint Cost Service,
   but with different time interval sizes for "num-pathbandwidth" and
   "string-service-status".

GET /calendars-directory HTTP/1.1
Host: custom.alto.example.com
Accept: application/alto-directory+json,application/alto-error+json
---------------

HTTP/1.1 200 OK
Content-Length: TODO
Content-Type: application/alto-directory+json

{
  "meta" : {
     "cost-types": {
        "num-routingcost": {
           "cost-mode" : "numerical",
           "cost-metric" : "routingcost"
        },
        "num-latency": {
           "cost-mode"  : "numerical",
           "cost-metric": "latency"
        },
        "num-pathbandwidth": {
           "cost-mode"  : "numerical",
           "cost-metric": "bandwidthscore",
        },
        "string-qual-status": {
           "cost-mode"  : "string",
           "cost-metric": "quality-status",
        }
      ... other meta ...
     },



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  "resources" : {
     "filtered-cost-map-calendar" : {
        "uri" :
           "http://custom.alto.example.com/calendar/costmap/filtered",
        "media-type" : "application/alto-costmap+json",
        "accepts" : "application/alto-costmapfilter+json",
        "capabilities" : {
           "cost-constraints" : true,
           "cost-type-names"  : [ "num-routingcost",
                                  "num-pathbandwidth",
                                  "string-service-status" ],
           "calendar-attributes" : [
             {"cost-type-names" : [ "num-routingcost",
                                    "num-pathbandwidth" ],
              "time-interval-size" : "1 hour",
              "number-of-intervals" : 24
             },
             {"cost-type-names" : [ "string-service-status" ],
              "time-interval-size" : "30 minute",
              "number-of-intervals" : 48
             }
            ] // end calendar-attributes
            "uses": [ "my-default-network-map" ]
        }
     },

     "endpoint-cost-calendar-map" : {
       "uri" :
          "http://custom.alto.example.com/calendar/endpointcost/lookup",
       "media-type" : "application/alto-endpointcost+json",
       "accepts" : "application/alto-endpointcostparams+json",
       "capabilities" : {
         "cost-constraints" : true,
         "cost-type-names" : [ "num-routingcost",
                               "num-latency",
                               "num-pathbandwidth",
                               "string-service-status" ],
         "calendar-attributes" : [
            {"cost-type-names" : [ "num-routingcost" ],
             "time-interval-size" : "1 hour",
             "number-of-intervals" : 24
            },
            {"cost-type-names" : [ "num-latency" ],
             "time-interval-size" : "5 minute",
             "number-of-intervals" : 12
            },
            {"cost-type-names" : [ "num-pathbandwidth" ],
             "time-interval-size" : "1 minute",



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             "number-of-intervals" : 60
            },
            {"cost-type-names" : [ "string-service-status" ],
             "time-interval-size" : "2 minute",
             "number-of-intervals" : 30
            }
         ] // Calendar attributes
       } // ECM capab
    } //info resource N
 } // ressources


   In this example IRD, for the Filtered Cost map Service:

   o  the Calendar for 'num-routingcost' and 'num-pathbandwidth' is an
      array of 24 values each provided on a time interval lasting 1
      hour.

   o  the Calendar for "string-service-status": "is an array of 48
      values each provided on a time interval lasting 30 minutes.

   For the Endpoint Cost service:

   o  the Calendar for 'num-routingcost': is an array of 24 values each
      provided on a time interval lasting 1 hour.

   o  the Calendar for 'latency': is an array of 12 values each provided
      on a time interval lasting 5 minutes.

   o  the Calendar for 'num-pathbandwidth': is an array of 60 values
      each provided on a time interval lasting 1 minute.

   o  the Calendar for "string-service-status": "is an array of 30
      values each provided on a time interval lasting 2 minutes.

4.  ALTO Calendar specification: Service Information Resources

   This section documents the individual information resources defined
   to provide the Calendared information services defined in this
   document.

   The reference time zone for the provided time values is GMT because
   the option chosen to express the time format is the HTTP header
   fields format:

                    Date: Tue, 15 Nov 2014 08:12:31 GMT





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4.1.  Calendar extensions for filtered cost maps

   A legacy ALTO client requests and gets Filtered Cost Map responses as
   specified in RFC7285.

4.1.1.  Calendar extensions in Filtered Cost Map requests

   The input parameters of a "legacy" request for a filtered cost map,
   defined by object ReqFilteredCostMap in section 11.3.2 of RFC7285,
   are augmented with one additional member.

   A Calendar-aware ALTO client requesting a Calendar on a given Cost
   Type for a filtered cost map resource having Calendar capabilities
   MUST add the following field to its input parameters:

                          JSONBoolean calendared<1..*>;

   This field is an array of 1 to N boolean values, where N is the
   number of requested metrics.  Each boolean value indicates whether or
   not the ALTO Server should provide the values for this Cost Type as a
   calendar.  The array MUST contain exactly N boolean values, otherwise
   the server returns an error.

   This field SHOULD NOT be specified if no member "calendar-attributes"
   is specified in this information resource.

   If a value of field 'calendared' is 'true' for a cost type name for
   which no calendar attributes have been specified: a Calendar-aware
   Server will return a response with a single cost value as specified
   in RFC 7285.

   If this field is not present, it MUST be assumed to have only values
   equal to 'false'.

   A Calendar-aware ALTO client supporting single cost type values, as
   specified in RFC7285, MUST provide an array of 1 element:

                          "calendared" : [true];

   A Calendar-aware ALTO client that is also Multi-Cost aware MUST
   provide an array of N values set to 'true' or 'false', depending
   whether it wants the applicable Cost Type values as a single or
   calendared value.








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4.1.2.  Calendar extensions in Filtered Cost Map responses

   The calendared costs are JSONArrays instead of JSONNumbers for the
   legacy ALTO implementation.  All arrays have a number of values equal
   to 'number-of-intervals'.

   The "meta" field of a Calendared Filtered Cost Map response MUST
   include at least:

   o  if the ALTO Client supports cost values for one Cost Type at a
      time only: the "meta" fields specified in RFC 7285 for these
      information service responses:

      *  "dependent-vtags ",

      *  "cost-type" field.

   o  if the ALTO Client supports cost values for several Cost Types at
      a time, as specified in [RFC8189] : the "meta" fields specified in
      [RFC8189] for these information service responses:

      *  "dependent-vtags ",

      *  "cost-type" field with value set to '{}', for backwards
         compatibility with RFC7285.

      *  "multi-cost-types" field.

   o  If the client request does not provide member "calendared" or if
      it provides it with a value equal to 'false', for all the
      requested Cost Types, then the ALTO Server response is exactly as
      specified in RFC 7285 [RFC7285] and [RFC8189].

   o  If the value of member "calendared" is equal to 'false' for a
      given requested Cost Type, the ALTO Server must return, for these
      Cost Types, a single cost value as specified in RFC 7285.

   In addition, the "meta" field of a Calendared Filtered Cost map
   response MUST include the member "calendar-response-attributes" for
   the requested information resource, together with the values provided
   by the ALTO Server for these attributes.  This member is an array of
   objects of type "CalendarResponseAttributes", defined as follows:









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   CalendarResponseAttributes calendar-response-attributes <1..*>;

   object{
     [JSONString cost-type-names <1..*>];
     JSONString calendar-start-time;
     JSONString time-interval-size;
     JSONNumber number-of-intervals;
     [JSONNumber repeated;]
   } CalendarResponseAttributes;

   Object CalendarResponseAttributes has the following attributes:

   o  "cost-type-names": member indicating the cost-type-names to which
      the capabilities apply.  This field MUST appear in responses to
      Multi-Cost ALTO requests.

   o  "calendar-start-time": indicates the date at which the first value
      of the calendar applies.  By default, the value provided for the
      "calendar-start-time" attribute SHOULD be no later than the
      request date.

   o  "time-interval-size": as specified in section "Calendar attributes
      in the IRD resources capabilities",

   o  "number-of-intervals": as specified in section "Calendar
      attributes in the IRD resources capabilities",

   o  "repeated": is an optional field provided for Calendars.  It is an
      integer N greater or equal to '1' that indicates how many
      iterations of the calendar value array starting at the date
      indicated by "calendar-start-time" have the same values.  The
      number N includes the provided iteration.

   Using the member "repeated" helps minimizing on the wire data
   exchange: by providing it, an ALTO Server will avoid unecessary
   processing of requests for Calendars with unchanged values while it
   allows ALTO Clients to save their resources as well.

   For example: if the "calendar-start-time" member has value "Mon, 30
   Jun 2014 at 00:00:00 GMT" and if the value of member "repeated" is
   equal to 4, it means that the calendar values are the same values on
   Monday, Tuesday, Wednesday and Thursday.  The ALTO Client thus may
   use the same calendar for the next 4 duration periods following
   "calendar-start-time".







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4.1.3.  Use case and example: FCM with a bandwidth Calendar

   An example of non-real time information that can be provisioned in a
   'calendar' is the expected path bandwidth.  While the transmission
   rate can be measured in real time by end systems, the operator of a
   data center is in the position of formulating preferences for given
   paths, at given time periods for example to avoid traffic peaks due
   to diurnal usage patterns.  In this example, we assume that an ALTO
   Client requests a bandwidth calendar as specified in the IRD to
   schedule its bulk data transfers as described in the use cases.

   In the example IRD, calendars for cost type name "num-pathbandwidth"
   are available for the information resources: "filtered-cost-calendar-
   map" and "endpoint-cost-calendar-map".  The ALTO Client requests a
   calendar for "num-pathbandwidth" via a POST request for a filtered
   cost map.

   We suppose in this example that the ALTO Client sends its request on
   Tuesday July 1st 2014 at 13:15
































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     POST /calendar/costmap/filtered HTTP/1.1
     Host: alto.example.com
     Content-Length: TODO
     Content-Type: application/alto-costmapfilter+json
     Accept: application/alto-costmap+json,application/alto-error+json

     {
       "cost-type" : {"cost-mode" : "numerical",
                      "cost-metric" : "bandwidthscore"},
       "calendared" : [true],

       "pids" : {
          "srcs" : [ "PID1", "PID2" ],
          "dsts" : [ "PID1", "PID2", "PID3" ]
       }
     }


     HTTP/1.1 200 OK
     Content-Length: TODO
     Content-Type: application/alto-costmap+json

     {
       "meta" : {
         "dependent-vtags" : [...],
         "cost-type" : {"cost-mode" : "numerical",
                        "cost-metric" : "bandwidthscore"},
         "calendar-response-attributes" : [
            "calendar-start-time" : Tue, 1 Jul 2014 13:00:00 GMT,
            "time-interval-size" : "2 hour",
            "number-of-intervals" : 12
          ]
        },

       "cost-map" : {
          "PID1": { "PID1": [v1,v2, ... v12],
                    "PID2": [v1,v2, ... v12],
                    "PID3": [v1,v2, ... v12] },
          "PID2": { "PID1": [v1,v2, ... v12],
                    "PID2": [v1,v2, ... v12],
                    "PID3": [v1,v2, ... v12] }
       }
     }








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4.2.  Calendar extensions in the Endpoint Cost Service

   This document extends the Endpoint Cost Service, as defined in
   {11.5.1} of [RFC7285], by adding new input parameters and
   capabilities, and by returning JSONArrays instead of JSONNumbers as
   the cost values.  The media type {11.5.1.1} and HTTP method
   {11.5.1.2} are unchanged.

4.2.1.  Calendar specific input in Endpoint Cost requests

   The extensions to the requests for calendared Endpoint Cost Maps are
   the same as for the Filtered Cost Map Service, specified in section
   Section 4.1.1 of this draft.

   The ReqEndpointCostMap object for a Calendared ECM request will have
   the following format:

   object {
     [CostType cost-type;]
     [CostType multi-cost-types<1..*>;]
     [JSONBoolean calendared<1..*>;]
     EndpointFilter endpoints;
   } ReqEndpointCostMap;

   object {
     [TypedEndpointAddr srcs<0..*>;]
     [TypedEndpointAddr dsts<0..*>;]
   } EndpointFilter;


4.2.2.  Calendar attributes in the Endpoint Cost response

   The "meta" field of a Calendared Endpoint Cost response MUST include
   at least:

   o  if the ALTO Client supports cost values for one Cost Type at a
      time only: the "meta" fields specified in {11.5.1.6} of RFC 7285
      for the Endpoint Cost response:

      *  "cost-type" field.

   o  if the ALTO Client supports cost values for several Cost Types at
      a time, as specified in [RFC8189] : the "meta" fields specified in
      [RFC8189] for the the Endpoint Cost response:

      *  "cost-type" field with value set to '{}', for backwards
         compatibility with RFC7285.




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      *  "multi-cost-types" field.

   If the client request does not provide member "calendared" or if it
   provides it with a value equal to 'false', for all the requested Cost
   Types, then the ALTO Server response is exactly as specified in RFC
   7285 [RFC7285] and [RFC8189].

   If the ALTO client provides member "calendared" in the input
   parameters with a value equal to 'true' for given requested Cost
   Types, the "meta" member of a Calendared Endpoint Cost response MUST
   include, for these Cost Types, the same additional member "calendar-
   response-attributes", as specified for the Filtered Cost Map Service.
   The Server response is thus changed as follows, w.r.t RFC 7285 and
   [RFC8189]:

   o  the "meta" member has one additional field
      "CalendarResponseAttributes", as specified for the Filtered Cost
      Map Service,

   o  the calendared costs are JSONArrays instead of JSONNumbers for the
      legacy ALTO implementation.  All arrays have a number of values
      equal to 'number-of-intervals'.

   If the value of member "calendared" is equal to 'false' for a given
   requested Cost Type, the ALTO Server must return, for these Cost
   Types, a single cost value as specified in RFC 7285.

4.2.3.  Use case and example: ECS with a routingcost Calendar

   Let us assume an Application Client is located in an end system with
   limited resources and having an access to the network that is either
   intermittent or provides an acceptable quality in limited but
   predictable time periods.  Therefore, it needs to both schedule its
   resources greedy networking activities and its ALTO transactions.

   The Application Client has the choice to trade content or resources
   with a set of Endpoints and needs to decide with which one it will
   connect and at what time.  For instance, the Endpoints are spread in
   different time-zones, or have intermittent access.  In this example,
   the 'routingcost' is assumed to be time-varying, with values provided
   as ALTO Calendars.

   The ALTO Client associated with the Application Client queries an
   ALTO Calendar on 'routingcost' and will get the Calendar covering the
   24 hours time period "containing" the date and time of the ALTO
   client request.





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   For Cost Type 'num-routingcost', the solicited ALTO Server has
   defined 3 different daily patterns each represented by a Calendar, to
   cover the week of Monday June 30th at 00:00 to Sunday July 6th 23:59:

   - C1 for Monday, Tuesday, Wednesday, Thursday, (week days)

   - C2 for Saturday, Sunday, (week end)

   - C3 for Friday (maintenance outage on July 4, 2014 from 02:00:00 GMT
   to 04:00:00 GMT, or big holiday such as New Year evening).

   In the following example, the ALTO Client sends its request on
   Tuesday July 1st 2014 at 13:15.






































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

  {
    "cost-type" : {"cost-mode" : "numerical",
                   "cost-metric" : "routingcost"},
    "calendared" : [true],
    "endpoints" : {
      "srcs": [ "ipv4:192.0.2.2" ],
      "dsts": [
        "ipv4:192.0.2.89",
        "ipv4:198.51.100.34",
        "ipv4:203.0.113.45",
        "ipv6:2000::1:2345:6789:abcd"
      ]
    }
  }


  HTTP/1.1 200 OK
  Content-Length: TODO
  Content-Type: application/alto-endpointcost+json

  {
    "meta" : {
      "cost-type" : {"cost-mode" : "numerical",
                     "cost-metric" : "routingcost"},
      "calendar-response-attributes" : [
         { "calendar-start-time" : Mon, 30 Jun 2014 00:00:00 GMT,
           "time-interval-size" : "1 hour",
           "number-of-intervals" : 24,
           "repeated": 4 }
        ],
      } // end meta

      "endpoint-cost-map" : {
        "ipv4:192.0.2.2": {
          "ipv4:192.0.2.89"    : [v1, v2, ... v24],
          "ipv4:198.51.100.34" : [v1, v2, ... v24],
          "ipv4:203.0.113.45"  : [v1, v2, ... v24],
          "ipv6:2000::1:2345:6789:abcd" : [v1, v2, ... v24]
        }
      }
  }




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   When the Client gets the Calendar for "routingcost", it sees that the
   "calendar-start-time" is Monday at 00h00 GMT and member "repeated" is
   equal to '4'.  It understands that the provided values are valid
   until Thursday included and will only need to get a Calendar update
   on Friday.

4.2.4.  Use case and example: ECS with a multi-cost calendar for
        routingcost and latency

   In this example, it is assumed that the ALTO Server implements multi-
   cost capabilities, as specified in [RFC8189] . That is, an ALTO
   client can request and receive values for several cost types in one
   single transaction.  An illustrating use case is a path selection
   done on the basis of 2 metrics: routing cost and latency.

   As in the previous example, the IRD indicates that the ALTO Server
   provides "routingcost" Calendars in terms of 24 time intervals of 1
   hour each.

   For metric "latency", the IRD indicates that the ALTO Server provides
   Calendars in terms of 12 time intervals values lasting each 5
   minutes.

   In the following example transaction, the ALTO Client sends its
   request on Tuesday July 1st 2014 at 13:15.

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

  {
    "cost-type" : {},
    "multi-cost-types" : [
        {"cost-mode" : "numerical", "cost-metric" : "routingcost"},
        {"cost-mode" : "numerical", "cost-metric" : "latency"}
    ],
    "calendared" : [true, true],
    "endpoints" : {
      "srcs": [ "ipv4:192.0.2.2" ],
      "dsts": [
        "ipv4:192.0.2.89",
        "ipv4:198.51.100.34",
        "ipv4:203.0.113.45",
        "ipv6:2000::1:2345:6789:abcd"
      ]
    }



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  }


  HTTP/1.1 200 OK
  Content-Length: TODO
  Content-Type: application/alto-endpointcost+json

  {
    "meta" : {
      "multi-cost-types" : [
        {"cost-mode" : "numerical", "cost-metric" : "routingcost"},
        {"cost-mode" : "numerical", "cost-metric" : "latency"}
       ],
      "calendar-response-attributes" : [
         { "cost-type-name : num-routingcost"
           "calendar-start-time" : Mon, 30 Jun 2014 00:00:00 GMT,
           "time-interval-size" : "1 hour",
           "number-of-intervals" : 24,
           "repeated": 4 },
         { "cost-type-name : num-latency"
           "calendar-start-time" : Tue, 1 Jul 2014 13:00:00 GMT,
           "time-interval-size" : "5 minute",
           "number-of-intervals" : 12}
       ],
      } // end meta

      "endpoint-cost-map" : {
        "ipv4:192.0.2.2": {
          "ipv4:192.0.2.89"    : [[r1, r2, ... r24], [l1, l2, ... l12]],
          "ipv4:198.51.100.34" : [[r1, r2, ... r24], [l1, l2, ... l12]],
          "ipv4:203.0.113.45"  : [[r1, r2, ... r24], [l1, l2, ... l12]],
          "ipv6:2000::1:2345:6789:abcd" : [[r1, r2, ... r24],
                                           [l1, l2, ... l12]]
        }
      }
  }


   When receiving the response, the client sees that the calendar values
   for 'routing cost' are repeated for 4 iterations.  Therefore, in its
   next requests until the routing cost calendar is expected to change,
   the client will only need to request a calendar for "latency".

   Without the ALTO Calendar extensions, the ALTO client would have no
   clue on the dynamicity of the metric value change and would spend
   needless time requesting values at an inappropriate pace.  In
   addition, without the Multi-Cost ALTO capabilities, the ALTO client




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   would duplicate this waste of time as it would need to send one
   request per cost metric.

5.  IANA Considerations

   This document does not define any new media types or introduce any
   new IANA considerations.

6.  Security Considerations

   As an extension of the base ALTO protocol [RFC7285], this document
   fits into the architecture of the base protocol, and hence the
   Security Considerations (Section 15) of the base protocol fully apply
   when this extension is provided by an ALTO server.  For example, the
   same authenticity and integrity considerations (Section 15.1 of
   [RFC7285]) still fully apply; the same considerations for the privacy
   of ALTO users (Section 15.4 of [RFC7285]) also still fully apply.

   The calendaring information provided by this extension requires
   additional considerations on three security considerations discussed
   in the base protocol: potential undesirable guidance to clients
   (Section 15.2 of [RFC7285]), confidentiality of ALTO information
   (Section 15.2 of [RFC7285]), and availability of ALTO (Section 15.5
   of [RFC7285]).  For example, by providing network information in the
   future in a calendar, this extension may improve availability of
   ALTO, when the ALTO server is unavailable but related information is
   already provided in the calendar.

   For confidentiality of ALTO information, an operator should be
   cognizant that this extension may introduce a new risk: an ALTO
   client may get information for future events that are scheduled
   through calendaring.  Possessing such information, the client may use
   it to achieve its goal: (1) initiating connections only at
   advantageous network costs, leading to unexpected network load; (2)
   generating massive connections to the network at times where its load
   is expected to be high.

   To mitigate this risk, the operator should address the risk of ALTO
   information being leaked to malicious clients or third parties.  As
   specified in Section 15.3.2 ("Protection Strategies") of [RFC7285],
   the ALTO server should authenticate ALTO clients and use the
   Transport Layer Security (TLS) protocol so that Man In The Middle
   (MITM) attacks to intercept an ALTO Calendar are not possible.
   [RFC7285] ensures the availability of such a solution in its
   Section 8.3.5.  "Authentication and Encryption", which specifies that
   "ALTO server implementations as well as ALTO client implementations
   MUST support the "https" URI scheme [RFC2818] and Transport Layer
   Security (TLS) [RFC5246].



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   For potential undesirable guidance of ALTO information, an ALTO
   client should be cognizant that using calendaring information can
   have risks: (1) a repeat pattern may be only statistical, and (2)
   future events may change.  Hence, a more robust ALTO client should
   adapt and extend protection strategies specified in Section 15.2 of
   the base protocol: it should develop self check and also ensure
   information update, to reduce the impact of this risk.

7.  Operational Considerations

   Conveying ALTO Cost Calendars tends to reduce the on-the-wire data
   exchange volume compared to multiple single cost ALTO transactions,
   as an application has a set of time-dependent values upon which it
   can plan its connections in advance with no need for the ALTO Client
   to query information at each time.  Additionally, the Calendar
   response attribute "repeated", when provided, saves additional data
   exchanges in that it indicates that the ALTO Client does not need to
   query Calendars during a period indicated by this attribute.

8.  Acknowledgements

   The authors would like to thank Fred Baker, Li Geng, Diego Lopez, He
   Peng and Haibin Song for fruitful discussions and feedback on earlier
   draft versions.  Dawn Chan, Vijay Gurbani, Yichen Qian and Jensen
   Zhang provided substantial review feedback and suggestions to the
   protocol design.

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>.


   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer
              Security (TLS) Protocol Version 1.2",
              BCP 14, RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC7285]  R. Alimi, R. Yang, R. Penno, Eds., "ALTO Protocol",
              BCP 14, RFC7285,
              DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.



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   [RFC8189]  S. Randriamasy, W. Roome, N. Schwan, "Multi-Cost
              Application-Layer Traffic Optimization (ALTO)",
              BCP 14, RFC 8189,
              DOI 10.17487/RFC8189, October 2017.
              <https://www.rfc-editor.org/info/rfc8189>.

9.2.  Informative References

   [draft-ietf-alto-performance-metrics]
              Q. Wu, Y. Yang, Y. Lee, D. Dhody, S. Randriamasy, "ALTO
              Performance Cost Metrics (work in progress)", June 2018.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", BCP 14, RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              DOI 10.17487/RFC5693, October 2009,
              <https://www.rfc-editor.org/info/rfc5693>.

Authors' Addresses

   Sabine Randriamasy
   Nokia Bell Labs
   Route de Villejust
   NOZAY  91460
   FRANCE

   Email: Sabine.Randriamasy@nokia-bell-labs.com


   Richard Yang
   Yale University
   51 Prospect st
   New Haven, CT  06520
   USA

   Email: yry@cs.yale.edu








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

   Email: sunseawq@huawei.com

   Lingli Deng
   China Mobile
   China

   Email: denglingli@chinamobile.com

   Nico Schwan
   Thales Deutschland
   Lorenzstrasse 10
   Stuttgart  70435
   Germany

   Email: nico.schwan@thalesgroup.com



























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