ALTO WG                                                     G. Bernstein
Internet-Draft                                         Grotto Networking
Intended status: Standards Track                                 S. Chen
Expires: January 4, 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
                                                            July 3,
                                                       December 18, 2017

                 ALTO Extension: Path Vector Cost Mode
                   draft-ietf-alto-path-vector-01.txt 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.

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

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

   This Internet-Draft will expire on January 4, June 21, 2018.

Copyright Notice

   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  . . . . . . . . . . . . . . . . . . . . . . . .   4   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5   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.
       4.1.1.  New Cost Metric for Path Vector . . . . . . . . . . .   7
       4.1.2.  New Cost Mode for Path Vector . . . . . . . . . . . .   7
     4.2.   8
       4.1.3.  Path Vector Cost Type Extension Semantics . . . . . . . . . . .   8
     4.2.  ANE Property Map  . . . . . . . . . .   8
     4.3.  Abstract Network Element Property Map . . . . . . . . . .   8
     4.4.  New Media Type:
     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  . . . . . . .   8  10
   5.  Path-Vector Extension: Basic Data Types . . . . . . . . . . .   9  10
     5.1.  Cost Type . . . . . . . . . . . . . . . . . . . . . . . .   9  10
       5.1.1.  Cost Metric . . . Mode: array  . . . . . . . . . . . . . . . . . .   9  11
       5.1.2.  Cost Mode . . . . . . Metric: ane-path . . . . . . . . . . . . . . . .  10  11
     5.2.  ANE Domain  . . . . . . . . . . . . . . . . . . . . . . .  10
       5.2.1.  Domain  11
     5.3.  Abstract Network Element Name . . . . . . . . . . . . . .  11

   6.  Path-Vector Extension: Services . . . . . . .  10
       5.2.2.  Domain-Specific Entity Addresses  . . . . . . . . . .  10
     5.3.  Abstract Network Element Name  11
     6.1.  Filtered Cost Map Extensions  . . . . . . . . . . . . . .  11
     5.4.  Version Tag . .
       6.1.1.  Capabilities  . . . . . . . . . . . . . . . . . . . .  12
       6.1.2.  Accept Input Parameters .  11
   6.  Path-Vector Extension: Services . . . . . . . . . . . . . .  12
       6.1.3.  Response  .  11
     6.1.  IRD Extensions . . . . . . . . . . . . . . . . . . . . .  11  12
     6.2.  Endpoint Cost Map Service Extensions  . . . . . . . . . . . . . . . . . . .  12  13
       6.2.1.  Media Type  .  Capabilities  . . . . . . . . . . . . . . . . . . . .  12  13
       6.2.2.  Capabilities  . . . . .  Accept Input Parameters . . . . . . . . . . . . . . .  12  13
       6.2.3.  Property-map  . . . . . . . . . . . . . . . . . . . .  12
       6.2.4.  Response  . . . . . . . . . . . . . . . . . . . . . .  13
     6.3.  Filtered  Multipart Cost Map Extensions  . Property Service . . . . . . . . . . . . .  13
       6.3.1.  Media Type  . . . . . . . . . . . . . . . . . . . . .  13  14
       6.3.2.  Capabilities  HTTP Method . . . . . . . . . . . . . . . . . . . .  13 .  14
       6.3.3.  Property-map  Accept Input Parameters . . . . . . . . . . . . . . .  14
       6.3.4.  Capabilities  . . . . .  14
       6.3.4.  Accept Input Parameters . . . . . . . . . . . . . . .  14
       6.3.5.  Response  Uses  . . . . . . . . . . . . . . . . . . . . . .  14
     6.4.  Endpoint Cost Service Extensions . .  14
       6.3.6.  Response  . . . . . . . . . .  14
       6.4.1.  Media Type . . . . . . . . . . . .  15
   7.  Examples  . . . . . . . . . .  15
       6.4.2.  Capabilities . . . . . . . . . . . . . . . .  15
     7.1.  Workflow  . . . .  15
       6.4.3.  Property-map . . . . . . . . . . . . . . . . . . . .  15
       6.4.4.  Accept Input Parameters . . . . . . . . . . . . . . .  15
       6.4.5.  Response  . . . . . . . . . . . . . . . . . . . . . .  15
   7.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  Workflow  . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.2.  Information Resource Directory Example  . . . . . . . . .  17  16
     7.3.  Single Query  Example # 1 . . . . . . . . . . . . . . . .  18
     7.4.  Single Query Example # 2  . . . . . . . . . . . . . . . .  20
     7.5.  Multiple Queries  17
     7.4.  Example # 2 . . . . . . . . . . . . . . . .  21
       7.5.1.  Endpoint Cost Service Example . . . . . . . . . . . .  21
       7.5.2.  Abstract Network Element Property Map Example . . . .  23  18
   8.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .  23  20
     8.1.  Compatibility with Legacy ALTO Clients/Servers  . . . . .  23  20
     8.2.  Compatibility with Multi-Cost Extensions  . . . . . . . .  23  20
     8.3.  Compatibility with Incremental Update . . . . . . . . . .  24  20
   9.  Design Decisions and Discussions  . . . . . . . . . . . . . .  24  21
     9.1.  Provide More General Calendar Extension . . . . . . . . .  24  21
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  24  21
     10.1.  Privacy Concerns . . . . . . . . . . . . . . . . . . . .  24  21
     10.2.  Resource Consumption on ALTO Servers . . . . . . . . . .  25  22
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25  22
     11.1.  ALTO Cost Mode Registry  . . . . . . . . . . . . . . . .  25  22
     11.2.  ALTO Cost Metric Registry  . . . . . . . . . . . . . . .  25  22
     11.3.  ALTO Entity Domain Registry  . . . . . . . . . . . . . .  26
     11.4.  ALTO Network Element Property Type Registry  . . . . . .  26  22
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  26  23
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26  23
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  27  23
     13.2.  Informative References . . . . . . . . . . . . . . . . .  27  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28  24

1.  Introduction

   The ALTO 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.

   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 and scheduling, scientific high-performance high-
   performance computing data transfers.  Specifically, the base ALTO protocol MUST 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 two
   additional functionalities:

   o  Providing information on shared bottlenecks: In the aforementioned
      use cases, the volume of path vector rather than a single flow can reach 10s - 100s Gbps,
      so that simple path cost of endpoint
      to endpoint.  The path vector exposes the network cannot treat the flows as independent like in
      the base ALTO protocol.  In this case, ALTO servers MUST be able
      to provide information on shared bottlenecks elements (e.g.,
      links, switches, middle boxes and their aggregations) that
      endpoint to help applications
      avoid congestion. endpoint traffic goes through.

   o  Encapsulating multiple cost values  Providing information of the network elements in a single session: Some flow
      scheduling problems take multiple metrics into consideration.
      Making multiple queries introduces larger communication overhead,
      and more importantly, out-of-sync data the path vector.
      The information can be "bandwidth" for different cost types.
      Encapsulating multiple cost values in a single query and response
      session reduces communication overhead links, "delay" between
      neighboring switches and simplifies the
      synchronization in use cases involving multiple cost types.

   This draft aims to extend other properties of network elements.
      These information may help the base ALTO protocol to application avoid network
      congestion, achieving better application performance.

   To support these new functionalities, with this document proposes the
   path-vector extension.  The path-vector
   extension specifies how to encode the shared bottlenecks in a network
   for a given set of flows with many design details driven by
   effectiveness, performance and backward compatibility considerations.

   The second functionality for simple cost types, such as those
   introduced in the base protocol, is already addressed in a recent extension, e.g.  [I-D.ietf-alto-multi-cost].  However, the path-
   vector extension in this document has introduced which introduces a new qualitative cost type
   which complicates the situation.  Thus, the multiple cost
   encapsulation must still be taken into consideration.
   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],
   [I-D.ietf-alto-multi-cost] [RFC8189]
   and [I-D.roome-alto-unified-props] [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:

      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 4.3. 4.2.  An
      abstract network element CAN can have several network element
      properties.

   o  Abstract Network Element Property Map (ANEP (ANE Property Map): An
      abstract network element property map is a Filtered Property Map
      defined in
      [I-D.roome-alto-unified-props] [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 abstract network
      elements, representing ALTO Abstract
      Network Elements (ANEs), which presents an abstract network path
      between entities (PIDs 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
      endpoints). want to estimate their
      performance.

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

   Consider the case that

   Once routing is given.  Then what has been configured in the network, application-layer
   traffic optimization will focus on is may want to schedule traffic scheduling among
   application-layer 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.

                                  +------+
                                  |      |
                                --+ 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 needs 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.

   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, it needs
   to provide the following new capabilities: 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 as possible. while providing enough information to
      applications.

   The path-vector extension defined in this document will satisfy 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 a non-normative overview of 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], [RFC7285] and their
   extensions defined in [I-D.ietf-alto-multi-cost] and [RFC8189].  It also uses features such as
   Filtered Property Map defined in [I-D.roome-alto-unified-props]. [I-D.ietf-alto-unified-props-new].

4.1.  Path Vector

   A path vector is an array Cost Type Extensions

   None of abstract network elements, representing
   an abstract current cost types defined in [RFC7285] can be used to convey
   path between entities (PIDs or endpoints).  Each abstract
   network element has two attributes: name vector information.  So, a new cost type with a new cost metric
   "ane-path" and property.  The abstract
   network element names are encoded in a new cost maps mode "array" is defined in this document.
   Below are brief descriptions.  Detailed information and the abstract
   network element properties
   specifications are encoded given in abstract network element
   property maps.

4.2. Section 5.1.1 and Section 5.1.2.

4.1.1.  New Cost Type Extension Metric for Path Vector

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

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", "ordinal" and none of which these can be used to
   present a list.

   This list of ANE names.  Therefore, this document specifies a
   new cost mode named "array" and a new for the cost metric "ane-path".  The new
   cost mode "array" means each cost value in the cost maps is a list.  The new cost metric "ane-path" means each cost
   value represents an abstract path consisting of abstract network
   element names between two entities (PIDs or endpoints).

4.1.3.  Path Vector Cost Type Semantics

   The new cost type follows the convention of the cost types in the
   base
   legacy ALTO protocol.  For example:

   +------------+--------------+---------------------------------------+
   | cost mode  |  Table 1 lists some of the current defined cost metric
   types and their semantics.

   +------------+--------------+---------------------------------------+
   | Cost Mode  | meaning 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 Meanings

4.3.  Abstract Network Element 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 between shared by different flows.
   However, only providing the abstract network element names without
   abstract network element properties is not enough, because some ALTO clients often
   require the
   may want to have information on specific metric values like the ANE properties such as link
   capacity.
   capacity or delay.  This document adopts the property map resources
   defined in a recent
   draft [I-D.roome-alto-unified-props] [I-D.ietf-alto-unified-props-new] to encode the properties
   of
   abstract network elements.  A ANEs.  Draft [I-D.ietf-alto-unified-props-new] defines a new
   entity domain called "ane" is registered in the
   property map.  Each and each entity in the "ane" domain is has an abstract network
   element.
   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 property map "Filtered
   Property Map" resource which supports support the "ane" domain is used to
   encode the properties of ane entities, and it is called an Abstract
   Network Element ANE
   Property Map.

4.4.  New Media Type: Map in this document.

4.3.  media type for path vector: multipart/related

   In the base 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 MUST needs to make multiple separate queries to get the
   information from services of different types. related services.  This has led to the 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 Path Vectors and the dependent abstract
   network element property maps ANE
   Property Maps might change more frequently.

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

   For backward compatibility, this extension

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 allows be used in the GET-mode Cost Map service from
   [RFC7285], the behaviours of the ALTO clients server and client for such a
   GET-mode service is not defined.  So it is not recommended to make multiple queries instead apply
   path vector costs to the GET-mode Cost Map service.

4.5.  Impact of encapsulating abstract network
   element property map along with backwards compatibility on the PV design

   The path vector.  Thus, each vector extension on Filtered Cost Map
   or and Endpoint Cost
   Service is backward compatible with this extension MUST include a "prop-
   map" in their capabilities to indicate where to retrieve the network
   element properties.  An additional field "query-id" MUST also be
   added to base ALTO protocol.  If the "vtag" field to uniquely identify a
   ALTO server provides path vector query
   session.

5.  Path-Vector Extension: Basic Data Types

   This section formally specifies the path-vector extension of some
   basic data types.

5.1. extended Filtered Cost Type

   This document extends Map or
   Endpoint Cost Service, but the cost types defined in Section 6.1 of
   [RFC7285] by introducing client is a new base ALTO client, then the
   client will ignore the path vector cost mode "array" and type without conducting any
   incompatibility.  If the client sents a new request with path vector cost
   metric "ane-path".

5.1.1.  Cost Metric

   This document specifies
   type, but the server is a new cost metric: "ane-path".  It is of type
   CostMetric as defined in Section 10.6 of [RFC7285].  The cost metric
   "ane-path" MUST NOT be used when base ALTO server, the cost mode is not "array" unless
   it is explicitly specified by a future extension.  Meanwhile, server will return an
   "E_INVALID_FIELD_VALUE" error.

4.6.  Requirements for PV on Clients and Servers

   A path vector extended ALTO server with path-vector extension MUST support implement the cost metric "ane-
   path".

   Cost metric "ane-path":  This cost metric MUST be encoded as the
      JSONString "ane-path".

5.1.2.  Cost Mode

   This document extends the CostMode defined legacy ALTO
   protocol specified in Section 10.5 of [RFC7285] with a new cost mode: "array".  The extended CostMode is
   encoded as a string and MUST have a value of either "numerical",
   "ordinal" or "array" unless it is explicitly specified by a future
   extension.  In particular, this extension has specified that when the
   cost metric is "ane-path", the cost value MUST be interpreted as a
   JSONArray of Abstract Network Element Names (defined in Section 5.3).

   An following additional
   requirements:

   o  If an ALTO cost service server supports path vector extension, it MUST return a JSONArray of JSONValue when the
   cost mode is "array" unless support
      the interpretation is explicitly
   specified by Unified Property Map defined in
      [I-D.ietf-alto-unified-props-new].

   o  If an ALTO extension. server supports path vector extended Filtered Cost mode "array":  This cost mode MUST be encoded as the JSONString
      "array".

5.2.  ANE Domain

   This document specifies a new domain in addition to the ones in [I-
   D.roome-alto-unified-props].

5.2.1.  Domain Name

   ane

5.2.2.  Domain-Specific Entity Addresses

   The entity address of ane domain is encoded as a JSON string.  The
   string MUST be no more than 64 characters, and it MUST NOT contain
   characters other than US-ASCII alphanumeric characters
   (U+0030-U+0039, U+0041-U+005A, and U+0061-U+007A), the hyphen ('-',
   U+002D), the colon (':', U+003A), the at sign ('@', code point
   U+0040), the low line ('_', U+005F), Map
      or Endpoint Cost Service, the '.' separator (U+002E).
   The '.' separator is reserved for future use and MUST NOT be used
   unless specifically indicated in this document, or an extension
   document.

5.3.  Abstract Network Element Name

   An Abstract Network Element Name MUST be encoded as an EntityAddr as
   defined in Section 5.2.2.  It server MUST belong to the "ane" domain.

5.4.  Version Tag

   This document extends provide the VersionTag, previously defined in
   Section 10.3 of [RFC7285] with an optional field "query-id". associated
      Property Map simultaneously.

   o  If an ALTO cost service supports server provides "multipart/related" media type for path
      vector, the path-vector extension, this field server MUST
   be included in provide the "vtag" field, associated Filtered Cost Map
      or Endpoint Cost Service and the "vtag" field Property Map simultaneously.

   An ALTO client supported path vector extension MUST be
   included in the "meta" field in the response in order able to provide
   interpret Unified Property Map correctly.  If the
   "query-id" information.

     object {
       ResourceID   resource-id;
       JSONString   tag;
       [JSONString  query-id;]
     } VersionTag;

   resource-id, tag:  As defined in Section 10.3 of [RFC7285].

   query-id:  A string used ALTO client wants
   to uniquely identify the abstract network
      element names in interpret "multipart/related" path vector response, the response and correlate abstract network
      element names with abstract network element properties.  A "query-
      id" client
   MUST be encoded in implement the same format as defined in Section 10.1
      of [RFC7285].

6. path vector extension on Filtered Cost Map or
   Endpoint Cost Service at first.

5.  Path-Vector Extension: Services Basic Data Types

   This section extends IRDResourceEntry, Cost Map Service and Endpoint formally specifies a new cost type.

5.1.  Cost Service.

6.1.  IRD Extensions Type

   This document extends IRDResourceEntry the cost types defined in Section 9.2.2 6.1 of
   [RFC7285] by introducing a new entry named "property-map", which
   indicates where the specific properties of the abstract network
   elements can be retrieved.  The IRDResourceEntry object is extended
   as follows:

     object {
       JSONString uri;
       JSONString media-type;
       [JSONString accepts;]
       [Capabilities capabilities;]
       [ResourceID uses<0..*>;]
       [ResourceID property-map;]
     } IRDResourceEntry;

   uri, media-type, accepts, capabilities, uses:  The same as defined in
      Section 9.2.2 of [RFC7285].

   property-map:  A resource ID defined in the same IRD pointing to an
      abstract network element property map as defined in Section 2.

6.2. cost mode "array" and a new cost
   metric "ane-path".

5.1.1.  Cost Map Extensions Mode: array

   This document extends the Cost Map defined in Section 11.2.3 of
   [RFC7285].

   The specifications for "HTTP method", "accept input parameters" and
   "uses" are the same as CostMode defined in Section 11.2.3 10.5 of [RFC7285].

6.2.1.  Media Type

   The path vector extension now enables ALTO clients to receive
   multiple services
   [RFC7285] with a new cost mode: "array".  This cost mode indicates
   that every cost value in a cost map response.

   Specifically, if represents an ALTO client accepts "multipart/related",
   "application/alto-costmap+json" and "application/alto-propmap+json"
   at the same time, the ALTO server MUST use "multipart/related" as the
   media array rather than a
   simple value.  The values are arrays of JSONValue.  The specific type
   of each element in the HTTP header.

6.2.2.  Capabilities

   If a service supports the path-vector extension, array depends on the "cost-type-
   names" field MUST include cost metric.

5.1.2.  Cost Metric: ane-path

   This document specifies a single new cost type with "ane-path" as metric: "ane-path".  This cost
   metric and "array" as cost mode.

6.2.3.  Property-map

   If a service supports the path-vector extension, indicates that the "property-map"
   field MUST be specified.  This field cost value is a resource ID list of an abstract network element property map where
   elements which the abstract network element
   properties path from a source to a destination goes across.
   The values are arrays of ANE Names which are provided.

6.2.4.  Response

   If an ALTO client accepts "multipart/related" as defined in Section 6.3.1, HTTP body of 5.3.

   The cost metric "ane-path" SHOULD NOT be used when the response MUST consists of two parts cost mode is
   not "array" unless it is explicitly specified by a future extension.
   If an ALTO client send queries with the media types "application/alto-costmap+json" cost metric "ane-path" and
   "application/alto-propmap+json" accordingly.  Specifically, a
   non "array" cost mode, the part ALTO server SHOULD return an error with media type "application/alto-costmap+json" MUST be the first
   part.

   The content of
   the "application/alto-costmap+json" part uses error code "E_INVALID_FIELD_VALUE"; If an ALTO server declares
   the
   format in Section 11.2.3.6 support of [RFC7285] a cost type with the following
   constraints:

   o  The cost value for metric "ane-path" and a path vector query, e.g. non
   "array" cost mode, the ALTO client SHOULD assume such a cost mode type is
      "array"
   invalid and ignore it.

5.2.  ANE Domain

   This document uses the cost metric 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 "ane-path", MUST be encoded as a
      JSONArray an EntityAddr of AbstractNetworkElementName.

   o  If the query sent by the client includes cost type path vector,
      the "vtag" field
   "ane" domain as defined in Section 5.4 has to be included in the
      response.  And the "query-id" information in "vtag" MUST be
      provided to ALTO clients.

6.3. 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
   [I-D.ietf-alto-multi-cost].
   [RFC8189].

   The specifications for the "media type", "HTTP method" and "uses" are
   the same as defined in Section 4.1 of [I-D.ietf-alto-multi-cost].

6.3.1.  Media Type [RFC8189].

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 6.2.1.

6.3.2.  Capabilities

   The 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 [I-D.ietf-alto-multi-cost] [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".

6.3.3.  Property-map

   The same as Section 6.2.3.

6.3.4.

6.1.2.  Accept Input Parameters

   The ReqFilteredCostMap uses the same format as defined in
   Section 4.1.2 of [I-D.ietf-alto-multi-cost], [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".

6.3.5.

6.1.3.  Response

   If an the ALTO client accepts "multipart/related" as defined in
   Section 6.3.1, HTTP body of the response MUST consist of two parts
   with the media types "application/alto-costmap+json" and
   "application/alto-propmap+json" accordingly.  Specifically, includes the part
   with media path vector cost type "application/alto-costmap+json" MUST be in the first
   part.

   The content "cost-
   type" or "multi-cost-types" field of the "application/alto-costmap+json" part has input parameter, the
   response use the same format as defined in Section 4.1.3 of [I-D.ietf-alto-multi-cost] with
   the following constraints:

   o  When the path vector cost type is included in "cost type" or
      "multi-cost-type",
   [RFC8189], but the corresponding cost value MUST be encoded as a
   JSONArray of AbstractNetworkElementName.

   o  If the query sent by the client includes cost type path vector,
      the "vtag" field defined in Section 5.4 has to be included in the
      response.  And the "query-id" information in "vtag" MUST be
      provided to ALTO clients.

6.4.

6.2.  Endpoint Cost Service Extensions

   This document extends the Endpoint Cost Service defined in
   Section 4.2 in [I-D.ietf-alto-multi-cost]. [RFC8189].

   The specifications for "HTTP method" and "uses" are the same as
   defined in Section 4.2 in [I-D.ietf-alto-multi-cost].

6.4.1.  Media Type

   The path vector extension now enables ALTO clients to receive
   multiple objects from the endpoint cost service response.

   Specifically, if an ALTO client accepts "multipart/related",
   "application/alto-endpointcost+json" and "application/alto-
   propmap+json" at the same time, the ALTO server MUST use "multipart/
   related" as the media type in the HTTP header.

6.4.2. [RFC8189].

6.2.1.  Capabilities

   The same as defined in Section 6.3.2.

6.4.3.  Property-map

   The same as Section 6.2.3.

6.4.4. 6.1.1.

6.2.2.  Accept Input Parameters

   The ReqEndpointCostMap uses the same format as defined in
   Section 4.2.2 of [I-D.ietf-alto-multi-cost], [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 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.

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 included in its "cost-type" capability.  If there are more than one
   resource id in the "testable-cost-types" field.  Otherwise, "uses" attribute, the ALTO server client SHOULD ignore
   any additional resource ids.

   According to Section 6.1.1, the "property-map" field MUST return an error with error code "E_INVALID_FIELD_VALUE".

6.4.5. 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.

6.3.6.  Response

   If an ALTO client sends a request of the media type "application/
   alto-costmapfilter+json" and accepts "multipart/related" as defined in
   Section 6.4.1, "multipart/related", the HTTP
   body of the response MUST consist of two parts with the media types "application/alto-endpointcost+json"
   "application/alto-costmap+json" and "application/alto-propmap+json"
   accordingly.  Specifically, the  The part with media type "application/alto-endpointcost+json" "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 4.2.3 6.1.3.

   If an ALTO client sends a request of [I-D.ietf-alto-multi-cost]
   with the following constraints:

   o  When the path vector cost media type is included in "cost type" or
      "multi-cost-type", "application/
   alto-endpointcostparams+json" and accepts "multipart/related", the corresponding cost value MUST be encoded as
      a JSONArray
   HTTP body of AbstractNetworkElementName.

   o  If the query sent by response MUST consist of two parts with the client includes cost media
   types "application/alto-endpointcost+json" and "application/alto-
   propmap+json" accordingly.  The part with media type path vector,
      the "vtag" field defined in Section 5.4 has to "application/
   alto-endpointcost+json" MUST be included in the
      response.  And first part.  The content of the "query-id" information
   "application/alto-endpointcost+json" part has the same format as
   defined in "vtag" MUST be
      provided to ALTO clients. Section 6.2.3.

7.  Examples

   This section lists a series of some examples to proceed of path vector queries and the flow
   scheduling use case in Section 3.
   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 Section 6.2.1, Section 6.3.1 or
       Section 6.4.1.

   Alternatively, one can replace step 4 with the following:

   1.  Send a path-vector request which accepts "application/alto-
       costmap+json" "application/alto-costmap+json" or "application/alto-endpointcost+json".

   2.  Find the "query-id" in "vtag" in the response.

   3.  Query the dependent abstract network element property map with
       the query ID and abstract network element names to retrieve the
       associated properties.
       "application/endpointcost+json".

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

7.3.  Single Query  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]
   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"
       },

       "vtag": {
         "resource-id": "cost-map-pv",
         "tag": "27612897acf278ffu3287c284dd28841da78213",
         "query-id": "query1"
       }
     },

     "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.  Single Query  Example # 2

POST /endpointcostmap/multicost HTTP/1.1
Host: alto.example.com
Accept: multipart/related, application/alto-costmap+json, application/alto-endpointcost+json,
        application/alto-propmap+json, application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-costmapfilter+json application/alto-endpointcostparams+json
{
  "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"}
    ]
    "vtag": {
      "resource-id": "endpoint-multicost-map",
      "tag": "47612897acf278ffa3287cb84dd28841da78213",
      "query-id": "query2"
    }
  },

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

--example-2--

7.5.  Multiple Queries Example

7.5.1.  Endpoint Cost Service Example
   POST /endpointcostmap/multicost HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-costmap+json, application/alto-error+json
   Content-Length: [TBD]
   Content-Type: application/alto-costmapfilter+json

   {
     "multi-cost-types": [
       {
         "cost-mode": "array",
         "cost-metric": "ane-path"
       },
       {
         "cost-mode": "numerical",
         "cost-metric": "routingcost"
       }
     ],
     "endpoints": {
       "srcs": [ "ipv6:2001:db8::10" ],
       "dsts": [ "ipv4:192.0.2.3",
                 "ipv4:203.0.113.56" ]
     }
   }

   HTTP/1.1 200 OK
   Content-Length: [TBD]
   Content-Type: application/alto-endpointcost+json

   {
     "meta": {
       "vtag": {
         "resource-id": "endpoint-multicost-map",
         "tag": "f7622897bcf278ffu3287c284dd23841da78213",
         "query-id": "query3"
       },
       "multi-cost-types": [
         { "cost-mode": "array", "cost-metric": "ane-path" },
         { "cost-mode": "numerical", "cost-metric": "routingcost"}
       ]
     },
     "endpoint-cost-map": {
       "ipv6:2001:db8::10": {
         "ipv4:192.0.2.3":    [ "ane:L001", "ane:L006" ],
         "ipv4:203.0.113.56": [ "ane:L001", "ane:L007" ]
       }
     }
   }

7.5.2.  Abstract Network Element Property Map Example

   POST /propmap/availbw HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-propmap+json,application/alto-error+json
   Content-Length: [TBD]
   Content-Type: application/alto-propmapparams+json

   {
     "query-id": "query3",
     "entities" :   [ "ane:L001",
                      "ane:L006" ],
     "properties" : [ "availbw" ]
   }

   HTTP/1.1 200 OK
   Content-Length: [TBD]
   Content-Type: application/alto-propmap+json

   {
     "property-map": {
       "ane:L001": { "availbw": 25 },
       "ane:L006": { "availbw": 40 }
     }
   }

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 legacy 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.

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.

   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 5.1.1 5.1.2   |
                   +-------------+---------------------+

                        Table 2: ALTO Cost Metrics

11.3.  ALTO Entity Domain Registry

   As proposed in Section 9.2 of [I-D.roome-alto-unified-props], "ALTO
   Entity Domain Registry" is requested.  Besides, a new domain is to be
   registered, listed in Table 3.

   +-------------+--------------------------+--------------------------+
   | Identifier  | Entity Address Encoding  | Hierarchy & Inheritance  |
   +-------------+--------------------------+--------------------------+
   | ane         | See Section 5.2.2        | None                     |
   +-------------+--------------------------+--------------------------+

                        Table 3: ALTO Entity Domain

11.4.  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 4. 3.

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

           Table 4: 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,
              <http://www.rfc-editor.org/info/rfc2119>. <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.gao-alto-fcs]
              Gao, K., Zhang, J., Wang, J., Xiang, Q., and Y. Yang,
              "ALTO Extension: Flow-based Cost Query", draft-gao-alto-
              fcs-01 (work in progress), March 2017.

   [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.

   [I-D.ietf-alto-incr-update-sse]

   [I-D.ietf-alto-unified-props-new]
              Roome, W. and Y. Yang, "ALTO Incremental Updates Using
              Server-Sent Events (SSE)", draft-ietf-alto-incr-update-
              sse-03 (work in progress), September 2016.

   [I-D.ietf-alto-multi-cost]
              Randriamasy, S., Roome, W., and N. Schwan, "Multi-Cost
              ALTO", draft-ietf-alto-multi-cost-07 "Extensible Property Maps for the
              ALTO Protocol", draft-ietf-alto-unified-props-new-00 (work
              in progress),
              March 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.

   [I-D.roome-alto-unified-props]
              Roome, W., "Extensible Property Maps for the ALTO
              Protocol", draft-roome-alto-unified-props-01 (work in
              progress), July 2016.

   [RFC2387]  Levinson, E., "The MIME Multipart/Related Content-type",
              RFC 2387, DOI 10.17487/RFC2387, August 1998,
              <http://www.rfc-editor.org/info/rfc2387>.
              <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,
              <http://www.rfc-editor.org/info/rfc7285>.
              <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
   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
   Jingxuan Jensen Zhang
   Tongji University
   4800 Caoan Road
   Shanghai  201804
   China

   Email: jingxuan.n.zhang@gmail.com