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Versions: 00                                                            
ALTO WG                                                        D. Lachos
Internet-Draft                                             C. Rothenberg
Intended status: Informational                                   Unicamp
Expires: January 14, 2021                                       Q. Xiang
                                                                 Y. Yang
                                                         Yale University
                                                               B. Ohlman
                                                       Ericsson Research
                                                          S. Randriamasy
                                                         Nokia Bell Labs
                                                                F. Boten
                                                           LM. Contreras
                                                                J. Zhang
                                                       Tongji University
                                                                  K. Gao
                                                      Sichuan University
                                                           July 13, 2020

             Multi-domainn Information Exposure using ALTO


   A common setting in emerging applications (e.g., data-intensive
   science applications, flexible inter-domain routing, multi-domain
   service function chaining) is that the traffic from a source to a
   destination traverses multiple networks domains.  Such multi-domain
   applications can benefit from network information exposure using
   ALTO.  This document summarizes the benefits of using such multi-
   domain information and discusses the ALTO design issues for gathering
   it.  Besides, it also presents key design requirements to be
   addressed in order to realize the proposal of providing multi-domain
   information by ALTO services.  Finally, another important objective
   of this document is to begin discussions into the ALTO WG concerning
   potential new items to be considered for the re-charter.

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/.

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

   This Internet-Draft will expire on January 14, 2021.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   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
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   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.  What does "multi-domain information exposure" mean? . . . . .   3
   3.  What Information do Multi-domain applications need? . . . . .   5
     3.1.  Basic Formulation . . . . . . . . . . . . . . . . . . . .   6
   4.  What are the ALTO issues of gathering multi-domain
       information?  . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Communication Mechanisms  . . . . . . . . . . . . . . . .   8
       4.1.1.  Server-to-Client ALTO communication . . . . . . . . .   8
       4.1.2.  Domain connectivity discovery . . . . . . . . . . . .   8
       4.1.3.  ALTO server discovery . . . . . . . . . . . . . . . .   8
     4.2.  Conceptual Query Interfaces and Data Representation . . .   8
       4.2.1.  Single-domain composition . . . . . . . . . . . . . .   8
       4.2.2.  Simple resource query language  . . . . . . . . . . .   9
     4.3.  Computation Model . . . . . . . . . . . . . . . . . . . .   9
       4.3.1.  Scalability . . . . . . . . . . . . . . . . . . . . .   9
       4.3.2.  Security and Privacy  . . . . . . . . . . . . . . . .   9
   5.  How to design a whole ALTO framework? . . . . . . . . . . . .   9
     5.1.  ALTO servers communication  . . . . . . . . . . . . . . .  10
     5.2.  Multi-domain Connectivity discovery . . . . . . . . . . .  10
     5.3.  Multi-domain ALTO Server discovery  . . . . . . . . . . .  11
     5.4.  Unified resource representation . . . . . . . . . . . . .  11
     5.5.  Flexible/Generic query language . . . . . . . . . . . . .  11
     5.6.  Computation complexity optimization . . . . . . . . . . .  12
     5.7.  Security/Privacy Preserving . . . . . . . . . . . . . . .  12

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   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Many multi-domain applications are emerging with the development of
   new technologies, such as SDN, NFV, and 5G.  Examples of such
   applications include data-intensive science
   applications [CMS][LCLS][LHC][SKA], multi-domain service function
   chaining  [NGMN-5G][SFC-MD][MD-ORCH-NFV][ETSI-ZSM], and flexible
   inter-domain routing [SFP][SDX][RFC5575].  Such cross-domain
   applications can benefit substantially from exposure of network
   information to improve both applications performance and resource

   The Application-Layer Optimization Protocol (ALTO) [RFC7285] already
   introduces basic mechanisms (e.g., modularity, dependency) and
   abstractions (e.g., map services) for applications to take optimized
   actions based on network information.  However, exposing network
   information to support multi-domain use cases introduces issues to be
   considered in the current ALTO design.

   This document provides a definition of multi-domain information
   exposure (Section 2) and identifies the benefits of using it in
   applications traversing multiple domains (Section 3).  Next, it
   elaborates key design requirements of ALTO for exposing multi-domain
   information (Section 4).  It then lists a set of mechanisms to design
   a multi-domain ALTO framework (Section 5).

   The overall rationale of this document is to arouse a discussion
   about potential rechartering topics to handle multi-domain with ALTO.

2.  What does "multi-domain information exposure" mean?

   For the purposes of this document, a domain is considered to be a
   separate administrative environment.  Specifically, the multi-domain
   approach involves multiple networks managed by different
   administrative domains.  Examples of such domains include, among
   others, science networks, mobile operators, cloud service providers,
   and transport network providers.

   In multi-domain information exposure, multiple networks perform
   exchange of information to handle applications traversing multiple
   domains.  For example, consider a collaboration network composed of

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   three-member domains, as shown in Figure 1.  An application (e.g., a
   large data analysis system) wants to reserve bandwidth for two flows
   f1: (S1, D1) and f2: (S2, D2).  In this example, the traffic from a
   source to a destination traverses multiple domains (A, B, and C), and
   hence the application needs to retrieve multi-domain information
   about topology and resources to take optimized allocation/placement

                               | Domain B   |
        .-------------.        |   30 Gbps  |
        | Domain A    |   _____o............o---D1
   S1   |             |  /     '------------'
     \  |   100 Gbps  | /
      \ o*************o/       .------------.
      / |             | \      | Domain C   |
     /  |             |  \     |   30 Gbps  |
   S2   |             |   \____o............|---D2
        '-------------'        '------------'

                                  ---- 1 Tbps link

    Figure 1: A collaboration network composed of three member domains.

   The current ALTO base protocol is not designed for a multi-domain
   setting of exposing network information.  For example, consider P2P
   applications (the first and main use case for the development of
   ALTO [RFC7971]).  Figure 2 depicts a tracker-based P2P application
   with a global tracker (ALTO client) in domain A accessing ALTO
   servers at two ISPs (domains B and C).  The ALTO server in each
   domain will provide only local information to ALTO clients, i.e., the
   tracker will receive topology-/policy-related information of a single
   domain (domain B or domain C).  Due to the lack of information
   exchange between different domains, ALTO servers will not be able to
   expose information across multiple domains, i.e., the tracker will
   not receive merged topology-/policy-related information from domain B
   and domain C.

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           ,---.               ,-'         `-.   +-----------+
        ,-'     `-.           /   domain B    \  |   Peer 1  |********
       /           \         / +-------------+ \ |           |       *
      /   domain A  \   ++====>| ALTO Server |  )+-----------+       *
     /               \  ||   \ +------^------+ / +-----------+       *
    ; +-----------+   : ||    \       #       /  |   Peer 2  |       *
    | |  Tracker  |<====++     `-.    #    ,-'   |           |****** *
    | |ALTO Client|   |           `---#---'      +-----------+     * *
    | +-----------+<====++        ,---#---.                        * *
    :        *        ; ||     ,-'    #    `-.   +-----------+     * *
     \       *       /  ||    /       #       \  |   Peer 3  |     * *
      \      *      /   ||   / +------v------+ \ |           |**** * *
       \     *     /    ++====>| ALTO Server |  )+-----------+   * * *
        `-.  *  ,-'          \ +-------------+ / +-----------+   * * *
           `-*-'              \               /  |   Peer 4  |** * * *
             *                 `-. domain C,-'   |           | * * * *
             *                    `-------'      +-----------+ * * * *
             *                                                 * * * *
             *                                                 * * * *
        *** Application protocol
        === ALTO protocol
        ### Multi-domain ALTO protocol (NOT EXISTS)

     Figure 2: Global Tracker Accessing ALTO Server at Various Domains
                         (Adapted from [RFC7971]).

3.  What Information do Multi-domain applications need?

   Many types of network information are needed by cross-domain
   applications to improve their performances, including network state
   (e.g., loss, delay, ECN bit [RFC3168], INT [INT]), performance
   metrics (e.g., throughput, max reservable Bandwidth), capability
   information (e.g., delivery/acquisition protocol), locality (e.g.,
   servers/domains location and paths), among others.

   In our previous example (See Figure 1), before the application can
   run a resource allocation algorithm to execute such submitted flows,
   it needs to gather some information from the network domains:

   o  End-to-End cost across multiple domains

      This cost may be expressed in terms of resource availability and
      sharing (e.g., network bandwidth) for the set of requested flows
      to be reserved.  In our presented scenario, for example, both

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      flows f1 and f2 are sharing the same network path in domain A.  It
      means that they share a common resource, the network bandwidth.

   o  Sequence of domains and candidate paths

      In multi-domain use cases, each flow will consume networking
      resources of multiple domains (if source node and destination node
      are located in different domains).  Therefore, the application
      needs to discover a sequence of domains and candidate paths
      between source nodes and destination nodes, i.e., which domains
      are involved for the different traffic flows.  In our example, the
      multi-domain network paths for f1 and f2 are [A , B], and [A, C],

3.1.  Basic Formulation

   Consider different services, for each domain, providing previous
   information.  Each service is defined as an object fi with a set of
   network properties, such as:

   o  Path (fi.path): representing the sequence of network devices that
      packets of flow fi will traverse.

   o  Available bandwidth (fi.abw): representing the bandwidth that flow
      fi can request.

   o  Delay (fi.delay): representing the average delay of packets of
      flow fi.

   In our example, consider each ALTO server providing the bandwidth
   property using a set of linear inequalities (See Figure 3).  Where x1
   and x2 represent the available bandwidth that can be reserved for
   (S1, D1 ), and (S2, D2), respectively.

               +-----------+---------------------- --------+
               | DOMAIN    |     LINEAR INEQUALITIES       |
               | Domain A  | x1 + x2 <= 100 ....... (le11) |
               | Domain B  |      x1 <= 30  ....... (le21) |
               | Domain C  |      x2 <= 30 ........ (le31) |

      Figure 3: Bandwidth properties for the reservation request from
                                 Figure 1.

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   Each linear inequality represents a constraint on the reservable
   bandwidths over different shared resources by the two flows.  For
   example, the inequality le11 indicates that both flows share a common
   resource and that the sum of their bandwidths can not exceed 100

   In a multi-domain setting, a network property to a flow fi may
   involve properties of multiple networks, e.g.,:

   o  fi.md-abw: min(fi.abw[A] + fi.abw[B] + fi.abw[C])

   o  fi.md-path: fi.path[A] . fi.path[B] . fi.path[C]

   o  fi.md-delay: fi.delay[A] + fi.delay[B] + fi.delay[C]

   The involved domains may exchange such multi-domain properties.  They
   also may apply composition mechanisms to create a unified
   representation to reveal a compact multi-domain network resource
   information.  For example, taking a look at the set of previous
   linear inequalities (See Figure 3), one can conclude that the
   constraint le21 at domain B (x1 <= 30) and the constraint le31 at
   domain C (x2 <= 30) can eliminate that at domain A (X1 + x2 <= 100).
   ALTO servers may compose this information and remove the cross-domain
   redundancy (e.g., using a classic compression algorithm [TELGEN83]).
   Therefore, the compressed multi-domain set of linear inequalities is
   reduced to two linear inequalities (i.e., le21 and le31).

4.  What are the ALTO issues of gathering multi-domain information?

   ALTO provides a generic framework to expose network information for
   applications to improve their performance.  In particular, ALTO
   introduces generic mechanisms such as: (i) information resource
   directory (IRD), (ii) information consistency (tag, dependency,
   multi-info resources [ALTO-MULTIPART]), and (iii) information update
   model (e.g., incremental update with server-sent events [ALTO-SSE]).
   ALTO also introduces abstractions exposing network information to the
   applications: (i) network and cost maps, (ii) a multi-cost
   map [RFC8189], (iii) the path vector abstraction [ALTO-PATH], and
   (iv) capability maps (e.g., CDNI [ALTO-CDNI] and unified property
   Map [ALTO-PROP]).  Another generic concept introduced is "filter", so
   that information resources can be filtered (e.g., filtered network/
   cost map).  Besides, each individual information resource is provided
   as a RESTful service with a very simple, but well-working grammar
   (essentially JSON grammar [RFC7159]).

   However, the multi-domain settings of exposing network information
   arise key issues to be considered in the current ALTO design.  Next,
   we list several design issues of using ALTO to provide multi-domain

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   information.  Such issues can be roughly categorized in three
   aspects: (i) communication mechanisms, (ii) conceptual query
   interfaces and data representation, and (iii) computation model.

4.1.  Communication Mechanisms

4.1.1.  Server-to-Client ALTO communication

   In multi-domain scenarios is not possible to optimize the traffic
   with only locally available network information (i.e., server-to-
   client ALTO communication).  For example, compute costs for source/
   destination pairs correctly if a source and/or a destination is
   outside the domain it belongs to.  Therefore, it also necessary
   multi-ALTO server communication to allow exchanging detailed network
   information from multiple domains.  The ALTO protocol specification
   states (See Section 3.1 of  [RFC7285]) that "It may also be possible
   for an ALTO server to exchange network information with other ALTO
   servers (either within the same administrative domain or another
   administrative domain with the consent of both parties) in order to
   adjust exported ALTO".  However, such a protocol is outside the scope
   of the specification.

4.1.2.  Domain connectivity discovery

   The connectivity information is the reachability between source nodes
   and the destination nodes.  In order to find the resources sharing
   between different source/destination pair, an application needs to
   know which domains are involved in the data movement of each node
   pair.  Besides, a set of candidate paths needs to be computed in
   order to know how to reach a remote destination node.  The current
   ALTO extensions do not have this feature.

4.1.3.  ALTO server discovery

   Once the multi-domain connectivity discovery is performed, an
   application (as an ALTO client) needs to be aware of the presence and
   the location of ALTO servers in order to get appropriate guidance.
   These ALTO servers will be located in different network domains, so
   that multi-domain ALTO server discovery mechanisms are needed.

4.2.  Conceptual Query Interfaces and Data Representation

4.2.1.  Single-domain composition

   In the current ALTO framework, each domain can have its own
   representation of the same network information.  For example, suppose
   that the path cost for member domain B (See Figure 1) is utilization
   charge instead of available bandwidth.  In this case, both values are

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   not comparable together.  Even, if all the member domains have the
   same utilization charge property, there would not necessarily a
   uniform form of billing because each member domain is autonomous.
   Member domain A may charge using dollar, member domain B may charge
   using euros, while member domain C may use some form of local units.

4.2.2.  Simple resource query language

   Applications need to express their objectives and requirements in a
   query.  For example, find the bandwidth the network can provide for
   flow f1 (S1, D1) subject to reachability requirements (e.g., from S1
   to D1), bi-direction symmetry (e.g., data traffic from S1 to D1 and
   from D1 to S1), waypoint traversal (e.g., f2 must traverse one
   middlebox m1), blacklist of devices (e.g., f1 should not pass a
   certain device m2), link/node disjointness (e.g., f1 and f2 flows
   being transmitted along two link-disjoint paths), and QoS metrics
   (e.g., the bandwidth of the flow f1 needs to be at least 30 Gbps).
   The current query interface in ALTO (e.g., filtered network/cost map)
   can not express such flexible queries.

4.3.  Computation Model

4.3.1.  Scalability

   The optimization problems specified by the applications can be
   computationally expensive and time-consuming.  For example, the
   number of available paths for each flow is increased exponentially
   with the number of domains involved.  As such, the number of
   available configurations for a set of flows would also increase
   exponentially with both the network size and the number of flows.

4.3.2.  Security and Privacy

   The information provided by the ALTO base protocol is considered
   coarse-grained in several recent multi-domain use cases.  New ALTO
   extensions have been designed to provide fine-grained network
   information to the application.  Using these ALTO extension services
   for multi-domain scenarios would raise new security and privacy

5.  How to design a whole ALTO framework?

   In order to address the aforementioned issues, this section
   summarizes envisioned solutions and on-going efforts to allow ALTO to
   expose network information across multiple domains.  See Table 1 to
   identify the relationship between the key design issues and their
   corresponding mechanisms to consider in a multi-domain ALTO

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   |               FROM              |                TO               |
   |      Server-to-Client ALTO      |    ALTO servers communication   |
   |          communication          |                                 |
   | ------------------------------- | ------------------------------- |
   |  Domain connectivity discovery  |    Multi-domain connectivity    |
   |                                 |            discovery            |
   | ------------------------------- | ------------------------------- |
   |      ALTO server discovery      |     Multi-domain ALTO server    |
   |                                 |            discovery            |
   | ------------------------------- | ------------------------------- |
   |    Single-domain composition    | Unified Resource Representation |
   | ------------------------------- | ------------------------------- |
   |  Simple resource query language | Generic/Flexible query language |
   | ------------------------------- | ------------------------------- |
   |           Scalability           |      Computation complexity     |
   |                                 |           optimization          |
   | ------------------------------- | ------------------------------- |
   |        Security & Privacy       |   Security/Privacy preserving   |

   Table 1: Issues of applying the current ALTO framework in the multi-
                        domain setting & solutions.

5.1.  ALTO servers communication

   ALTO servers may consider either a hierarchical or mesh architectural
   deployment design [INTER-ALTO][MD-ANALY][MD-BROKER][MD-SFC].  When a
   hierarchical architecture is used, ALTO servers in domain partitions
   gather locally-available network information and send it to central
   server, which in turn merges data and distributes ALTO services.  In
   a mesh deployment, ALTO servers may be set up in each domain
   independently, connected to each other, and gathering the network
   information from other domains.

5.2.  Multi-domain Connectivity discovery

   Multi-domain mechanisms combining domains sequence computation and
   paths computation need to be defined, or standardized computation
   protocols could be re-used.  In the latter case, the IETF has a set
   of well defined protocols, such as BGP [RFC4271], PCE ([RFC5441]
   , [RFC6805]), or BGP-LS [RFC7752].  The BGP protocol, for instance,
   provides multi-domain sequence computation to know how to reach a
   destination just identifying the next hop for IP traffic delivery;
   however, it does not advertise multiple alternative routes.  BGP-LS
   allows visibility of the network topology (real physical or
   abstracted) and export traffic engineering information with external

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   domains using the BGP routing protocol.  Following the PCE-based
   architecture [RFC4655] for computing optimal multi-domain end-to-end
   paths, [RFC5441], [RFC6805] define mechanisms where a PCE entity
   cooperates either with other PCE entities in adjacent domains or with
   a parent PCE entity, respectively.  A mix between BGP-LP and PCE may
   also be considered, with the first one providing topology/link-state
   network information, and with the second one making the necessary
   path computations between domains.

5.3.  Multi-domain ALTO Server discovery

   The ALTO cross-domain server discovery document [RFC8686] specifies a
   procedure for identifying ALTO servers outside of the ALTO client's
   own network domain.  Other mechanisms could also be leveraged, such
   as those based on PCE or BGP architectures.  For example, [RFC4674]
   proposes a set of functional requirements to allow a path computation
   client (PCC) to automatically and dynamically discover the location
   of PCEs entities (including additional information about supported
   capabilities) for each controller domain.  Inline with those
   requirements, [PROTO-BGP] is defining extensions to BGP to also carry
   PCE discovery information.  Specifically, this document extends BGP
   to allow a PCE entities to advertise their location and some useful
   information to a PCC for the PCE selection.

5.4.  Unified resource representation

   Therefore, multi-domain composition mechanisms are necessaries so
   that network information from ALTO servers in multiple domains can
   fit into a single and consistent "virtual" domain abstraction.  ALTO
   information services such as network maps, cost maps, unified entity
   properties, network capabilities, and routing path abstractions (path
   vectors) of individual domains need to follow a common semantic as
   well as be consistently integrated to provide the abstraction of a
   single, coherent network to the applications. ... design options of
   multi-domain composition

5.5.  Flexible/Generic query language

   With a flexible/generic query language, the network can filter out a
   large number of unqualified domains.  The language specification
   could be inspired by standard [GSM][NFV-NSD] or pre-
   standard [SOCKET-INTENTS][IBN] mechanisms, implemented with a user-
   friendly grammar (e.g., SQL-style query).

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5.6.  Computation complexity optimization

   Therefore, ALTO servers need to support mechanisms to improve the
   scalability and performance (e.g., pre-computation and projection).
   For example, the ALTO Routing State Abstraction extension
   document [DRAFT-RSA] describes equivalent transformation algorithms
   that can effectively reduce the redundancy in the network view as
   much as possible while still providing the same information.  Such
   algorithms may be integrated with any ALTO service (e.g., path vector
   extension) as a post-processing step.

5.7.  Security/Privacy Preserving

   ALTO needs mechanisms (with little overhead) that provide accurate
   sharing network information, and at the same time, protects each
   member domain.  This privacy-preserving interdomain information
   process may consider, for instance, a secure multi-party computation
   (SMPC) protocol [MD-ANALY][MERCATOR].

6.  IANA Considerations

   This document includes no request to IANA.

7.  Security Considerations


8.  References

8.1.  Normative References

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,

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   [RFC4674]  Le Roux, J., Ed., "Requirements for Path Computation
              Element (PCE) Discovery", RFC 4674, DOI 10.17487/RFC4674,
              October 2006, <https://www.rfc-editor.org/info/rfc4674>.

   [RFC5441]  Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
              "A Backward-Recursive PCE-Based Computation (BRPC)
              Procedure to Compute Shortest Constrained Inter-Domain
              Traffic Engineering Label Switched Paths", RFC 5441,
              DOI 10.17487/RFC5441, April 2009,

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,

   [RFC6805]  King, D., Ed. and A. Farrel, Ed., "The Application of the
              Path Computation Element Architecture to the Determination
              of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
              DOI 10.17487/RFC6805, November 2012,

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

   [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,

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,

   [RFC7971]  Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and
              S. Previdi, "Application-Layer Traffic Optimization (ALTO)
              Deployment Considerations", RFC 7971,
              DOI 10.17487/RFC7971, October 2016,

   [RFC8189]  Randriamasy, S., Roome, W., and N. Schwan, "Multi-Cost
              Application-Layer Traffic Optimization (ALTO)", RFC 8189,
              DOI 10.17487/RFC8189, October 2017,

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   [RFC8686]  Kiesel, S. and M. Stiemerling, "Application-Layer Traffic
              Optimization (ALTO) Cross-Domain Server Discovery",
              RFC 8686, DOI 10.17487/RFC8686, February 2020,

8.2.  Informative References

              Seedorf, J., Yang, Y., Ma, K., Peterson, J., and J. Zhang,
              "Content Delivery Network Interconnection (CDNI) Request
              Routing: CDNI Footprint and Capabilities Advertisement
              using ALTO", draft-ietf-alto-cdni-request-routing-alto-11
              (work in progress), April 2020.

              Zhang, J. and Y. Yang, "Multiple ALTO Resources Query
              Using Multipart Message", draft-zhang-alto-multipart-03
              (work in progress), March 2020.

              Gao, K., Randriamasy, S., Yang, Y., and J. Zhang, "ALTO
              Extension: Path Vector", draft-ietf-alto-path-vector-10
              (work in progress), March 2020.

              Roome, W., Randriamasy, S., Yang, Y., Zhang, J., and K.
              Gao, "Unified Properties for the ALTO Protocol", draft-
              ietf-alto-unified-props-new-10 (work in progress),
              November 2019.

              Roome, W. and Y. Yang, "ALTO Incremental Updates Using
              Server-Sent Events (SSE)", draft-ietf-alto-incr-update-
              sse-17 (work in progress), July 2019.

   [CMS]      The CMS Collaboration, "The CMS experiment at the CERN
              LHC", 2008,

              Gao, K., xinwang2014@hotmail.com, x., Xiang, Q., Gu, C.,
              Yang, Y., and G. Chen, "Compressing ALTO Path Vectors",
              draft-gao-alto-routing-state-abstraction-08 (work in
              progress), March 2018.

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              ETSI, "Zero Touch Network and Service Management", 2020,

   [GSM]      GSM Association, "Generic Network Slice Template", 2019,

   [IBN]      Clemm, A., Ciavaglia, L., Granville, L., and J. Tantsura,
              "Intent-Based Networking - Concepts and Definitions",
              draft-irtf-nmrg-ibn-concepts-definitions-01 (work in
              progress), March 2020.

   [INT]      Kim, C., Sivaraman, A., Katta, N., Bas, A., Dixit, A., and
              L. Wobker, "In-band network telemetry via programmable
              dataplanes", Book Title ACM SIGCOMM, 2015.

              Dulinski, Z., Wydrych, P., and R. Stankiewicz, "Inter-ALTO
              Communication Problem Statement", draft-dulinski-alto-
              inter-problem-statement-02 (work in progress), July 2015.

   [LCLS]     SLAC National Accelerator Laboratory, "The Linac Coherent
              Light Source", 2020, <https://lcls.slac.stanford.edu/>.

   [LHC]      CERN: European Council for Nuclear Research, "The Large
              Hadron Collider (LHC) Experiment", 2020,

              Xiang, Q., Zhang, J., Le, F., Yang, Y., and H. Newman,
              "Resource Orchestration for Multi-Domain, Exascale, Geo-
              Distributed Data Analytics", draft-xiang-alto-multidomain-
              analytics-03 (work in progress), March 2020.

              Perez, D. and C. Rothenberg, "ALTO-based Broker-assisted
              Multi-domain Orchestration", draft-lachosrothenberg-alto-
              brokermdo-03 (work in progress), March 2020.

              Katsalis, K., Nikaein, N., and A. Edmonds, "Multi-domain
              orchestration for NFV: Challenges and research
              directions", focus 189--195, 2016.

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   [MD-SFC]   Perez, D., Xiang, Q., Rothenberg, C., and Y. Yang, "Multi-
              domain Service Function Chaining with ALTO", draft-lachos-
              sfc-multi-domain-alto-00 (work in progress), March 2020.

              Xiang, Q., Zhang, J., Wang, T., Liu, J., Guok, C., Le, F.,
              MacAuley, J., Newman, H., and R. Yang, "Fine-Grained,
              Multi-Domain Network Resource Abstraction as a Fundamental
              Primitive to Enable High-Performance, Collaborative Data
              Sciences", Publisher IEEE, BookTitle SC18: International
              Conference for High Performance Computing, Networking,
              Storage and Analysis, Pages 58-70, 2018.

              Xiang, Q., Zhang, J., Wang, T., Liu, J., Guok, C., Le, F.,
              MacAuley, J., Newman, H., and R. Yang, "Toward Fine-
              Grained, Privacy-Preserving, Efficient Multi-Domain
              Network Resource Discovery", Publisher IEEE, Journal IEEE
              Journal on Selected Areas in Communications, Volume 37,
              Number 8, Pages 1924-1940, 2019.

   [NFV-NSD]  ETSI ISG, "Network functions virtualisation (NFV);
              management and orchestration; network service templates
              specification", 2019,

   [NGMN-5G]  Alliance, NGMN, "5G White Paper", 2015,

              Dong, J., Chen, M., Dhody, D., Tantsura, J., Kumaki, K.,
              and T. Murai, "BGP Extensions for Path Computation Element
              (PCE) Discovery", draft-dong-pce-discovery-proto-bgp-07
              (work in progress), July 2017.

   [SDX]      Gupta, A., Vanbever, L., Shahbaz, M., Donovan, S.,
              Schlinker, B., Feamster, N., Rexford, J., Shenker, S.,
              Clark, R., and E. Katz-Bassett, "Sdx: A software defined
              internet exchange", focus 551--562, 2015.

   [SFC-MD]   Sun, G., Li, Y., Liao, D., and V. Chang, "Service function
              chain orchestration across multiple domains: A full mesh
              aggregation approach", Journal IEEE Transactions on
              Network and Service Management, Volumen 15, Number 3,
              Pages 1175--1191, Publisher IEEE, 2018.

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   [SFP]      Xiang, Q., Guok, C., Le, F., MacAuley, J., Newman, H., and
              R. Yang, "SFP: Toward Interdomain Routing for SDN
              Networks", focus 87--89, 2018.

   [SKA]      SKA Organisation, "The Square Kilometre Array", 2020,

              Schmidt, P., Enghardt, T., Khalili, R., and A. Feldmann,
              "Socket Intents: Leveraging Application Awareness for
              Multi-Access Connectivity", Publisher ACM, Series CoNEXT
              '13, Pages 295-300, 2013.

              Telgen, J., "Identifying redundant constraints and
              implicit equalities in systems of linear constraints",
              Journal Management Science, Volume 29, Number 10, Pages
              1209--1222, Publisher INFORMS, 1983.

              Xiang, Q., Zhang, J., Le, F., and Y. Yang, "ALTO
              Extension: Unified Resource Representation", draft-xiang-
              alto-unified-representation-02 (work in progress), March

   [UNICORN]  Xiang, Q., Wang, T., Zhang, J., Newman, H., Yang, R., and
              J. Liu, "Unicorn: Unified resource orchestration for
              multi-domain, geo-distributed data analytics",
              Journal Future Generation Computer Systems, Volumen 93,
              Pages 188-197, 2019.

Authors' Addresses

   Danny Alex Lachos Perez
   University of Campinas
   Av. Albert Einstein 400
   Campinas, Sao Paulo  13083-970

   Email: dlachosp@dca.fee.unicamp.br
   URI:   https://intrig.dca.fee.unicamp.br/danny-lachos/

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   Christian Esteve Rothenberg
   University of Campinas
   Av. Albert Einstein 400
   Campinas, Sao Paulo  13083-970

   Email: chesteve@dca.fee.unicamp.br
   URI:   https://intrig.dca.fee.unicamp.br/christian/

   Qiao Xiang
   Yale University
   51 Prospect Street
   New Haven, CT

   Email: qiao.xiang@cs.yale.edu

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

   Email: yang.r.yang@gmail.com

   Borje Ohlman
   Ericsson Research
   S-16480 Stockholm

   Email: Borje.Ohlman@ericsson.com

   Sabine Randriamasy
   Nokia Bell Labs
   Route de Villejust
   NOZAY  91460

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

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   Farni Boten

   Email: farni.weaver@sprint.com

   Luis M. Contreras
   Ronda de la Comunicacion, s/n
   Madrid  28050

   Email: luismiguel.contrerasmurillo@telefonica.com
   URI:   http://lmcontreras.com/

   Jingxuan Jensen Zhang
   Tongji University
   4800 Caoan Road
   Shanghai  201804

   Email: jingxuan.n.zhang@gmail.com

   Kai Gao
   Sichuan University
   Chengdu  610000

   Email: kaigao@scu.edu.cn

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