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ALTO                                                              K. Gao
Internet-Draft                                        Sichuan University
Intended status: Standards Track                                  Y. Lee
Expires: 10 September 2020
                                                          S. Randriamasy
                                                         Nokia Bell Labs
                                                               Y.R. Yang
                                                         Yale University
                                                                J. Zhang
                                                       Tongji University
                                                            9 March 2020


                      ALTO Extension: Path Vector
                   draft-ietf-alto-path-vector-10

Abstract

   This document is an extension to the base Application-Layer Traffic
   Optimization protocol [RFC7285].  The current ALTO Cost Services
   allow applications to obtain cost values on an end-to-end path
   defined by its source and destination.  The present extension
   provides abstracted information on particular network parts or
   elements traversed by a path between its source and destination.
   Examples of such abstracted parts are networks, data centers or
   links.  This is useful for applications whose performance is impacted
   by particular network parts they traverse or by their properties.
   Applications having the choice among several connection paths may use
   this information to select paths accordingly and improve their
   performance.  In particular, they may infer that several paths share
   common links and prevent traffic bottlenecks by avoiding such paths.
   This document introduces a new cost type called Path Vector.  A Path
   Vector is an array of entities that each identifies an abstracted
   representation of a network part and that are called Abstract Network
   Element (ANE).  Each ANE is defined by a set of properties.  ANE
   properties are conveyed by an ALTO information resource called
   "Property Map", that can be packed together with the Path Vectors in
   a multipart response.  They can also be obtained via a separate ALTO
   request to a Property Map. An ALTO Property Map is an extension to
   the ALTO protocol, that is specified in another document entitled
   "Unified Properties for the ALTO Protocol"
   [I-D.ietf-alto-unified-props-new].

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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   This Internet-Draft will expire on 10 September 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Capacity Region for Multi-Flow Scheduling . . . . . . . .   6
     2.2.  Recent Use Cases  . . . . . . . . . . . . . . . . . . . .   7
       2.2.1.  Large-scale Data Analytics  . . . . . . . . . . . . .   8
       2.2.2.  Context-aware Data Transfer . . . . . . . . . . . . .   8
       2.2.3.  CDN and Service Edge  . . . . . . . . . . . . . . . .   8
     2.3.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   8
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.1.  Abstract Network Element  . . . . . . . . . . . . . . . .  10
       3.1.1.  ANE Name  . . . . . . . . . . . . . . . . . . . . . .  10
       3.1.2.  ANE Properties  . . . . . . . . . . . . . . . . . . .  11
     3.2.  Path Vector . . . . . . . . . . . . . . . . . . . . . . .  12
     3.3.  Multipart Path Vector Response  . . . . . . . . . . . . .  12
       3.3.1.  Identifying the Media Type of the Root Object . . . .  13
       3.3.2.  References to Part Messages . . . . . . . . . . . . .  14
       3.3.3.  Order of Part Messages  . . . . . . . . . . . . . . .  15
   4.  Basic Data Types  . . . . . . . . . . . . . . . . . . . . . .  15
     4.1.  ANE Name  . . . . . . . . . . . . . . . . . . . . . . . .  15
     4.2.  ANE Domain  . . . . . . . . . . . . . . . . . . . . . . .  15



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       4.2.1.  Entity Domain Type  . . . . . . . . . . . . . . . . .  15
       4.2.2.  Domain-Specific Entity Identifier . . . . . . . . . .  15
       4.2.3.  Hierarchy and Inheritance . . . . . . . . . . . . . .  15
     4.3.  New Resource-Specific Entity Domain Exports . . . . . . .  16
       4.3.1.  ANE Domain of Cost Map Resource . . . . . . . . . . .  16
       4.3.2.  ANE Domain of Endpoint Cost Service Resource  . . . .  16
     4.4.  ANE Property Name . . . . . . . . . . . . . . . . . . . .  16
       4.4.1.  ANE Property: Maximum Reservable Bandwidth  . . . . .  16
       4.4.2.  ANE Property: Persistent Entities . . . . . . . . . .  17
     4.5.  Path Vector Cost Type . . . . . . . . . . . . . . . . . .  17
       4.5.1.  Cost Metric: ane-path . . . . . . . . . . . . . . . .  17
       4.5.2.  Cost Mode: array  . . . . . . . . . . . . . . . . . .  17
     4.6.  Part Resource ID  . . . . . . . . . . . . . . . . . . . .  17
   5.  Service Extensions  . . . . . . . . . . . . . . . . . . . . .  18
     5.1.  Multipart Filtered Cost Map for Path Vector . . . . . . .  18
       5.1.1.  Media Type  . . . . . . . . . . . . . . . . . . . . .  18
       5.1.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . .  18
       5.1.3.  Accept Input Parameters . . . . . . . . . . . . . . .  18
       5.1.4.  Capabilities  . . . . . . . . . . . . . . . . . . . .  18
       5.1.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . .  19
       5.1.6.  Response  . . . . . . . . . . . . . . . . . . . . . .  19
     5.2.  Multipart Endpoint Cost Service for Path Vector . . . . .  20
       5.2.1.  Media Type  . . . . . . . . . . . . . . . . . . . . .  21
       5.2.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . .  21
       5.2.3.  Accept Input Parameters . . . . . . . . . . . . . . .  21
       5.2.4.  Capabilities  . . . . . . . . . . . . . . . . . . . .  21
       5.2.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . .  21
       5.2.6.  Response  . . . . . . . . . . . . . . . . . . . . . .  21
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  22
     6.1.  Example: Information Resource Directory . . . . . . . . .  23
     6.2.  Example: Multipart Filtered Cost Map  . . . . . . . . . .  24
     6.3.  Example: Multipart Endpoint Cost Resource . . . . . . . .  26
     6.4.  Example: Incremental Updates  . . . . . . . . . . . . . .  28
   7.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .  29
     7.1.  Compatibility with Legacy ALTO Clients/Servers  . . . . .  29
     7.2.  Compatibility with Multi-Cost Extension . . . . . . . . .  30
     7.3.  Compatibility with Incremental Update . . . . . . . . . .  30
     7.4.  Compatibility with Cost Calendar  . . . . . . . . . . . .  30
   8.  General Discussions . . . . . . . . . . . . . . . . . . . . .  30
     8.1.  Constraint Tests for General Cost Types . . . . . . . . .  31
     8.2.  General Multipart Resources Query . . . . . . . . . . . .  31
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  31
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  32
     10.1.  ALTO Cost Mode Registry  . . . . . . . . . . . . . . . .  32
     10.2.  ALTO Entity Domain Registry  . . . . . . . . . . . . . .  32
     10.3.  ALTO Entity Property Type Registry . . . . . . . . . . .  32
     10.4.  ALTO Resource Entity Domain Export Registries  . . . . .  33
       10.4.1.  costmap  . . . . . . . . . . . . . . . . . . . . . .  33



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       10.4.2.  endpointcost . . . . . . . . . . . . . . . . . . . .  33
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  33
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  33
     12.2.  Informative References . . . . . . . . . . . . . . . . .  34
   Appendix A.  Changes since -08  . . . . . . . . . . . . . . . . .  36
   Appendix B.  Changes Since Version -06  . . . . . . . . . . . . .  36
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

1.  Introduction

   Network performance metrics are crucial to the Quality of Experience
   (QoE) of today's applications.  The ALTO protocol allows Internet
   Service Providers (ISPs) to provide guidance, such as topological
   distance between different end hosts, to overlay applications.  Thus,
   the overlay applications can potentially improve the QoE by better
   orchestrating their traffic to utilize the resources in the
   underlying network infrastructure.

   The base protocol [RFC7285] defines Cost Map and Endpoint Cost
   Service that expose the topological distances of a set of <source,
   destination> pairs.  Various extensions have been proposed extend the
   capability of these services to express other performance metrics
   [I-D.ietf-alto-performance-metrics], to query multiple costs
   simultaneously [RFC8189], and to obtain the time-varying values
   [I-D.ietf-alto-cost-calendar].

   Existing ALTO services provide only cost information on an end-to-end
   path defined by its <source, destination> endpoints.  However, the
   QoE of many overlay applications depends not only on the end-to-end
   costs, but also on some intermediate network components and their
   properties.  For example, job completion time, which is an important
   QoE metric for a large scale data analytics application, is impacted
   by shared bottlenecks inside the carrier network.

   Predicting such information can be very complex without the help of
   the ISP [AAAI2019].  On the other hand, ISPs are not likely to expose
   details on their network paths: first for the sake of
   confidentiality, second because it may represent a huge volume and
   overhead and last, because it is difficult for ISPs to figure out
   what information and what details an application needs.  Likewise,
   applications do not necessarily need all the network path details and
   are likely not able to understand them.

   It may be helpful as well for ISPs if applications could avoid using
   bottlenecks or challenging the network with poorly scheduled traffic.
   Therefore, it is beneficial for both parties if an ALTO server
   provides ALTO clients with an "abstract network state" that provides



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   the necessary details to applications, while hiding the network
   complexity and confidential information.  An "abstract network state"
   is a selected set of abstract representations of intermediate network
   components traversed by the paths between <source, destination> pairs
   combined with properties of these components that are relevant to the
   overlay applications' QoE.  Both an application via its ALTO Client
   and the ISP via the ALTO server can achieve better confidentiality
   and resource utilization by appropriately abstracting relevant path
   components.  The pressure on the server scalability can also be
   reduced by abstracting components and their properties and combining
   them in a single response.

   This document extends [RFC7285] to allow an ALTO server convey
   "abstract network state", for paths defined by their <source,
   destination> pairs.  To this end, it introduces a new cost type
   called "Path Vector".  A Path Vector is an array of identifiers of
   so-called Abstract Network Element (ANE).  An ANE represents an
   abstract intermediate component traversed by a path.  It can be
   associated with various properties.  The associations between ANEs
   and their properties are encoded in an ALTO information resource
   called Unified Property Map, which is specified in
   [I-D.ietf-alto-unified-props-new].

   For better confidentiality, this document aims to minimize
   information exposure.  In particular, this document enables and
   recommends that first ANEs are constructed on demand, and second an
   ANE is only associated with properties that are requested by an ALTO
   client.  A Path Vector response involved two ALTO Maps: the Cost Map
   that contains the Path Vector results and the up to date Unified
   Property Map that contains the properties requested for these ANEs.
   To enforce consistency and improve server scalability, this document
   uses the "multipart/related" message defined in [RFC2387] to return
   the two maps in a single response.

   The rest of the document are organized as follows.  Section 3 gives
   an overview of the protocol design.  Section 4 and Section 5 specify
   the Path Vector extension to the ALTO IRD and the information
   resources, with some concrete examples presented in Section 6.
   Section 7 discusses the backward compatibility with the base protocol
   and existing extensions.  Security and IANA considerations are
   discussed in Section 9 and Section 10 respectively.

2.  Use Cases








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2.1.  Capacity Region for Multi-Flow Scheduling

   Assume that an application has control over a set of flows, which may
   go through shared links or switches and share a bottleneck.  The
   application hopes to schedule the traffic among multiple flows to get
   better performance.  The capacity region information for those flows
   will benefit the scheduling.  However, existing cost maps can not
   reveal such information.

   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.  Endhosts 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
                      +------+                      +------+
                             |                      |
                             +----------------------+




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              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:

   *  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 at
      most.

   *  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 at
      most.

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

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

   *  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 propose a solution
   to provide these details.

2.2.  Recent Use Cases

   This section highlights some recent use cases that are reported in
   IETF and ALTO working group.  See [I-D.bernstein-alto-topo] for a
   more comprehensive survey of use cases where extended network
   topology information is needed.










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2.2.1.  Large-scale Data Analytics

   One potential use case of the Path Vector extension is for large-
   scale data analytics such as [SENSE] and [LHC], where data of
   Gigabytes, Terabytes and even Petabytes are transferred.  For these
   applications, the QoE is usually measured as the job completion time,
   which is related to the completion time of the slowest data transfer.
   With the Path Vector extension, an ALTO client can identify
   bottlenecks inside the network.  Therefore, the overlay application
   can make optimal traffic distribution or resource reservation (i.e.,
   proportional to the size of the transferred data), leading to optimal
   job completion time and network resource utilization.

2.2.2.  Context-aware Data Transfer

   It is sometimes important to know how the capabilities of various
   network components between two end hosts.  With the Path Vector
   extension, an ALTO client may query the "network context"
   information, i.e., whether the two hosts are connected to the access
   network through a wireless link or a wire, and the capabilities of
   the access network.  Thus, the client may use different data transfer
   mechanisms, or even deploy different 5G User Plane Functions (UPF)
   [I-D.ietf-dmm-5g-uplane-analysis] to optimize the data transfer.

2.2.3.  CDN and Service Edge

   A growing trend in today's applications is to bring storage and
   computation closer to the end user for better QoE, such as Content
   Delivery Network (CDN), AR/VR, and cloud gaming, as reported in
   various recent documents ([I-D.contreras-alto-service-edge],
   [I-D.huang-alto-mowie-for-network-aware-app], and
   [I-D.yang-alto-deliver-functions-over-networks]).

   With the Path Vector extension, an ALTO server can selectively reveal
   the CDNs and service edges that reside along the paths between
   different end hosts, together with their properties such as available
   Service Level Agreement (SLA) plans.  Otherwise, the ALTO client may
   have to make multiple queries and potentially with the complete list
   of CDNs and/or service edges.  While both approaches offer the same
   information, making multiple queries introduce larger delay and more
   overhead on both the ALTO server and the ALTO client.

2.3.  Terminology

   This document extends the ALTO base protocol [RFC7285] and the
   Unified Property Map extension [I-D.ietf-alto-unified-props-new].  In
   addition to the terms defined in these documents, this document also
   uses the following additional terms:



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   *  Abstract Network Element (ANE): An Abstract Network Element is an
      abstraction representation of network components.  It can be a
      link, a middlebox, a virtualized network function (VNF), etc., or
      their aggregations.  An ANE can be constructed either statically
      in advance or on demand based on the requested information.  In a
      response, each ANE is represented by a unique ANE Name.  Note that
      an ALTO client MUST NOT assume ANEs in different responses but
      with the same ANE Name refer to the same aggregation of network
      components.

   *  Path Vector: A Path Vector, or an ANE Path Vector, is a JSON array
      of ANE Names.  It conveys the information that the path between a
      source and a destination traverses the ANEs in the same order as
      they appear in the Path Vector.

   *  Path Vector resource: A Path Vector resource refers to an ALTO
      resource which supports the extension defined in this document.

   *  Path Vector cost type: The Path Vector cost type is a special cost
      type, which is specified in Section 4.5.  When this cost type is
      present in an IRD entry, it indicates that the information
      resource is a Path Vector resource.  When this cost type is
      present in a Cost Map or an Endpoint Cost Map, it indicates each
      cost value must be interpreted as a Path Vector.

   *  Path Vector request: A Path Vector request refers to the POST
      message sent to an ALTO Path Vector resource.

   *  Path Vector response: A Path Vector response refers to the
      multipart/related message returned by a Path Vector resource.

3.  Overview

   This section gives a non-normative overview of the Path Vector
   extension.  It is assumed that readers are familiar with both the
   base protocol [RFC7285] and the Unified Property Map extension
   [I-D.ietf-alto-unified-props-new].

   Fundamentally, this extension conveys two pieces of information:

   1.  The abstract network state: The abstract network state is modeled
       as an annotated graph, where each node is an Abstract Network
       Element (ANE) and each annotation is a property associated with
       an ANE.

   2.  Routing information: The routing information is modeled as an
       array of nodes in the annotated graph that is traversed by the
       path between a source and a destination.



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   However, it can be observed that the routing information already
   conveys the connectivity of the abstract network.  Thus, this
   extensions allows an ALTO server to provide the routing information
   and the association between ANEs and their properties.  Specifically,
   this document uses the following designs:

   1.  This extension conveys the routing information in the abstract
       network in an ALTO Cost Map or Endpoint Cost Map which accepts a
       Path Vector, i.e., a JSON array of ANEs traversed by the path
       between a source and a destination, as the cost value.  With the
       Path Vectors, an ALTO client can simultaneously reconstruct the
       structure of the abstract network and the routing for the paths
       between endpoints.

   2.  This extension uses the ALTO Unified Property Map to convey the
       properties associated with the ANEs, which offers more fine-
       grained abstract network state for overlay applications.

   3.  This extension uses the multipart message TBD-ALTO-MULTIPART to
       include both information resources in the same Path Vector
       response.

3.1.  Abstract Network Element

   This extension introduce Abstract Network Element (ANE) as an
   indirect and network-agnostic way to specify an aggregation of
   intermediate network components which can be treated as if they are
   placed in the same location in the network, based on geo-location,
   OSPF domain, service type, algebraic properties, or other criteria.

3.1.1.  ANE Name

   Each ANE is uniquely identified by a string of type ANEName as
   specified in Section 4.1.  An important observation is that for
   different requests, an ALTO server may selectively apply different
   methods to create the abstract network state based on confidentiality
   and performance considerations.  Thus, the ANEs inside the abstract
   network may be constructed on demand.  This indicates that the scope
   of an ANEName is limited to the Path Vector response.

   Since each ANE is also an entity in the Unified Property Map, the ANE
   Name MUST conform to the encoding of an Entity Identifier.  Thus,
   this document also specifies a new EntityDomainName following the
   instructions in [I-D.ietf-alto-unified-props-new].







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3.1.2.  ANE Properties

   In this extension, the associations between ANE and the properties
   are conveyed in a Unified Property Map. Thus, they MUST follow the
   mechanisms specified in the [I-D.ietf-alto-unified-props-new] with
   some additional considerations.

   1.  As a property may not exist in every ANE, it must be interpreted
       in the same way by the ALTO server and the ALTO client.  Thus,
       when an ANE property is specified, its intended semantics MUST
       specify how to interpret the case that a requested ANE property
       does not exist in an ANE.

   2.  As each ANE is an aggregation of multiple network components, its
       properties are the aggregated results of the components'
       properties.  For different ALTO server implementations, different
       properties MAY have different rules when they are aggregated into
       a single ANE.  For example, if an ANE is the aggregation of two
       networks where each network contains a CDN, an ALTO server may
       selectively expose one CDN, expose none, or expose both in the
       ANE, according to its own aggregation policies.

       However, it is common that an ALTO client needs to compute the
       aggregated property value of some ANEs, e.g., to infer the end-
       to-end property for a <source, destination> pair.  It is
       RECOMMENDED that the intended semantics of an ANE property
       specifies how to compute the aggregated value without loss of
       information.  Thus, the information is interpreted by the ALTO
       server and the ALTO client in the same way.  For example,
       properties with algebraic properties can be aggregated following
       the algebraic rules [TON2019].

       NOTE: The aggregation rule ONLY specifies how to compute the
       aggregated property for a Path Vector, NOT how the ANEs can be
       aggregated in the Path Vector response.  This is because the
       change of Path Vectors may change the routing information and the
       abstract network topology, leading to inaccurate results.

   3.  An ALTO Path Vector resource MAY only support a set of ANE
       properties.  Meanwhile, an ALTO client MAY only require a subset
       of the available properties.  Thus, a property negotiation
       process is required.

       This document uses a similar approach as the negotiation process
       of cost types: the available properties for a given resource are
       announced in the Information Resource Directory as a new
       capability called "ane-property-names"; the selected properties
       SHOULD be specified in a new filter called "ane-property-names"



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       in the request body; the response MUST return and only return the
       selected properties for the ANEs in the response, if applicable.

3.2.  Path Vector

   For an ALTO client to correctly interpret the Path Vector, this
   extension specifies a new cost type called the Path Vector cost type,
   which MUST be included both in the Information Resource Directory and
   the ALTO Cost Map or Endpoint Cost Map so that an ALTO client can
   correct interpret the cost values.

   The Path Vector cost type MUST convey both the interpretation and
   semantics in the "cost-mode" and "cost-metric" respectively.
   Unfortunately, a single "cost-mode" value cannot fully specify the
   interpretation of a Path Vector, which is a compound data type.  For
   example, in programming languages such as Java, a Path Vector will
   have the type of JSONArray[ANEName].

   Instead of extending the "type system" of ALTO, this document takes a
   simple and backward compatible approach.  Specifically, the "cost-
   mode" of the Path Vector cost type is "array", which indicates the
   value is a JSON array.  Then, an ATLO client MUST check the value of
   the "cost-metric".  If the value is "ane-path", meaning the JSON
   array should be further interpreted as a path of ANENames.

   The Path Vector cost type is specified in Section 4.5

3.3.  Multipart Path Vector Response

   For a basic ALTO information resource, the response contains only one
   type of ALTO resources, e.g., Network Map, Cost Map, or Property Map.
   Thus, only one round of communication is required: An ALTO client
   sends a request to an ALTO server, and the ALTO server returns a
   response, as shown in Figure 3.

            ALTO Client                              ALTO Server
                 |-------------- Request ---------------->|
                 |<------------- Response ----------------|

               Figure 3: A Typical ALTO Request and Response

            ALTO Client                              ALTO Server
                 |------------- PV Request -------------->|
                 |<----- PV Response (Cost Map Part) -----|
                 |<--- PV Response (Property Map Part) ---|

          Figure 4: The Path Vector Extension Request and Response




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   The Path Vector extension, on the other hand, involves two types of
   information resources: Path Vectors conveyed in a Cost Map or an
   Endpoint Cost Map, and ANE properties conveyed in a Unified Property
   Map. Instead of two consecutive message exchanges, the Path Vector
   extension enforces one round of communication.  Specifically, the
   Path Vector extension requires the ALTO client to include the source
   and destination pairs and the requested ANE properties in a single
   request, and encapsulates both Path Vectors and properties associated
   with the ANEs in a single response, as shown in Figure 4.

   This design is based on the following considerations:

   1.  Since ANEs MAY be constructed on demand, and potentially based on
       the requested properties (See Section 3.1 for more details).  If
       sources and destinations are not in the same request as the
       properties, an ALTO server either CANNOT construct ANEs on-
       demand, or MUST wait until both requests are received.

   2.  As ANEs MAY be constructed on demand, mappings of each ANE to its
       underlying network devices and resources CAN be specific to the
       request.  In order to respond to the second request correctly, an
       ALTO server MUST store the mapping of each Path Vector request
       until the client fully retrieves the property information.  The
       "stateful" behavior CAN substantially harm the server scalability
       and potentially lead to Denial-of-Service attacks.

   One approach to realize the one-round communication is to define a
   new media type to contain both objects, but this violates modular
   design.  This document uses standard-conforming usage of "multipart/
   related" media type defined in [RFC2387] to elegantly combine the
   objects.  Path Vectors are encoded as a Cost Map or an Endpoint Cost
   Map, and the Property Map is encoded as a Unified Propert Map. They
   are encapsulated as parts of a multipart message.  The modular
   composition allows ALTO servers and clients to reuse the data models
   of the existing information resources.  Specifically, this document
   addresses the following practical issues using "multipart/related".

3.3.1.  Identifying the Media Type of the Root Object

   ALTO uses media type to indicate the type of an entry in the
   Information Resource Directory (IRD) (e.g., "application/alto-
   costmap+json" for Cost Map and "application/alto-endpointcost+json"
   for Endpoint Cost Map).  Simply putting "multipart/related" as the
   media type, however, makes it impossible for an ALTO client to
   identify the type of service provided by related entries.

   To address this issue, this document uses the "type" parameter to
   indicate the root object of a multipart/related message.  For a Cost



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   Map resource, the "media-type" in the IRD entry MUST be "multipart/
   related" with the parameter "type=application/alto-costmap+json"; for
   an Endpoint Cost Service, the parameter MUST be "type=application/
   alto-endpointcost+json".

3.3.2.  References to Part Messages

   The ALTO SSE extension (see [I-D.ietf-alto-incr-update-sse]) uses
   "client-id" to demultiplex push updates.  However, "client-id" is
   provided for each request, which introduces ambiguity when applying
   SSE to a Path Vector resource.

   To address this issue, an ALTO server MUST assign a unique identifier
   to each part of the "multipart/related" response message.  This
   identifier, referred to as a Part Resource ID (See Section 4.6 for
   details), MUST be present in the part message's "Resource-Id" header.
   The MIME part header MUST also contain the "Content-Type" header,
   whose value is the media type of the part (e.g., "application/alto-
   costmap+json", "application/alto-endpointcost+json", or "application/
   alto-propmap+json").

   If an ALTO server provides incremental updates for this Path Vector
   resource, it MUST generate incremental updates for each part
   separately.  The client-id MUST have the following format:

      pv-client-id '.' part-resource-id

   where pv-client-id is the client-id assigned to the Path Vector
   request, and part-resource-id is the "Resource-Id" header value of
   the part.  The media-type MUST match the "Content-Type" of the part.

   The same problem happens inside the part messages as well.  The two
   parts MUST contain a version tag, which SHOULD contain a unique
   Resource ID.  This document requires the resource-id in a Version Tag
   to have the following format:

      pv-resource-id '.' part-resource-id

   where pv-resource-id is the resource ID of the Path Vector resource
   in the IRD entry, and the part-resource-id has the same value as the
   "Resource-Id" header of the part.










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3.3.3.  Order of Part Messages

   According to RFC 2387 [RFC2387], the Path Vector part, whose media
   type is the same as the "type" parameter of the multipart response
   message, is the root object.  Thus, it is the element the application
   processes first.  Even though the "start" parameter allows it to be
   placed anywhere in the part sequence, it is RECOMMENDED that the
   parts arrive in the same order as they are processed, i.e., the Path
   Vector part is always put as the first part, followed by the property
   map part.  It is also RECOMMENDED that when doing so, an ALTO server
   SHOULD NOT set the "start" parameter, which implies the first part is
   the root object.

4.  Basic Data Types

4.1.  ANE Name

   An ANE Name is encoded as a JSON string, which has the same format as
   EntityIdentifer (Section 3.1.3 of [I-D.ietf-alto-unified-props-new])
   and the EntityDomainName MUST be "ane", indicating that this entity
   belongs to the "ane" Entity Domain.

   The type ANEName is used in this document to indicate a string of
   this format.

4.2.  ANE Domain

   This document specifies a new ALTO entity domain called "ane" in
   addition to the ones in [I-D.ietf-alto-unified-props-new].  The ANE
   domain associates property values with the ANEs in a network.  The
   entity in ANE domain is often used in the Path Vector by Cost Map or
   Endpoint Cost Service resources.  Accordingly, the ANE domain always
   depends on a Cost Map or an Endpoint Cost Map.

4.2.1.  Entity Domain Type

   ane

4.2.2.  Domain-Specific Entity Identifier

   The entity identifier of ANE domain uses the same encoding as ANEName
   (Section 4.1).

4.2.3.  Hierarchy and Inheritance

   There is no hierarchy or inheritance for properties associated with
   ANEs.




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4.3.  New Resource-Specific Entity Domain Exports

4.3.1.  ANE Domain of Cost Map Resource

   If an ALTO Cost Map resource supports the Path Vector cost type, it
   can export an "ane" typed entity domain defined by the union of all
   sets of ANE names, where each set of ANE names are an "ane-path"
   metric cost value in this ALTO Cost Map resource.

4.3.2.  ANE Domain of Endpoint Cost Service Resource

   If an ALTO Endpoint Cost Service resource supports the Path Vector
   cost type, it can export an "ane" typed entity domain defined by the
   union of all sets of ANE names, where each set of ANE names are an
   "ane-path" metric cost value in this ALTO Endpoint Cost Service
   resource.

4.4.  ANE Property Name

   An ANE Property Name is encoded as an Entity Property Name
   (Section 3.2.2 of [I-D.ietf-alto-unified-props-new]) where

   *  the ResourceID part of an ANE Property Name MUST be empty;

   *  the EntityPropertyType part MUST be a valid property of an ANE
      entity, i.e., the mapping of the ANE domain type and the Entity
      Property Type MUST be registered to the ALTO Resource Entity
      Property Mapping Registries (Section 11.5 in
      [I-D.ietf-alto-unified-props-new]).

4.4.1.  ANE Property: Maximum Reservable Bandwidth

   The maximum reservable bandwidth property conveys the maximum
   bandwidth that can be reserved for all the traffic that traverses an
   ANE.  The Entity Property Type of the maximum reservable bandwidth is
   "maxresbw", and the value MUST be encoded as a non-negative numerical
   cost value as defined in Section 6.1.2.1 of [RFC7285] and the unit is
   bit per second.

   If this property is requested but not present in an ANE, it MUST be
   interpreted as that the ANE has sufficiently large bandwidth to be
   reserved.  If the ANE does not support bandwidth reservation, the
   value MUST be present and be set to 0.

   The aggregated value of a Path Vector is the minimum value of all the
   ANEs in the Path Vector.





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4.4.2.  ANE Property: Persistent Entities

   The persistent entities property conveys the physical or logical
   network entities (e.g., links, in-network caching service) that are
   contained by an ANE.  It is indicated by the property name
   "persistent-entities".  The value is encoded as a JSON array of
   entity identifiers ([I-D.ietf-alto-unified-props-new]).  These entity
   identifiers are persistent so that a client CAN further query their
   properties for future use.

   If this property is requested but is missing for a given ANE, it MUST
   be interpreted as that no such entities exist in this ANE.

4.5.  Path Vector Cost Type

   This document defines a new cost type, which is referred to as the
   "Path Vector" cost type.  An ALTO server MUST offer this cost type if
   it supports the Path Vector extension.

4.5.1.  Cost Metric: ane-path

   This cost metric conveys an array of ANE names, where each ANE name
   uniquely represents an ANE traversed by traffic from a source to a
   destination.

4.5.2.  Cost Mode: array

   This cost mode indicates that every cost value in a Cost Map or an
   Endpoint Cost Map MUST be interpreted as a JSON array object.

   Note that this cost mode only requires the cost value to be a JSON
   array of JSONValue.  However, an ALTO server that enables this
   extension MUST return a JSON array of ANEName (Section 4.1) when the
   cost metric is "ane-path".

4.6.  Part Resource ID

   A Part Resource ID is encoded as a JSON string with the same format
   as that of the Resource ID (Section 10.2 of [RFC7285]).

   WARNING: Even though the client-id assigned to a Path Vector request
   and the Part Resource ID MAY contain up to 64 characters by their own
   definition.  Their concatenation (see Section 3.3.2) MUST also
   conform to the same length constraint.  The same requirement applies
   to the resource ID of the Path Vector resource, too.  Thus, it is
   RECOMMENDED to limit the length of resource ID and client ID related
   to a Path Vector resource to 31 characters.




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5.  Service Extensions

5.1.  Multipart Filtered Cost Map for Path Vector

   This document introduces a new ALTO resource called multipart
   filtered cost map resource, which allows an ALTO server to provide
   other ALTO resources associated to the cost map resource in the same
   response.

5.1.1.  Media Type

   The media type of the multipart filtered cost map resource is
   "multipart/related;type=application/alto-costmap+json".

5.1.2.  HTTP Method

   The multipart filtered cost map is requested using the HTTP POST
   method.

5.1.3.  Accept Input Parameters

   The input parameters of the multipart filtered cost map are supplied
   in the body of an HTTP POST request.  This document extends the input
   parameters to a filtered cost map with a data format indicated by the
   media type "application/alto-costmapfilter+json", which is a JSON
   object of type PVReqFilteredCostMap, where:

   object {
     [EntityPropertyName ane-property-names<0..*>;]
   } PVReqFilteredCostMap : ReqFilteredCostMap;

   with fields:

   ane-property-names:  A list of properties that are associated with
      the ANEs.  Each property in this list MUST match one of the
      supported ANE properties indicated in the resource's "ane-
      property-names" capability.  If the field is NOT present, it MUST
      be interpreted as an empty list, indicating that the ALTO server
      MUST NOT return any property in the unified property part.

5.1.4.  Capabilities

   The multipart filtered cost map resource extends the capabilities
   defined in Section 11.3.2.4 of [RFC7285].  The capabilities are
   defined by a JSON object of type PVFilteredCostMapCapabilities:






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   object {
     [EntityPropertyName ane-property-names<0..*>;]
   } PVFilteredCostMapCapabilities : FilteredCostMapCapabilities;

   with fields:

   cost-type-names:  The "cost-type-names" field MUST only include the
      Path Vector cost type, unless explicitly documented by a future
      extension.  This also implies that the Path Vector cost type MUST
      be defined in the "cost-types" of the Information Resource
      Directory's "meta" field.

   cost-constraints:  If the "cost-type-names" field includes the Path
      Vector cost type, "cost-constraints" field MUST be "false" or not
      present unless specifically instructed by a future document.

   testable-cost-type-names:  If the "cost-type-names" field includes
      the Path Vector cost type, the Path Vector cost type MUST NOT be
      included in the "testable-cost-type-names" field unless
      specifically instructed by a future document.

   ane-property-names:  Defines a list of ANE properties that can be
      returned.  If the field is NOT present, it MUST be interpreted as
      an empty list, indicating the ALTO server CANNOT provide any ANE
      property.

5.1.5.  Uses

   The resource ID of the network map based on which the PIDs in the
   returned cost map will be defined.  If this resource supports
   "persistent-entities", it MUST also include ALL the resources that
   exposes the entities that MAY appear in the response.

5.1.6.  Response

   The response MUST indicate an error, using ALTO protocol error
   handling, as defined in Section 8.5 of [RFC7285], if the request is
   invalid.

   The "Content-Type" header of the response MUST be "multipart/related"
   as defined by [RFC2387] with the following parameters:

   type:  The type parameter MUST be "application/alto-costmap+json".
      Note that [RFC2387] permits both parameters with and without the
      double quotes.

   start:  The start parameter MUST be a quoted string where the quoted




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      part has the same value as the "Resource-ID" header in the first
      part.

   boundary:  The boundary parameter is as defined in [RFC2387].

   The body of the response consists of two parts.

   The first part MUST include "Resource-Id" and "Content-Type" in its
   header.  The value of "Resource-Id" MUST has the format of a Part
   Resource ID.  The "Content-Type" MUST be "application/alto-
   costmap+json".

   The body of the first part MUST be a JSON object with the same format
   as defined in Section 11.2.3.6 of [RFC7285].  The JSON object MUST
   include the "vtag" field in the "meta" field, which provides the
   version tag of the returned cost map.  The resource ID of the version
   tag MUST follow the format in Section 3.3.2.  The "meta" field MUST
   also include the "dependent-vtags" field, whose value is a single-
   element array to indicate the version tag of the network map used,
   where the network map is specified in the "uses" attribute of the
   multipart filtered cost map resource in IRD.

   The second part MUST also include "Resource-Id" and "Content-Type" in
   its header.  The value of "Resource-Id" has the format of a Part
   Resource ID.  The "Content-Type" MUST be "application/alto-
   propmap+json".

   The body of the second part MUST be a JSON object with the same
   format as defined in Section 4.6 of
   [I-D.ietf-alto-unified-props-new].  The JSON object MUST include the
   "dependent-vtags" field in the "meta" field.  The value of the
   "dependent-vtags" field MUST be an array of VersionTag objects as
   defined by Section 10.3 of [RFC7285].  The "vtag" of the first part
   MUST be included in the "dependent-vtags".  If "persistent-entities"
   is requested, the version tags of the dependent resources that MAY
   expose the entities in the response MUST also be included.  The
   PropertyMapData has one member for each ANEName that appears in the
   first part, where the EntityProps has one member for each property
   requested by the client if applicable.

5.2.  Multipart Endpoint Cost Service for Path Vector

   This document introduces a new ALTO resource called multipart
   endpoint cost resource, which allows an ALTO server to provide other
   ALTO resources associated to the endpoint cost resource in the same
   response.





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5.2.1.  Media Type

   The media type of the multipart endpoint cost resource is
   "multipart/related;type=application/alto-endpointcost+json".

5.2.2.  HTTP Method

   The multipart endpoint cost resource is requested using the HTTP POST
   method.

5.2.3.  Accept Input Parameters

   The input parameters of the multipart endpoint cost resource are
   supplied in the body of an HTTP POST request.  This document extends
   the input parameters to an endpoint cost map with a data format
   indicated by the media type "application/alto-
   endpointcostparams+json", which is a JSON object of type
   PVEndpointCostParams, where

   object {
     [EntityPropertyName ane-property-names<0..*>;]
   } PVReqEndpointcost : ReqEndpointcost;

   with fields:

   ane-property-names:  This document defines the "ane-property-names"
      in PVReqEndpointcost as the same as in PVReqFilteredCostMap.  See
      Section 5.1.3.

5.2.4.  Capabilities

   The capabilities of the multipart endpoint cost resource are defined
   by a JSON object of type PVEndpointcostCapabilities, which is defined
   as the same as PVFilteredCostMapCapabilities.  See Section 5.1.4.

5.2.5.  Uses

   If a multipart endpoint cost resource supports "persistent-entities",
   the "uses" field in its IRD entry MUST include ALL the resources
   which exposes the entities that MAY appear in the response.

5.2.6.  Response

   The response MUST indicate an error, using ALTO protocol error
   handling, as defined in Section 8.5 of [RFC7285], if the request is
   invalid.





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   The "Content-Type" header of the response MUST be "multipart/related"
   as defined by [RFC7285] with the following parameters:

   type:  The type parameter MUST be "application/alto-
      endpointcost+json".

   start:  The start parameter MUST be a quoted string where the quoted
      part has the same value as the "Resource-ID" header in the first
      part.

   boundary:  The boundary parameter is as defined in [RFC2387].

   The body consists of two parts:

   The first part MUST include "Resource-Id" and "Content-Type" in its
   header.  The value of "Resource-Id" MUST has the format of a Part
   Resource ID.  The "Content-Type" MUST be "application/alto-
   endpointcost+json".

   The body of the first part MUST be a JSON object with the same format
   as defined in Section 11.5.1.6 of [RFC7285].  The JSON object MUST
   include the "vtag" field in the "meta" field, which provides the
   version tag of the returned endpoint cost map.  The resource ID of
   the version tag MUST follow the format in Section 3.3.2.

   The second part MUST also include "Resource-Id" and "Content-Type" in
   its header.  The value of "Resource-Id" MUST has the format of a Part
   Resource ID.  The "Content-Type" MUST be "application/alto-
   propmap+json".

   The body of the second part MUST be a JSON object with the same
   format as defined in Section 4.6 of
   [I-D.ietf-alto-unified-props-new].  The JSON object MUST include the
   "dependent-vtags" field in the "meta" field.  The value of the
   "dependent-vtags" field MUST be an array of VersionTag objects as
   defined by Section 10.3 of [RFC7285].  The "vtag" of the first part
   MUST be included in the "dependent-vtags".  If "persistent-entities"
   is requested, the version tags of the dependent resources that MAY
   expose the entities in the response MUST also be included.  The
   PropertyMapData has one member for each ANEName that appears in the
   first part, where the EntityProps has one member for each property
   requested by the client if applicable.

6.  Examples

   This section lists some examples of path vector queries and the
   corresponding responses.  Some long lines are truncated for better
   readability.



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6.1.  Example: Information Resource Directory

   Below is an example of an Information Resource Directory which
   enables the path vector extension.  Some critical modifications
   include:

   *  The "path-vector" cost type (Section 4.5) is defined in the "cost-
      types" of the "meta" field.

   *  The "cost-map-pv" information resource provides a multipart
      filtered cost map resource, which exposes the Maximum Reservable
      Bandwidth ("maxresbw") property.

   *  The "http-proxy-props" information resource provides a filtered
      unified property map resource, which exposes the HTTP proxy entity
      domain (encoded as "http-proxy") and the "price" property.  Note
      that HTTP proxy is NOT a valid entity domain yet and is used here
      only for demonstration.

   *  The "endpoint-cost-pv" information resource provides a multipart
      endpoint cost resource.  It exposes the Maximum Reservable
      Bandwidth ("maxresbw") property and the Persistent Entity property
      ("persistent-entities").  The persistent entities MAY come from
      the "http-proxy-props" resource.

   *  The "update-pv" information resource provides the incremental
      update ([I-D.ietf-alto-incr-update-sse]) service for the
      "endpoint-cost-pv" resource.

   {
     "meta": {
       "cost-types": {
         "path-vector": {
           "cost-mode": "array",
           "cost-metric": "ane-path"
         }
       }
     },
     "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": "multipart/related;
                        type=application/alto-costmap+json",
         "accepts": "application/alto-costmapfilter+json",



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         "capabilities": {
           "cost-type-names": [ "path-vector" ],
           "ane-property-names": [ "maxresbw" ]
         },
         "uses": [ "my-default-networkmap" ]
       },
       "http-proxy-props": {
         "uri": "http://alto.example.com/proxy-props",
         "media-type": "application/alto-propmap+json",
         "accepts": "application/alto-propmapparams+json",
         "capabilities": {
           "mappings": {
             "http-proxy": [ "price" ]
           }
         }
       },
       "endpoint-cost-pv": {
         "uri": "http://alto.exmaple.com/endpointcost/pv",
         "media-type": "multipart/related;
                        type=application/alto-endpointcost+json",
         "accepts": "application/alto-endpointcostparams+json",
         "capabilities": {
           "cost-type-names": [ "path-vector" ],
           "ane-property-names": [ "maxresbw", "persistent-entities" ]
         },
         "uses": [ "http-proxy-props" ]
       },
       "update-pv": {
         "uri": "http://alto.example.com/updates/pv",
         "media-type": "text/event-stream",
         "uses": [ "endpoint-cost-pv" ],
         "accepts": "application/alto-updatestreamparams+json",
         "capabilities": {
           "support-stream-control": true
         }
       }
     }
   }

6.2.  Example: Multipart Filtered Cost Map

   The following examples demonstrate the request to the "cost-map-pv"
   resource and the corresponding response.

   The request uses the path vector cost type in the "cost-type" field.
   The "ane-property-names" field is missing, indicating that the client
   only requests for the path vector but not the ANE properties.




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   The response consists of two parts.  The first part returns the array
   of ANEName for each source and destination pair.  There are three
   ANEs, where "ane:L001" is shared by traffic from "PID1" to both
   "PID2" and "PID3".

   The second part returns an empty property map.  Note that the ANE
   entries are omitted since they have no properties (See Section 3.1 of
   [I-D.ietf-alto-unified-props-new]).

   POST /costmap/pv HTTP/1.1
   Host: alto.example.com
   Accept: multipart/related;type=application/alto-costmap+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=example-1;
                 type=application/alto-costmap+json

   --example-1
   Resource-Id: costmap
   Content-Type: application/alto-costmap+json

   {
     "meta": {
       "vtag": {
         "resource-id": "cost-map-pv.costmap",
         "tag": "d827f484cb66ce6df6b5077cb8562b0a"
       },
       "dependent-vtags": [
         {
           "resource-id": "my-default-networkmap",
           "tag": "75ed013b3cb58f896e839582504f6228"
         }
       ],



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       "cost-type": {
         "cost-mode": "array",
         "cost-metric": "ane-path"
       }
     },
     "cost-map": {
       "PID1": {
         "PID2": [ "ane:L001", "ane:L003" ],
         "PID3": [ "ane:L001", "ane:L004" ]
       }
     }
   }
   --example-1
   Resource-Id: propmap
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "cost-map-pv.costmap",
           "tag": "d827f484cb66ce6df6b5077cb8562b0a"
         }
       ]
     },
     "property-map": {
     }
   }

6.3.  Example: Multipart Endpoint Cost Resource

   The following examples demonstrate the request to the "endpoint-cost-
   pv" resource and the corresponding response.

   The request uses the path vector cost type in the "cost-type" field,
   and queries the Maximum Reservable Bandwidth ANE property and the
   Persistent Entity property.

   The response consists of two parts.  The first part returns the array
   of ANEName for each valid source and destination pair.

   The second part returns the requested properties of ANEs in the first
   part.  The "ane:NET001" element contains an HTTP proxy entity, which
   can be further used by the client.  Since it does not contain a
   "maxresbw" property, the client SHOULD assume it does NOT support
   bandwidth reservation but will NOT become a traffic bottleneck, as
   specified in Section 4.4.1.




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   POST /endpointcost/pv HTTP/1.1
   Host: alto.example.com
   Accept: multipart/related;
           type=application/alto-endpointcost+json,
           application/alto-error+json
   Content-Length: [TBD]
   Content-Type: application/alto-endpointcostparams+json

   {
     "cost-type": {
       "cost-mode": "array",
       "cost-metric": "ane-path"
     },
     "endpoints": {
       "srcs": [ "ipv4:192.0.2.2" ],
       "dsts": [ "ipv4:192.0.2.89",
                 "ipv4:203.0.113.45",
                 "ipv6:2001:db8::10" ]
     },
     "ane-property-names": [ "maxresbw", "persistent-entities" ]
   }

   HTTP/1.1 200 OK
   Content-Length: [TBD]
   Content-Type: multipart/related; boundary=example-2;
                 type=application/alto-endpointcost+json

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

   {
     "meta": {
       "vtags": {
         "resource-id": "endpoint-cost-pv.ecs",
         "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
       },
       "cost-type": {
         "cost-mode": "array",
         "cost-metric": "ane-path"
       }
     },
     "endpoint-cost-map": {
       "ipv4:192.0.2.2": {
         "ipv4:192.0.2.89":   [ "ane:NET001", "ane:L002" ],
         "ipv4:203.0.113.45": [ "ane:NET001", "ane:L003" ]
       }
     }



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

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "endpoint-cost-pv.ecs",
           "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
         },
         {
           "resource-id": "http-proxy-props",
           "tag": "bf3c8c1819d2421c9a95a9d02af557a3"
         }
       ]
     },
     "property-map": {
       "ane:NET001": {
         "persistent-entities": [ "http-proxy:192.0.2.1" ]
       },
       "ane:L002": { "maxresbw": 48000000 },
       "ane:L003": { "maxresbw": 35000000 }
     }
   }

6.4.  Example: Incremental Updates

   In this example, an ALTO client subscribes to the incremental update
   for the multipart endpoint cost resource "endpoint-cost-pv".

   POST /updates/pv HTTP/1.1
   Host: alto.example.com
   Accept: text/event-stream
   Content-Type: application/alto-updatestreamparams+json
   Content-Length: [TBD]

   {
     "add": {
       "ecspvsub1": {
         "resource-id": "endpoint-cost-pv",
         "input": <ecs-input>
       }
     }
   }





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   Based on the server-side process defined in
   [I-D.ietf-alto-incr-update-sse], the ALTO server will send the
   "control-uri" first using Server-Sent Event (SSE), followed by the
   full response of the multipart message.

   HTTP/1.1 200 OK
   Connection: keep-alive
   Content-Type: text/event-stream

   event: application/alto-updatestreamcontrol+json
   data: {"control-uri": "http://alto.example.com/updates/streams/1414"}

   event: multipart/related;boundary=example-3;
          type=application/alto-endpointcost+json,ecspvsub1
   data: --example-3
   data: Resource-ID: ecsmap
   data: Content-Type: application/alto-endpointcost+json
   data:
   data: <endpoint-cost-map-entry>
   data: --example-3
   data: Resource-ID: propmap
   data: Content-Type: application/alto-propmap+json
   data:
   data: <property-map-entry>
   data: --example-3--

   When the contents change, the ALTO server will publish the updates
   for each node in this tree separately.

   event: application/merge-patch+json, ecspvsub1.ecsmap
   data: <Merge patch for endpoint-cost-map-update>

   event: application/merge-patch+json, ecspvsub1.propmap
   data: <Merge patch for property-map-update>

7.  Compatibility

7.1.  Compatibility with Legacy ALTO Clients/Servers

   The multipart filtered cost map resource and the multipart endpoint
   cost resource has no backward compatibility issue with legacy ALTO
   clients and servers.  Although these two types of resources reuse the
   media types defined in the base ALTO protocol for the accept input
   parameters, they have different media types for responses.  If the
   ALTO server provides these two types of resources, but the ALTO
   client does not support them, the ALTO client will ignore the
   resources without conducting any incompatibility.




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7.2.  Compatibility with Multi-Cost Extension

   This document does not specify how to integrate the "path-vector"
   cost mode with the multi-cost extension [RFC8189].  Although there is
   no reason why somebody has to compound the path vectors with other
   cost types in a single query, there is no compatible issue doing it
   without constraint tests.

7.3.  Compatibility with Incremental Update

   The extension specified in this document is NOT compatible with the
   original incremental update extension
   [I-D.ietf-alto-incr-update-sse].  A legacy ALTO client CANNOT
   recognize the compound client-id, and a legacy ALTO server MAY use
   the same client-id for updates of both parts.

   ALTO clients and servers MUST follow the specifications given in this
   document to ensure compatibility with the incremental update
   extension.

7.4.  Compatibility with Cost Calendar

   The extension specified in this document is compatible with the Cost
   Calendar extension [I-D.ietf-alto-cost-calendar].  When used together
   with the Cost Calendar extension, the cost value between a source and
   a destination is an array of path vectors, where the k-th path vector
   refers to the abstract network paths traversed in the k-th time
   interval by traffic from the source to the destination.

   When used with time-varying properties, e.g., maximum reservable
   bandwidth (maxresbw), a property of a single entity may also have
   different values in different time intervals.  In this case, an ANE
   with different property values MUST be considered as different ANEs.

   The two extensions combined together CAN provide the historical
   network correlation information for a set of source and destination
   pairs.  A network broker or client MAY use this information to derive
   other resource requirements such as Time-Block-Maximum Bandwidth,
   Bandwidth-Sliding-Window, and Time-Bandwidth-Product (TBP) (See
   [SENSE] for details.)

8.  General Discussions









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8.1.  Constraint Tests for General Cost Types

   The constraint test is a simple approach to query the data.  It
   allows users to filter the query result by specifying some boolean
   tests.  This approach is already used in the ALTO protocol.
   [RFC7285] and [RFC8189] allow ALTO clients to specify the
   "constraints" and "or-constraints" tests to better filter the result.

   However, the current defined syntax is too simple and can only be
   used to test the scalar cost value.  For more complex cost types,
   like the "array" mode defined in this document, it does not work
   well.  It will be helpful to propose more general constraint tests to
   better perform the query.

   In practice, it is too complex to customize a language for the
   general-purpose boolean tests, and can be a duplicated work.  So it
   may be a good idea to integrate some already defined and widely used
   query languages (or their subset) to solve this problem.  The
   candidates can be XQuery and JSONiq.

8.2.  General Multipart Resources Query

   Querying multiple ALTO information resources continuously MAY be a
   general requirement.  And the coming issues like inefficiency and
   inconsistency are also general.  There is no standard solving these
   issues yet.  So we need some approach to make the ALTO client request
   the compound ALTO information resources in a single query.

9.  Security Considerations

   This document is an extension of the base ALTO protocol, so the
   Security Considerations [RFC7285] of the base ALTO protocol fully
   apply when this extension is provided by an ALTO server.

   The path vector extension requires additional considerations on two
   security considerations discussed in the base protocol:
   confidentiality of ALTO information (Section 15.3 of [RFC7285]) and
   availability of ALTO service (Section 15.5 of [RFC7285]).

   For confidentiality of ALTO information, a network operator should be
   aware of that this extension may introduce a new risk: the path
   vector information may make network attacks easier.  For example, as
   the path vector information may reveal more fine-grained internal
   network structures than the base protocol, an ALTO client may detect
   the bottleneck link and start a distributed denial-of-service (DDoS)
   attack involving minimal flows to conduct the in-network congestion.





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   To mitigate this risk, the ALTO server should consider protection
   mechanisms to reduce information exposure or obfuscate the real
   information, in particular, in settings where the network and the
   application do not belong to the same trust domain.  But the
   implementation of path vector extension involving reduction or
   obfuscation should guarantee the constraints on the requested
   properties are still accurate.

   For availability of ALTO service, an ALTO server should be cognizant
   that using path vector extension might have a new risk: frequent
   requesting for path vectors might conduct intolerable increment of
   the server-side storage and break the ALTO server.  It is known that
   the computation of path vectors is unlikely to be cacheable, in that
   the results will depend on the particular requests (e.g., where the
   flows are distributed).  Hence, the service providing path vectors
   may become an entry point for denial-of-service attacks on the
   availability of an ALTO server.  To avoid this risk, authenticity and
   authorization of this ALTO service may need to be better protected.

10.  IANA Considerations

10.1.  ALTO Cost Mode Registry

   This document specifies a new cost mode "path-vector".  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.

10.2.  ALTO Entity Domain Registry

   This document registers a new entry to the ALTO Domain Entity
   Registry, as instructed by Section 9.2 of
   [I-D.ietf-alto-unified-props-new].  See below in Table 1.

    +------------+-------------------------+-------------------------+
    | Identifier | Entity Address Encoding | Hierarchy & Inheritance |
    +============+=========================+=========================+
    | ane        | See Section 4.2.2       | None                    |
    +------------+-------------------------+-------------------------+

                       Table 1: ALTO Entity Domain

10.3.  ALTO Entity Property Type Registry

   Two initial entries are registered to the ALTO Domain "ane" in the
   "ALTO Entity Property Type Registry".  See below in Table 2.




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             +-------------------------+--------------------+
             | Identifier              | Intended Semantics |
             +=========================+====================+
             | ane:maxresbw            | See Section 4.4.1  |
             +-------------------------+--------------------+
             | ane:persistent-entities | See Section 4.4.2  |
             +-------------------------+--------------------+

                Table 2: Initial Entries for ane Domain in
                 the ALTO Entity Property Types Registry

10.4.  ALTO Resource Entity Domain Export Registries

10.4.1.  costmap

                +--------------------+-------------------+
                | Entity Domain Type | Export Function   |
                +====================+===================+
                | ane                | See Section 4.3.1 |
                +--------------------+-------------------+

                   Table 3: ALTO Cost Map Entity Domain
                                  Export

10.4.2.  endpointcost

                +--------------------+-------------------+
                | Entity Domain Type | Export Function   |
                +====================+===================+
                | ane                | See Section 4.3.2 |
                +--------------------+-------------------+

                    Table 4: ALTO Endpoint Cost Entity
                              Domain Export

11.  Acknowledgments

   The authors would like to thank discussions with Andreas Voellmy,
   Erran Li, Haibin Song, Haizhou Du, Jiayuan Hu, Qiao Xiang, Tianyuan
   Liu, Xiao Shi, Xin Wang, and Yan Luo. The authors thank Greg
   Bernstein (Grotto Networks), Dawn Chen (Tongji University), Wendy
   Roome, and Michael Scharf for their contributions to earlier drafts.

12.  References

12.1.  Normative References





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   [I-D.ietf-alto-cost-calendar]
              Randriamasy, S., Yang, Y., WU, Q., Lingli, D., and N.
              Schwan, "Application-Layer Traffic Optimization (ALTO)
              Cost Calendar", Work in Progress, Internet-Draft, draft-
              ietf-alto-cost-calendar-19, 2 March 2020,
              <http://www.ietf.org/internet-drafts/draft-ietf-alto-cost-
              calendar-19.txt>.

   [I-D.ietf-alto-incr-update-sse]
              Roome, W. and Y. Yang, "ALTO Incremental Updates Using
              Server-Sent Events (SSE)", Work in Progress, Internet-
              Draft, draft-ietf-alto-incr-update-sse-20, 20 February
              2020, <http://www.ietf.org/internet-drafts/draft-ietf-
              alto-incr-update-sse-20.txt>.

   [I-D.ietf-alto-performance-metrics]
              WU, Q., Yang, Y., Lee, Y., Dhody, D., and S. Randriamasy,
              "ALTO Performance Cost Metrics", Work in Progress,
              Internet-Draft, draft-ietf-alto-performance-metrics-08, 4
              November 2019, <http://www.ietf.org/internet-drafts/draft-
              ietf-alto-performance-metrics-08.txt>.

   [I-D.ietf-alto-unified-props-new]
              Roome, W., Randriamasy, S., Yang, Y., Zhang, J., and K.
              Gao, "Unified Properties for the ALTO Protocol", Work in
              Progress, Internet-Draft, draft-ietf-alto-unified-props-
              new-10, 4 November 2019, <http://www.ietf.org/internet-
              drafts/draft-ietf-alto-unified-props-new-10.txt>.

   [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>.

12.2.  Informative References

   [AAAI2019] Xiang, Q., Yu, H., Aspnes, J., Le, F., Kong, L., and Y.R.
              Yang, "Optimizing in the dark: Learning an optimal



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              solution through a simple request interface", Proceedings
              of the AAAI Conference on Artificial Intelligence 33,
              1674-1681 , 2019.

   [I-D.bernstein-alto-topo]
              Bernstein, G., Yang, Y., and Y. Lee, "ALTO Topology
              Service: Uses Cases, Requirements, and Framework", Work in
              Progress, Internet-Draft, draft-bernstein-alto-topo-00, 21
              October 2013, <http://www.ietf.org/internet-drafts/draft-
              bernstein-alto-topo-00.txt>.

   [I-D.contreras-alto-service-edge]
              Contreras, L., Perez, D., and C. Rothenberg, "Use of ALTO
              for Determining Service Edge", Work in Progress, Internet-
              Draft, draft-contreras-alto-service-edge-00, 4 November
              2019, <http://www.ietf.org/internet-drafts/draft-
              contreras-alto-service-edge-00.txt>.

   [I-D.huang-alto-mowie-for-network-aware-app]
              "TBD", 2020.

   [I-D.ietf-dmm-5g-uplane-analysis]
              Homma, S., Miyasaka, T., Matsushima, S., and D. Voyer,
              "User Plane Protocol and Architectural Analysis on 3GPP 5G
              System", Work in Progress, Internet-Draft, draft-ietf-dmm-
              5g-uplane-analysis-03, 3 November 2019,
              <http://www.ietf.org/internet-drafts/draft-ietf-dmm-5g-
              uplane-analysis-03.txt>.

   [I-D.yang-alto-deliver-functions-over-networks]
              Yang, S., Cui, L., Xu, M., Shen, H., and L. Chen,
              "Delivering Functions over Networks: Traffic and
              Performance Optimization for Edge Computing using ALTO",
              Work in Progress, Internet-Draft, draft-yang-alto-deliver-
              functions-over-networks-00, 29 November 2019,
              <http://www.ietf.org/internet-drafts/draft-yang-alto-
              deliver-functions-over-networks-00.txt>.

   [LHC]      "CERN - LHC", 2019, <https://atlas.cern/tags/lhc>.

   [SENSE]    "Services - SENSE", 2019, <http://sense.es.net/services>.

   [TON2019]  Gao, K., Xiang, Q., Wang, X., Yang, Y.R., and J. Bi, "An
              objective-driven on-demand network abstraction for
              adaptive applications", IEEE/ACM Transactions on
              Networking (TON) Vol 27, no. 2 (2019): 805-818., 2019.





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Appendix A.  Changes since -08

   This revision

   *  fixes a few spelling errors

   *  emphasizes that abstract network elements can be generated on
      demand in both introduction and motivating use cases

Appendix B.  Changes Since Version -06

   *  We emphasize the importance of the path vector extension in two
      aspects:

      1.  It expands the problem space that can be solved by ALTO, from
          preferences of network paths to correlations of network paths.

      2.  It is motivated by new usage scenarios from both application's
          and network's perspectives.

   *  More use cases are included, in addition to the original capacity
      region use case.

   *  We add more discussions to fully explore the design space of the
      path vector extension and justify our design decisions, including
      the concept of abstract network element, cost type (reverted to
      -05), newer capabilities and the multipart message.

   *  Fix the incremental update process to be compatible with SSE -16
      draft, which uses client-id instead of resource-id to demultiplex
      updates.

   *  Register an additional ANE property (i.e., persistent-entities) to
      cover all use cases mentioned in the draft.

Authors' Addresses

   Kai Gao
   China
   610000
   Chengdu
   No.24 South Section 1, Yihuan Road
   Sichuan University

   Email: kaigao@scu.edu.cn


   Young Lee



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   Sabine Randriamasy
   Nokia Bell Labs
   Route de Villejust
   91460 Nozay
   France

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


   Yang Richard Yang
   Yale University
   51 Prospect Street
   New Haven,  CT
   United States of America

   Email: yry@cs.yale.edu


   Jingxuan Jensen Zhang
   China
   201804
   Shanghai
   4800 Caoan Road
   Tongji University

   Email: jingxuan.n.zhang@gmail.com

























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