\
ALTO                                                              K. Gao
Internet-Draft                                        Sichuan University
Intended status: Experimental                                     Y. Lee
Expires: 21 September 2022                                       Samsung
                                                          S. Randriamasy
                                                         Nokia Bell Labs
                                                               Y.R. Yang
                                                         Yale University
                                                                J. Zhang
                                                       Tongji University
                                                           20 March 2022


                     An ALTO Extension: Path Vector
                     draft-ietf-alto-path-vector-25

Abstract

   This document is an extension to the base Application-Layer Traffic
   Optimization (ALTO) protocol.  It extends the ALTO Cost Map and ALTO
   Property Map services so that an application can decide which
   endpoint(s) to connect based on not only numerical/ordinal cost
   values but also fine-grained abstract information of the paths.  This
   is useful for applications whose performance is impacted by specified
   components of a network on the end-to-end paths, e.g., they may infer
   that several paths share common links and prevent traffic bottlenecks
   by avoiding such paths.  This extension introduces a new abstraction
   called Abstract Network Element (ANE) to represent these components
   and encodes a network path as a vector of ANEs.  Thus, it provides a
   more complete but still abstract graph representation of the
   underlying network(s) for informed traffic optimization among
   endpoints.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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

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




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   This Internet-Draft will expire on 21 September 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements Languages  . . . . . . . . . . . . . . . . . . .   6
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Requirements and Use Cases  . . . . . . . . . . . . . . . . .   7
     4.1.  Design Requirements . . . . . . . . . . . . . . . . . . .   7
     4.2.  Sample Use Cases  . . . . . . . . . . . . . . . . . . . .  10
       4.2.1.  Exposing Network Bottlenecks  . . . . . . . . . . . .  11
       4.2.2.  Resource Exposure for CDN and Service Edge  . . . . .  15
   5.  Path Vector Extension: Overview . . . . . . . . . . . . . . .  17
     5.1.  Abstract Network Element (ANE)  . . . . . . . . . . . . .  18
       5.1.1.  ANE Entity Domain . . . . . . . . . . . . . . . . . .  19
       5.1.2.  Ephemeral and Persistent ANEs . . . . . . . . . . . .  19
       5.1.3.  Property Filtering  . . . . . . . . . . . . . . . . .  20
     5.2.  Path Vector Cost Type . . . . . . . . . . . . . . . . . .  20
     5.3.  Multipart Path Vector Response  . . . . . . . . . . . . .  21
       5.3.1.  Identifying the Media Type of the Root Object . . . .  22
       5.3.2.  References to Part Messages . . . . . . . . . . . . .  22
   6.  Specification: Basic Data Types . . . . . . . . . . . . . . .  23
     6.1.  ANE Name  . . . . . . . . . . . . . . . . . . . . . . . .  23
     6.2.  ANE Entity Domain . . . . . . . . . . . . . . . . . . . .  23
       6.2.1.  Entity Domain Type  . . . . . . . . . . . . . . . . .  23
       6.2.2.  Domain-Specific Entity Identifier . . . . . . . . . .  23
       6.2.3.  Hierarchy and Inheritance . . . . . . . . . . . . . .  23
       6.2.4.  Media Type of Defining Resource . . . . . . . . . . .  23
     6.3.  ANE Property Name . . . . . . . . . . . . . . . . . . . .  24
     6.4.  Initial ANE Property Types  . . . . . . . . . . . . . . .  24
       6.4.1.  Maximum Reservable Bandwidth  . . . . . . . . . . . .  24
       6.4.2.  Persistent Entity ID  . . . . . . . . . . . . . . . .  25
       6.4.3.  Examples  . . . . . . . . . . . . . . . . . . . . . .  25
     6.5.  Path Vector Cost Type . . . . . . . . . . . . . . . . . .  26



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       6.5.1.  Cost Metric: ane-path . . . . . . . . . . . . . . . .  26
       6.5.2.  Cost Mode: array  . . . . . . . . . . . . . . . . . .  27
     6.6.  Part Resource ID and Part Content ID  . . . . . . . . . .  27
   7.  Specification: Service Extensions . . . . . . . . . . . . . .  27
     7.1.  Notations . . . . . . . . . . . . . . . . . . . . . . . .  27
     7.2.  Multipart Filtered Cost Map for Path Vector . . . . . . .  28
       7.2.1.  Media Type  . . . . . . . . . . . . . . . . . . . . .  28
       7.2.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . .  28
       7.2.3.  Accept Input Parameters . . . . . . . . . . . . . . .  28
       7.2.4.  Capabilities  . . . . . . . . . . . . . . . . . . . .  29
       7.2.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . .  30
       7.2.6.  Response  . . . . . . . . . . . . . . . . . . . . . .  30
     7.3.  Multipart Endpoint Cost Service for Path Vector . . . . .  34
       7.3.1.  Media Type  . . . . . . . . . . . . . . . . . . . . .  34
       7.3.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . .  34
       7.3.3.  Accept Input Parameters . . . . . . . . . . . . . . .  34
       7.3.4.  Capabilities  . . . . . . . . . . . . . . . . . . . .  35
       7.3.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . .  35
       7.3.6.  Response  . . . . . . . . . . . . . . . . . . . . . .  35
   8.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  39
     8.1.  Sample Setup  . . . . . . . . . . . . . . . . . . . . . .  39
     8.2.  Information Resource Directory  . . . . . . . . . . . . .  39
     8.3.  Multipart Filtered Cost Map . . . . . . . . . . . . . . .  42
     8.4.  Multipart Endpoint Cost Service Resource  . . . . . . . .  43
     8.5.  Incremental Updates . . . . . . . . . . . . . . . . . . .  48
     8.6.  Multi-cost  . . . . . . . . . . . . . . . . . . . . . . .  50
   9.  Compatibility with Other ALTO Extensions  . . . . . . . . . .  52
     9.1.  Compatibility with Legacy ALTO Clients/Servers  . . . . .  53
     9.2.  Compatibility with Multi-Cost Extension . . . . . . . . .  53
     9.3.  Compatibility with Incremental Update . . . . . . . . . .  53
     9.4.  Compatibility with Cost Calendar  . . . . . . . . . . . .  53
   10. General Discussions . . . . . . . . . . . . . . . . . . . . .  54
     10.1.  Constraint Tests for General Cost Types  . . . . . . . .  54
     10.2.  General Multi-Resource Query . . . . . . . . . . . . . .  54
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  55
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  57
     12.1.  ALTO Cost Metric Registry  . . . . . . . . . . . . . . .  57
     12.2.  ALTO Cost Mode Registry  . . . . . . . . . . . . . . . .  58
     12.3.  ALTO Entity Domain Type Registry . . . . . . . . . . . .  58
     12.4.  ALTO Entity Property Type Registry . . . . . . . . . . .  59
       12.4.1.  New ANE Property Type: Maximum Reservable
               Bandwidth . . . . . . . . . . . . . . . . . . . . . .  59
       12.4.2.  New ANE Property Type: Persistent Entity ID  . . . .  60
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  60
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  60
     13.2.  Informative References . . . . . . . . . . . . . . . . .  61
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  64
   Appendix B.  Revision Logs (To be removed before publication) . .  64



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     B.1.  Changes since -20 . . . . . . . . . . . . . . . . . . . .  64
     B.2.  Changes since -19 . . . . . . . . . . . . . . . . . . . .  65
     B.3.  Changes since -18 . . . . . . . . . . . . . . . . . . . .  65
     B.4.  Changes since -17 . . . . . . . . . . . . . . . . . . . .  65
     B.5.  Changes since -16 . . . . . . . . . . . . . . . . . . . .  65
     B.6.  Changes since -15 . . . . . . . . . . . . . . . . . . . .  65
     B.7.  Changes since -14 . . . . . . . . . . . . . . . . . . . .  65
     B.8.  Changes since -13 . . . . . . . . . . . . . . . . . . . .  66
     B.9.  Changes since -12 . . . . . . . . . . . . . . . . . . . .  66
     B.10. Changes since -11 . . . . . . . . . . . . . . . . . . . .  66
     B.11. Changes since -10 . . . . . . . . . . . . . . . . . . . .  66
     B.12. Changes since -09 . . . . . . . . . . . . . . . . . . . .  67
     B.13. Changes since -08 . . . . . . . . . . . . . . . . . . . .  67
     B.14. Changes Since Version -06 . . . . . . . . . . . . . . . .  67
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  68

1.  Introduction

   Network performance metrics are crucial to assess the Quality of
   Experience (QoE) of 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 perceived QoE by
   better orchestrating their traffic to utilize the resources in the
   underlying network infrastructure.

   Existing ALTO Cost Map (Section 11.2.3 of [RFC7285]) and Endpoint
   Cost Service (Section 11.5 of [RFC7285]) provide only cost
   information on an end-to-end path defined by its <source,
   destination> endpoints: The base protocol [RFC7285] allows the
   services to expose the topological distances of end-to-end paths,
   while various extensions have been proposed to extend the capability
   of these services, e.g., to express other performance metrics
   [I-D.ietf-alto-performance-metrics], to query multiple costs
   simultaneously [RFC8189], and to obtain the time-varying values
   [RFC8896].

   While the existing extensions are sufficient for many overlay
   applications, the QoE of some overlay applications depends not only
   on the cost information of end-to-end paths, but also on particular
   components of a network on the paths 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
   bottleneck links inside the carrier network as link capacity may
   impact the rate of data input/output to the job.  We refer to such
   components of a network as Abstract Network Elements (ANE).





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   Predicting such information can be very complex without the help of
   ISPs, for example, [BOXOPT] has shown that finding the optimal
   bandwidth reservation for multiple flows can be NP-hard without
   further information than whether a reservation succeeds.  With proper
   guidance from the ISP, an overlay application may be able to schedule
   its traffic for better QoE.  In the meantime, it may be helpful as
   well for ISPs if applications could avoid using bottlenecks or
   challenging the network with poorly scheduled traffic.

   Despite the claimed benefits, ISPs are not likely to expose raw
   details on their network paths: first for the sake of topology hiding
   requirement, second because it may increase volume and computation
   overhead, and last because applications do not necessarily need all
   the network path details and are likely not able to understand them.

   Therefore, it is beneficial for both ISPs and applications if an ALTO
   server provides ALTO clients with an "abstract network state" that
   provides the necessary information to applications, while hiding the
   network complexity and confidential information.  An "abstract
   network state" is a selected set of abstract representations of
   Abstract Network Elements traversed by the paths between <source,
   destination> pairs combined with properties of these Abstract Network
   Elements 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 Abstract Network Elements.  Server
   scalability can also be improved by combining Abstract Network
   Elements and their properties in a single response.

   This document extends [RFC7285] to allow an ALTO server to convey
   "abstract network state", for paths defined by their <source,
   destination> pairs.  To this end, it introduces a new cost type
   called "Path Vector" following the cost metric registration specified
   in [RFC7285] and the updated cost mode registration specified in
   [I-D.bw-alto-cost-mode].  A Path Vector is an array of identifiers
   that identifies an Abstract Network Element, which 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 of an ALTO server when providing Path Vector
   service.  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 involves two ALTO Maps: the Cost Map that
   contains the Path Vector results and the up-to-date Unified Property



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   Map that contains the properties requested for these ANEs.  To
   enforce consistency and improve server scalability, this document
   uses the "multipart/related" content type defined in [RFC2387] to
   return the two maps in a single response.

   As a single ISP may not have the knowledge of the full Internet paths
   between arbitrary endpoints, this document is mainly applicable 1)
   when there is a single ISP between the requested source and
   destination PIDs or endpoints, for example, ISP-hosted CDN/edge,
   tenant interconnection in a single public cloud platform, etc.; or 2)
   when the Path Vectors are generated from end-to-end measurement data.

2.  Requirements Languages

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   When the words appear in lower case, they are to be interpreted with
   their natural language meanings.

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:

   Abstract Network Element (ANE):  An abstract representation for a
      component in a network that handles data packets and whose
      properties can potentially have an impact on the end-to-end
      performance of traffic.  An ANE can be a physical device such as a
      router, a link or an interface, or an aggregation of devices such
      as a subnetwork or a data center.

      The definition of Abstract Network Element is similar to Network
      Element defined in [RFC2216] in the sense that they both provide
      an abstract representation of specific components of a network.
      However, they have different criteria on how these particular
      components are selected.  Specifically, a Network Element requires
      the components to be capable of exercising QoS control, while
      Abstract Network Element only requires the components to have an
      impact on the end-to-end performance.

   ANE Name:  A string that uniquely identifies an ANE in a specific




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      scope.  An ANE can be constructed either statically in advance or
      on demand based on the requested information.  Thus, different
      ANEs may only be valid within a particular scope, either ephemeral
      or persistent.  Within each scope, an ANE is uniquely identified
      by an ANE Name, as defined in Section 6.1.  Note that an ALTO
      client must not assume ANEs in different scopes but with the same
      ANE Name refer to the same component(s) of the network.

   Path Vector:  Path Vector, or ANE Path Vector, refers to a JSON array
      of ANE Names.  It is a generalization of BGP path vector.  While
      standard BGP path vector (Section 5.1.2 of [RFC4271]) specifies a
      sequence of autonomous systems for a destination IP prefix, the
      Path Vector defined in this extension specifies a sequence of ANEs
      either for a source Provider-Defined Identifier (PID) and a
      destination PID as in the CostMapData (11.2.3.6 in [RFC7285]), or
      for a source endpoint and a destination endpoint as in the
      EndpointCostMapData object (Section 11.5.1.6 of [RFC7285]).

   Path Vector resource:  An ALTO information resource (Section 8.1 of
      [RFC7285]) which supports the extension defined in this document.

   Path Vector cost type:  A special cost type, which is specified in
      Section 6.5.  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 Filtered Cost Map request or
      an Endpoint Cost Service request, it indicates each cost value
      must be interpreted as a Path Vector.

   Path Vector request:  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.

4.  Requirements and Use Cases

4.1.  Design Requirements

   This section gives an illustrative example of how an overlay
   application can benefit from the extension defined in this document.

   Assume that an application has control over a set of flows, which may
   go through shared links/nodes and share bottlenecks.  The application
   seeks to schedule the traffic among multiple flows to get better
   performance.  The constraints of feasible rate allocations of those
   flows will benefit the scheduling.  However, Cost Maps as defined in
   [RFC7285] can not reveal such information.




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   Specifically, consider a network as shown in Figure 1.  The network
   has 7 switches (sw1 to sw7) forming a dumb-bell topology.  Switches
   "sw1", "sw2", "sw3" and "sw4" are access switches, 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 is 150 Mbps, and the bandwidth of the other
   links is 100 Mbps.

                                 +-----+
                                 |     |
                               --+ sw6 +--
                              /  |     |  \
        PID1 +-----+         /   +-----+   \          +-----+  PID2
        eh1__|     |_       /               \     ____|     |__eh2
   192.0.2.2 | sw1 | \   +--|--+         +--|--+ /    | sw2 | 192.0.2.3
             +-----+  \  |     |         |     |/     +-----+
                       \_| sw5 +---------+ sw7 |
        PID3 +-----+   / |     |         |     |\     +-----+  PID4
        eh3__|     |__/  +-----+         +-----+ \____|     |__eh4
   192.0.2.4 | sw3 |                                  | sw4 | 192.0.2.5
             +-----+                                  +-----+

   bw(eh1--sw1) = bw(sw1--sw5) = 150 Mbps
   bw(eh2--sw2) = bw(eh3--sw3) = bw(eh4--sw4) = 100 Mbps
   bw(sw1--sw5) = bw(sw3--sw5) = bw(sw2--sw7) = bw(sw4--sw7) = 100 Mbps
   bw(sw5--sw6) = bw(sw5--sw7) = bw(sw6--sw7) = 100 Mbps

                       Figure 1: Raw Network Topology

   The base ALTO topology abstraction of the network is shown in
   Figure 2.  Assume the cost map returns an hypothetical cost type
   representing the available bandwidth between a source and a
   destination.

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

                    Figure 2: Base Topology Abstraction




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   Now assume the application wants to maximize the total rate of the
   traffic among a set of <source, destination> pairs, say "eh1 -> eh2"
   and "eh1 -> eh4".  Let "x" denote the transmission rate of "eh1 ->
   eh2" and "y" denote the rate of "eh1 -> eh4".  The objective function
   is

       max(x + y).

   With the ALTO Cost Map, the cost between PID1 and PID2 and between
   PID1 and PID4 will both be 100 Mbps.  The client can get a capacity
   region of

       x <= 100 Mbps,
       y <= 100 Mbps.

   With this information, the client may mistakenly think it can achieve
   a maximum total rate of 200 Mbps.  However, this rate is infeasible,
   as there are only two potential cases:

   *  Case 1: "eh1 -> eh2" and "eh1 -> eh4" take different path segments
      from "sw5" to "sw7".  For example, if "eh1 -> eh2" uses path "eh1
      -> sw1 -> sw5 -> sw6 -> sw7 -> sw2 -> eh2" and "eh1 -> eh4" uses
      path "eh1 -> sw1 -> sw5 -> sw7 -> sw4 -> eh4", then the shared
      bottleneck links are "eh1 -> sw1" and "sw1 -> sw5".  In this case,
      the capacity region is:

          x     <= 100 Mbps
          y     <= 100 Mbps
          x + y <= 150 Mbps

      and the real optimal total rate is 150 Mbps.

   *  Case 2: "eh1 -> eh2" and "eh1 -> eh4" take the same path segment
      from "sw5" to "sw7".  For example, if "eh1 -> eh2" uses path "eh1
      -> sw1 -> sw5 -> sw7 -> sw2 -> eh2" and "eh1 -> eh4" also uses
      path "eh1 -> sw1 -> sw5 -> sw7 -> sw4 -> eh4", then the shared
      bottleneck link is "sw5 -> sw7".  In this case, the capacity
      region is:

          x     <= 100 Mbps
          y     <= 100 Mbps
          x + y <= 100 Mbps

      and the real optimal total rate is 100 Mbps.







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   Clearly, with more accurate and fine-grained information, the
   application can gain a better prediction of its traffic and may
   orchestrate its resources accordingly.  However, to provide such
   information, the network needs to expose abstract information beyond
   the simple cost map abstraction.  In particular:

   *  The ALTO server must expose abstract information about the network
      paths that are traversed by the traffic between a source and a
      destination beyond a simple numerical value, which allows the
      overlay application to distinguish between Cases 1 and 2 and to
      compute the optimal total rate accordingly.

   *  The ALTO server must allow the client to distinguish the common
      ANE shared by "eh1 -> eh2" and "eh1 -> eh4", e.g., "eh1 - sw1" and
      "sw1 - sw5" in Case 1.

   *  The ALTO server must expose abstract information on the properties
      of the ANEs used by "eh1 -> eh2" and "eh1 -> eh4".  For example,
      an ALTO server can either expose the available bandwidth between
      "eh1 - sw1", "sw1 - sw5", "sw5 - sw7", "sw5 - sw6", "sw6 - sw7",
      "sw7 - sw2", "sw7 - sw4", "sw2 - eh2", "sw4 - eh4" in Case 1, or
      expose 3 abstract elements "A", "B" and "C", which represent the
      linear constraints that define the same capacity region in Case 1.

   In general, we can conclude that to support the multiple flow
   scheduling use case, the ALTO framework must be extended to satisfy
   the following additional requirements:

   AR1:  An ALTO server must provide the ANEs that are important to
      assess the QoE of the overlay application on the path of a
      <source, destination> pair.

   AR2:  An ALTO server must provide information to identify how ANEs
      are shared on the paths of different <source, destination> pairs.

   AR3:  An ALTO server must provide information on the properties that
      are important to assess the QoE of the application for ANEs.

   The extension defined in this document specifies a solution to expose
   such abstract information.

4.2.  Sample Use Cases

   While the multiple flow scheduling problem is used to help identify
   the additional requirements, the extension defined in this document
   can be applied to a wide range of applications.  This section
   highlights some use cases that are reported.




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4.2.1.  Exposing Network Bottlenecks

   An important use case of the Path Vector extension is to expose
   network bottlenecks.  Applications which need to perform large scale
   data transfers can benefit from being aware of the resource
   constraints exposed by this extension even if they have different
   objectives.  One such example is the Worldwide LHC Computing Grid
   (WLCG), the largest example of a distributed computation
   collaboration in the research and education world.

   Figure 3 illustrates an example of using ALTO Path Vector as an
   interface between the job optimizer for a data analytics system and
   the network manager.  In particular, we assume the objective of the
   job optimizer is to minimize the job completion time.

   In such a setting, the network-aware job optimizer (e.g., [CLARINET])
   takes a query and generates multiple query execution plans (QEP).  It
   can encode the QEPs as Path Vector requests that are send to an ALTO
   server.  The ALTO server obtains the routing information for the
   flows in a QEP and finds links, routers, or middleboxes (e.g., a
   stateful firewall) that can potentially become bottlenecks of the QEP
   (e.g., see [NOVA] and [G2] for mechanisms to identify bottleneck
   links under different settings).  The resource constraint information
   is encoded in a Path Vector response and returned to the ALTO client.

   With the network resource constraints, the job optimizer may choose
   the QEP with the optimal job completion time to be executed.  It must
   be noted that the ALTO framework itself does not offer the capability
   to control the traffic.  However, certain network managers may offer
   ways to enforce resource guarantees, such as on-demand tunnels (e.g.,
   [SWAN]), demand vector (e.g., [HUG], [UNICORN]), etc.  The traffic
   control interfaces and mechanisms are out of the scope of this
   document.


















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                                     Data schema      Queries
                                          |             |
                                          \             /
       +-------------+                   +-----------------+
       | ALTO Client | <===============> |  Job Optimizer  |
       +-------------+                   +-----------------+
   PV       |   ^ PV                                    |
   Request  |   | Response                              |
            |   |                  On-demand resource   |
   (Data    |   | (Network         allocation, demand   |
   Transfer |   | Resource         vector, etc.         |
   Intents) |   | Constraints)     (Non-ALTO interfaces)|
            v   |                                       v
       +-------------+                   +-----------------+
       | ALTO Server | <===============> | Network Manager |
       +-------------+                   +-----------------+
                                           /      |      \
                                           |      |      |
                                          WAN    DC1    DC2

               Figure 3: Example Use Case for Data Analytics

   Another example is as illustrated in Figure 4.  Consider a network
   consisting of multiple sites and a non-blocking core network, i.e.,
   the links in the core network have sufficient bandwidth that they
   will not become the bottleneck of the data transfers.

























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                  On-going transfers   New transfer requests
                                \----\        |
                                     |        |
                                     v        v
      +-------------+               +---------------+
      | ALTO Client | <===========> | Data Transfer |
      +-------------+               |   Scheduler   |
        ^ |      ^ | PV request     +---------------+
        | |      | \--------------\
        | |      \--------------\ |
        | v       PV response   | v
      +-------------+          +-------------+
      | ALTO Server |          | ALTO Server |
      +-------------+          +-------------+
            ||                       ||
        +---------+              +---------+
        | Network |              | Network |
        | Manager |              | Manager |
        +---------+              +---------+
         .                           .
        .             _~_  __         . . .
       .             (   )(  )             .___
     ~v~v~       /--(         )------------(   )
    (     )-----/    (       )            (     )
     ~w~w~            ~^~^~^~              ~v~v~
    Site 1        Non-blocking Core        Site 2

       Figure 4: Example Use Case for Cross-site Bottleneck Discovery























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   Site 1:

   [c]
    .
    ........................................> [d]
     +---+ 10 Gbps +---+ 10 Gbps +----+ 50 Gbps
     | A |---------| B |---------| GW |--------- Core
     +---+         +---+         +----+
    ...................
    .                 .
    .                 v
   [a]               [b]

   Site 2:

   [d] <........................................ [c]
     +---+ 5 Gbps +---+ 10 Gbps +----+ 20 Gbps
     | X |--------| Y |---------| GW |--------- Core
     +---+        +---+         +----+
                ....................
                .                  .
                .                  v
               [e]                [f]

                Figure 5: Example: Three Flows in Two Sites

   With the Path Vector extension, a site can reveal the bottlenecks
   inside its own network with necessary information (such as link
   capacities) to the ALTO client, instead of providing the full
   topology and routing information, or no bottleneck information at
   all.  The bottleneck information can be used to analyze the impact of
   adding/removing data transfer flows, e.g., using the [G2] framework.
   For example, assume hosts "a", "b", "c" are in site 1 and hosts "d",
   "e", "f" are in site 2, and there are 3 flows in two sites: "a -> b",
   "c -> d", "e -> f".  For these flows, site 1 returns:

   a: { b: [ane1] },
   c: { d: [ane1, ane2, ane3] }

   ane1: bw = 10 Gbps (link: A->B)
   ane2: bw = 10 Gbps (link: B->GW)
   ane3: bw = 50 Gbps (link: GW->Core)

   and site 2 returns:







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   c: { d: [anei, aneii, aneiii] }
   e: { f: [aneiv] }

   anei: bw = 5 Gbps (link Y->X)
   aneii: bw = 10 Gbps (link GW->Y)
   aneiii: bw = 20 Gbps (link Core->GW)
   aneiv: bw = 10 Gbps (link Y->GW)

   With the information, the data transfer scheduler can use algorithms
   such as the theory on bottleneck structure [G2] to predict the
   potential throughput of the flows.

4.2.2.  Resource Exposure for CDN and Service Edge

   A growing trend in today's applications (2021) is to bring storage
   and computation closer to the end users for better QoE, such as
   Content Delivery Network (CDN), AR/VR, and cloud gaming, as reported
   in various documents (e.g., [SEREDGE] and [MOWIE]).  Internet Service
   Providers may deploy multiple layers of CDN caches, or more generally
   service edges, with different latency and available resources
   including number of CPU cores, memory, and storage.

   For example, Figure 6 illustrates a typical edge-cloud scenario where
   memory is measured in Gigabytes (G) and storage is measured in
   Terabytes (T).  The "on-premise" edge nodes are closest to the end
   hosts and have the smallest latency, and the site-radio edge node and
   access central office (CO) have larger latency but more available
   resources.























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         +-------------+              +----------------------+
         | ALTO Client | <==========> | Application Provider |
         +-------------+              +----------------------+
   PV         |   ^ PV                      |
   Request    |   | Response                | Resource allocation,
              |   |                         | service establishment,
   (End hosts |   | (Edge nodes             | etc.
   and cloud  |   | and metrics)            |
   servers)   |   |                         |
              v   |                         v
         +-------------+             +---------------------+
         | ALTO Server | <=========> | Cloud-Edge Provider |
         +-------------+             +---------------------+
          ____________________________________/\___________
         /                                                 \
         |           (((o                                  |
                        |
                       /_\             _~_            __   __
     a               (/\_/\)          (   )          (  )~(  )_
      \      /------(      )---------(     )----\\---(          )
      _|_   /        (______)         (___)          (          )
      |_| -/         Site-radio     Access CO       (__________)
     /---\          Edge Node 1         |             Cloud DC
   On premise                           |
                              /---------/
              (((o           /
                 |          /
    Site-radio  /_\        /
   Edge Node 2(/\_/\)-----/
             /(_____)\
      ___   /         \   ---
   b--|_| -/           \--|_|--c
     /---\               /---\
   On premise          On premise

            Figure 6: Example Use Case for Service Edge Exposure















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   a: { b: [ane1, ane2, ane3, ane4, ane5],
        c: [ane1, ane2, ane3, ane4, ane6],
        DC: [ane1, ane2, ane3] }
   b: { c: [ane5, ane4, ane6], DC: [ane5, ane4, ane3] }

   ane1: latency=5ms cpu=2 memory=8G storage=10T
   (on premise, a)

   ane2: latency=20ms cpu=4 memory=8G storage=10T
   (Site-radio Edge Node 1)

   ane3: latency=100ms cpu=8 memory=128G storage=100T
   (Access CO)

   ane4: latency=20ms cpu=4 memory=8G storage=10T
   (Site-radio Edge Node 2)

   ane5: latency=5ms cpu=2 memory=8G storage=10T
   (on premise, b)

   ane6: latency=5ms cpu=2 memory=8G storage=10T
   (on premise, c)

                Figure 7: Example Service Edge Query Results

   With the extension defined in this document, an ALTO server can
   selectively reveal the CDNs and service edges that reside along the
   paths between different end hosts and/or the cloud servers, together
   with their properties such as capabilities (e.g., storage, GPU) and
   available Service Level Agreement (SLA) plans.  See Figure 7 for an
   example where the query is made for sources [a, b] and destinations
   [b, c, DC].  Here each ANE represents a service edge and the
   properties include access latency, available resources, etc.  Note
   the properties here are only used for illustration purposes and are
   not part of this extension.

   With the service edge information, an ALTO client may better conduct
   CDN request routing or offload functionalities from the user
   equipment to the service edge, with considerations on customized
   quality of experience.

5.  Path Vector Extension: Overview

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




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   To satisfy the additional requirements listed in Section 4.1, this
   extension:

   1.  introduces the concept of Abstract Network Element (ANE) as the
       abstraction of components in a network whose properties may have
       an impact on the end-to-end performance of the traffic handled by
       those components,

   2.  extends the Cost Map and Endpoint Cost Service to convey the ANEs
       traversed by the path of a <source, destination> pair as Path
       Vectors, and

   3.  uses the Unified Property Map to convey the association between
       the ANEs and their properties.

   Thus, an ALTO client can learn about the ANEs that are important to
   assess the QoE of different <source, destination> pairs by
   investigating the corresponding Path Vector value (AR1), identify
   common ANEs if an ANE appears in the Path Vectors of multiple
   <source, destination> pairs (AR2), and retrieve the properties of the
   ANEs by searching the Unified Property Map (AR3).

5.1.  Abstract Network Element (ANE)

   This extension introduces ANE as an indirect and network-agnostic way
   to specify a component or an aggregation of components of a network
   whose properties have an impact on the end-to-end performance for
   application traffic between endpoints.

   ANEs allow ALTO servers to focus on common properties of different
   types of network components.  For example, the throughput of a flow
   can be constrained by different components in a network: the capacity
   of a physical link, the maximum throughput of a firewall, the
   reserved bandwidth of an MPLS tunnel, etc.  See the example below,
   assume the throughput of the firewall is 100 Mbps and the capacity
   for link (A, B) is also 100 Mbps, they result in the same constraint
   on the total throughput of f1 and f2.  Thus, they are identical when
   treated as an ANE.

      f1 |      ^                  f1
         |      |                 ----------------->
       +----------+                +---+     +---+
       | Firewall |                | A |-----| B |
       +----------+                +---+     +---+
         |      |                 ----------------->
         v      | f2               f2





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   When an ANE is defined by an ALTO server, it is assigned an
   identifier by the ALTO server, i.e., a string of type ANEName as
   specified in Section 6.1, and a set of associated properties.

5.1.1.  ANE Entity Domain

   In this extension, the associations between ANE and the properties
   are conveyed in a Unified Property Map. Thus, ANEs must constitute an
   entity domain (Section 5.1 of [I-D.ietf-alto-unified-props-new]), and
   each ANE property must be an entity property (Section 5.2 of
   [I-D.ietf-alto-unified-props-new]).

   Specifically, this document defines a new entity domain called "ane"
   as specified in Section 6.2 and defines two initial properties for
   the ANE entity domain.

5.1.2.  Ephemeral and Persistent ANEs

   By design, ANEs are ephemeral and not to be used in further requests
   to other ALTO resources.  More precisely, the corresponding ANE names
   are no longer valid beyond the scope of a Path Vector response or the
   incremental update stream for a Path Vector request.  Compared with
   globally unique ANE names, ephemeral ANE has several benefits
   including better privacy of the ISP's internal structure and more
   flexible ANE computation.

   For example, an ALTO server may define an ANE for each aggregated
   bottleneck link between the sources and destinations specified in the
   request.  For requests with different sources and destinations, the
   bottlenecks may be different but can safely reuse the same ANE names.
   The client can still adjust its traffic based on the information but
   is difficult to infer the underlying topology with multiple queries.

   However, sometimes an ISP may intend to selectively reveal some
   "persistent" network components which, opposite to being ephemeral,
   have a longer life cycle.  For example, an ALTO server may define an
   ANE for each service edge cluster.  Once a client chooses to use a
   service edge, e.g., by deploying some user-defined functions, it may
   want to stick to the service edge to avoid the complexity of state
   transition or synchronization, and continuously query the properties
   of the edge cluster.

   This document provides a mechanism to expose such network components
   as persistent ANEs.  A persistent ANE has a persistent ID that is
   registered in a Property Map, together with their properties.  See
   Section 6.2.4 and Section 6.4.2 for more detailed instructions on how
   to identify ephemeral ANEs and persistent ANEs.




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5.1.3.  Property Filtering

   Resource-constrained ALTO clients (see Section 4.1.2 of [RFC7285])
   may benefit from the filtering of Path Vector query results at the
   ALTO server, as an ALTO client may only require a subset of the
   available properties.

   Specifically, the available properties for a given resource are
   announced in the Information Resource Directory as a new capability
   called "ane-property-names".  The properties selected by a client as
   being of interest are specified in the subsequent Path Vector queries
   using the filter called 'ane-property-names'.  The response includes
   and only includes the selected properties for the ANEs in the
   response.

   The "ane-property-names" capability for Cost Map and for Endpoint
   Cost Service is specified in Section 7.2.4 and Section 7.3.4
   respectively.  The "ane-property-names" filter for Cost Map and
   Endpoint Cost Service is specified in Section 7.2.3 and Section 7.3.3
   accordingly.

5.2.  Path Vector Cost Type

   For an ALTO client to correctly interpret the Path Vector, this
   extension specifies a new cost type called the Path Vector cost type.

   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 C++ where there existed a
   JSON array type named JSONArray, 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 ALTO client must check the value of
   the "cost-metric".  If the value is "ane-path", it means that the
   JSON array should be further interpreted as a path of ANENames.

   The Path Vector cost type is specified in Section 6.5.









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5.3.  Multipart Path Vector Response

   For a basic ALTO information resource, a 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 8.

            ALTO client                              ALTO server
                 |-------------- Request ---------------->|
                 |<------------- Response ----------------|

               Figure 8: A Typical ALTO Request and Response

   The extension defined in this document, on the other hand, involves
   two types of information resources: Path Vectors conveyed in an
   InfoResourceCostMap (defined in Section 11.2.3.6 of [RFC7285]) or an
   InfoResourceEndpointCostMap (defined in Section 11.5.1.6 of
   [RFC7285]), and ANE properties conveyed in an InfoResourceProperties
   (defined in Section 7.6 of [I-D.ietf-alto-unified-props-new]).

   Instead of two consecutive message exchanges, the extension defined
   in this document enforces one round of communication.  Specifically,
   the ALTO client must include the source and destination pairs and the
   requested ANE properties in a single request, and the ALTO server
   must return a single response containing both the Path Vectors and
   properties associated with the ANEs in the Path Vectors, as shown in
   Figure 9.  Since the two parts are bundled together in one response
   message, their orders are interchangeable.  See Section 7.2.6 and
   Section 7.3.6 for details.

            ALTO client                              ALTO server
                 |------------- PV Request -------------->|
                 |<----- PV Response (Cost Map Part) -----|
                 |<--- PV Response (Property Map Part) ---|

          Figure 9: The Path Vector Extension Request and Response

   This design is based on the following considerations:

   1.  ANEs may be constructed on demand, and potentially based on the
       requested properties (See Section 5.1 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.






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   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 Property Map 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 may 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 follows the standard-conforming usage of
   "multipart/related" media type defined in [RFC2387] to elegantly
   combine the objects.  Path Vectors are encoded in an
   InfoResourceCostMap or an InfoResourceEndpointCostMap, and the
   Property Map is encoded in an InfoResourceProperties.  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".

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

5.3.2.  References to Part Messages

   As the response of a Path Vector resource is a multipart message with
   two different parts, it is important that each part can be uniquely
   identified.  Following the designs of [RFC8895], this extension
   requires that an ALTO server assigns a unique identifier to each part
   of the multipart response message.  This identifier, referred to as a
   Part Resource ID (See Section 6.6 for details), is present in the
   part message's "Content-ID" header.  By concatenating the Part
   Resource ID to the identifier of the Path Vector request, an ALTO
   server/client can uniquely identify the Path Vector Part or the



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   Property Map part.

6.  Specification: Basic Data Types

6.1.  ANE Name

   An ANE Name is encoded as a JSON string with the same format as that
   of the type PIDName (Section 10.1 of [RFC7285]).

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

6.2.  ANE Entity Domain

   The ANE entity domain associates property values with the Abstract
   Network Elements in a Property Map. Accordingly, the ANE entity
   domain always depends on a Property Map.

   It must be noted that the term "domain" here does not refer to a
   network domain.  Rather, it is inherited from the "entity domain"
   defined in Sec 3.2 in [I-D.ietf-alto-unified-props-new] that
   represents the set of valid entities defined by an ALTO information
   resource (called the defining information resource).

6.2.1.  Entity Domain Type

   The Entity Domain Type is "ane".

6.2.2.  Domain-Specific Entity Identifier

   The entity identifiers are the ANE Names in the associated Property
   Map.

6.2.3.  Hierarchy and Inheritance

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

6.2.4.  Media Type of Defining Resource

   The defining resource for entity domain type "ane" MUST be a Property
   Map, i.e., the media type of defining resources is:

   application/alto-propmap+json

   Specifically, for ephemeral ANEs that appear in a Path Vector
   response, their entity domain names MUST be exactly ".ane" and the
   defining resource of these ANEs is the Property Map part of the



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   multipart response.  Meanwhile, for any persistent ANE whose defining
   resource is a Property Map resource, its entity domain name MUST have
   the format of "PROPMAP.ane" where PROPMAP is the resource ID of the
   defining resource.  Persistent entities are "persistent" because
   standalone queries can be made by an ALTO client to their defining
   resource(s) when the connection to the Path Vector service is closed.

   For example, the defining resource of an ephemeral ANE whose entity
   identifier is ".ane:NET1" is the Property Map part that contains this
   identifier.  The defining resource of a persistent ANE whose entity
   identifier is "dc-props.ane:DC1" is the Property Map with the
   resource ID "dc-props".

6.3.  ANE Property Name

   An ANE Property Name is encoded as a JSON string with the same format
   as that of Entity Property Name (Section 5.2.2 of
   [I-D.ietf-alto-unified-props-new]).

6.4.  Initial ANE Property Types

   Two initial ANE property types are specified, "max-reservable-
   bandwidth" and "persistent-entity-id".

   Note that these property types do not depend on any information
   resource.  As such, the EntityPropertyName MUST only have the
   EntityPropertyType part.

6.4.1.  Maximum Reservable Bandwidth

   The maximum reservable bandwidth property ("max-reservable-
   bandwidth") stands for the maximum bandwidth that can be reserved for
   all the traffic that traverses an ANE.  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 (bps).  If this property is
   requested by the ALTO client but not present for an ANE in the server
   response, it MUST be interpreted as that the property is not defined
   for the ANE.

   This property can be offered in a setting where the ALTO server is
   part of a network system that provides on-demand resource allocation
   and the ALTO client is part of a user application.  One existing
   example is [NOVA]: the ALTO server is part of an SDN controller and
   exposes a list of traversed network elements and associated link
   bandwidth to the client.  The encoding in [NOVA] differs from the
   Path Vector response defined in this document that the Path Vector
   part and Property Map part are put in the same JSON object.




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   In such a framework, the ALTO server exposes resource (e.g.,
   reservable bandwidth) availability information to the ALTO client.
   How the client makes resource requests based on the information and
   how the resource allocation is achieved respectively depend on
   interfaces between the management system and the users or a higher-
   layer protocol (e.g., SDN network intents or MPLS tunnels), which are
   out of the scope of this document.

6.4.2.  Persistent Entity ID

   The persistent entity ID property is the entity identifier of the
   persistent ANE which an ephemeral ANE presents (See Section 5.1.2 for
   details).  The value of this property is encoded with the format
   EntityID defined in Section 5.1.3 of
   [I-D.ietf-alto-unified-props-new].

   In this format, the entity ID combines:

   *  a defining information resource for the ANE on which a
      "persistent-entity-id" is queried, which is the Property Map
      resource defining the ANE as a persistent entity, together with
      the properties;

   *  the persistent name of the ANE in that Property Map.

   With this format, the client has all the needed information for
   further standalone query properties on the persistent ANE.

6.4.3.  Examples

   To illustrate the use of "max-reservable-bandwidth", consider the
   following network with 5 nodes.  Assume the client wants to query the
   maximum reservable bandwidth from H1 to H2.  An ALTO server may split
   the network into two ANEs: "ane1" that represents the subnetwork with
   routers A, B, and C, and "ane2" that represents the subnetwork with
   routers B, D and E.  The maximum reservable bandwidth for "ane1" is
   15 Mbps (using path A->C->B) and the maximum reservable bandwidth for
   "ane2" is 20 Mbps (using path B->D->E).

                        20 Mbps  20 Mbps
             10 Mbps +---+   +---+    +---+
                /----| B |---| D |----| E |---- H2
          +---+/     +---+   +---+    +---+
   H1 ----| A | 15 Mbps|
          +---+\     +---+
                \----| C |
             15 Mbps +---+




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   To illustrate the use of "persistent-entity-id", consider the
   scenario in Figure 6.  As the life cycle of service edges are
   typically long, they may contain information that is not specific to
   the query.  Such information can be stored in an individual unified
   property map and later be accessed by an ALTO client.

   For example, "ane1" in Figure 7 represents the on-premise service
   edge closest to host a.  Assume the properties of the service edges
   are provided in a unified property map called "se-props" and the ID
   of the on-premise service edge is "9a0b55f7-7442-4d56-8a2c-
   b4cc6a8e3aa1", the "persistent-entity-id" of "ane1" will be "se-
   props.ane:9a0b55f7-7442-4d56-8a2c-b4cc6a8e3aa1".  With this
   persistent entity ID, an ALTO client may send queries to the "se-
   props" resource with the entity ID ".ane:9a0b55f7-7442-4d56-8a2c-
   b4cc6a8e3aa1".

6.5.  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 extension defined in this document.

6.5.1.  Cost Metric: ane-path

   The cost metric "ane-path" indicates the value of such a cost type
   conveys an array of ANE names, where each ANE name uniquely
   represents an ANE traversed by traffic from a source to a
   destination.

   An ALTO client MUST interpret the Path Vector as if the traffic
   between a source and a destination logically traverses the ANEs in
   the same order as they appear in the Path Vector.

   When the Path Vector procedures defined in this document are in use,
   an ALTO server using the "ane-path" cost metric and the "array" cost
   mode (see Section 6.5.2) MUST return as the cost value a JSON array
   of ANEName and the client MUST also check that each element contained
   in the array is an ANEName (Section 6.1).  Otherwise, the client MUST
   discard the response and SHOULD follow the instructions in
   Section 8.3.4.3 of [RFC7285] to handle the error.











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6.5.2.  Cost Mode: array

   The cost mode "array" indicates that every cost value in the response
   body of a (Filtered) Cost Map or an Endpoint Cost Service MUST be
   interpreted as a JSON array object.  While this cost mode can be
   applied to all cost metrics, additional specifications will be needed
   to clarify the semantics of the array cost mode when combined with
   cost metrics other than 'ane-path'.

6.6.  Part Resource ID and Part Content ID

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

   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 5.3.2) 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.

   A Part Content ID conforms to the format of msg-id as specified in
   [RFC2387] and [RFC5322].  Specifically, it has the following format:

   "<" PART-RESOURCE-ID "@" DOMAIN-NAME ">"

   PART-RESOURCE-ID:  PART-RESOURCE-ID has the same format as the Part
      Resource ID.  It is used to identify whether a part message is a
      Path Vector or a Property Map.

   DOMAIN-NAME:  DOMAIN-NAME has the same format as dot-atom-text
      specified in Section 3.2.3 of [RFC5322].  It must be the domain
      name of the ALTO server.

7.  Specification: Service Extensions

7.1.  Notations

   This document uses the same syntax and notations as introduced in
   Section 8.2 of RFC 7285 [RFC7285] to specify the extensions to
   existing ALTO resources and services.









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7.2.  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 with the Cost Map resource in the
   same response.

7.2.1.  Media Type

   The media type of the multipart Filtered Cost Map resource is
   "multipart/related" and the required "type" parameter MUST have a
   value of "application/alto-costmap+json".

7.2.2.  HTTP Method

   The multipart Filtered Cost Map is requested using the HTTP POST
   method.

7.2.3.  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, which is defined as a JSON object
   of type ReqFilteredCostMap in Section 4.1.2 of RFC 8189 [RFC8189],
   with a data format indicated by the media type "application/alto-
   costmapfilter+json", which is a JSON object of type
   PVReqFilteredCostMap:

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

   with fields:

   ane-property-names:  A list of selected ANE properties to be included
      in the response.  Each property in this list MUST match one of the
      supported ANE properties indicated in the resource's "ane-
      property-names" capability (Section 7.2.4).  If the field is not
      present, it MUST be interpreted as an empty list.

   Example: Consider the network in Figure 1.  If an ALTO client wants
   to query the "max-reservable-bandwidth" between PID1 and PID2, it can
   submit the following request.








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      POST /costmap/pv HTTP/1.1
      Host: alto.example.com
      Accept: multipart/related;type=application/alto-costmap+json,
              application/alto-error+json
      Content-Length: 201
      Content-Type: application/alto-costmapfilter+json

      {
        "cost-type": {
          "cost-mode": "array",
          "cost-metric": "ane-path"
        },
        "pids": {
          "srcs": [ "PID1" ],
          "dsts": [ "PID2" ]
        },
        "ane-property-names": [ "max-reservable-bandwidth" ]
      }

7.2.4.  Capabilities

   The multipart Filtered Cost Map resource extends the capabilities
   defined in Section 4.1.1 of [RFC8189].  The capabilities are defined
   by a JSON object of type PVFilteredCostMapCapabilities:

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

   with fields:

   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.

   This extension also introduces additional restrictions for the
   following fields:

   cost-type-names:  The "cost-type-names" field MUST 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.



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   testable-cost-type-names (Section 4.1.1 of [RFC8189]):  If the "cost-
      type-names" field includes the Path Vector cost type and the
      "testable-cost-type-names" field is present, the Path Vector cost
      type MUST NOT be included in the "testable-cost-type-names" field
      unless specifically instructed by a future document.

7.2.5.  Uses

   This member MUST include the resource ID of the network map based on
   which the PIDs are defined.  If this resource supports "persistent-
   entity-id", it MUST also include the defining resources of persistent
   ANEs that may appear in the response.

7.2.6.  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.

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

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

   start:  The start parameter is as defined in [RFC2387] and is
      optional.  If present, it MUST have the same value as the
      "Content-ID" header of the Path Vector part.

   boundary:  The boundary parameter is as defined in Section 5.1.1 of
      [RFC2046] and is mandatory.

   The body of the response MUST consist of two parts:

   *  The Path Vector part MUST include "Content-ID" and "Content-Type"
      in its header.  The "Content-Type" MUST be "application/alto-
      costmap+json".  The value of "Content-ID" MUST have the same
      format as the Part Content ID as specified in Section 6.6.

      The body of the Path Vector part MUST be a JSON object with the
      same format as defined in Section 11.2.3.6 of [RFC7285] when the
      "cost-type" field is present in the input parameters and MUST be a
      JSON object with the same format as defined in Section 4.1.3 of
      [RFC8189] if the "multi-cost-types" field is present.  The JSON
      object MUST include the "vtag" field in the "meta" field, which
      provides the version tag of the returned CostMapData.  The
      resource ID of the version tag MUST follow the format of



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      resource-id '.' part-resource-id

      where "resource-id" is the resource Id of the Path Vector
      resource, and "part-resource-id" has the same value as the PART-
      RESOURCE-ID in the "Content-ID" of the Path Vector part.  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 Unified Property Map part MUST also include "Content-ID" and
      "Content-Type" in its header.  The "Content-Type" MUST be
      "application/alto-propmap+json".  The value of "Content-ID" MUST
      have the same format as the Part Content ID as specified in
      Section 6.6.

      The body of the Unified Property Map part is a JSON object with
      the same format as defined in Section 7.6 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 Path
      Vector part MUST be included in the "dependent-vtags".  If
      "persistent-entity-id" 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 Path Vector part, which is an entity identifier belonging
      to the self-defined entity domain as defined in Section 5.1.2.3 of
      [I-D.ietf-alto-unified-props-new].  The EntityProps for each ANE
      has one member for each property that is both 1) associated with
      the ANE, and 2) specified in the "ane-property-names" in the
      request.  If the Path Vector cost type is not included in the
      "cost-type" field or the "multi-cost-type" field, the "property-
      map" field MUST be present and the value MUST be an empty object
      ({}).

   A complete and valid response MUST include both the Path Vector part
   and the Property Map part in the multipart message.  If any part is
   NOT present, the client MUST discard the received information and
   send another request if necessary.

   According to [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



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   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.  When doing so, an ALTO server MAY choose not to set the
   "start" parameter, which implies the first part is the root object.

   Example: Consider the network in Figure 1.  The response of the
   example request in Section 7.2.3 is as follows, where "ANE1"
   represents the aggregation of all the switches in the network.











































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   HTTP/1.1 200 OK
   Content-Length: 859
   Content-Type: multipart/related; boundary=example-1;
                 type=application/alto-costmap+json

   --example-1
   Content-ID: <costmap@alto.example.com>
   Content-Type: application/alto-costmap+json

   {
     "meta": {
       "vtag": {
         "resource-id": "filtered-cost-map-pv.costmap",
         "tag": "fb20b76204814e9db37a51151faaaef2"
       },
       "dependent-vtags": [
         {
           "resource-id": "my-default-networkmap",
           "tag": "75ed013b3cb58f896e839582504f6228"
         }
       ],
       "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }
     },
     "cost-map": {
       "PID1": { "PID2": ["ANE1"] }
     }
   }
   --example-1
   Content-ID: <propmap@alto.example.com>
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "filtered-cost-map-pv.costmap",
           "tag": "fb20b76204814e9db37a51151faaaef2"
         }
       ]
     },
     "property-map": {
       ".ane:ANE1": { "max-reservable-bandwidth": 100000000 }
     }
   }







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7.3.  Multipart Endpoint Cost Service for Path Vector

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

7.3.1.  Media Type

   The media type of the multipart Endpoint Cost Service resource is
   "multipart/related" and the required "type" parameter MUST have a
   value of "application/alto-endpointcost+json".

7.3.2.  HTTP Method

   The multipart Endpoint Cost Service resource is requested using the
   HTTP POST method.

7.3.3.  Accept Input Parameters

   The input parameters of the multipart Endpoint Cost Service resource
   are supplied in the body of an HTTP POST request.  This document
   extends the input parameters to an Endpoint Cost Service, which is
   defined as a JSON object of type ReqEndpointCost in Section 4.2.2 of
   [RFC8189], with a data format indicated by the media type
   "application/alto-endpointcostparams+json", which is a JSON object of
   type PVReqEndpointCost:

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

   with fields:

   ane-property-names:  This document defines the "ane-property-names"
      in PVReqEndpointcost as the same as in PVReqFilteredCostMap.  See
      Section 7.2.3.

   Example: Consider the network in Figure 1.  If an ALTO client wants
   to query the "max-reservable-bandwidth" between eh1 and eh2, it can
   submit the following request.










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   POST /ecs/pv HTTP/1.1
   Host: alto.example.com
   Accept: multipart/related;type=application/alto-endpointcost+json,
           application/alto-error+json
   Content-Length: 227
   Content-Type: application/alto-endpointcostparams+json

   {
     "cost-type": {
       "cost-mode": "array",
       "cost-metric": "ane-path"
     },
     "endpoints": {
       "srcs": [ "ipv4:192.0.2.2" ],
       "dsts": [ "ipv4:192.0.2.18" ]
     },
     "ane-property-names": [ "max-reservable-bandwidth" ]
   }

7.3.4.  Capabilities

   The capabilities of the multipart Endpoint Cost Service resource are
   defined by a JSON object of type PVEndpointcostCapabilities, which is
   defined as the same as PVFilteredCostMapCapabilities.  See
   Section 7.2.4.

7.3.5.  Uses

   If this resource supports "persistent-entity-id", it MUST also
   include the defining resources of persistent ANEs that may appear in
   the response.

7.3.6.  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 [RFC7285] with the following parameters:

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

   start:  The start parameter is as defined in Section 7.2.6.

   boundary:  The boundary parameter is as defined in Section 5.1.1 of
      [RFC2046] and is mandatory.



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   The body MUST consist of two parts:

   *  The Path Vector part MUST include "Content-ID" and "Content-Type"
      in its header.  The "Content-Type" MUST be "application/alto-
      endpointcost+json".  The value of "Content-ID" MUST have the same
      format as the Part Content ID as specified in Section 6.6.

      The body of the Path Vector part MUST be a JSON object with the
      same format as defined in Section 11.5.1.6 of [RFC7285] when the
      "cost-type" field is present in the input parameters and MUST be a
      JSON object with the same format as defined in Section 4.2.3 of
      [RFC8189] if the "multi-cost-types" field is present.  The JSON
      object MUST include the "vtag" field in the "meta" field, which
      provides the version tag of the returned EndpointCostMapData.  The
      resource ID of the version tag MUST follow the format of

      resource-id '.' part-resource-id

      where "resource-id" is the resource Id of the Path Vector
      resource, and "part-resource-id" has the same value as the PART-
      RESOURCE-ID in the "Content-ID" of the Path Vector part.

   *  The Unified Property Map part MUST also include "Content-ID" and
      "Content-Type" in its header.  The "Content-Type" MUST be
      "application/alto-propmap+json".  The value of "Content-ID" MUST
      have the same format as the Part Content ID as specified in
      Section 6.6.

      The body of the Unified Property Map part MUST be a JSON object
      with the same format as defined in Section 7.6 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 Path
      Vector part MUST be included in the "dependent-vtags".  If
      "persistent-entity-id" is requested, the version tags of the
      dependent resources that may expose the entities in the response
      MUST also be included.













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      The PropertyMapData has one member for each ANEName that appears
      in the Path Vector part, which is an entity identifier belonging
      to the self-defined entity domain as defined in Section 5.1.2.3 of
      [I-D.ietf-alto-unified-props-new].  The EntityProps for each ANE
      has one member for each property that is both 1) associated with
      the ANE, and 2) specified in the "ane-property-names" in the
      request.  If the Path Vector cost type is not included in the
      "cost-type" field or the "multi-cost-type" field, the "property-
      map" field MUST be present and the value MUST be an empty object
      ({}).

   A complete and valid response MUST include both the Path Vector part
   and the Property Map part in the multipart message.  If any part is
   NOT present, the client MUST discard the received information and
   send another request if necessary.

   According to [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.  When doing so, an ALTO server MAY choose not to set the
   "start" parameter, which implies the first part is the root object.

   Example: Consider the network in Figure 1.  The response of the
   example request in Section 7.3.3 is as follows.























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   HTTP/1.1 200 OK
   Content-Length: 845
   Content-Type: multipart/related; boundary=example-1;
                 type=application/alto-endpointcost+json

   --example-1
   Content-ID: <ecs@alto.example.com>
   Content-Type: application/alto-endpointcost+json

   {
     "meta": {
       "vtag": {
         "resource-id": "ecs-pv.ecs",
         "tag": "ec137bb78118468c853d5b622ac003f1"
       },
       "dependent-vtags": [
         {
           "resource-id": "my-default-networkmap",
           "tag": "677fe5f4066848d282ece213a84f9429"
         }
       ],
       "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }
     },
     "cost-map": {
       "ipv4:192.0.2.2": { "ipv4:192.0.2.18": ["ANE1"] }
     }
   }
   --example-1
   Content-ID: <propmap@alto.example.com>
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "ecs-pv.ecs",
           "tag": "ec137bb78118468c853d5b622ac003f1"
         }
       ]
     },
     "property-map": {
       ".ane:ANE1": { "max-reservable-bandwidth": 100000000 }
     }
   }







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8.  Examples

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

8.1.  Sample Setup

                                         ----- L1
                                        /
            PID1   +----------+ 10 Gbps +----------+    PID3
     192.0.2.0/28+-+ +------+ +---------+          +--+192.0.2.32/28
                   | | MEC1 | |         |          |   2001:db8::3:0/16
                   | +------+ |   +-----+          |
            PID2   |          |   |     +----------+
    192.0.2.16/28+-+          |   |         NET3
                   |          |   | 15 Gbps
                   |          |   |        \
                   +----------+   |         -------- L2
                       NET1       |
                                +----------+
                                | +------+ |   PID4
                                | | MEC2 | +--+192.0.2.48/28
                                | +------+ |   2001:db8::4:0/16
                                +----------+
                                    NET2

                   Figure 10: Examples of ANE Properties

   In this document, Figure 10 is used to illustrate the message
   contents.  There are 3 sub-networks (NET1, NET2 and NET3) and two
   interconnection links (L1 and L2).  It is assumed that each sub-
   network has sufficiently large bandwidth to be reserved.

8.2.  Information Resource Directory

   To give a comprehensive example of the extension defined in this
   document, we consider the network in Figure 10.  Assume that the ALTO
   server provides the following information resources:

   *  "my-default-networkmap": A Network Map resource which contains the
      PIDs in the network.

   *  "filtered-cost-map-pv": A Multipart Filtered Cost Map resource for
      Path Vector, which exposes the "max-reservable-bandwidth" property
      for the PIDs in "my-default-networkmap".





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   *  "ane-props": A filtered Unified Property resource that exposes the
      information for persistent ANEs in the network.

   *  "endpoint-cost-pv": A Multipart Endpoint Cost Service for Path
      Vector, which exposes the "max-reservable-bandwidth" and the
      "persistent-entity-id" properties.

   *  "update-pv": An Update Stream service, which provides the
      incremental update service for the "endpoint-cost-pv" service.

   *  "multicost-pv": A Multipart Endpoint Cost Service with both Multi-
      Cost and Path Vector.

   Below is the Information Resource Directory of the example ALTO
   server.  To enable the extension defined in this document, the "path-
   vector" cost type (Section 6.5) is defined in the "cost-types" of the
   "meta" field, and is included in the "cost-type-names" of resources
   "filtered-cost-map-pv" and "endpoint-cost-pv".

   {
     "meta": {
       "cost-types": {
         "path-vector": {
           "cost-mode": "array",
           "cost-metric": "ane-path"
         },
         "num-rc": {
           "cost-mode": "numerical",
           "cost-metric": "routingcost"
         }
       }
     },
     "resources": {
       "my-default-networkmap": {
         "uri": "https://alto.example.com/networkmap",
         "media-type": "application/alto-networkmap+json"
       },
       "filtered-cost-map-pv": {
         "uri": "https://alto.example.com/costmap/pv",
         "media-type": "multipart/related;
                        type=application/alto-costmap+json",
         "accepts": "application/alto-costmapfilter+json",
         "capabilities": {
           "cost-type-names": [ "path-vector" ],
           "ane-property-names": [ "max-reservable-bandwidth" ]
         },
         "uses": [ "my-default-networkmap" ]
       },



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       "ane-props": {
         "uri": "https://alto.example.com/ane-props",
         "media-type": "application/alto-propmap+json",
         "accepts": "application/alto-propmapparams+json",
         "capabilities": {
           "mappings": {
             ".ane": [ "cpu" ]
           }
         }
       },
       "endpoint-cost-pv": {
         "uri": "https://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": [
             "max-reservable-bandwidth", "persistent-entity-id"
           ]
         },
         "uses": [ "ane-props" ]
       },
       "update-pv": {
         "uri": "https://alto.example.com/updates/pv",
         "media-type": "text/event-stream",
         "uses": [ "endpoint-cost-pv" ],
         "accepts": "application/alto-updatestreamparams+json",
         "capabilities": {
           "support-stream-control": true
         }
       },
       "multicost-pv": {
         "uri": "https://alto.exmaple.com/endpointcost/mcpv",
         "media-type": "multipart/related;
                        type=application/alto-endpointcost+json",
         "accepts": "application/alto-endpointcostparams+json",
         "capabilities": {
           "cost-type-names": [ "path-vector", "num-rc" ],
           "max-cost-types": 2,
           "testable-cost-type-names": [ "num-rc" ],
           "ane-property-names": [
             "max-reservable-bandwidth", "persistent-entity-id"
           ]
         },
         "uses": [ "ane-props" ]
       }
     }



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   }

8.3.  Multipart Filtered Cost Map

   The following examples demonstrate the request to the "filtered-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.

   The response consists of two parts.  The first part returns the array
   of ANEName for each source and destination pair.  There are two ANEs,
   where "L1" represents the interconnection link L1, and "L2"
   represents the interconnection link L2.

   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: 153
   Content-Type: application/alto-costmapfilter+json

   {
     "cost-type": {
       "cost-mode": "array",
       "cost-metric": "ane-path"
     },
     "pids": {
       "srcs": [ "PID1" ],
       "dsts": [ "PID3", "PID4" ]
     }
   }

   HTTP/1.1 200 OK
   Content-Length: 855
   Content-Type: multipart/related; boundary=example-1;
                 type=application/alto-costmap+json

   --example-1
   Content-ID: <costmap@alto.example.com>
   Content-Type: application/alto-costmap+json




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   {
     "meta": {
       "vtag": {
         "resource-id": "filtered-cost-map-pv.costmap",
         "tag": "d827f484cb66ce6df6b5077cb8562b0a"
       },
       "dependent-vtags": [
         {
           "resource-id": "my-default-networkmap",
           "tag": "c04bc5da49534274a6daeee8ea1dec62"
         }
       ],
       "cost-type": {
         "cost-mode": "array",
         "cost-metric": "ane-path"
       }
     },
     "cost-map": {
       "PID1": {
         "PID3": [ "L1" ],
         "PID4": [ "L1", "L2" ]
       }
     }
   }
   --example-1
   Content-ID: <propmap@alto.example.com>
   Content-Type: application/alto-propmap+json

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

8.4.  Multipart Endpoint Cost Service Resource

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






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   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 for two IPv4 source and destination pairs
   (192.0.2.34 -> 192.0.2.2 and 192.0.2.34 -> 192.0.2.50) and one IPv6
   source and destination pair (2001:db8::3:1 -> 2001:db8::4:1).

   The response consists of two parts.  The first part returns the array
   of ANEName for each valid source and destination pair.  As one can
   see in Figure 10, flow 192.0.2.34 -> 192.0.2.2 traverses NET2, L1 and
   NET1, and flows 192.0.2.34 -> 192.0.2.50 and 2001:db8::3:1 ->
   2001:db8::4:1 traverse NET2, L2 and NET3.

   The second part returns the requested properties of ANEs.  Assume
   NET1, NET2 and NET3 has sufficient bandwidth and their "max-
   reservable-bandwidth" values are set to a sufficiently large number
   (50 Gbps in this case).  On the other hand, assume there are no prior
   reservation on L1 and L2, and their "max-reservable-bandwidth" values
   are the corresponding link capacity (10 Gbps for L1 and 15 Gbps for
   L2).

   Both NET1 and NET2 have a mobile edge deployed, i.e., MEC1 in NET1
   and MEC2 in NET2.  Assume the ANEName for MEC1 and MEC2 are "MEC1"
   and "MEC2" and their properties can be retrieved from the Property
   Map "ane-props".  Thus, the "persistent-entity-id" property of NET1
   and NET3 are "ane-props.ane:MEC1" and "ane-props.ane:MEC2"
   respectively.

























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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: 362
   Content-Type: application/alto-endpointcostparams+json

   {
     "cost-type": {
       "cost-mode": "array",
       "cost-metric": "ane-path"
     },
     "endpoints": {
       "srcs": [
         "ipv4:192.0.2.34",
         "ipv6:2001:db8::3:1"
       ],
       "dsts": [
         "ipv4:192.0.2.2",
         "ipv4:192.0.2.50",
         "ipv6:2001:db8::4:1"
       ]
     },
     "ane-property-names": [
       "max-reservable-bandwidth",
       "persistent-entity-id"
     ]
   }

   HTTP/1.1 200 OK
   Content-Length: 1432
   Content-Type: multipart/related; boundary=example-2;
                 type=application/alto-endpointcost+json

   --example-2
   Content-ID: <ecs@alto.example.com>
   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"



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       }
     },
     "endpoint-cost-map": {
       "ipv4:192.0.2.34": {
         "ipv4:192.0.2.2":   [ "NET3", "L1", "NET1" ],
         "ipv4:192.0.2.50":   [ "NET3", "L2", "NET2" ]
       },
       "ipv6:2001:db8::3:1": {
         "ipv6:2001:db8::4:1": [ "NET3", "L2", "NET2" ]
       }
     }
   }
   --example-2
   Content-ID: <propmap@alto.example.com>
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "endpoint-cost-pv.ecs",
           "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
         },
         {
           "resource-id": "ane-props",
           "tag": "bf3c8c1819d2421c9a95a9d02af557a3"
         }
       ]
     },
     "property-map": {
       ".ane:NET1": {
         "max-reservable-bandwidth": 50000000000,
         "persistent-entity-id": "ane-props.ane:MEC1"
       },
       ".ane:NET2": {
         "max-reservable-bandwidth": 50000000000,
         "persistent-entity-id": "ane-props.ane:MEC2"
       },
       ".ane:NET3": {
         "max-reservable-bandwidth": 50000000000
       },
       ".ane:L1": {
         "max-reservable-bandwidth": 10000000000
       },
       ".ane:L2": {
         "max-reservable-bandwidth": 15000000000
       }
     }



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   }

   Under certain scenarios where the traversal order is not crucial, an
   ALTO server implementation may choose to not follow strictly the
   physical traversal order and may even obfuscate the order
   intentionally to preserve its own privacy or conform to its own
   policies.  For example, an ALTO server may choose to aggregate NET1
   and L1 as a new ANE with ANE name "AGGR1", and aggregate NET2 and L2
   as a new ANE with ANE name "AGGR2".  The "max-reservable-bandwidth"
   of "AGGR1" takes the value of L1, which is smaller than that of NET1,
   and the "persistent-entity-id" of "AGGR1" takes the value of NET1.
   The properties of "AGGR2" are computed in a similar way and the
   obfuscated response is as shown below.  Note that the obfuscation of
   Path Vector responses is implementation-specific and is out of the
   scope of this document, and developers may refer to Section 11 for
   further references.

   HTTP/1.1 200 OK
   Content-Length: 1263
   Content-Type: multipart/related; boundary=example-2;
                 type=application/alto-endpointcost+json

   --example-2
   Content-ID: <ecs@alto.example.com>
   Content-Type: application/alto-endpointcost+json

   {
     "meta": {
       "vtags": {
         "resource-id": "endpoint-cost-pv.ecs",
         "tag": "bb975862fbe3422abf4dae386b132c1d"
       },
       "cost-type": {
         "cost-mode": "array",
         "cost-metric": "ane-path"
       }
     },
     "endpoint-cost-map": {
       "ipv4:192.0.2.34": {
         "ipv4:192.0.2.2":   [ "NET3", "AGGR1" ],
         "ipv4:192.0.2.50":   [ "NET3", "AGGR2" ]
       },
       "ipv6:2001:db8::3:1": {
         "ipv6:2001:db8::4:1": [ "NET3", "AGGR2" ]
       }
     }
   }
   --example-2



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   Content-ID: <propmap@alto.example.com>
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "endpoint-cost-pv.ecs",
           "tag": "bb975862fbe3422abf4dae386b132c1d"
         },
         {
           "resource-id": "ane-props",
           "tag": "bf3c8c1819d2421c9a95a9d02af557a3"
         }
       ]
     },
     "property-map": {
       ".ane:AGGR1": {
         "max-reservable-bandwidth": 10000000000,
         "persistent-entity-id": "ane-props.ane:MEC1"
       },
       ".ane:AGGR2": {
         "max-reservable-bandwidth": 15000000000,
         "persistent-entity-id": "ane-props.ane:MEC2"
       },
       ".ane:NET3": {
         "max-reservable-bandwidth": 50000000000
       }
     }
   }

8.5.  Incremental Updates

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
















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   POST /updates/pv HTTP/1.1
   Host: alto.example.com
   Accept: text/event-stream
   Content-Type: application/alto-updatestreamparams+json
   Content-Length: 112

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

   Based on the server-side process defined in [RFC8895], 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": "https://alto.example.com/updates/streams/123"}

   event: multipart/related;boundary=example-3;
          type=application/alto-endpointcost+json,ecspvsub1
   data: --example-3
   data: Content-ID: <ecsmap@alto.example.com>
   data: Content-Type: application/alto-endpointcost+json
   data:
   data: <endpoint-cost-map-entry>
   data: --example-3
   data: Content-ID: <propmap@alto.example.com>
   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, based on Section 6.7.3 of
   [RFC8895].








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

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

8.6.  Multi-cost

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

   The request asks for two cost types: the first is the Path Vector
   cost type, and the second is a numerical routing cost.  It also
   queries the Maximum Reservable Bandwidth ANE property and the
   Persistent Entity property for two IPv4 source and destination pairs
   (192.0.2.34 -> 192.0.2.2 and 192.0.2.34 -> 192.0.2.50) and one IPv6
   source and destination pair (2001:db8::3:1 -> 2001:db8::4:1).

   The response consists of two parts.  The first part returns a
   JSONArray that contains two JSONValue for each requested source and
   destination pair: the first JSONValue is a JSONArray of ANENames,
   which is the value of the Path Vector cost type, and the second
   JSONValue is a JSONNumber which is the value of the routing cost.
   The second part contains a Property Map that maps the ANEs to their
   requested properties.


























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   POST /endpointcost/mcpv HTTP/1.1
   Host: alto.example.com
   Accept: multipart/related;
           type=application/alto-endpointcost+json,
           application/alto-error+json
   Content-Length: 433
   Content-Type: application/alto-endpointcostparams+json

   {
     "multi-cost-types": [
       { "cost-mode": "array", "cost-metric": "ane-path" },
       { "cost-mode": "numerical", "cost-metric": "routingcost" }
     ],
     "endpoints": {
       "srcs": [
         "ipv4:192.0.2.34",
         "ipv6:2001:db8::3:1"
       ],
       "dsts": [
         "ipv4:192.0.2.2",
         "ipv4:192.0.2.50",
         "ipv6:2001:db8::4:1"
       ]
     },
     "ane-property-names": [
       "max-reservable-bandwidth",
       "persistent-entity-id"
     ]
   }

   HTTP/1.1 200 OK
   Content-Length: 1350
   Content-Type: multipart/related; boundary=example-4;
                 type=application/alto-endpointcost+json

   --example-4
   Content-ID: <ecs@alto.example.com>
   Content-Type: application/alto-endpointcost+json

   {
     "meta": {
       "vtags": {
         "resource-id": "endpoint-cost-pv.ecs",
         "tag": "84a4f9c14f9341f0983e3e5f43a371c8"
       },
       "multi-cost-types": [
         { "cost-mode": "array", "cost-metric": "ane-path" },
         { "cost-mode": "numerical", "cost-metric": "routingcost" }



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       ]
     },
     "endpoint-cost-map": {
       "ipv4:192.0.2.34": {
         "ipv4:192.0.2.2":   [[ "NET3", "AGGR1" ], 3],
         "ipv4:192.0.2.50":   [[ "NET3", "AGGR2" ], 2]
       },
       "ipv6:2001:db8::3:1": {
         "ipv6:2001:db8::4:1": [[ "NET3", "AGGR2" ], 2]
       }
     }
   }
   --example-4
   Content-ID: <propmap@alto.example.com>
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "endpoint-cost-pv.ecs",
           "tag": "84a4f9c14f9341f0983e3e5f43a371c8"
         },
         {
           "resource-id": "ane-props",
           "tag": "be157afa031443a187b60bb80a86b233"
         }
       ]
     },
     "property-map": {
       ".ane:AGGR1": {
         "max-reservable-bandwidth": 10000000000,
         "persistent-entity-id": "ane-props.ane:MEC1"
       },
       ".ane:AGGR2": {
         "max-reservable-bandwidth": 15000000000,
         "persistent-entity-id": "ane-props.ane:MEC2"
       },
       ".ane:NET3": {
         "max-reservable-bandwidth": 50000000000
       }
     }
   }

9.  Compatibility with Other ALTO Extensions






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9.1.  Compatibility with Legacy ALTO Clients/Servers

   The multipart Filtered Cost Map resource and the multipart Endpoint
   Cost Service 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 incurring any incompatibility problem.

9.2.  Compatibility with Multi-Cost Extension

   The extension defined in this document is compatible with the multi-
   cost extension [RFC8189].  Such a resource has a media type of either
   "multipart/related; type=application/alto-costmap+json" or
   "multipart/related; type=application/alto-endpointcost+json".  Its
   "cost-constraints" field must either be "false" or not present and
   the Path Vector cost type must be present in the "cost-type-names"
   capability field but must not be present in the "testable-cost-type-
   names" field, as specified in Section 7.2.4 and Section 7.3.4.

9.3.  Compatibility with Incremental Update

   This extension is compatible with the incremental update extension
   [RFC8895].  ALTO clients and servers MUST follow the specifications
   given in Sections 5.2 and 6.7.3 of [RFC8895] to support incremental
   updates for a Path Vector resource.

9.4.  Compatibility with Cost Calendar

   The extension specified in this document is compatible with the Cost
   Calendar extension [RFC8896].  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, a property of a single ANE may also have different values
   in different time intervals.  In this case, if such an ANE has
   different property values in two time intervals, it MUST be treated
   as two different ANEs, i.e., with different entity identifiers.
   However, if it has the same property values in two time intervals, it
   MAY use the same identifier.






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   This rule allows the Path Vector extension to represent both changes
   of ANEs and changes of the ANEs' properties in a uniform way.  The
   Path Vector part is calendared in a compatible way, and the Property
   Map part is not affected by the calendar extension.

   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).

10.  General Discussions

10.1.  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 syntax can only be used to test scalar cost
   types, and cannot easily express constraints on complex cost types,
   e.g., the Path Vector cost type defined in this document.

   In practice, developing a bespoke language for general-purpose
   boolean tests can be a complex undertaking, and it is conceivable
   that there are some existing implementations already (the authors
   have not done an exhaustive search to determine whether there are
   such implementations).  One avenue to develop such a language may be
   to explore extending current query languages like XQuery [XQuery] or
   JSONiq [JSONiq] and integrating these with ALTO.

   Filtering the Path Vector results or developing a more sophisticated
   filtering mechanism is beyond the scope of this document.

10.2.  General Multi-Resource Query

   Querying multiple ALTO information resources continuously is a
   general requirement.  Enabling such a capability, however, must
   address general issues like efficiency and consistency.  The
   incremental update extension [RFC8895] supports submitting multiple
   queries in a single request, and allows flexible control over the
   queries.  However, it does not cover the case introduced in this
   document where multiple resources are needed for a single request.





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   This extension gives an example of using a multipart message to
   encode the responses from two specific ALTO information resources: a
   Filtered Cost Map or an Endpoint Cost Service, and a Property Map. By
   packing multiple resources in a single response, the implication is
   that servers may proactively push related information resources to
   clients.

   Thus, it is worth looking into the direction of extending the SSE
   mechanism as used in the incremental update extension [RFC8895], or
   upgrading to HTTP/2 [I-D.ietf-httpbis-http2bis] and HTTP/3
   [I-D.ietf-quic-http], which provides the ability to multiplex queries
   and to allow servers proactively send related information resources.

   Defining a general multi-resource query mechanism is out of the scope
   of this document.

11.  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 scrutiny on three
   security considerations discussed in the base protocol:
   confidentiality of ALTO information (Section 15.3 of [RFC7285]),
   potential undesirable guidance from authenticated ALTO information
   (Section 15.2 of [RFC7285]), and availability of ALTO service
   (Section 15.5 of [RFC7285]).

   For confidentiality of ALTO information, a network operator should be
   aware that this extension may introduce a new risk: the Path Vector
   information, when used together with sensitive ANE properties such as
   capacities of bottleneck links, 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 attacker may
   identify the bottleneck link and start a distributed denial-of-
   service (DDoS) attack involving minimal flows to conduct the in-
   network congestion.  Given the potential risk of leaking sensitive
   information, the Path Vector extension is mainly applicable in
   scenarios where 1) the ANE structures and ANE properties do not
   impose security risks to the ALTO service provider, e.g., not
   carrying sensitive information, or 2) the ALTO server and client have
   established a reliable trust relationship, for example, operated in
   the same administrative domain, or managed by business partners with
   legal contracts.






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   Three risk types are identified in Section 15.3.1 of [RFC7285]: (1)
   Excess disclosure of the ALTO service provider's data to an
   unauthorized ALTO client; (2) Disclosure of the ALTO service
   provider's data (e.g., network topology information or endpoint
   addresses) to an unauthorized third party; and (3) Excess retrieval
   of the ALTO service provider's data by collaborating ALTO clients.
   To mitigate these risks, an ALTO server MUST follow the guidelines in
   Section 15.3.2 of [RFC7285].  Furthermore, an ALTO server MUST follow
   the following additional protections strategies for risk types (1)
   and (3).

   For risk type (1), an ALTO server MUST use the authentication methods
   specified in Section 15.3.2 of [RFC7285] to authenticate the identify
   of an ALTO client, and apply access control techniques to restrict
   unprivileged ALTO clients from retrieving sensitive Path Vector
   information.  For settings where the ALTO server and client are not
   in the same trust domain, the ALTO server should reach agreements
   with the ALTO client on protecting the confidentiality before
   granting the access to Path Vector service with sensitive
   information.  Such agreements may include legal contracts or Digital
   Right Management (DRM) techniques.  Otherwise, the ALTO server MUST
   NOT offer the Path Vector service carrying sensitive information to
   the clients unless the potential risks are fully assessed and
   mitigated.

   For risk type (3), an ALTO service provider must be aware that
   persistent ANEs may be used as "landmarks" in collaborative
   inferences.  Thus, they should only be used when exposing public
   service access points (e.g., API gateways, CDNi) and/or when the
   granularity is coarse-grained (e.g., when an ANE represents an AS, a
   data center or a WAN).  Otherwise, an ALTO server MUST use dynamic
   mappings from ephemeral ANE names to underlying physical entities.
   Specifically, for the same physical entity, an ALTO server SHOULD
   assign a different ephemeral ANE name when the entity appears in the
   responses to different clients or even for different request from the
   same client.  A RECOMMENDED assignment strategy is to generate ANE
   names from random numbers.

   Further, to protect the network topology from graph reconstruction
   (e.g., through isomorphic graph identification [BONDY]), the ALTO
   server SHOULD consider protection mechanisms to reduce information
   exposure or obfuscate the real information.  When doing so, the ALTO
   server must be aware that information reduction/obfuscation may lead
   to potential Undesirable Guidance from Authenticated ALTO Information
   risk (Section 15.2 of [RFC7285]).






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   Thus, implementations of ALTO servers involving reduction or
   obfuscation of the Path Vector information SHOULD consider reduction/
   obfuscation mechanisms that can preserve the integrity of ALTO
   information, for example, by using minimal feasible region
   compression algorithms [NOVA] or obfuscation protocols
   [RESA][MERCATOR].  However, these obfuscation methods are
   experimental and their practical applicability of these methods to
   the generic capability provided by this extension is not fully
   assessed.  The ALTO server MUST carefully verify that the deployment
   scenario satisfies the security assumptions of these methods before
   applying them to protect Path Vector services with sensitive network
   information.

   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 consume intolerable amounts of the
   server-side computation and storage, which can break the ALTO server.
   For example, if an ALTO server implementation dynamically computes
   the Path Vectors for each request, the service providing Path Vectors
   may become an entry point for denial-of-service attacks on the
   availability of an ALTO server.

   To mitigate this risk, an ALTO server may consider using
   optimizations such as precomputation-and-projection mechanisms
   [MERCATOR] to reduce the overhead for processing each query.  Also,
   an ALTO server may also protect itself from malicious clients by
   monitoring the behaviors of clients and stopping serving clients with
   suspicious behaviors (e.g., sending requests at a high frequency).

   The ALTO service providers must be aware that providing incremental
   updates of the "max-reservable-bandwidth" may provide information
   about other consumers of the network.  For example, a change of the
   value may indicate one or more reservations has been made or changed.
   To mitigate this risk, an ALTO server can batch the updates and/or
   add a random delay before publishing the updates.

12.  IANA Considerations

12.1.  ALTO Cost Metric Registry

   This document registers a new entry to the ALTO Cost Metric Registry,
   as instructed by Section 14.2 of [RFC7285].  The new entry is as
   shown below in Table 1.








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       +============+====================+=========================+
       | Identifier | Intended Semantics | Security Considerations |
       +============+====================+=========================+
       | ane-path   | See Section 6.5.1  | See Section 11          |
       +------------+--------------------+-------------------------+

                     Table 1: ALTO Cost Metric Registry

12.2.  ALTO Cost Mode Registry

   This document registers a new entry to the ALTO Cost Mode Registry,
   as instructed by Section 4 of [I-D.bw-alto-cost-mode].  The new entry
   is as shown below in Table 2.

                    +============+====================+
                    | Identifier | Intended Semantics |
                    +============+====================+
                    | array      | See Section 6.5.2  |
                    +------------+--------------------+

                      Table 2: ALTO Cost Mode Registry

12.3.  ALTO Entity Domain Type Registry

   This document registers a new entry to the ALTO Domain Entity Type
   Registry, as instructed by Section 12.2 of
   [I-D.ietf-alto-unified-props-new].  The new entry is as shown below
   in Table 3.

   +============+============+=============+===================+=======+
   | Identifier |Entity      | Hierarchy & |Media Type of      |Mapping|
   |            |Identifier  | Inheritance |Defining Resoucrce |to ALTO|
   |            |Encoding    |             |                   |Address|
   |            |            |             |                   |Type   |
   +============+============+=============+===================+=======+
   | ane        |See Section | None        |application/alto-  |false  |
   |            |6.2.2       |             |propmap+json       |       |
   +------------+------------+-------------+-------------------+-------+

                 Table 3: ALTO Entity Domain Type Registry

   Identifier:  See Section 6.2.1.

   Entity Identifier Encoding:  See Section 6.2.2.

   Hierarchy:  None

   Inheritance:  None



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   Media Type of Defining Resource:  See Section 6.2.4.

   Mapping to ALTO Address Type:  This entity type does not map to ALTO
      address type.

   Security Considerations:  In some usage scenarios, ANE addresses
      carried in ALTO Protocol messages may reveal information about an
      ALTO client or an ALTO service provider.  Applications and ALTO
      service providers using addresses of ANEs will be made aware of
      how (or if) the addressing scheme relates to private information
      and network proximity, in further iterations of this document.

12.4.  ALTO Entity Property Type Registry

   Two initial entries "max-reservable-bandwidth" and "persistent-
   entity-id" are registered to the ALTO Domain "ane" in the "ALTO
   Entity Property Type Registry", as instructed by Section 12.3 of
   [I-D.ietf-alto-unified-props-new].  The two new entries are shown
   below in Table 4 and their details can be found in Section 12.4.1 and
   Section 12.4.2.

   +==========================+====================+===================+
   | Identifier               | Intended           | Media Type of     |
   |                          | Semantics          | Defining Resource |
   +==========================+====================+===================+
   | max-reservable-bandwidth | See Section        | application/alto- |
   |                          | 6.4.1              | propmap+json      |
   +--------------------------+--------------------+-------------------+
   | persistent-entity-id     | See Section        | application/alto- |
   |                          | 6.4.2              | propmap+json      |
   +--------------------------+--------------------+-------------------+

         Table 4: Initial Entries for ane Domain in the ALTO Entity
                          Property Types Registry

12.4.1.  New ANE Property Type: Maximum Reservable Bandwidth

   Identifier:  "max-reservable-bandwidth"

   Intended Semantics:  See Section 6.4.1.

   Media Type of Defining Resource:  application/alto-propmap+json

   Security Considerations:  This property is essential for applications
      such as large-scale data transfers or overlay network
      interconnection to make better choice of bandwidth reservation.
      It may reveal the bandwidth usage of the underlying network and
      can potentially be leveraged to reduce the cost of conducting



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      denial-of-service attacks.  Thus, the ALTO server MUST consider
      protection mechanisms including only providing the information to
      authorized clients, and information reduction and obfuscation as
      introduced in Section 11.

12.4.2.  New ANE Property Type: Persistent Entity ID

   Identifier:  "persistent-entity-id"

   Intended Semantics:  See Section 6.4.2.

   Media Type of Defining Resource:  application/alto-propmap+json

   Security Considerations:  This property is useful when an ALTO server
      wants to selectively expose certain service points whose detailed
      properties can be further queried by applications.  The entity IDs
      may consider sensitive information about the underlying network,
      and an ALTO server should follow the security considerations in
      Section 11 of [I-D.ietf-alto-unified-props-new].

13.  References

13.1.  Normative References

   [I-D.bw-alto-cost-mode]
              Boucadair, M. and Q. Wu, "A Cost Mode Registry for the
              Application-Layer Traffic Optimization (ALTO) Protocol",
              Work in Progress, Internet-Draft, draft-bw-alto-cost-mode-
              01, 4 March 2022, <https://datatracker.ietf.org/doc/html/
              draft-bw-alto-cost-mode-01>.

   [I-D.ietf-alto-unified-props-new]
              Roome, W., Randriamasy, S., Yang, Y. R., Zhang, J. J., and
              K. Gao, "An ALTO Extension: Entity Property Maps", Work in
              Progress, Internet-Draft, draft-ietf-alto-unified-props-
              new-24, 28 February 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-alto-
              unified-props-new-24>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <https://www.rfc-editor.org/rfc/rfc2046>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.



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

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <https://www.rfc-editor.org/rfc/rfc5322>.

   [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/rfc/rfc7285>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [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/rfc/rfc8189>.

   [RFC8895]  Roome, W. and Y. Yang, "Application-Layer Traffic
              Optimization (ALTO) Incremental Updates Using Server-Sent
              Events (SSE)", RFC 8895, DOI 10.17487/RFC8895, November
              2020, <https://www.rfc-editor.org/rfc/rfc8895>.

   [RFC8896]  Randriamasy, S., Yang, R., Wu, Q., Deng, L., and N.
              Schwan, "Application-Layer Traffic Optimization (ALTO)
              Cost Calendar", RFC 8896, DOI 10.17487/RFC8896, November
              2020, <https://www.rfc-editor.org/rfc/rfc8896>.

13.2.  Informative References

   [BONDY]    Bondy, J.A. and R.L. Hemminger, "Graph reconstruction—a
              survey", Journal of Graph Theory, Volume 1, Issue 3, pp
              227-268 , 1977, <https://doi.org/10.1002/jgt.3190010306>.

   [BOXOPT]   Xiang, Q., Yu, H., Aspnes, J., Le, F., Kong, L., and Y.R.
              Yang, "Optimizing in the dark: Learning an optimal
              solution through a simple request interface", Proceedings
              of the AAAI Conference on Artificial Intelligence 33,
              1674-1681 , 2019,
              <https://doi.org/10.1609/aaai.v33i01.33011674>.






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   [CLARINET] Viswanathan, R., Ananthanarayanan, G., and A. Akella,
              "CLARINET: WAN-Aware Optimization for Analytics Queries",
              In 12th USENIX Symposium on Operating Systems Design and
              Implementation (OSDI 16), USENIX Association, Savannah,
              GA, 435-450 , 2016,
              <https://dl.acm.org/doi/abs/10.5555/3026877.3026911>.

   [G2]       Ros-Giralt, J., Bohara, A., Yellamraju, S., Langston,
              M.H., Lethin, R., Jiang, Y., Tassiulas, L., Li, J., Tan,
              Y., and M. Veeraraghavan, "On the Bottleneck Structure of
              Congestion-Controlled Networks", Proceedings of the ACM on
              Measurement and Analysis of Computing Systems, Volume 3,
              Issue 3, pp 1-31 , 2019,
              <https://dl.acm.org/doi/10.1145/3366707>.

   [HUG]      Chowdhury, M., Liu, Z., Ghodsi, A., and I. Stoica, "HUG:
              Multi-Resource Fairness for Correlated and Elastic
              Demands", 13th USENIX Symposium on Networked Systems
              Design and Implementation (NSDI 16) (Santa Clara, CA,
              2016), 407-424. , 2016,
              <https://dl.acm.org/doi/10.5555/2930611.2930638>.

   [I-D.ietf-alto-performance-metrics]
              Wu, Q., Yang, Y. R., Lee, Y., Dhody, D., Randriamasy, S.,
              and L. M. C. Murillo, "ALTO Performance Cost Metrics",
              Work in Progress, Internet-Draft, draft-ietf-alto-
              performance-metrics-26, 2 March 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-alto-
              performance-metrics-26>.

   [I-D.ietf-httpbis-http2bis]
              Thomson, M. and C. Benfield, "HTTP/2", Work in Progress,
              Internet-Draft, draft-ietf-httpbis-http2bis-07, 24 January
              2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
              httpbis-http2bis-07>.

   [I-D.ietf-quic-http]
              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
              quic-http-34, 2 February 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-quic-
              http-34>.

   [JSONiq]   "The JSON Query language", 2020,
              <https://www.jsoniq.org/>.






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   [MERCATOR] Xiang, Q., Zhang, J., Wang, X., Liu, Y., Guok, C., Le, F.,
              MacAuley, J., Newman, H., and Y.R. Yang, "Toward Fine-
              Grained, Privacy-Preserving, Efficient Multi-Domain
              Network Resource Discovery", IEEE/ACM IEEE Journal on
              Selected Areas of Communication 37(8): 1924-1940, 2019,
              <https://doi.org/10.1109/JSAC.2019.2927073>.

   [MOWIE]    Zhang, Y., Li, G., Xiong, C., Lei, Y., Huang, W., Han, Y.,
              Walid, A., Yang, Y.R., and Z. Zhang, "MoWIE: Toward
              Systematic, Adaptive Network Information Exposure as an
              Enabling Technique for Cloud-Based Applications over 5G
              and Beyond", In Proceedings of the Workshop on Network
              Application Integration/CoDesign, ACM, Virtual Event USA,
              20-27. , 2020, <https://doi.org/10.1145/3405672.3409489>.

   [NOVA]     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,
              <https://doi.org/10.1109/IWQoS.2017.7969117>.

   [RESA]     Xiang, Q., Zhang, J., Wang, X., Liu, Y., Guok, C., Le, F.,
              MacAuley, J., Newman, H., and Y.R. Yang, "Fine-grained,
              multi-domain network resource abstraction as a fundamental
              primitive to enable high-performance, collaborative data
              sciences", Proceedings of the Super Computing 2018,
              5:1-5:13 , 2019, <https://doi.org/10.1109/SC.2018.00008>.

   [RFC2216]  Shenker, S. and J. Wroclawski, "Network Element Service
              Specification Template", RFC 2216, DOI 10.17487/RFC2216,
              September 1997, <https://www.rfc-editor.org/rfc/rfc2216>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/rfc/rfc4271>.

   [SENSE]    "Software Defined Networking (SDN) for End-to-End
              Networked Science at the Exascale", 2019,
              <https://www.es.net/network-r-and-d/sense/>.

   [SEREDGE]  Contreras, L., Baliosian, J., Martı́nez-Julia, P., and J.
              Serrat, "Computing at the Edge: But, what Edge?", In
              proceedings of the NOMS 2020 - 2020 IEEE/IFIP Network
              Operations and Management Symposium. pp. 1-9. , 2020,
              <https://doi.org/10.1109/NOMS47738.2020.9110342>.





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   [SWAN]     Hong, C., Kandula, S., Mahajan, R., Zhang, M., Gill, V.,
              Nanduri, M., and R. Wattenhofer, "Achieving High
              Utilization with Software-driven WAN", In Proceedings of
              the ACM SIGCOMM 2013 Conference on SIGCOMM (SIGCOMM '13),
              ACM, New York, NY, USA, 15-26. , 2013,
              <http://doi.acm.org/10.1145/2486001.2486012>.

   [UNICORN]  Xiang, Q., Chen, S., Gao, K., Newman, H., Taylor, I.,
              Zhang, J., and Y.R. Yang, "Unicorn: Unified Resource
              Orchestration for Multi-Domain, Geo-Distributed Data
              Analytics", 2017 IEEE SmartWorld, Ubiquitous Intelligence
              Computing, Advanced Trusted Computed, Scalable Computing
              Communications, Cloud Big Data Computing, Internet of
              People and Smart City Innovation
              (SmartWorld/SCALCOM/UIC/ATC/CBDCom/IOP/SCI) (Aug. 2017),
              1-6. , 2017,
              <https://doi.org/10.1016/j.future.2018.09.048>.

   [XQuery]   "XQuery 3.1: An XML Query Language", 2017,
              <https://www.w3.org/TR/xquery-31/>.

Appendix A.  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, Dawn Chen, Wendy Roome, and Michael Scharf for their
   contributions to earlier drafts.

   The authors would also like to thank Tim Chown, Luis Contreras, Roman
   Danyliw, Benjamin Kaduk, Erik Kline, Suresh Krishnan, Murray
   Kucherawy, Warren Kumari, Danny Lachos, Francesca Palombini, Eric
   Vyncke, Samuel Weiler, and Qiao Xiang whose feedback and suggestions
   are invaluable to improve the practicability and conciseness of this
   document, and Mohamed Boucadair, Martin Duke, Vijay Gurbani, Jan
   Seedorf, and Qin Wu who provide great support and guidance.

Appendix B.  Revision Logs (To be removed before publication)

B.1.  Changes since -20

   Reivision -21

   *  changes the normative requirement on protecting confidentiality of
      PV information with softer language






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B.2.  Changes since -19

   Revision -20

   *  changes the IANA registry information

   *  adopts the comments from IESG reviews

B.3.  Changes since -18

   Revision -19

   *  adds detailed examples for use cases

   *  clarify terms with ambiguous meanings

B.4.  Changes since -17

   Revision -18

   *  changes the specification for content-id to conform to [RFC2387]
      and [RFC5322]

   *  adds IPv6 examples

B.5.  Changes since -16

   Revision -17

   *  adds items for media type of defining resources in IANA
      considerations

B.6.  Changes since -15

   Revision -16

   *  resolves the compatibility with the Multi-Cost extension (RFC
      8189)

   *  adds media types of defining resources for ANE property types (for
      IANA registration)

B.7.  Changes since -14

   Revision -15

   *  fixes the IDNits warnings,




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   *  fixes grammar issues,

   *  addresses the comments in the AD review.

B.8.  Changes since -13

   Revision -14

   *  addresses the comments in the chair review,

   *  fixes most issues raised by IDNits.

B.9.  Changes since -12

   Revision -13

   *  changes the abstract based on the chairs' reviews

   *  integrates Richard's responds to WGLC reviews

B.10.  Changes since -11

   Revision -12

   *  clarifies the definition of ANEs in a similar way as how Network
      Elements is defined in [RFC2216]

   *  restructures several paragraphs that are not clear (Sec 3, Path
      Vector bullet, Sec 4.2, Sec 5.1.3, Sec 6.2.4, Sec 6.4.2, Sec 9.3)

   *  uses "ALTO Entity Domain Type Registry"

B.11.  Changes since -10

   Revision -11

   *  replaces "part" with "components" in the abstract;

   *  identifies additional requirements (AR) derived from the flow
      scheduling example, and introduces how the extension addresses the
      additional requirements

   *  fixes the inconsistent use of "start" parameter in multipart
      responses;

   *  specifies explicitly how to handle "cost-constraints";





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   *  uses the latest IANA registration mechanism defined in
      [I-D.ietf-alto-unified-props-new];

   *  renames "persistent-entities" to "persistent-entity-id";

   *  makes "application/alto-propmap+json" as the media type of
      defining resources for the "ane" domain;

   *  updates the examples;

   *  adds the discussion on ephemeral and persistent ANEs.

B.12.  Changes since -09

   Revision -10

   *  revises the introduction which

      -  extends the scope where the PV extension can be applied beyond
         the "path correlation" information

   *  brings back the capacity region use case to better illustrate the
      problem

   *  revises the overview to explain and defend the concepts and
      decision choices

   *  fixes inconsistent terms, typos

B.13.  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

B.14.  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.



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   *  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
   Sichuan University
   No.24 South Section 1, Yihuan Road
   Chengdu
   610000
   China
   Email: kaigao@scu.edu.cn


   Young Lee
   Samsung
   South Korea
   Email: younglee.tx@gmail.com


   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





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   Jingxuan Jensen Zhang
   Tongji University
   4800 Caoan Road
   Shanghai
   201804
   China
   Email: jingxuan.n.zhang@gmail.com












































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