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Versions: (draft-yang-alto-path-vector) 00 01 02 03 04 05 06 07 08

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


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

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
   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



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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 20, 2019.

Copyright Notice

   Copyright (c) 2019 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Use Case: Capacity Region for Co-Flow Scheduling  . . . . . .   5
   4.  Overview of Path Vector Extensions  . . . . . . . . . . . . .   7
     4.1.  New Cost Mode to Encode Path Vectors  . . . . . . . . . .   7
     4.2.  New ALTO Entity Domain for ANE Properties . . . . . . . .   8
     4.3.  Multipart/Related Resource for Consistency  . . . . . . .   8
   5.  Path-Vector Cost Type . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Cost Mode: path-vector  . . . . . . . . . . . . . . . . .  10
     5.2.  Cost Metric: Link Maximum Reservable Bandwidth  . . . . .  10
   6.  ANE Domain  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Domain Name . . . . . . . . . . . . . . . . . . . . . . .  11
     6.2.  Domain-Specific Entity Identifier . . . . . . . . . . . .  11
     6.3.  Hierarchy and Inheritance . . . . . . . . . . . . . . . .  11
   7.  Multipart Filtered Cost Map for Path Vector . . . . . . . . .  11
     7.1.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  11
     7.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .  11
     7.3.  Accept Input Parameters . . . . . . . . . . . . . . . . .  12
     7.4.  Capabilities  . . . . . . . . . . . . . . . . . . . . . .  12
     7.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.6.  Response  . . . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Multipart Endpoint Cost Service for Path Vector . . . . . . .  13
     8.1.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  13
     8.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .  13
     8.3.  Accept Input Parameters . . . . . . . . . . . . . . . . .  13
     8.4.  Capabilities  . . . . . . . . . . . . . . . . . . . . . .  13



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     8.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.6.  Response  . . . . . . . . . . . . . . . . . . . . . . . .  14
   9.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Information Resource Directory Example  . . . . . . . . .  14
     9.2.  Example #1  . . . . . . . . . . . . . . . . . . . . . . .  16
     9.3.  Example #2  . . . . . . . . . . . . . . . . . . . . . . .  17
     9.4.  Example for Incremental Update  . . . . . . . . . . . . .  19
   10. Compatibility . . . . . . . . . . . . . . . . . . . . . . . .  20
     10.1.  Compatibility with Base ALTO Clients/Servers . . . . . .  20
     10.2.  Compatibility with Multi-Cost Extension  . . . . . . . .  21
     10.3.  Compatibility with Incremental Update  . . . . . . . . .  21
   11. General Discussions . . . . . . . . . . . . . . . . . . . . .  21
     11.1.  Provide Calendar for Property Map  . . . . . . . . . . .  21
     11.2.  Constraint Tests for General Cost Types  . . . . . . . .  22
     11.3.  General Multipart Resources Query  . . . . . . . . . . .  22
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  22
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
     13.1.  ALTO Cost Mode Registry  . . . . . . . . . . . . . . . .  23
     13.2.  ALTO Entity Domain Registry  . . . . . . . . . . . . . .  23
     13.3.  ALTO Property Type Registry  . . . . . . . . . . . . . .  24
   14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  24
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     15.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

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




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   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 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 introduces a new
   cost type.  Section 6 registers a new domain in Domain Registry.
   Section 7 and Section 8 define new ALTO resources to support Path



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   Vector query by using the request format of Filtered Cost Map and
   Endpoint Cost Service.  Section 9 presents several examples.
   Section 10 and Section 11 discusses compatibility issues with other
   existing ALTO extensions and design decisions.  Section 12 and
   Section 13 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: 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.














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

                      Figure 1: Raw Network Topology.

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

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

             Figure 2: Base Single-Node Topology Abstraction.

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

   The application will receive from ALTO server that the bandwidth of
   eh1 -> eh2 and 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.





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   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 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.



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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, 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
      by the "cost-metric" that generated the ANEs in the query.

   Detailed information and specifications are given in Section 6.

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-



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      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 a new cost mode "path-vector".  In the rest
   of the document, we use "path-vector" to indicate the cost type with
   the cost-mode "path-vector" for short.



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5.1.  Cost Mode: path-vector

   This document extends 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.

   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 for "path-vector", which are motivated by the co-flow
   scheduling use case.  The ALTO client SHOULD ignore the "path-vector"
   cost mode with any other cost metrics, unless the future documents
   define other cost metrics or specify the semantics of existing cost
   metrics for "path-vector" cost mode for some additional requirements.

5.2.  Cost Metric: Link Maximum Reservable Bandwidth

   This document uses 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" cost mode only.

   Metric Description:  When used with "path-vector" cost mode, it is to
      specify the path vector computed by using the spatial and temporal
      maximum reservable bandwidth over each network link.  The value of
      the maximum reservable bandwidth of each 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 by some algorithm
      which can guarantee the equivalent Maximum Reservable Bandwidth
      constraints.

6.  ANE Domain

   This document specifies a new ALTO entity domain called "ane" in
   addition to the ones in [I-D.ietf-alto-unified-props-new].  The ANE
   domain associates property values with the ANEs in a network.  The
   entity in ANE domain is often used in the path vector by cost maps or
   endpoint cost resources.  Accordingly, the ANE domain always depends
   on a cost map or an endpoint cost map.






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6.1.  Domain Name

   ane

6.2.  Domain-Specific Entity Identifier

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

   To simplify the description, we use "ANE name" to indicate the
   identifier of an entity in ANE domain in this document.

   The ANE name is usually unrelated to the physical device information.
   It is usually generated by the ALTO server on demand and used to
   distinguish from other ANEs in its dependent cost map or endpoint
   cost map.

6.3.  Hierarchy and Inheritance

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

7.  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.  Media Type

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

7.2.  HTTP Method

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






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7.3.  Accept Input Parameters

   The input parameters of the Multipart Filtered Cost Map MUST be
   encoded as a JSON object in the body of an HTTP POST request.  The
   media type of the request MUST be one of "application/alto-
   costmapfilter+json".  The format of the request body MUST be the same
   type as defined by section 11.3.2.3 of [RFC7285].

7.4.  Capabilities

   The Multipart Filtered Cost Map resource uses the same capabilities
   as 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 of it
   for the Multipart Filtered Cost Map resource.

7.5.  Uses

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

7.6.  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 response to a valid request MUST be a "multipart/related" message
   as defined by [RFC2387].  The body consists of two parts:

   o  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 body of this part MUST be a JSON object with the
      same format as defined in Section 11.2.3.6 of [RFC7285]; The JSON
      object MUST include the "vtag" field in the "meta" field, which
      provides the version tag of the returned cost map.  The resource
      id of the version tag MUST be as 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 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 "."



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      character.  The body of this 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 VersionTag
      object as defined by section 10.3 of [RFC7285].  The "resource-id"
      of this VersionTag MUST be the value of "Resource-Id" header of
      the first part.  The "tag" of this VersionTag MUST be the "tag" of
      "vtag" of the first part body.

8.  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.  Media Type

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

8.2.  HTTP Method

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

8.3.  Accept Input Parameters

   The input parameters of the Multipart Endpoint Cost resource MUST be
   encoded as a JSON object in the body of an HTTP POST request.  The
   media type of the request MUST be one of "application/alto-
   endpointcostparams+json".  The format of the request body MUST be the
   same type as defined by section 11.5.1.3 of [RFC7285].

8.4.  Capabilities

   The Multipart Endpoint Cost resource uses the same capabilities as
   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 of it for
   the Multipart Endpoint Cost resource.








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8.5.  Uses

   The Multipart Endpoint Cost resource MUST NOT specify the "uses"
   attribute.

8.6.  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 response to a valid request MUST be a "multipart/related" message
   as defined by [RFC2387].  The body consists of two parts:

   o  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 (U+002E).  The body of this 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 same as the value of
      the "Resource-Id" header.

   o  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 body of this 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 VersionTag
      object as defined by section 10.3 of [RFC7285].  The "resource-id"
      of this VersionTag MUST be the value of "Resource-Id" header of
      the first part.  The "tag" of this VersionTag MUST be the "tag" of
      "vtag" of the first part body.

9.  Examples

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

9.1.  Information Resource Directory Example

   Here is an example of an Information Resource Directory.  In this
   example, the "cost-map-pv" information resource provides a Multipart
   Cost Map resource for path-vector; the "endpoint-cost-pv" information
   resource provides a MultipartEndpoint Cost resource for path-vector.



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   Both of them support the Maximum Reservable Bandwidth ("maxresbw")
   cost metric in "path-vector" cost mode.

     {
       "meta": {
         "cost-types": {
           "pv-maxresbw": {
             "cost-mode": "path-vector",
             "cost-metric": "maxresbw"
           }
         }
       },
       "resources": {
         "my-default-networkmap": {
           "uri" : "http://alto.example.com/networkmap",
           "media-type" : "application/alto-networkmap+json"
         },
         "cost-map-pv": {
           "uri": "http://alto.example.com/costmap/pv",
           "media-type": `multipart/related;
                          type=application/alto-costmap+json`,
           "accepts": "application/alto-costmapfilter+json",
           "capabilities": {
             "cost-type-names": [ "pv-maxresbw" ]
           },
           "uses": [ "my-default-networkmap" ]
         },
         "endpoint-cost-pv": {
           "uri": "http://alto.exmaple.com/endpointcost/pv",
           "media-type": `multipart/related;
                          type=application/alto-endpointcost+json`,
           "accepts": "application/alto-endpointcostparams+json",
           "capabilities": {
             "cost-type-names": [ "pv-maxresbw" ]
           }
         },
         "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
           }
         }
       }
     }




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9.2.  Example #1

   Query filtered cost map to get the path vectors.

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

   {
     "cost-type": {
       "cost-mode": "path-vector",
       "cost-metric": "maxresbw"
     },
     "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
                 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",
         "cost-metric": "maxresbw"



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       }
     },
     "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





















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

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

   HTTP/1.1 200 OK
   Content-Length: [TBD]
   Content-Type: multipart/related; boundary=example-2;
                 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",
         "cost-metric": "maxresbw"
       }
     },
     "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" ],



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         "ipv6:2001:db8::10": [ "ane:L001", "ane:L005",
                                "ane:L007" ]
       }
     }
   }
   --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"
         }
       ]
     },
     "property-map": {
       "ane:L001": { "maxresbw": 50000000 },
       "ane:L003": { "maxresbw": 48000000 },
       "ane:L004": { "maxresbw": 55000000 },
       "ane:L005": { "maxresbw": 60000000 },
       "ane:L007": { "maxresbw": 35000000 }
     }
   }

9.4.  Example for Incremental Update

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

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

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





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   Based on the server process defined in
   [I-D.ietf-alto-incr-update-sse], the ALTO server will send the
   control-uri first using Server-Sent Event (SSE), and follow 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
   data: Content-Type: application/alto-endpointcost+json
   data:
   data: <endpoint-cost-map-entry>
   data: --example-3
   data: Content-ID: nepmap
   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, the ALTO server will publish the data updates
   for each node in this tree separately.

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

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

10.  Compatibility

10.1.  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



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   client does not support them, the ALTO client will ignore the
   resources without conducting any incompatibility.

10.2.  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.  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.  General Discussions

11.1.  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.






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11.2.  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.  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.  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.




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

13.1.  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.  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.








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

                        Table 1: ALTO Entity Domain

13.3.  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.  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.  References

15.1.  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>.








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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.

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

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

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

Authors' Addresses








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   Kai Gao
   Tsinghua University
   Beijing  Beijing
   China

   Email: gaok12@mails.tsinghua.edu.cn


   Young Lee
   Huawei
   TX
   USA

   Email: leeyoung@huawei.com


   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










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