ALTO WG                                                           K. Gao
Internet-Draft                                       Tsinghua                                        Sichuan University
Intended status: Standards Track                                  Y. Lee
Expires: December 20, 2019 January 9, 2020                                          Huawei
                                                          S. Randriamasy
                                                         Nokia Bell Labs
                                                                 Y. Yang
                                                         Yale University
                                                                J. Zhang
                                                       Tongji University
                                                           June 18,
                                                            July 8, 2019

                 ALTO Extension: Path Vector Cost Type
                     draft-ietf-alto-path-vector-06
                     draft-ietf-alto-path-vector-07

Abstract

   The Application-Layer Traffic Optimization (ALTO) protocol [RFC7285]
   has defined cost maps and endpoint cost maps to provide basic network
   information.  However, they provide only scalar (numerical or
   ordinal) cost mode values, which are insufficient to satisfy the
   demands of solving more complex network optimization problems.  This
   document introduces an extension to the base ALTO protocol, namely
   the path-vector extension, which allows ALTO clients to query
   information such as the capacity region for a given set of flows
   (called co-flows).  A non-normative example called co-flow scheduling
   is presented to illustrate the limitations of existing ALTO endpoint
   cost maps.  After that, details of the extension are defined.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 20, 2019. January 9, 2020.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Use Case: Capacity Region for Co-Flow Scheduling  . Case  . . . . .   5
   4.  Overview of Path Vector Extensions . . . . . . . . . . . . .   7
     4.1.  New Cost Mode to Encode Path Vectors . . . . . . . .   5
     3.1.  Capacity Region for Co-Flow Scheduling  . .   7
     4.2.  New ALTO Entity Domain for ANE Properties . . . . . . .   5
     3.2.  In-Network Caching  .   8
     4.3.  Multipart/Related Resource for Consistency . . . . . . .   8
   5.  Path-Vector Cost Type . . . . . . . . . . .   7
   4.  Overview  . . . . . . . . .   9
     5.1.  Cost Mode: path-vector . . . . . . . . . . . . . . . . .  10
     5.2.   8
     4.1.  New Cost Metric: Link Maximum Reservable Bandwidth Mode to Encode Path Vectors  . . . . .  10
   6.  ANE . . . . .   8
     4.2.  New ALTO Entity Domain for ANE Properties . . . . . . . .   8
     4.3.  Multipart/Related Resource for Consistency  . . . . . . .   9
   5.  Basic Data Types  . . . . . . . . . .  10
     6.1.  Domain Name . . . . . . . . . . . .  10
     5.1.  ANE Identifier  . . . . . . . . . . .  11
     6.2.  Domain-Specific Entity Identifier . . . . . . . . . .  10
     5.2.  Path Vector Cost Type . .  11
     6.3.  Hierarchy and Inheritance . . . . . . . . . . . . . . . .  11
   7.  Multipart Filtered  10
       5.2.1.  Cost Map for Path Vector Metric: ane-path . . . . . . . . . .  11
     7.1.  Media Type . . . . . .  11
       5.2.2.  Cost Mode: array  . . . . . . . . . . . . . . . . . .  11
     7.2.  HTTP Method
     5.3.  ANE Domain  . . . . . . . . . . . . . . . . . . . . . . .  11
     7.3.  Accept Input Parameters
       5.3.1.  Domain Name . . . . . . . . . . . . . . . . .  12
     7.4.  Capabilities . . . .  11
       5.3.2.  Domain-Specific Entity Identifier . . . . . . . . . .  11
       5.3.3.  Hierarchy and Inheritance . . . . . . . . . . . .  12
     7.5.  Uses . .  11
     5.4.  ANE Properties  . . . . . . . . . . . . . . . . . . . . .  11
       5.4.1.  ANE Property: Maximum Reservable Bandwidth  . . . . .  11
       5.4.2.  ANE Property: Persistent Entity . . . . . . . .  12
     7.6.  Response . . .  12
   6.  Service Extensions  . . . . . . . . . . . . . . . . . . . . .  12
   8.
     6.1.  Multipart Endpoint Filtered Cost Service Map for Path Vector . . . . . . .  13
     8.1.  12
       6.1.1.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  13
     8.2.  12
       6.1.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .  13
     8.3.  12
       6.1.3.  Accept Input Parameters . . . . . . . . . . . . . . .  12
       6.1.4.  Capabilities  . .  13
     8.4.  Capabilities . . . . . . . . . . . . . . . . . .  13
       6.1.5.  Uses  . . . .  13
     8.5.  Uses . . . . . . . . . . . . . . . . . . . .  13
       6.1.6.  Response  . . . . . .  14
     8.6.  Response . . . . . . . . . . . . . . . .  13
     6.2.  Multipart Endpoint Cost Service for Path Vector . . . . .  15
       6.2.1.  Media Type  . . .  14
   9.  Examples . . . . . . . . . . . . . . . . . .  15
       6.2.2.  HTTP Method . . . . . . . .  14
     9.1.  Information Resource Directory Example . . . . . . . . .  14
     9.2.  Example #1 . . . .  15
       6.2.3.  Accept Input Parameters . . . . . . . . . . . . . . .  15
       6.2.4.  Capabilities  . . . .  16
     9.3.  Example #2 . . . . . . . . . . . . . . . .  15
       6.2.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . .  15
       6.2.6.  Response  . . . . . . . . . . . . . . . . . . . . . .  16
   7.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     9.4.
     7.1.  Information Resource Directory Example for Incremental Update  . . . . . . . . .  17
     7.2.  Example: Multipart Filtered Cost Map  . . . . . . . . . .  19
   10.
     7.3.  Example: Multipart Endpoint Cost Service  . . . . . . . .  20
     7.4.  Example: Incremental Updates  . . . . . . . . . . . . . .  22
   8.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .  20
     10.1.  24
     8.1.  Compatibility with Base ALTO Clients/Servers  . . . . . .  20
     10.2.  24
     8.2.  Compatibility with Multi-Cost Extension . . . . . . . .  21
     10.3. .  24
     8.3.  Compatibility with Incremental Update . . . . . . . . .  21
   11. .  24
   9.  General Discussions . . . . . . . . . . . . . . . . . . . . .  21
     11.1.  25
     9.1.  Provide Calendar for Property Map . . . . . . . . . . .  21
     11.2. .  25
     9.2.  Constraint Tests for General Cost Types . . . . . . . .  22
     11.3. .  25
     9.3.  General Multipart Resources Query . . . . . . . . . . .  22
   12. .  25
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  22
   13.  26
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
     13.1.  27
     11.1.  ALTO Cost Mode Registry  . . . . . . . . . . . . . . . .  23
     13.2.  27
     11.2.  ALTO Entity Domain Registry  . . . . . . . . . . . . . .  23
     13.3.  27
     11.3.  ALTO Property Type Registry  . . . . . . . . . . . . . .  24
   14.  27
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  24
   15.  27
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     15.1.  28
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     15.2.  28
     13.2.  Informative References . . . . . . . . . . . . . . . . .  25  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25  29

1.  Introduction

   The base ALTO protocol [RFC7285] is designed to expose network
   information through services such as cost maps and endpoint cost
   service.  These services use an extreme "single-node" network
   abstraction, which represents a whole network as a single node, and
   hosts as "endpoint groups" directly connected to the node.

   Although the "single-node" abstraction works well in many settings,
   it lacks the ability to support emerging use cases, such as co-flow
   scheduling for large-scale data analytics.  For such a use case,
   applications require a more powerful network view abstraction beyond
   the "single-node" abstraction.

   To support capabilities like co-flow scheduling, this document uses a
   "path vector" abstraction to represent more detailed network graph
   information like capacity regions.  A path vector is a sequence of
   abstract network elements (ANEs), and each ANE represents a network
   device that end-to-end traffic goes through, such as links, switches,
   middleboxes, and their aggregations.  An ANE can have properties such
   as "bandwidth", and "delay".  Providing such information can help
   both applications to achieve better application performance and
   networks to avoid network congestion.

   Providing path vector abstraction using ALTO introduces the following
   additional requirements (ARs):

   AR-1:  The path vector abstraction requires the encoding of array-
      like cost values rather than scalar cost values in cost maps or
      endpoint cost maps.

      Specifically, the path vector abstraction requires the
      specification of the sequence of ANEs between sources and
      destinations.  Such a sequence, however, cannot be encoded by the
      scalar types (numerical or ordinal) which the base ALTO protocol
      supports.

   AR-2:  The path vector abstraction requires the encoding of the
      properties of aforementioned ANEs.

      Specifically, only the sequences of ANEs are not enough for
      existing use cases.  Properties of ANEs such as "bandwidth" and
      "delay" are needed by applications to properly construct network
      constraints or states.

   AR-3:  The path vector abstraction requires consistent encoding of
      path vectors (AR-1) and the properties of the ANEs in a path
      vector (AR-2).

      Specifically, path vectors and the properties of ANEs in the
      vectors are dependent.  A mechanism to query both of them
      consistently is necessary.

   This document proposes the path vector extension to the ALTO protocol
   to satisfy these additional requirements .

   Specifically, the extension encodes the array (AR-1) of ANEs over an
   end-to-end path using a new cost type, and conveys the properties of
   ANEs (AR-2) using unified property map
   [I-D.ietf-alto-unified-props-new].  The path vector and ANE
   properties are conveyed in a single message encoded as a multipart/
   related message to satisfy AR-3.

   The rest of this document is organized as follows.  Section 3 3.1 gives
   an example of co-flow scheduling and illustrates the limitations of
   the base ALTO protocol in such a use case.  Section 4 gives an
   overview of the path vector extension.  Section 5 5.2 introduces a new
   cost type.  Section 6 5.3 registers a new domain in Domain Registry.
   Section 7 6.1 and Section 8 6.2 define new ALTO resources to support Path
   Vector query by using the request format of Filtered Cost Map and
   Endpoint Cost Service.  Section 9 7 presents several examples.
   Section 10 8 and Section 11 9 discusses compatibility issues with other
   existing ALTO extensions and design decisions.  Section 12 10 and
   Section 13 11 review the security and IANA considerations.

2.  Terminology

   Besides the terms defined in [RFC7285] and
   [I-D.ietf-alto-unified-props-new], this document also uses the
   following additional terms: Abstract Network Element and Path Vector.

   o  Abstract Network Element (ANE): An abstract network element is an
      abstraction of network components.  It can be an aggregation of
      links, middleboxes, virtualized network function (VNF), etc.  An
      abstract network element has two types of attributes: a name and a
      set of properties.

   o  Path Vector: A path vector is an array of ANEs.  It presents an
      abstract network path between source/destination points such as
      PIDs or endpoints.

3.  Use Case: Case

3.1.  Capacity Region for Co-Flow Scheduling

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

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

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

                      Figure 1: Raw Network Topology.

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

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

             Figure 2: Base Single-Node Topology Abstraction.

   Consider an application overlay (e.g., a large data analysis system)
   which wants to schedule the traffic among a set of end host source-
   destination pairs, say eh1 -> eh2 and eh3 -> eh4.  The application
   can request a cost map providing end-to-end available bandwidth,
   using "availbw" 'availbw' as cost-metric and "numerical" 'numerical' as cost-mode.

   The application will receive from ALTO server that the bandwidth of
   eh1 -> eh2 and eh3 -> eh4 are both 100 Mbps.  But this information is
   not enough.  Consider the following two cases:

   o  Case 1: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw6 ->
      sw7 -> sw2 -> eh2 and eh3 -> eh4 uses path eh3 -> sw3 -> sw5 ->
      sw7 -> sw4 -> eh4, then the application will obtain 200 Mbps.

   o  Case 2: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw7 ->
      sw2 -> eh2 and eh3 -> eh4 uses the path eh3 -> sw3 -> sw5 -> sw7
      -> sw4 -> eh4, then the application will obtain only 100 Mbps due
      to the shared link from sw5 to sw7.

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

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

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

   The path vector extension defined in this document provides a
   solution to address the preceding issue.

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

4.  Overview of Path Vector Extensions

   This section presents an overview of approaches adopted by the path
   vector extension.  It assumes that the readers

3.2.  In-Network Caching

   Consider a network as shown in Figure 3.  Two clients (C1/eh2 and C2/
   eh3) are familiar with cost
   map downloading data from a server (S/eh1) and endpoint cost service defined in [RFC7285].  The path vector
   extension also requires the support of Filtered Property Map defined
   in [I-D.ietf-alto-unified-props-new]. network
   provides an HTTP proxy which can cache results.  The clients and the
   server are controlled by an ALTO client.

                                     +---------+
                                     | Caching |
                                    -+ Proxy   |
                                   / |         |
         S      +-------+         /  +---------+
           eh1__| sub   |_       /
                | net 1 | \   +--|---+         +----------+
                +-------+  ---|      |         |          |     C2
                              | Gate +---------+ Internet |__eh3
         C1     +-------+   --| way  |         |          |
           eh2__| sub   |__/  +------+         +----------+
                | net 2 |
                +-------+

        Figure 3: Raw Topology for the In-Network Caching Use Case.

   Without the traffic correlation information, the ALTO client cannot
   know whether or how the traffic goes through the proxy.  For example,
   if subnet1 and subnet2 are directly connected and the traffic from
   eh1 to eh2 bypasses the gateway, the in-network cache can only be
   used for traffic from C2 to S and is less effective.

4.  Overview

   This section presents an overview of approaches adopted by the path
   vector extension.  It assumes that the readers are familiar with cost
   map and endpoint cost service defined in [RFC7285].  The path vector
   extension also requires the support of Filtered Property Map defined
   in [I-D.ietf-alto-unified-props-new].

   The path vector extension is composed of three building blocks: (1) a
   new cost mode to encode path vectors in a cost map or an endpoint
   cost map; (2) a new ALTO entity domain to enable ANE property
   encoding using the unified property extension
   [I-D.ietf-alto-unified-props-new]; and (3) a generic mechanism to put
   multiple ALTO information objects in a single response to enforce
   consistency, to preserve modularity and to avoid complex linking of
   multiple responses.

4.1.  New Cost Mode to Encode Path Vectors

   Existing cost modes defined in [RFC7285] allow only scalar cost
   values.  However, the "path vector" abstraction requires to convey
   vector format information (AR-1).  To fulfill this requirement, this
   document defines a new "cost-mode" named path vector to indicate that
   the cost value is an array of ANEs.  A path vector abstraction should
   be computed for a specific performance metric, and this is achieved
   using the existing "cost-metric" component of cost type.  The details
   of the new "cost-mode" is given in Section 5. 5.2.

4.2.  New ALTO Entity Domain for ANE Properties

   A path vector of ANEs contains only the abstracted routing elements
   between a source and a destination.  Hence, an application can find
   shared ANEs of different source-destination pairs but cannot know the
   shared ANEs' properties.  For the capacity region use case in
   Section 3, 3.1, knowing that eh1->eh2 and eh3->eh4 share ANEs but not
   the available bandwidth of the shared ANEs, is not enough.

   To encode ANE properties like the available bandwidth in a path
   vector query response, this document uses the unified property
   extension defined in [I-D.ietf-alto-unified-props-new].
   Specifically, for each path vector query, the ALTO server generates a
   property map associated to the (endpoint) cost map as follows:

   o  a dynamic entity domain of an entity domain type "ane" is
      generated to contain the generated ANEs.  Each ANE has the same
      unique identifier in the path vectors and in the dynamic entity
      domain;

   o  each entity in this dynamic entity domain has the property defined properties
      specified by the "cost-metric" that generated the ANEs in the query. client.

   Detailed information and specifications are given in Section 6. 5.3.

4.3.  Multipart/Related Resource for Consistency

   Path vectors and the property map containing the ANEs are two
   different types of objects, but they require strong consistency.  One
   approach to achieving strong consistency is to define a new media
   type to contain both objects, but this violates modular design.

   Another approach is to provide the objects in two different
   information resources.  Thus, an ALTO client needs to make separate
   queries to get the information of related services.  This may cause a
   data synchronization problem between two queries.  Also, as the
   generation of ANE is dynamic, an ALTO server must cache the results
   of a query before a client fully retrieves all related resources,
   which hurts the scalability and security of an ALTO server.

   This document uses standard-conforming usage of "multipart/related"
   media type defined in [RFC2387] to elegantly solve the problem.

   Specifically, using "multipart/related" needs to address two issues:

   o  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-
      endpointcostmap+json" for endpoint cost map).  Simply putting
      "multipart/related" as the media type, however, makes it
      impossible for an ALTO client to identify the type of service
      provided by related entries.

   o  The ALTO SSE extension (see [I-D.ietf-alto-incr-update-sse])
      depends on resource-id to identify push updates, but resource-id
      is provided only in IRD and hence each entry in the IRD has only
      one resource-id.

   This design addresses the two issues as follows:

   o  To address the first issue, the multipart/related media type
      includes the type parameter to allow type indication of the root
      object.  For a cost map service, the "media-type" will be
      "multipart/related" with the parameter "type=application/alto-
      costmap+json"; for an endpoint cost map service, the parameter
      will be "type=application/alto-endpointcostmap+json".  This design
      is highly extensible.  The entries can still use "application/
      alto-costmapfilter+json" or "application/alto-
      endpointcostparams+json" as the accept input parameters, and hence
      an ALTO client still sends the filtered cost map request or
      endpoint cost service request.  The ALTO server sends the response
      as a "multipart/related" message.  The body of the response
      includes two parts: the first one is of the media type specified
      by the "type" parameter; the second one is a property map
      associated to the first map.

   o  To address the second issue, each part of the "multipart/related"
      response message has the MIME part header information including
      "Content-Type" and "Resource-Id".  An ALTO server MAY generate
      incremental updates (see [I-D.ietf-alto-incr-update-sse]) for each
      part separately using the "Resource-Id" header.

   By applying the design above, for each path vector query, an ALTO
   server returns the path vectors and the associated property map
   modularly and consistently.  An ALTO server can reuse the data models
   of the existing information resources.  And an ALTO client can
   subscribe to the incremental updates for the dynamic generated
   information resources without any changes, if th ALTO server provides
   incremental updates for them.

5.  Path-Vector Cost Type

   This document extends the cost types defined in Section 6.1 of
   [RFC7285] by introducing  Basic Data Types

5.1.  ANE Identifier

   An ANE identifier is encoded as a new cost mode "path-vector".  In JSON string.  The string MUST be no
   more than 64 characters, and it MUST NOT contain characters other
   than US-ASCII alphanumeric characters (U+0030-U+0039, U+0041-U+005A,
   and U+0061-U+007A), the rest
   of hyphen ("-", U+002D), the document, we use "path-vector" to indicate colon (":",
   U+003A), the cost type with at sign ("@", code point U+0040), the cost-mode "path-vector" for short.

5.1.  Cost Mode: path-vector

   This document extends low line ("_",
   U+005F), or the CostMode defined in Section 10.5 of
   [RFC7285] with a new cost mode: "path-vector".  This cost mode
   indicates that every cost value in a cost map represents an array of
   ANEs which are defined in Section 6.2, rather than a JSON number or a
   ranking order. "." separator (U+002E).  The ANEs computed by the ALTO server associate to the cost metric for
   the "path-vector" cost mode.  This document re-defines some cost
   metrics "." separator is
   reserved for "path-vector", which are motivated by the co-flow
   scheduling future use case.  The ALTO client SHOULD ignore the "path-vector"
   cost mode with any other cost metrics, and MUST NOT be used unless the future documents
   define other cost metrics specifically
   indicated in this document, or specify the semantics an extension document.

   The type ANEIdentifier is used in this document to indicate a string
   of existing cost
   metrics for "path-vector" cost mode for some additional requirements. this format.

5.2.  Path Vector Cost Metric: Link Maximum Reservable Bandwidth Type

   This document uses defines a new cost type, which is referred to as the same metric name, units of measurement and
   measurement point(s) with potential measurement domain defined by
   section 4.1 of [I-D.ietf-alto-performance-metrics], but specifies
   different metric description and method of measurement or calculation
   for "path-vector"
   "path vector" cost mode only.

   Metric Description:  When used with "path-vector" type.  An ALTO server MUST offer this cost mode, type if
   it is to
      specify supports the path vector computed by using the spatial and temporal
      maximum reservable bandwidth over each network link.  The value of
      the maximum reservable bandwidth extension.

5.2.1.  Cost Metric: ane-path

   This cost metric conveys an array of ANE identifiers, where each
   identifier uniquely represents an ANE in the path vector is
      specified in the associated property map.

   Method of Measurement or Calculation:  The value of Maximum
      Reservable Bandwidth is the bandwidth measured between two
      directly connected IS-IS neighbors, OSPF neighbors or BGP
      neighbors.  The associated ANEs are computed traversed by some algorithm
      which can guarantee the equivalent Maximum Reservable Bandwidth
      constraints.

6.  ANE Domain

   This document specifies traffic from a new ALTO entity domain called "ane" in
   addition
   source to the ones in [I-D.ietf-alto-unified-props-new].  The ANE
   domain associates property values with the ANEs in a network.  The
   entity in ANE domain is often used in the path vector by destination.

5.2.2.  Cost Mode: array

   This cost maps or
   endpoint mode indicates that every cost resources.  Accordingly, the ANE domain always depends
   on value in a cost map or an
   endpoint cost map.

6.1.  Domain Name

   ane

6.2.  Domain-Specific Entity Identifier

   The entity identifier of ane domain is encoded map MUST be interpreted as a JSON string.  The
   string MUST array object.

   Note that this cost mode only requires the cost value to be no more than 64 characters, and it a JSON
   array of JSONValue.  However, an ALTO server that enables this
   extension MUST NOT contain
   characters other than US-ASCII alphanumeric characters
   (U+0030-U+0039, U+0041-U+005A, and U+0061-U+007A), the hyphen ("-",
   U+002D), the colon (":", U+003A), the at sign ("@", code point
   U+0040), the low line ("_", U+005F), or return a JSON array of ANEIdentifier (Section 5.1)
   when the "." separator (U+002E).
   The "." separator cost metric is reserved for future use and MUST NOT be used
   unless specifically indicated "ane-path".

5.3.  ANE Domain

   This document specifies a new ALTO entity domain called "ane" in this document, or an extension
   document.

   To simplify the description, we use "ANE name"
   addition to indicate the
   identifier of an entity ones in [I-D.ietf-alto-unified-props-new].  The ANE
   domain associates property values with the ANEs in this document. a network.  The
   entity in ANE name domain is usually unrelated to often used in the physical device information.
   It is usually generated path vector by cost maps or
   endpoint cost resources.  Accordingly, the ALTO server ANE domain always depends
   on demand and used to
   distinguish from other ANEs in its dependent a cost map or an endpoint cost map.

6.3.

5.3.1.  Domain Name

   ane

5.3.2.  Domain-Specific Entity Identifier

   The entity identifier of ANE domain uses the same encoding as
   ANEIdentifier (Section 5.1).

5.3.3.  Hierarchy and Inheritance

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

7.

5.4.  ANE Properties

5.4.1.  ANE Property: Maximum Reservable Bandwidth

   The maximum reservable bandwidth property conveys the maximum
   bandwidth that can be reserved for traffic from a source to a
   destination and is indicated by the property name "maxresbw".  The
   value MUST be encoded as a numerical cost value as defined in
   Section 6.1.2.1 of [RFC7285] and the unit is bit per second.

   If this property is requested but is missing for a given ANE, it MUST
   be interpreted as that the ANE does not support bandwidth reservation
   but have sufficiently large bandwidth for all traffic that traverses
   it.

5.4.2.  ANE Property: Persistent Entity

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

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

6.  Service Extensions

6.1.  Multipart Filtered Cost Map for Path Vector

   This document introduces a new ALTO resource called Multipart
   Filtered Cost Map resource, which allows an ALTO server to provide
   other ALTO resources associated to the Cost Map resource in the same
   response.

7.1.

6.1.1.  Media Type

   The media type of the Multipart Filtered Cost Map Resource is
   "multipart/related;type=application/alto-costmap+json".

7.2.

6.1.2.  HTTP Method

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

7.3.

6.1.3.  Accept Input Parameters

   The input parameters of the Multipart Filtered Cost Map MUST be
   encoded as a JSON object Map are supplied
   in the body of an HTTP POST request.  The  This document extends the input
   parameters to a filtered Cost Map with a data format indicated by the
   media type "application/alto-costmapfilter+json", which is a JSON
   object of type PVReqFilteredCostMap, where:

   object {
     [PropertyName ane-properties<0..*>;]
   } PVReqFilteredCostMap : ReqFilteredCostMap;
   with fields:

   ane-properties:  A list of properties that are associated with the request
      ANEs.  Each property in this list MUST be match one of "application/alto-
   costmapfilter+json".  The format of the request body supported
      ANE properties indicated in the resource's "ane-properties"
      capability.  If the field is NOT present, it MUST be the same
   type interpreted
      as defined by section 11.3.2.3 of [RFC7285].

7.4. an empty list, indicating that the ALTO server MUST NOT return
      any property in the unified property part.

6.1.4.  Capabilities

   The Multipart Filtered Cost Map resource uses extends the same capabilities
   as
   defined by section in Section 11.3.2.4 of [RFC7285].  But the "cost-type-
   names"  The capabilities are
   defined by a JSON object of type PVFilteredCostMapCapabilities:

   object {
     [PropertyName ane-properties<0..*>;]
   } PVFilteredCostMapCapabilities : FilteredCostMapCapabilities;

   with fields:

   cost-type-names:  The "cost-type-names" field SHOULD MUST only includes cost types in "path-vector" cost
   mode.  Otherwise, include the ALTO client SHOULD ignore
      path vector cost type, unless explicitly documented by a future
      extension.  This also implies that the path vector cost type MUST
      be defined in other
   cost mode, unless additional documents define the specification "cost-types" of the Information Resource
      Directory's "meta" field.

   ane-properties:  Defines a list of ANE properties that can be
      returned.  If the field is NOT present, it
   for MUST be interpreted as
      an empty list, indicating the Multipart Filtered Cost Map resource.

7.5. ALTO server CANNOT provide any ANE
      property.

6.1.5.  Uses

   The resource ID of the network map based on which the PIDs in the
   returned cost map will be defined.

7.6.  If this resource supports
   "persistent-entities", it MUST also include ALL the resources that
   exposes the entities that MAY appear in the response.

6.1.6.  Response

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

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

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

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

   boundary:  The response to a valid request MUST be a "multipart/related" message boundary parameter is as defined by in [RFC2387].

   The body of the response consists of two parts:

   o  the parts.

   The first part MUST include "Resource-Id" and "Content-Type" in its
   header.  The value of "Resource-Id" MUST be prefixed by the resource
   id of the Multipart Filtered Cost Map appended by a "." character.
   The "Content-Type" MUST be "application/alto-costmap+json".

   The body of this the first part MUST be a JSON object with the same format
   as defined in Section 11.2.3.6 of [RFC7285]; [RFC7285].  The JSON object MUST
   include the "vtag" field in the "meta" field, which provides the
   version tag of the returned cost map.  The resource id of the version
   tag MUST be as the same as the value of the "Resource-Id" header.  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 Cost Map resource in IRD.

   o  the

   The second part MUST also include "Resource-Id" and "Content-Type" in
   its header.  The value of "Resource-Id" MUST be prefixed by the
   resource id of the Multipart Filtered Cost Map appended by a "."
   character.  The "Content-Type" MUST be "application/alto-
   propmap+json".

   The body of this the second part MUST be a JSON object with the same
   format as defined in Section 4.6 of
   [I-D.ietf-alto-unified-props-new].  The JSON object MUST include the
   "dependent-vtags" field in the "meta" field.  The value of the
   "dependent-vtags" field MUST be an array with a single of VersionTag
      object objects as
   defined by section Section 10.3 of [RFC7285].  The "resource-id" "vtag" of this VersionTag the first part
   MUST be included in the value of "Resource-Id" header of "dependent-vtags".  If "persistent-entities"
   is requested, the first part.  The "tag" version tags of this VersionTag the dependent resources that MAY
   expose the entities in the response MUST also be the "tag" of
      "vtag" of included.  The
   PropertyMapData has one member for each ANE identifier that appears
   in the first part body.

8. part, where the EntityProps has one member for each
   property requested by the client if applicable.

6.2.  Multipart Endpoint Cost Service for Path Vector

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

8.1.

6.2.1.  Media Type

   The media type of the Multipart Endpoint Cost Resource is
   "multipart/related;type=application/alto-endpointcostmap+json".

8.2.

6.2.2.  HTTP Method

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

8.3.

6.2.3.  Accept Input Parameters

   The input parameters of the Multipart Endpoint Cost resource MUST be
   encoded as a JSON object are
   supplied in the body of an HTTP POST request.  The  This document extends
   the input parameters to an Endpoint Cost Map with a data format
   indicated by the media type of the request MUST be one of "application/alto-
   endpointcostparams+json".  The format
   endpointcostparams+json", which is a JSON object of type
   PVEndpointCostParams, where

   object {
     [PropertyName ane-properties<0..*>;]
   } PVReqEndpointCostMap : ReqEndpointCostMap;

   with fields:

   ane-properties:  This document defines the request body MUST be "ane-properties" in
      PVReqEndpointCostMap as the same type as defined by section 11.5.1.3 of [RFC7285].

8.4. in PVReqFilteredCostMap.  See
      Section 6.1.3.

6.2.4.  Capabilities

   The capabilities of the Multipart Endpoint Cost resource uses the same capabilities as Service are defined
   by section 11.3.2.4 of [RFC7285].  But the "cost-type-names"
   field SHOULD only includes cost types in "path-vector" cost mode.
   Otherwise, the ALTO client SHOULD ignore a cost type in other cost
   mode, unless additional documents define the specification JSON object of it for type PVEndpointCostMapCapabilities, which is
   defined as the Multipart Endpoint Cost resource.

8.5. same as PVFilteredCostMapCapabilities.  See
   Section 6.1.4.

6.2.5.  Uses

   The

   If a Multipart Endpoint Cost resource supports "persistent-entities",
   the "uses" field in its IRD entry MUST NOT specify include ALL the "uses"
   attribute.

8.6. resources
   which exposes the entities that MAY appear in the response.

6.2.6.  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 to a valid request MUST be a "multipart/related" message
   as defined by [RFC2387] with the following parameters:

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

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

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

   The body consists of two parts:

   o  the

   The first part MUST include "Resource-Id" and "Content-Type" in its
   header.  The value of "Resource-Id" MUST be prefixed by the resource
   id of the Multipart Filtered Endpoint Cost Map Service appended by a "." character
   (U+002E).  The "Content-Type" MUST be "application/alto-
   endpointcostmap+json".

   The body of this the first part MUST be a JSON object with the same format
   as defined in Section 11.5.1.6 of [RFC7285]; The JSON object MUST
   include the "vtag" field in the "meta" field, which provides the
   version tag of the returned endpoint cost map.  The resource id of
   the version tag MUST be as the same as the value of the "Resource-Id"
   header.

   o  the

   The second part MUST also include "Resource-Id" and "Content-Type" in
   its header.  The value of "Resource-Id" MUST be prefixed by the
   resource id of the Multipart Filtered Cost Map appended by a "."
   character (U+002E).  The "Content-Type" MUST be "application/alto-
   propmap+json".

   The body of this the second part MUST be a JSON object with the same
   format as defined in Section 4.6 of
   [I-D.ietf-alto-unified-props-new].  The JSON object MUST include the
   "dependent-vtags" field in the "meta" field.  The value of the
   "dependent-vtags" field MUST be an array with a single of VersionTag
      object objects as
   defined by section Section 10.3 of [RFC7285].  The "resource-id" "vtag" of this VersionTag the first part
   MUST be included in the value of "Resource-Id" header of "dependent-vtags".  If "persistent-entities"
   is requested, the first part.  The "tag" version tags of this VersionTag the dependent resources that MAY
   expose the entities in the response MUST also be the "tag" of
      "vtag" of included.  The
   PropertyMapData has one member for each ANE identifier that appears
   in the first part body.

9. part, where the EntityProps has one member for each
   property requested by the client if applicable.

7.  Examples

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

9.1.  Some long lines are truncated for better
   readability.

7.1.  Information Resource Directory Example

   Here

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

   o  The "path-vector" cost type (Section 5.2) is defined in the "cost-
      types" of the "meta" field.

   o  The "cost-map-pv" information resource provides a Multipart Cost
      Map resource, which exposes the Maximum Reservable Bandwidth
      ("maxresbw") property.

   o  The "http-proxy-props" information resource for path-vector; provides a filtered
      Unified Property Map resource, which exposes the HTTP proxy entity
      domain (encoded as "http-proxy") and the "price" property.  Note
      that HTTP proxy is NOT a valid entity domain yet and is used here
      only for demonstration.

   o  The "endpoint-cost-pv" information resource provides a MultipartEndpoint Multipart
      Endpoint Cost resource for path-vector.

   Both of them support Service.  It exposes the Maximum Reservable
      Bandwidth ("maxresbw")
   cost metric in "path-vector" cost mode. property and the Persistent Entity
      property.  The persistent entities MAY come from the "http-proxy-
      props" resource.

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

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

9.2.  Example #1

   Query filtered cost map

7.2.  Example: Multipart Filtered Cost Map

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

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

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

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

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

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

   HTTP/1.1 200 OK
   Content-Length: [TBD]
   Content-Type: multipart/related;
                 boundary=example-1;
                 start=cost-map-pv.costmap
                 start=cost-map-pv.costmap;
                 type=application/alto-costmap+json

   --example-1
   Resource-Id: cost-map-pv.costmap
   Content-Type: application/alto-costmap+json

   {
     "meta": {
       "vtag": {
         "resource-id": "cost-map-pv.costmap",
         "tag": "d827f484cb66ce6df6b5077cb8562b0a"
       },
       "dependent-vtags": [
         {
           "resource-id": "my-default-networkmap",
           "tag": "75ed013b3cb58f896e839582504f6228"
         }
       ],
       "cost-type": {
         "cost-mode": "path-vector", "array",
         "cost-metric": "maxresbw" "ane-path"
       }
     },
     "cost-map": {
       "PID1": {
         "PID2": [ "ane:L001", "ane:L003" ],
         "PID3": [ "ane:L001", "ane:L004" ]
       }
     }
   }
   --example-1
   Resource-Id: cost-map-pv.propmap
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "cost-map-pv.costmap",
           "tag": "d827f484cb66ce6df6b5077cb8562b0a"
         }
       ]
     },
     "property-map": {
       "ane:L001": { "maxresbw": 100000000},
       "ane:L003": { "maxresbw": 150000000},
       "ane:L004": { "maxresbw": 50000000}
     }
   }

9.3.  Example #2

7.3.  Example: Multipart Endpoint Cost Service

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

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

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

   The second part returns the requested properties of ANEs in the first
   part.  The "ane:NET001" element contains an HTTP proxy entity, which
   can be further used by the client.  Since it does not contain a
   "maxresbw" property, the client SHOULD assume it does NOT support
   bandwidth reservation but will NOT become a traffic bottleneck, as
   specified in Section 5.4.1.

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

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

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

   --example-2
   Resource-Id: endpoint-cost-pv.ecs
   Content-Type: application/alto-endpointcost+json

   {
     "meta": {
       "vtags": {
         "resource-id": "endpoint-cost-pv.ecs",
         "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
       },
       "cost-type": {
         "cost-mode": "path-vector", "array",
         "cost-metric": "maxresbw" "ane-path"
       }
     },
     "endpoint-cost-map": {
       "ipv4:192.0.2.2": {
         "ipv4:192.0.2.89":   [ "ane:L001", "ane:L003",
                                "ane:L004" ],
         "ipv4:203.0.113.45": [ "ane:L001", "ane:L004",
                                "ane:L005" "ane:NET001", "ane:L002" ],

         "ipv6:2001:db8::10":
         "ipv4:203.0.113.45": [ "ane:L001", "ane:L005",
                                "ane:L007" "ane:NET001", "ane:L003" ]
       }
     }
   }
   --example-2
   Resource-Id: endpoint-cost-pv.propmap
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {
           "resource-id": "endpoint-cost-pv.ecs",
           "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
         },
         {
           "resource-id": "http-proxy-props",
           "tag": "bf3c8c1819d2421c9a95a9d02af557a3"
         }
       ]
     },
     "property-map": {
       "ane:L001":
       "ane:NET001": { "maxresbw": 50000000
         "persistent-entities": [ "http-proxy:192.0.2.1" ]
       },
       "ane:L003":
       "ane:L002": { "maxresbw": 48000000 },
       "ane:L004": { "maxresbw": 55000000 },
       "ane:L005": { "maxresbw": 60000000 },
       "ane:L007":
       "ane:L003": { "maxresbw": 35000000 }
     }
   }

9.4.  Example for

7.4.  Example: Incremental Update Updates

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

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

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

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

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

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

   event: multipart/related;boundary=example-3;start=pvmap;
          type=application/alto-endpointcost+json,ecspvsub1
   data: --example-3
   data: Content-ID: pvmap Resource-ID: endpoint-cost-pv.ecsmap02695067
   data: Content-Type: application/alto-endpointcost+json
   data:
   data: <endpoint-cost-map-entry>
   data: --example-3
   data: Content-ID: nepmap Resource-ID: endpoint-cost-pv.propmapbbc868aa
   data: Content-Type: application/alto-propmap+json
   data:
   data: <property-map-entry>
   data: --example-3--

   Then, the ALTO server will subscribe the whole tree of the multipart
   message automatically.

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

   event: application/merge-patch+json,ecspvsub1.pvmap application/merge-patch+json,
          ecspvsub1.endpoint-cost-pv.ecsmap02695067
   data: <Merge patch for endpoint-cost-map-update>

   event: application/merge-patch+json,ecspvsub2.nepmap application/merge-patch+json,
          ecspvsub1.endpoint-cost-pv.propmapbbc868aa
   data: <Merge patch for property-map-update>

10.

8.  Compatibility

10.1.

8.1.  Compatibility with Base ALTO Clients/Servers

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

10.2.

8.2.  Compatibility with Multi-Cost Extension

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

10.3.

8.3.  Compatibility with Incremental Update

   As this document still follows the basic request/response protocol
   with JSON encoding, it is surely compatible with the incremental
   update service as defined by [I-D.ietf-alto-incr-update-sse].  But
   the following details are to be noticed:

   o  When using the compound response, updates on both cost map and
      property map SHOULD be notified.

   o  When not using the compound response, because the cost map is in
      the "uses" attribute of the property map, once the path vectors in
      the cost map change, the ALTO server MUST send the updates of the
      cost map before the updates of the property map.

11.

9.  General Discussions

11.1.

9.1.  Provide Calendar for Property Map

   Fetching the historical network information is useful for many
   traffic optimization problem.  [I-D.ietf-alto-cost-calendar] already
   proposes an ALTO extension called Cost Calendar which provides the
   historical cost values using Filtered Cost Map and Endpoint Cost
   Service.  However, the calendar for only path costs is not enough.

   For example, as the properties of ANEs (e.g., available bandwidth and
   link delay) are usually the real-time network states, they change
   frequently in the real network.  It is very helpful to get the
   historical value of these properties.  Applications may predicate the
   network status using these information to better optimize their
   performance.

   So the coming requirement may be a general calendar service for the
   ALTO information resources.

11.2.

9.2.  Constraint Tests for General Cost Types

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

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

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

11.3.

9.3.  General Multipart Resources Query

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

12.

10.  Security Considerations

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

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

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

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

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

   Even if there is no intentional attack, the dependent property map of
   path vector might be still dynamically enriched, in that every new
   request for path vectors will make the ALTO server generate a new
   property map.  So the properties of the abstract network elements can
   consume a large amount of resources when cached.  To avoid this, the
   ALTO server providing the path vector extension should support a
   time-to-live configuration for the property map, so that the outdated
   entries can be removed from the property map resource.

13.

11.  IANA Considerations

13.1.

11.1.  ALTO Cost Mode Registry

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

13.2.

11.2.  ALTO Entity Domain Registry

   As proposed in Section 9.2 of [I-D.ietf-alto-unified-props-new],
   "ALTO Domain Entity Registry" is requested.  Besides, a new domain is
   to be registered, listed in Table 1.

   +-------------+--------------------------+--------------------------+
   | Identifier  | Entity Address Encoding  | Hierarchy & Inheritance  |
   +-------------+--------------------------+--------------------------+
   | ane         | See Section 6.2 5.3.2        | None                     |
   +-------------+--------------------------+--------------------------+

                        Table 1: ALTO Entity Domain

13.3.

11.3.  ALTO Property Type Registry

   The "ALTO Property Type Registry" is required by the ALTO Domain
   "ane", listed in Table 2.

   +-------------+------------+----------------------------------------+
   | Identifier  | Intended   | Dependencies and Interpretation        |
   |             | Semantics  |                                        |
   +-------------+------------+----------------------------------------+
   | ane:maxresb | The        | application/alto-costmap+json, or      |
   | w           | maximum    | application/alto-endpointcostmap+json, |
   |             | reservable | where the ANE names are used.          |
   |             | bandwidth  |                                        |
   |             | for the    |                                        |
   |             | ANE        |                                        |
   +-------------+------------+----------------------------------------+

           Table 2: ALTO Abstract Network Element Property Types

14.

12.  Acknowledgments

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

15.

13.  References

15.1.

13.1.  Normative References

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

15.2.  Informative References

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

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

   [I-D.ietf-alto-incr-update-sse]
              Roome, W. and Y. Yang, "ALTO Incremental Updates Using
              Server-Sent Events (SSE)", draft-ietf-alto-incr-update-
              sse-16 (work in progress), March 2019.

   [I-D.ietf-alto-performance-metrics]
              Wu, Q., Yang, Y., Lee, Y., Dhody, D., and S. Randriamasy,
              "ALTO Performance Cost Metrics", draft-ietf-alto-
              performance-metrics-06 (work in progress), November 2018.

   [I-D.ietf-alto-unified-props-new]
              Roome, W., Randriamasy, S., Yang, Y., and J. Zhang,
              "Unified Properties for the ALTO Protocol", draft-ietf-
              alto-unified-props-new-07 (work in progress), March 2019.

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

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

   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.

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

13.2.  Informative References

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

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

   [I-D.ietf-alto-performance-metrics]
              Wu, Q., Yang, Y., Lee, Y., Dhody, D., and S. Randriamasy,
              "ALTO Performance Cost Metrics", draft-ietf-alto-
              performance-metrics-06 (work in progress), November 2018.

Authors' Addresses

   Kai Gao
   Tsinghua
   Sichuan University
   Beijing  Beijing
   Chengdu  610000
   China

   Email: gaok12@mails.tsinghua.edu.cn kai.gao@scu.edu.cn

   Young Lee
   Huawei
   TX
   USA

   Email: leeyoung@huawei.com

   Sabine Randriamasy
   Nokia Bell Labs
   Route de Villejust
   NOZAY  91460
   FRANCE

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

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

   Email: yry@cs.yale.edu

   Jingxuan Jensen Zhang
   Tongji University
   4800 Caoan Road
   Shanghai  201804
   China

   Email: jingxuan.n.zhang@gmail.com