ALTO Extension: Path Vector Cost Type
draft-ietf-alto-path-vector-02

Document Type Active Internet-Draft (alto WG)
Last updated 2017-12-18
Replaces draft-yang-alto-path-vector
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ALTO WG                                                     G. Bernstein
Internet-Draft                                         Grotto Networking
Intended status: Standards Track                                 S. Chen
Expires: June 21, 2018                                 Tongji University
                                                                  K. Gao
                                                     Tsinghua University
                                                                  Y. Lee
                                                                  Huawei
                                                                W. Roome
                                                               M. Scharf
                                                                   Nokia
                                                                 Y. Yang
                                                         Yale University
                                                                J. Zhang
                                                       Tongji University
                                                       December 18, 2017

                 ALTO Extension: Path Vector Cost Type
                   draft-ietf-alto-path-vector-02.txt

Abstract

   The Application-Layer Traffic Optimization (ALTO) protocol [RFC7285]
   has defined several resources and services to provide clients with
   basic network information.  However, the base ALTO protocol and
   latest extensions only provide end-to-end metrics, which are
   insufficient to satisfy the demands of solving more complex network
   optimization problems.  This document introduces an extension to the
   base ALTO protocol, namely the path-vector extension, which allows
   ALTO clients to query information such as capacity regions for a
   given set of flows.  A non-normative example called multi-flow
   scheduling is presented to illustrate the limitations of existing
   ALTO (endpoint) cost maps.  After that, details of the extension are
   defined.

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.

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   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Use Case: Capacity Region for Multi-Flow Scheduling . . . . .   5
   4.  Overview of Path Vector Extensions  . . . . . . . . . . . . .   7
     4.1.  Path Vector Cost Type Extensions  . . . . . . . . . . . .   7
       4.1.1.  New Cost Metric for Path Vector . . . . . . . . . . .   7
       4.1.2.  New Cost Mode for Path Vector . . . . . . . . . . . .   8
       4.1.3.  Path Vector Cost Type Semantics . . . . . . . . . . .   8
     4.2.  ANE Property Map  . . . . . . . . . . . . . . . . . . . .   8
     4.3.  media type for path vector: multipart/related . . . . . .   9
     4.4.  Applicable ALTO services for Path Vector costs  . . . . .   9
     4.5.  Impact of backwards compatibility on the PV design  . . .  10
     4.6.  Requirements for PV on Clients and Servers  . . . . . . .  10
   5.  Path-Vector Extension: Basic Data Types . . . . . . . . . . .  10
     5.1.  Cost Type . . . . . . . . . . . . . . . . . . . . . . . .  10
       5.1.1.  Cost Mode: array  . . . . . . . . . . . . . . . . . .  11
       5.1.2.  Cost Metric: ane-path . . . . . . . . . . . . . . . .  11
     5.2.  ANE Domain  . . . . . . . . . . . . . . . . . . . . . . .  11
     5.3.  Abstract Network Element Name . . . . . . . . . . . . . .  11

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   6.  Path-Vector Extension: Services . . . . . . . . . . . . . . .  11
     6.1.  Filtered Cost Map Extensions  . . . . . . . . . . . . . .  11
       6.1.1.  Capabilities  . . . . . . . . . . . . . . . . . . . .  12
       6.1.2.  Accept Input Parameters . . . . . . . . . . . . . . .  12
       6.1.3.  Response  . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  Endpoint Cost Service Extensions  . . . . . . . . . . . .  13
       6.2.1.  Capabilities  . . . . . . . . . . . . . . . . . . . .  13
       6.2.2.  Accept Input Parameters . . . . . . . . . . . . . . .  13
       6.2.3.  Response  . . . . . . . . . . . . . . . . . . . . . .  13
     6.3.  Multipart Cost Property Service . . . . . . . . . . . . .  13
       6.3.1.  Media Type  . . . . . . . . . . . . . . . . . . . . .  14
       6.3.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . .  14
       6.3.3.  Accept Input Parameters . . . . . . . . . . . . . . .  14
       6.3.4.  Capabilities  . . . . . . . . . . . . . . . . . . . .  14
       6.3.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . .  14
       6.3.6.  Response  . . . . . . . . . . . . . . . . . . . . . .  15
   7.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.1.  Workflow  . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.2.  Information Resource Directory Example  . . . . . . . . .  16
     7.3.  Example # 1 . . . . . . . . . . . . . . . . . . . . . . .  17
     7.4.  Example # 2 . . . . . . . . . . . . . . . . . . . . . . .  18
   8.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .  20
     8.1.  Compatibility with Legacy ALTO Clients/Servers  . . . . .  20
     8.2.  Compatibility with Multi-Cost Extensions  . . . . . . . .  20
     8.3.  Compatibility with Incremental Update . . . . . . . . . .  20
   9.  Design Decisions and Discussions  . . . . . . . . . . . . . .  21
     9.1.  Provide More General Calendar Extension . . . . . . . . .  21
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  21
     10.1.  Privacy Concerns . . . . . . . . . . . . . . . . . . . .  21
     10.2.  Resource Consumption on ALTO Servers . . . . . . . . . .  22
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     11.1.  ALTO Cost Mode Registry  . . . . . . . . . . . . . . . .  22
     11.2.  ALTO Cost Metric Registry  . . . . . . . . . . . . . . .  22
     11.3.  ALTO Network Element Property Type Registry  . . . . . .  22
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  23
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     13.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   The base ALTO protocol [RFC7285] is designed for exposing network
   information through services such as the Network Map service and the
   Cost Map service.  These services use an extreme "single-node"
   network view abstraction, which represents the whole network with a
   single node and hosts with "endpoint groups" directly connected to
   the node.

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   Although the "single-node" network view abstraction works well in
   many settings, it lacks the ability to support new emerging use
   cases, such as inter-datacenter flow scheduling, scientific high-
   performance computing data transfers and end-to-end paths crossing
   heterogeneous technologies.  For these use cases, more powerful
   network view abstraction is required.  To provide a better network
   view abstraction, ALTO services need to support the following
   additional functionalities:

   o  Providing path vector rather than a simple path cost of endpoint
      to endpoint.  The path vector exposes the network elements (e.g.,
      links, switches, middle boxes and their aggregations) that
      endpoint to endpoint traffic goes through.

   o  Providing information of the network elements in the path vector.
      The information can be "bandwidth" for links, "delay" between
      neighboring switches and other properties of network elements.
      These information may help the application avoid network
      congestion, achieving better application performance.

   To support these new functionalities, this document proposes the
   path-vector extension, which introduces a qualitative cost type
   listing selected groups of one or more abstracted network elements in
   an e2e path and optionally conveys some of their properties.

   The rest of this document is organized as follows.  Section 3 gives
   an example of flow scheduling and illustrates the limitations of the
   base ALTO protocol in such a use case.  Section 4 gives an overview
   of the path-vector extension, before specifying the details of the
   extension in Section 5 and Section 6.  Section 7 presents several
   examples, and Section 9 explains some design decisions.  Section 8
   discusses compatibility issues with some other ALTO extensions.
   Section 10 and Section 11 discusses about security and IANA
   considerations.

2.  Terminology

   This document uses the same terms as defined in [RFC7285], [RFC8189]
   and [I-D.ietf-alto-unified-props-new] with the following additional
   terms: Abstract Network Element, Abstract Network Element Name,
   Abstract Network Element Property, Abstract Network Element Property
   Map and Path Vector.

   o  Abstract Network Element (ANE): An abstract network element is an
      abstraction of network components, it can be an aggregation of
      links, middle boxes, Virtualized Network Function (VNF), or even a
      sub-network.  An abstract network element has two attributes:

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      abstract network element name and abstract network element
      property, which are defined below.

   o  Abstract Network Element Name (ANEN): An abstract network element
      name is an identifier which uniquely identifies an abstract
      network element, as defined in Section 5.3.

   o  Abstract Network Element Property (ANEP): An abstract network
      element property is a specific metric associated with a given
      abstract network element, as introduced in Section 4.2.  An
      abstract network element can have several network element
      properties.

   o  Abstract Network Element Property Map (ANE Property Map): An
      abstract network element property map is a Filtered Property Map
      defined in [I-D.ietf-alto-unified-props-new] which supports the
      "ane" domain in its "domain-types" capability.

   o  Path Vector (PV): A path vector is an array of ALTO Abstract
      Network Elements (ANEs), which presents an abstract network path
      between entities such as PIDs or endpoints.  An ANE represents a
      selected part of an end-to-end path that the ALTO Server considers
      worth exposing.  An ANE is a set of one or more network elements
      such as links, switches, middle boxes and their aggregations, it
      is expected to have properties that may influence the applications
      e.g. when they select an endpoint or want to estimate their
      performance.

3.  Use Case: Capacity Region for Multi-Flow Scheduling

   Once routing has been configured in the network, application-layer
   traffic optimization may want to schedule traffic among application-
   layer paths.  Specifically, assume that an application has control
   over a set of flows F = {f_1, f_2, ..., f_|F|}. If routing is given,
   what the application can control is x_1, x_2, ..., x_|F|, where x_i
   is the amount of traffic for flow i.  Let x = [x_1, ..., x_|F|] be
   the vector of the flow traffic amounts.  Due to shared links,
   feasible values of x where link capacities are not exceeded can be a
   complex polytype.

   Specifically, consider a network as shown in Figure 1.  The network
   has 7 switches (sw1 to sw7) forming a dumb-bell topology.  Switches
   sw1/sw3 provide access on one side, sw2/sw4 provide access on the
   other side, and sw5-sw7 form the backbone.  End hosts eh1 to eh4 are
   connected to access switches sw1 to sw4 respectively.  Assume that
   the bandwidth of link eh1 -> sw1 and link sw1 -> sw5 are 150 Mbps,
   and the bandwidth of the rest links are 100 Mbps.

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                                  +------+
                                  |      |
                                --+ sw6  +--
                              /   |      |  \
        PID1 +-----+         /    +------+   \          +-----+  PID2
        eh1__|     |_       /                 \     ____|     |__eh2
             | sw1 | \   +--|---+         +---|--+ /    | sw2 |
             +-----+  \  |      |         |      |/     +-----+
                       \_| sw5  +---------+ sw7  |
        PID3 +-----+   / |      |         |      |\     +-----+  PID4
        eh3__|     |__/  +------+         +------+ \____|     |__eh4
             | sw3 |                                    | sw4 |
             +-----+                                    +-----+

                      Figure 1: Raw Network Topology.

   The single-node ALTO topology abstraction of the network is shown in
   Figure 2.

                          +----------------------+
                 {eh1}    |                      |     {eh2}
                 PID1     |                      |     PID2
                   +------+                      +------+
                          |                      |
                          |                      |
                 {eh3}    |                      |     {eh4}
                 PID3     |                      |     PID4
                   +------+                      +------+
                          |                      |
                          +----------------------+

             Figure 2: Base Single-Node Topology Abstraction.

   Consider an application overlay (e.g., a large data analysis system)
   which wants to schedule the traffic among a set of end host source-
   destination pairs, say eh1 -> eh2 and eh1 -> eh4.  The application
   can request a cost map providing end-to-end available bandwidth,
   using 'availbw' as cost-metric and 'numerical' as cost-mode.

   The application will receive from ALTO server that the bandwidth of
   eh1 -> eh2 and eh1 -> eh4 are both 100 Mbps.  But this information is
   not enough.  Consider the following two cases:

   o  Case 1: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw6 ->
      sw7 -> sw2 -> eh2 and eh1 -> eh4 uses path eh1 -> sw1 -> sw5 ->
      sw7 -> sw4 -> eh4, then the application will obtain 150 Mbps.

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   o  Case 2: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw7 ->
      sw2 -> eh2 and eh1 -> eh4 uses the path eh1 -> sw1 -> sw5 -> sw7
      -> sw4 -> eh4, then the application will obtain only 100 Mbps.

   To allow applications to distinguish the two aforementioned cases,
   the network needs to provide more details.  In particular:

   o  The network needs to expose more detailed routing information to
      show the shared bottlenecks.

   o  The network needs to provide the necessary abstraction to hide the
      real topology information while providing enough information to
      applications.

   The path-vector extension defined in this document meets all the
   requirements.

   See [I-D.bernstein-alto-topo] for a survey of use-cases where
   extended network topology information is needed.

4.  Overview of Path Vector Extensions

   This section presents the approaches taken to support the path-vector
   extension.  It assumes the readers are familiar with (Filtered) Cost
   Map and Endpoint Cost Service defined in [RFC7285] and their
   extensions defined in [RFC8189].  It also uses features such as
   Filtered Property Map defined in [I-D.ietf-alto-unified-props-new].

4.1.  Path Vector Cost Type Extensions

   None of current cost types defined in [RFC7285] can be used to convey
   path vector information.  So, a new cost type with a new cost metric
   "ane-path" and a new cost mode "array" is defined in this document.
   Below are brief descriptions.  Detailed information and
   specifications are given in Section 5.1.1 and Section 5.1.2.

4.1.1.  New Cost Metric for Path Vector

   To represent an abstract network path, this document introduces a new
   cost metric named "ane-path".  A cost value in this metric is a list
   containing the names of the ALTO ANEs that the ALTO Server has
   specified as describing the network path elements.  The ANE names
   array is organized as a sequence beginning at the source of the path
   and ending at its destination.

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4.1.2.  New Cost Mode for Path Vector

   A cost mode as defined in Section 6.1.2 of [RFC7285], a cost mode is
   either "numerical" or "ordinal" and none of these can be used to
   present a list of ANE names.  Therefore, this document specifies a
   new cost mode named "array" for the cost metric "ane-path".  The new
   cost mode "array" means each cost value in the cost maps is a list.

4.1.3.  Path Vector Cost Type Semantics

   The new cost type follows the convention of the cost types in the
   legacy ALTO protocol.  Table 1 lists some of the current defined cost
   types and their semantics.

   +------------+--------------+---------------------------------------+
   | Cost Mode  | Cost Metric  | Semantics                             |
   +------------+--------------+---------------------------------------+
   | numerical  | routingcost  | a number representing the routing     |
   |            |              | cost                                  |
   | numerical  | hopcount     | a number representing the hop count   |
   | ordinal    | routingcost  | a ranking representing the routing    |
   |            |              | cost                                  |
   | ordinal    | hopcount     | a ranking representing the hop count  |
   | array      | ane-path     | a list representing the ane path      |
   +------------+--------------+---------------------------------------+

                  Table 1: Cost Types and Their Semantics

   The "routingcost" and "hopcount" can encoded in "numerical" or
   "ordinal", however, the cost metric "ane-path" can only be applied to
   the cost mode "array" defined in this document to convey path vector
   information.  The cost metric "ane-path" can not be used in
   "numerical" or "ordinal" unless it is defined in future extensions.
   If the ALTO server declares that it support cost type with cost
   metric being "ane-path" and cost mode not being "array", the ALTO
   client SHOULD ignore them.

4.2.  ANE Property Map

   Given that Cost Map and Endpoint Cost service now provide the
   abstract network element names along a flow path, ALTO clients can
   learn that there exist bottlenecks shared by different flows.
   However, only providing the abstract network element names without
   abstract network element properties is not enough, some ALTO clients
   may want to have information on specific ANE properties such as link
   capacity or delay.  This document adopts the property map resources
   defined in [I-D.ietf-alto-unified-props-new] to encode the properties
   of ANEs.  Draft [I-D.ietf-alto-unified-props-new] defines a new

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   entity domain called "ane" and each entity in the "ane" domain has an
   identifier of an ANE.  An ANE identifier is the ANE name used in the
   values of the "ane-path" metric defined in the present draft.  ANE
   properties are provided in information resources called "Property Map
   Resource" and "Filtered Property Map Resource".  The "Filtered
   Property Map" resource which support the "ane" domain is used to
   encode the properties of ane entities, and it is called an ANE
   Property Map in this document.

4.3.  media type for path vector: multipart/related

   In the legacy ALTO protocol, ALTO servers use media types in the HTTP
   header to indicate the type of the response.  Typically one response
   only contains a single media type, such as "application/alto-
   costmap+json" or "application/alto-propmap+json".  This has limited
   the capability of ALTO servers to return multiple services in a
   single response.

   Thus, an ALTO client needs to make separate queries to get the
   information of related services.  This may cause a data
   synchronization problem between dependent ALTO services because when
   making the second query, the result for the first query may have
   already changed.  The very same problem can happen to Network Map and
   Cost Map resources.  However, unlike Network Map and Cost Map which
   are considered more stable, Path Vectors and the dependent ANE
   Property Maps might change more frequently.

   Instead of introducing a new media type to encapsulate multiple types
   in a single response, this document adopts the "multipart/related"
   media type defined in [RFC2387].  In this way, a response can contain
   both the Path Vectors in a Filtered Cost Map (or Endpoint Cost Map)
   and the associated ANE Property Map. The media types of the cost map
   and the property map can still be retrieved from the response.  The
   interpretation of each media type in the "multipart/related" response
   is consistent with the base ALTO protocol.

4.4.  Applicable ALTO services for Path Vector costs

   This document defines Filtered Cost Map and Endpoint Cost Map are
   applicable for path vector costs.  Although the new cost type for
   path vector can also be used in the GET-mode Cost Map service from
   [RFC7285], the behaviours of the ALTO server and client for such a
   GET-mode service is not defined.  So it is not recommended to apply
   path vector costs to the GET-mode Cost Map service.

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4.5.  Impact of backwards compatibility on the PV design

   The path vector extension on Filtered Cost Map and Endpoint Cost
   Service is backward compatible with the base ALTO protocol.  If the
   ALTO server provides path vector extended Filtered Cost Map or
   Endpoint Cost Service, but the client is a base ALTO client, then the
   client will ignore the path vector cost type without conducting any
   incompatibility.  If the client sents a request with path vector cost
   type, but the server is a base ALTO server, the server will return an
   "E_INVALID_FIELD_VALUE" error.

4.6.  Requirements for PV on Clients and Servers

   A path vector extended ALTO server MUST implement the legacy ALTO
   protocol specified in [RFC7285] with the following additional
   requirements:

   o  If an ALTO server supports path vector extension, it MUST support
      the Unified Property Map defined in
      [I-D.ietf-alto-unified-props-new].

   o  If an ALTO server supports path vector extended Filtered Cost Map
      or Endpoint Cost Service, the server MUST provide the associated
      Property Map simultaneously.

   o  If an ALTO server provides "multipart/related" media type for path
      vector, the server MUST provide the associated Filtered Cost Map
      or Endpoint Cost Service and the Property Map simultaneously.

   An ALTO client supported path vector extension MUST be able to
   interpret Unified Property Map correctly.  If the ALTO client wants
   to interpret "multipart/related" path vector response, the client
   MUST implement the path vector extension on Filtered Cost Map or
   Endpoint Cost Service at first.

5.  Path-Vector Extension: Basic Data Types

   This section formally specifies a new cost type.

5.1.  Cost Type

   This document extends the cost types defined in Section 6.1 of
   [RFC7285] by introducing a new cost mode "array" and a new cost
   metric "ane-path".

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5.1.1.  Cost Mode: array

   This document extends the CostMode defined in Section 10.5 of
   [RFC7285] with a new cost mode: "array".  This cost mode indicates
   that every cost value in a cost map represents an array rather than a
   simple value.  The values are arrays of JSONValue.  The specific type
   of each element in the array depends on the cost metric.

5.1.2.  Cost Metric: ane-path

   This document specifies a new cost metric: "ane-path".  This cost
   metric indicates that the cost value is a list of abstract network
   elements which the path from a source to a destination goes across.
   The values are arrays of ANE Names which are defined in Section 5.3.

   The cost metric "ane-path" SHOULD NOT be used when the cost mode is
   not "array" unless it is explicitly specified by a future extension.
   If an ALTO client send queries with the cost metric "ane-path" and a
   non "array" cost mode, the ALTO server SHOULD return an error with
   the error code "E_INVALID_FIELD_VALUE"; If an ALTO server declares
   the support of a cost type with the cost metric "ane-path" and a non
   "array" cost mode, the ALTO client SHOULD assume such a cost type is
   invalid and ignore it.

5.2.  ANE Domain

   This document uses the same definition of entity domain name 'ane' as
   defined in Section 3.4 of [I-D.ietf-alto-unified-props-new].

5.3.  Abstract Network Element Name

   An Abstract Network Element Name is encoded as an EntityAddr of the
   "ane" domain as defined in Section 3.4.2 of
   [I-D.ietf-alto-unified-props-new].

6.  Path-Vector Extension: Services

   This section extends Filtered Cost Map Service and Endpoint Cost
   Service.

6.1.  Filtered Cost Map Extensions

   This document extends the Filtered Cost Map defined in Section 4.1 of
   [RFC8189].

   The specifications for the "media type", "HTTP method" and "uses" are
   the same as defined in Section 4.1 of [RFC8189].

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6.1.1.  Capabilities

   The FilteredCostMapCapabilities object is extended with a new member
   "property-map":

   object {
     [ResourceID property-map;]
   } PathVectorFilteredCostMapCapabilities : FilteredCostMapCapabilities

   property-map:  A resource ID defined in the same IRD pointing to an
      ANE Property Map as defined in Section 2.  This field MUST be
      present if the path vector cost type is present in the "cost-type-
      names" field.

   Other fields of the FilteredCostMapCapabilities object has the same
   format as defined in Section 4.1.1 of [RFC8189] with the following
   constraint:

   testable-cost-type-names:  The path vector cost type with "ane-path"
      as the cost metric and "array" as the cost mode MUST NOT be
      included in "testable-cost-type-names".

6.1.2.  Accept Input Parameters

   The ReqFilteredCostMap uses the same format as defined in
   Section 4.1.2 of [RFC8189], with the following constraints:

   constraints, or-constraints:  If the path vector cost type is
      included in either "cost-type" or "multi-cost-types", ALTO clients
      MUST NOT use it in "constraints" or "or-constraints".  Otherwise,
      the ALTO server MUST return an error with error code
      "E_INVALID_FIELD_VALUE".

   testable-cost-types:  The path vector cost type MUST NOT be included
      in the "testable-cost-types" field.  Otherwise, the ALTO server
      MUST return an error with error code "E_INVALID_FIELD_VALUE".

6.1.3.  Response

   If the ALTO client includes the path vector cost type in the "cost-
   type" or "multi-cost-types" field of the input parameter, the
   response use the same format as defined in Section 4.1.3 of
   [RFC8189], but the corresponding cost value MUST be encoded as a
   JSONArray of AbstractNetworkElementName.

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6.2.  Endpoint Cost Service Extensions

   This document extends the Endpoint Cost Service defined in
   Section 4.2 in [RFC8189].

   The specifications for "HTTP method" and "uses" are the same as
   defined in Section 4.2 in [RFC8189].

6.2.1.  Capabilities

   The same as defined in Section 6.1.1.

6.2.2.  Accept Input Parameters

   The ReqEndpointCostMap uses the same format as defined in
   Section 4.2.2 of [RFC8189], with the following constraints:

   cost-type, multi-cost-types:  ALTO clients MUST include the path
      vector cost type, e.g.  the one with "ane-path" as cost metric and
      "array" as cost mode, in either "cost-type" or "multi-cost-types"
      to activate the path vector extension.

   constraints, or-constraints:  If the path vector cost type is
      included in either "cost-type" or "multi-cost-types", ALTO clients
      MUST NOT use it in "constraints" or "or-constraints".  Otherwise,
      the ALTO server MUST return an error with error code
      "E_INVALID_FIELD_VALUE".

   testable-cost-types:  The path vector cost type MUST NOT be included
      in the "testable-cost-types" field.  Otherwise, the ALTO server
      MUST return an error with error code "E_INVALID_FIELD_VALUE".

6.2.3.  Response

   If the ALTO client specifies the path vector cost type in the "cost-
   type" or "multi-cost-types" field of the input parameter, the
   response use the same format as defined in Section 4.2.3 of
   [RFC8189], but the corresponding cost value MUST be encoded as a
   JSONArray of AbstractNetworkElementName.

6.3.  Multipart Cost Property Service

   This document introduces a new ALTO service called "Multipart Cost
   Property Service", which provides the path vector information and the
   associated ANE property information in the same response.

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6.3.1.  Media Type

   The media type of the Multipart Cost Property service is "multipart/
   related".

6.3.2.  HTTP Method

   The Multipart Cost Property service is requested using the HTTP POST
   method.

6.3.3.  Accept Input Parameters

   The input parameters of the Multipart Cost Property service MUST be
   encoded as a JSON object in the body of an HTTP POST request.  The
   media type of the request SHOULD be one of "application/alto-
   costmapfilter+json" and "application/alto-endpointcostparams+json".
   The format of the request body depends on the media type:

   o  If the media type of the request is "application/alto-
      costmapfilter+json", the request body MUST be the same type as
      defined by Section 6.1.2.

   o  If the media type of the request is "application/alto-
      endpointcostparams+json", the request body MUST be the same type
      as defined by Section 6.2.2.

   The path vector cost type MUST be the only cost type in the input
   parameter.

6.3.4.  Capabilities

   TBD

6.3.5.  Uses

   The "uses" attribute MUST be an array with at least one resource id.
   The first resource id MUST point to a Filtered Cost Map or an
   Endpoint Cost Service resource.  And the path vector cost type MUST
   be in its "cost-type" capability.  If there are more than one
   resource id in the "uses" attribute, the ALTO client SHOULD ignore
   any additional resource ids.

   According to Section 6.1.1, the "property-map" field MUST be present
   in the first resource.  So the ALTO client MUST infer that the
   Property Map pointed by the "property-map" field of the first
   resource is also a dependent resource.

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6.3.6.  Response

   If an ALTO client sends a request of the media type "application/
   alto-costmapfilter+json" and accepts "multipart/related", the HTTP
   body of the response MUST consist of two parts with the media types
   "application/alto-costmap+json" and "application/alto-propmap+json"
   accordingly.  The part with media type "application/alto-
   costmap+json" MUST be the first part.  The content of the
   "application/alto-endpointcost+json" part has the same format as
   defined in Section 6.1.3.

   If an ALTO client sends a request of the media type "application/
   alto-endpointcostparams+json" and accepts "multipart/related", the
   HTTP body of the response MUST consist of two parts with the media
   types "application/alto-endpointcost+json" and "application/alto-
   propmap+json" accordingly.  The part with media type "application/
   alto-endpointcost+json" MUST be the first part.  The content of the
   "application/alto-endpointcost+json" part has the same format as
   defined in Section 6.2.3.

7.  Examples

   This section lists some examples of path vector queries and the
   corresponding responses.

7.1.  Workflow

   This section gives a typical workflow of an ALTO client using the
   path-vector extension.

   1.  Send a GET request for the whole Information Resource Directory.

   2.  Look for the resource of the (Filtered) Cost Map/Endpoint Cost
       Service which contains the path vector cost type and get the
       resource ID of the dependent abstract network element property
       map.

   3.  Check whether the capabilities of the property map includes the
       desired "prop-types".

   4.  Send a path-vector request which accepts "multipart/related"
       media type following "application/alto-costmap+json" or
       "application/endpointcost+json".

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7.2.  Information Resource Directory Example

   Here is an example of an Information Resource Directory.  In this
   example, filtered cost map "cost-map-pv" doesn't support the multi-
   cost extension but support the path-vector extension, "endpoint-
   multicost-map" supports both multi-cost extension and path-vector
   extension.  Filtered Property Map "propmap-delay-availbw" supports
   properties "availbw" and "delay", and "propmap-location" supports
   property "location".

     {
       "meta": {
         "cost-types": {
           "pv": {
             "cost-mode": "array",
             "cost-metric": "ane-path"
           },
           "num-routingcost": {
             "cost-mode": "numerical",
             "cost-metric": "routingcost"
           },
           "num-hopcount": {
             "cost-mode": "numerical",
             "cost-metric": "hopcount"
           }
         }
       },
       "resources": {
         "my-default-networkmap": {
           "uri" : "http://alto.example.com/networkmap",
           "media-type" : "application/alto-networkmap+json"
         }
         "cost-map-pv" : {
           "uri": "http://alto.example.com/costmap/pv",
           "media-type": "application/alto-costmap+json",
           "accepts": "application/alto-costmapfilter+json",
           "capabilities": {
             "cost-type-names": [ "pv", "num-hopcount" ]
           },
           "property-map": "propmap-delay",
           "uses": [ "my-default-networkmap" ]
         },
         "endpoint-multicost-map" : {
           "uri": "http://alto.exmaple.com/endpointcostmap/multicost",
           "media-type": "application/alto-endpointcost+json",
           "accepts": "application/alto-endpointcostparams+json",
           "capabilities": {
             "cost-constraints": true,

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             "cost-type-names": [ "pv", "num-routingcost" ],
             "max-cost-types": 2
           },
           "property-map": "propmap-availbw"
         },
         "propmap-availbw-delay" : {
           "uri": "http://alto.exmaple.com/propmap/availbw",
           "media-type": "application/alto-propmap+json",
           "accepts": "application/alto-propmapparams+json",
           "capabilities": {
             "domain-types": [ "ane" ],
             "prop-types": [ "availbw" ]
           }
         },
         "propmap-location" : {
           "uri": "http://alto.exmaple.com/propmap/delay",
           "media-type": "application/alto-propmap+json",
           "accepts": "application/alto-propmapparams+json",
           "capabilities": {
             "domain-types": [ "pid" ],
             "prop-types": [ "location" ]
           }
         }
       }
     }

7.3.  Example # 1

   POST /costmap/pv HTTP/1.1
   Host: alto.example.com
   Accept: multipart/related, application/alto-costmap+json,
           application/alto-propmap+json, application/alto-error+json
   Content-Length: [TBD]
   Content-Type: application/alto-costmapfilter+json

   {
     "cost-type": {
       "cost-mode": "array",
       "cost-metric": "ane-path"
     },
     "pids": {
       "srcs": [ "PID1" ],
       "dsts": [ "PID2", "PID3" ]
     }
   }

   HTTP/1.1 200 OK
   Content-Length: [TBD]

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   Content-Type: multipart/related; boundary=42

   --42
   Content-Type: application/alto-costmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "default-network-map",
           "tag": "75ed013b3cb58f896e839582504f622838ce670f"
         }
       ],
       "cost-type": {
         "cost-mode": "array",
         "cost-metric": "ane-path"
       },
     },

     "cost-map": {
       "PID1": {
         "PID2": [ "ane:L001", "ane:L003" ],
         "PID3": [ "ane:L001", "ane:L004" ]
       }
     }
   }

   --42
   Content-Type: application/alto-propmap+json

   {
     "property-map": {
       "ane:L001": { "delay": 46},
       "ane:L003": { "delay": 50},
       "ane:L004": { "delay": 70}
     }
   }

   --42--

7.4.  Example # 2

POST /endpointcostmap/multicost HTTP/1.1
Host: alto.example.com
Accept: multipart/related, application/alto-endpointcost+json,
        application/alto-propmap+json, application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-endpointcostparams+json

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{
  "multi-cost-types": [
    {
      "cost-mode": "array",
      "cost-metric": "ane-path"
    },
    {
      "cost-mode": "numerical",
      "cost-metric": "routingcost"
    }
  ],
  "endpoints": {
    "srcs": [ "ipv4:192.0.2.2" ],
    "dsts": [ "ipv4:192.0.2.89",
              "ipv4:203.0.113.45",
              "ipv6:2001:db8::10" ]
  }
}

HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related; boundary=example-2

--example-2
Content-Type: application/alto-endpointcost+json

{
  "meta": {
    "multi-cost-types": [
      {"cost-mode": "array", "cost-metric": "ane-path"},
      {"cost-mode": "numerical", "cost-metric": "routingcost"}
    ]
  },

  "endpoint-cost-map": {
    "ipv4:192.0.2.2": {
      "ipv4:192.0.2.89":   [[ "ane:L001", "ane:L003", "ane:L004" ], 77],
      "ipv4:203.0.113.45": [[ "ane:L001", "ane:L004", "ane:L005" ], 68],
      "ipv6:2001:db8::10": [[ "ane:L001", "ane:L005", "ane:L007" ], 98]
    }
  }
}

--example-2
Content-Type: application/alto-propmap+json

{
  "property-map": {

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    "ane:L001": { "availbw": 50 },
    "ane:L003": { "availbw": 48 },
    "ane:L004": { "availbw": 55 },
    "ane:L005": { "availbw": 60 },
    "ane:L007": { "availbw": 35 }
  }
}

--example-2--

8.  Compatibility

8.1.  Compatibility with Legacy ALTO Clients/Servers

   Legacy ALTO clients SHOULD NOT send queries with the path-vector
   extension and ALTO servers with this extension SHOULD NOT have any
   compatibility issue.  Legacy ALTO servers do not support cost types
   with cost mode being "array" and cost metric being "ane-path", so
   they MUST NOT announce the extended cost types in IRD.  Thus, ALTO
   clients MUST NOT send queries specified in this extension to base
   ALTO servers according to Section 11.3.2.3 [RFC7285].

8.2.  Compatibility with Multi-Cost Extensions

   Path Vector is not a testable cost type.  Any format of constraints
   SHOULD NOT be applied to cost type path-vector in order for multi-
   cost to support the path-vector extension.  Specifically,

   o  Cost type path-vector MUST NOT be included in "testable-cost-
      types-names" or "testable-cost-types".

   o  When "testable-cost-types-names" is omitted in the "capabilities"
      and "testable-cost-types" is omitted in the input parameters,
      "constraints" or "or-constraints" SHOULD NOT add any format of
      constraints on cost type path-vector.

8.3.  Compatibility with Incremental Update

   Without considering the incremental update of multipart/related
   information, there is no compatibility issue with incremental update
   extension.  Compatibility issue with the incremental update of
   multipart/related information will be discussed and addressed in the
   next version.

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9.  Design Decisions and Discussions

9.1.  Provide More General Calendar Extension

   Cost Calendar is proposed as a useful ALTO extension to provide the
   historical cost values for Filtered Cost Map Service and Endpoint
   Cost Service.  Since path vector is an extension to these services,
   it SHOULD be compatible with Cost Calendar extension.

   However, the calendar of a path-vector (Endpoint) Cost Map is
   insufficient for the application which requires the historical data
   of routing state information.  The (Endpoint) Cost Map can only
   provide the changes of the paths.  But more useful information is the
   history of network element properties which are recorded in the
   dependent Network Element Property Map.

   Before the Unified Property Map is introduced as an ALTO extension,
   Filtered Cost Map Service and Endpoint Cost Service are the only
   resources which require the calendar supported.  Because other
   resources don't have to be updated frequently.  But Network Element
   Property Map as a use case of Unified Property Map will collect the
   real-time information of the network.  It SHOULD be updated as soon
   as possible once the metrics of network elements change.

   So the requirement is to provide a general calendar extension which
   not only meets the Filtered Cost Map and Endpoint Cost Service but
   also applies to the Property Map Service.

10.  Security Considerations

10.1.  Privacy Concerns

   We can identify multiple potential security issues.  A main security
   issue is network privacy, as the path-vector information may reveal
   more network internal structures than the more abstract single-node
   abstraction.  The network should consider protection mechanisms to
   reduce information exposure, in particular, in settings where the
   network and the application do not belong to the same trust domain.
   On the other hand, in a setting of the same trust domain, a key
   benefit of the path-vector abstraction is reduced information
   transfer from the network to the application.

   The path-vector query may also reveal more information about the
   application.  In particular, the application may reveal all potential
   transfers sites (e.g., where the data source is replicated, and where
   the potential replication sites are).  The application should
   evaluate the potential privacy concerns.

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   Beyond the privacy issues, the computation of the path-vector is
   unlikely to be cachable, in that the results will depend on the
   particular requests (e.g., where the flows are distributed).  Hence,
   this service may become an entry point for denial of service attacks
   on the availability of an ALTO server.  Hence, authenticity and
   authorization of this ALTO service may need to be better protected.

10.2.  Resource Consumption on ALTO Servers

   The Abstract Network Element Property Map is dynamically enriched
   when the (Filtered) Cost Map/Endpoint Cost Service is queried of the
   path-vector information.  The properties of the abstract network
   elements can consume a large amount of resources when cached.  So, a
   time-to-live is needed to remove outdated entries in the Network
   Element Property Map.

11.  IANA Considerations

11.1.  ALTO Cost Mode Registry

   This document specifies a new cost mode "array".  However, the base
   ALTO protocol does not have a Cost Mode Registry where new cost mode
   can be registered.  This new cost mode will be registered once the
   registry is defined either in a revised version of [RFC7285] or in
   another future extension.

11.2.  ALTO Cost Metric Registry

   A new cost metric needs to be registered in the "ALTO Cost Metric
   Registry", listed in Table 2.

                   +-------------+---------------------+
                   | Identifier  | Intended Semantics  |
                   +-------------+---------------------+
                   | ane-path    | See Section 5.1.2   |
                   +-------------+---------------------+

                        Table 2: ALTO Cost Metrics

11.3.  ALTO Network Element Property Type Registry

   The "ALTO Abstract Network Element Property Type Registry" is
   required by the ALTO Entity Domain "ane", listed in Table 3.

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                +-------------+--------------------------+
                | Identifier  | Intended Semantics       |
                +-------------+--------------------------+
                | availbw     | The available bandwidth  |
                | delay       | The transmission delay   |
                +-------------+--------------------------+

           Table 3: ALTO Abstract Network Element Property Types

12.  Acknowledgments

   The authors would like to thank discussions with Randriamasy Sabine,
   Andreas Voellmy, Erran Li, Haibin Son, Haizhou Du, Jiayuan Hu, Qiao
   Xiang, Tianyuan Liu, Xiao Shi, Xin Wang, and Yan Luo.

13.  References

13.1.  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>.

13.2.  Informative References

   [I-D.amante-i2rs-topology-use-cases]
              Medved, J., Previdi, S., Lopez, V., and S. Amante,
              "Topology API Use Cases", draft-amante-i2rs-topology-use-
              cases-01 (work in progress), October 2013.

   [I-D.bernstein-alto-topo]
              Bernstein, G., Yang, Y., and Y. Lee, "ALTO Topology
              Service: Uses Cases, Requirements, and Framework", draft-
              bernstein-alto-topo-00 (work in progress), October 2013.

   [I-D.clemm-i2rs-yang-network-topo]
              Clemm, A., Medved, J., Tkacik, T., Varga, R., Bahadur, N.,
              and H. Ananthakrishnan, "A YANG Data Model for Network
              Topologies", draft-clemm-i2rs-yang-network-topo-01 (work
              in progress), October 2014.

   [I-D.ietf-alto-cost-calendar]
              Randriamasy, S., Yang, Y., Wu, Q., Lingli, D., and N.
              Schwan, "ALTO Cost Calendar", draft-ietf-alto-cost-
              calendar-01 (work in progress), February 2017.

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   [I-D.ietf-alto-unified-props-new]
              Roome, W. and Y. Yang, "Extensible Property Maps for the
              ALTO Protocol", draft-ietf-alto-unified-props-new-00 (work
              in progress), July 2017.

   [I-D.lee-alto-app-net-info-exchange]
              Lee, Y., Bernstein, G., Choi, T., and D. Dhody, "ALTO
              Extensions to Support Application and Network Resource
              Information Exchange for High Bandwidth Applications",
              draft-lee-alto-app-net-info-exchange-02 (work in
              progress), July 2013.

   [RFC2387]  Levinson, E., "The MIME Multipart/Related Content-type",
              RFC 2387, DOI 10.17487/RFC2387, August 1998,
              <https://www.rfc-editor.org/info/rfc2387>.

   [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>.

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

Authors' Addresses

   Greg Bernstein
   Grotto Networking
   Fremont, CA
   USA

   Email: gregb@grotto-networking.com

   Shiwei Dawn Chen
   Tongji University
   4800 Caoan Road
   Shanghai  201804
   China

   Email: dawn_chen_f@hotmail.com

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   Kai Gao
   Tsinghua University
   Beijing  Beijing
   China

   Email: gaok12@mails.tsinghua.edu.cn

   Young Lee
   Huawei
   TX
   USA

   Email: leeyoung@huawei.com

   Wendy Roome
   Nokia/Bell Labs
   600 Mountain Ave, Rm 3B-324
   Murray Hill, NJ  07974
   USA

   Phone: +1-908-582-7974
   Email: wendy.roome@nokia.com

   Michael Scharf
   Nokia
   Germany

   Email: michael.scharf@nokia.com

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

   Email: yry@cs.yale.edu

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   Jingxuan Jensen Zhang
   Tongji University
   4800 Caoan Road
   Shanghai  201804
   China

   Email: jingxuan.n.zhang@gmail.com

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