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Modern Problem Statement, Use Cases, and Framework

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This is an older version of an Internet-Draft that was ultimately published as RFC 8396.
Authors Jon Peterson , Tom McGarry
Last updated 2018-02-22 (Latest revision 2017-07-03)
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Network Working Group                                        J. Peterson
Internet-Draft                                                T. McGarry
Intended status: Informational                             NeuStar, Inc.
Expires: January 4, 2018                                    July 3, 2017

           Modern Problem Statement, Use Cases, and Framework


   The functions of the public switched telephone network (PSTN) are
   rapidly migrating to the Internet.  This is generating new
   requirements for many traditional elements of the PSTN, including
   telephone numbers (TNs).  TNs no longer serve simply as telephone
   routing addresses: they are now identifiers which may be used by
   Internet-based services for a variety of purposes including session
   establishment, identity verification, and service enablement.  This
   problem statement examines how the existing tools for allocating and
   managing telephone numbers do not align with the use cases of the
   Internet environment, and proposes a framework for Internet-based
   services relying on TNs.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 4, 2018.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Actors  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Data Types  . . . . . . . . . . . . . . . . . . . . . . .   7
     2.3.  Data Management Architectures . . . . . . . . . . . . . .   8
   3.  Framework . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  Acquisition . . . . . . . . . . . . . . . . . . . . . . .  11
       4.1.1.  Acquiring TNs from Registrar  . . . . . . . . . . . .  12
       4.1.2.  Acquiring TNs from CSPs . . . . . . . . . . . . . . .  13
     4.2.  Management  . . . . . . . . . . . . . . . . . . . . . . .  14
       4.2.1.  Management of Administrative Data . . . . . . . . . .  14  Managing Data at a Registrar  . . . . . . . . . .  14  Mangaing Data at a CSP  . . . . . . . . . . . . .  15
       4.2.2.  Management of Service Data  . . . . . . . . . . . . .  15  CSP to other CSPs . . . . . . . . . . . . . . . .  15  User to CSP . . . . . . . . . . . . . . . . . . .  16
       4.2.3.  Managing Change . . . . . . . . . . . . . . . . . . .  16  Changing the CSP for an Existing Service  . . . .  16  Terminating a Service . . . . . . . . . . . . . .  17
     4.3.  Retrieval . . . . . . . . . . . . . . . . . . . . . . . .  17
       4.3.1.  Retrieval of Public Data  . . . . . . . . . . . . . .  18
       4.3.2.  Retrieval of Semi-restricted Administrative Data  . .  18
       4.3.3.  Retrieval of Semi-restricted Service Data . . . . . .  18
       4.3.4.  Retrieval of Restricted Data  . . . . . . . . . . . .  19
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   8.  Informative References  . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Problem Statement

   The challenges of utilizing telephone numbers (TNs) on the Internet
   have been known for some time.  Internet telephony provided the first
   use case for routing telephone numbers on the Internet in a manner
   similar to how calls are routed in the public switched telephone
   network (PSTN).  As the Internet had no service for discovering the
   endpoints associated with telephone numbers, ENUM [3] created a DNS-

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   based mechanism for resolving TNs in an IP environment, by defining
   procedures for translating TNs into URIs for use by protocols such as
   SIP [2].  The resulting database was designed to function in a manner
   similar to the systems that route calls in the PSTN.  Originally, it
   was envisioned that ENUM would be deployed as a global hierarchical
   service, though in practice, it has only been deployed piecemeal by
   various parties.  Most notably, ENUM is used as an internal network
   function, and is rarely used between service provider networks.  The
   original ENUM concept of a single root,, proved to be
   politically and practically challenging, and less centralized models
   have thus flourished.  Subsequently, the DRINKS [4] framework showed
   ways that service providers might provision information about TNs at
   an ENUM service or similar Internet-based directory.  These
   technologies have also generally tried to preserve the features and
   architecture familiar to the PSTN numbering environment.

   Over time, Internet telephony has encompassed functions that differ
   substantially from traditional PSTN routing and management,
   especially as non-traditional providers have begun to utilize
   numbering resources.  An increasing number of enterprises, over-the-
   top voice-over-IP (VoIP) providers, text messaging services, and
   related non-carrier services have become heavy users of telephone
   numbers.  An enterprise, for example, can deploy an IP PBX that
   receives a block of telephone numbers from a carrier and then in turn
   distribute those numbers to new IP telephones when they associate
   with the PBX.  Internet services offer users portals where they can
   allocate new telephone numbers on the fly, assign multiple "alias"
   telephone numbers to a single line service, implement various
   mobility or find-me-follow-me applications, and so on.  Peer-to-peer
   telephone networks have encouraged experiments with distributed
   databases for telephone number routing and even allocation.

   This dynamic control over telephone numbers has few precedents in the
   traditional PSTN outside of number portability.  Number portability
   allows the capability of a user to choose and change their service
   provider while retaining their TN; it has been implemented in many
   countries; either for all telephony services or for subsets such as
   mobile.  However, TN administration processes rooted in PSTN
   technology and policies dictate that this be an exception process
   fraught with problems and delays.  Originally, processes were built
   to associate a specific TN to a specific service provider and never
   change it.  With number portability, the industry had to build new
   infrastructure, new administrative functions and processes to change
   the association of the TN from one service provider to another.
   Thanks to the increasing sophistication of consumer mobile devices as
   Internet endpoints as well as telephones, users now associate TNs
   with many Internet applications other than telephony.  This has
   generated new interest in models similar to those in place for

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   administering freephone services in the United States, where a user
   purchases a number through a sort of number registrar and controls
   its administration (such as routing) on their own, typically using
   Internet services to directly make changes to the service associated
   with telephone numbers.

   Most TNs today are assigned to specific geographies, at both an
   international level and within national numbering plans.  Numbering
   practices today are tightly coupled with the manner that service
   providers interconnect, as well as how TNs are routed and
   administered: the PSTN was carefully designed to delegate switching
   intelligence geographically.  In interexchange carrier routing in
   North America, for example, calls to a particular TN are often handed
   off to the terminating service provider close to the geography where
   that TN is assigned.  But the overwhelming success of mobile
   telephones has increasingly eroded the connection between numbers and
   regions.  Furthermore, the topology of IP networks is not anchored to
   geography in the same way that the telephone network is.  In an
   Internet environment, establishing a network architecture for routing
   TNs could depend little on geography, relying instead on network
   topologies or other architectural features.  Adapting TNs to the
   Internet requires more security, richer datasets and more complex
   query and response capabilities than previous efforts have provided.

   This document attempts to create a common understanding of the
   problem statement related to allocating, managing, and resolving TNs
   in an IP environment.  It outlines a framework and lists motivating
   use cases for creating IP-based mechanisms for TNs.  It is important
   to acknowledge at the outset that there are various evolving
   international and national policies and processes related to TNs, and
   any solutions need to be flexible enough to account for variations in
   policy and requirements.

2.  Definitions

   This section provides definitions for actors, data types and data
   management architectures as they are discussed in this document.
   Different numbering spaces may instantiate these roles and concepts
   differently: practices that apply to non-geographic freephone
   numbers, for example, may not apply to geographic numbers, and
   practices that exist under one Numbering Authority may not be
   permitted under another.  The purpose of this framework is to
   identify the characteristics of protocol tools that will satisfy the
   diverse requirements for telephone number acquisition, management,
   and retrieval on the Internet.

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2.1.  Actors

   The following roles of actors are defined in this document:

   Numbering Authority:  A regulatory body within a country that manages
      that country's TNs.  The Numbering Authority decides national
      numbering policy for the nation, region, or other domain for which
      it has authority, including what TNs can be allocated, which are
      reserved, and which entities may obtain TNs.

   Registry:  An entity that administers the allocation of TNs based on
      a Numbering Authority's policies.  Numbering authorities can act
      as the Registries themselves, or they can outsource the function
      to other entities.  Traditional registries are single entities
      with sole authority and responsibility for specific numbering
      resources, though distributed registries (see Section 2.3) are
      also in the scope of this framework.

   Credential Authority:  An entity that distributes credentials, such
      as certificates that attest the authority of assignees (defined
      below) and delegates.  This document assumes that one of more
      credential authorities may be trusted by actors in any given
      regulatory environment; policies for establishing such trust
      anchors are outside the scope of this document.

   Registrar:  An entity that distributes the telephone numbers
      administered by a Registry; typically, there are many Registrars
      that can distribute numbers from a single Registry, though
      Registrars may serve multiple Registries as well.  A Registrar has
      business relationships with number assignees and collects
      administrative information from them.

   Communication Service Provider (CSP):  A provider of communications
      services, where those services can be identified by TNs.  This
      includes both traditional telephone carriers or enterprises as
      well as service providers with no presence on the PSTN who use
      TNs.  This framework does not assume that any single CSP provides
      all the communications service related to a particular TN.

   Service Enabler:  An entity that works with CSPs to enable
      communication service to a User; perhaps a vendor, a service
      bureau, or third-party integrator.

   User:  An individual reachable through a communications service;
      usually a customer of a communication service provider.

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   Government Entity:  An entity that, due to legal powers deriving from
      national policy, has privileged access to information about number
      administration under certain conditions.

   Note that an individual, organization, or other entity may act in one
   or more of the roles above; for example, a company may be a CSP and
   also a Registrar.  Although Numbering Authorities are listed as
   actors, they are unlikely to actually participate in the protocol
   flows themselves, though in some situations a Numbering Authority and
   Registry may be the same administrative entity.

   All actors that are recipients of numbering resources, be they a CSP,
   Service Enabler, or User, can also be said to have a relationship to
   a Registry of either an assignee or delegate:

   Assignee:  An actor that is assigned a TN directly by a Registrar; an
      assignee always has a direct relationship with a Registrar.

   Delegate:  An actor that is delegated a TN from an assignee or
      another delegate, who does not necessarily have a direct
      relationship with a Registrar.  Delegates may delegate one or more
      of their TN assignment(s) to one or more further downstream

   As an example, consider a case where a Numbering Authority also acts
   as a Registry, and it issues 10,000 blocks of TNs to CSPs, which in
   this case also act as Registrars.  CSP/Registrars would then be
   responsible for distributing numbering resources to Users and other
   CSPs.  In this case, an enterprise deploying IP PBXs also acts as a
   CSP, and it acquires number blocks for its enterprise seats in chunks
   of 100 from a CSP acting as a Registrar with whom the enterprise has
   a business relationship.  The enterprise is in this case the
   assignee, as it receives numbering resources directly from a
   Registrar.  As it doles out individual numbers to its Users, the
   enterprise delegates its own numbering resources to those Users and
   their communications endpoints.  The overall ecosystem might look as

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                     V 10,000 TNs
                |   CSP   |Registrar
                     V  100 TNs
                |   PBX   |Assignee
                     V    1 TN
                |  User   |Delegate

                   Figure 1: Chain of Number Assignment

2.2.  Data Types

   The following data types are defined in this document:

   Administrative Data:  assignment data related to the TN and the
      relevant actors; it includes TN status (assigned, unassigned,
      etc.), contact data for the assignee or delegate, and typically
      does not require real-time access as this data is not required for
      ordinary call or session establishment.

   Service Data:  data necessary to enable service for the TN; it
      includes addressing data and service features.  Since this data is
      necessary to complete calls, it must be obtained in real time.

   Administrative and service data can fit into three access categories:

   Public:  Anyone can access public data.  Such data might include a
      list of which numbering resources (unallocated number ranges) are
      available for acquisition from the Registry.

   Semi-restricted:  Only a subset of actors can access semi-restricted
      data.  For example CSPs may be able to access other CSP's service
      data in some closed environment.

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   Restricted:  Only a small subset of actors can access restricted
      data.  For example a Government Entity may be able access contact
      information for a User.

   While it might appear there are really only two categories, public
   and restricted based on requestor, the distinction between semi-
   restricted and restricted is helpful for the use cases below.

2.3.  Data Management Architectures

   This framework generally assumes that administrative and service data
   is maintained by CSPs, Registrars, and Registries.  The terms
   "registrar" and "registry" are familiar from DNS operations, and
   indeed the DNS provides an obvious inspiration for the relationships
   between those entities described here.  Protocols for transferring
   names between registries and registrars have been standardized in the
   DNS space for some time (see [14]).  Similarly, the division between
   service data acquired by resolving names with the DNS protocol vs.
   administrative data about names acquired through WHOIS [15] is
   directly analogous to the distinction between service and
   administrative data described in Section 2.2.  The major difference
   between the data management architecture of the DNS and this
   framework is that the distinction between the CSP and User, due to
   historical policies of the telephone network, will often not exactly
   correspond to the distinction between a name service and a registrant
   in the DNS world - a User in the telephone network is today at least
   rarely in a direct relationship with a Registrar comparable to that
   of a DNS registrant.

   The role of a Registry described here is a "thin" one, where the
   Registry manages basic allocation information for the numbering
   space, such as information about whether or not the number is
   assigned, and if assigned, by which Registrar.  It is the Registrar
   that in turn manages detailed administrative data about those
   assignments, such as contact or billing information for the assignee.
   In some models, CSPs and Registrars will be combined (the same
   administrative entity), and in others the Registry and Registrar may
   similarly be composed.  Typically, service data resides largely at
   the CSP itself, though in some models a "thicker" Registry may itself
   contain a pointer to the servicing CSP for a number or number block.
   In addition to traditional centralized Registries, this framework
   also supports environments where the same data is being managed by
   multiple administrative entities, and stored in many locations.  A
   distributed registry system is discussed further in [19].  To support
   those use cases, it is important to distinguish the following:

   Data store:  A Data Store is a service that stores and enables access
      to administrative and/or service data.

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   Reference Address:  A Reference Address is a URL that dereferences to
      the location of the data store.

   Distributed data stores:  In a Distributed Data Store, administrative
      or service data can be stored with multiple actors.  For example,
      CSPs could provision their service data to multiple other CSPs.

   Distributed Registries:  Multiple Registries can manage the same
      numbering resource.  In these architectures, actors could interact
      with one or multiple Registries.  The Registries would update each
      other when change occurs.  The Registries have to ensure that data
      remains consistent, e.g. that the same TN is not assigned to two
      different actors.

3.  Framework

   The framework outlined in this document requires three Internet-based
   mechanisms for managing and resolving telephone numbers (TNs) in an
   IP environment.  These mechanisms will likely reuse existing
   protocols for sharing structured data; it is unlikely that new
   protocol development work will be required, though new information
   models specific to the data itself will be a major focus of framework
   development.  Likely candidates for reuse here include work done in
   DRINKS [4] and WEIRDS [12], as well as the TeRI [16] framework.

   These protocol mechanisms are scoped in a way that makes them likely
   to apply to a broad range of future policies for number
   administration.  It is not the purpose of this framework to dictate
   number policy, but instead to provide tools that will work with
   policies as they evolve going forward.  These mechanisms therefore do
   not assume that number administration is centralized, nor that number
   allocations are restricted to any category of service providers,
   though these tools must and will work in environments with those

   The three mechanisms are:

   Acquisition:  a protocol mechanism for acquiring TNs, including an
      enrollment process.

   Management:  a protocol mechanism for associating data with TNs.

   Retrieval:  a protocol mechanism for retrieving data about TNs.

   The acquisition mechanism will enable actors to acquire TNs for use
   with a communications service by requesting numbering resources from
   a service operated by a Registrar, CSP or similar actor.  TNs may be
   requested either on a number-by-number basis, or as inventory blocks.

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   Any actor who grants numbering resources will retain metadata about
   the assignment, including the responsible organization or individual
   to whom numbers have been assigned.

   The management mechanism will let actors provision data associated
   with TNs.  For example, if a User has been assigned a TN, they may
   select a CSP to provide a particular service associated with the TN,
   or a CSP may assign a TN to a User upon service activation.  In
   either case, a mechanism is needed to provision data associated with
   the TN at that CSP, and to extend those data sets as CSPs (and even
   Users) require.

   The retrieval mechanism will enable actors to learn information about
   TNs.  For real-time service data, this typically involves sending a
   request to a CSP; for other information, an actor may need to send a
   request to a Registry rather than a CSP.  Different parties may be
   authorized to receive different information about TNs.

   As an example, a CSP might use the acquisition interface to acquire a
   chunk of numbers from a Registrar.  Users might then provision
   administrative data associated with those numbers at the CSP through
   the management interface, and query for service data relating to
   those numbers through the retrieval interface of the CSP.

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          Acquisition \\
                          \  CSP  |
                           A     A
                           |     |
                Management |     | Retrieval
                           |     |
                           |     |
                   +-------++   ++-------+
                   |  User  |   |  User  |
                   +--------+   +--------+
                   (delegate)    (caller)

                 Figure 2: Example of the Three Interfaces

4.  Use Cases

   The high-level use cases in this section will provide an overview of
   the expected operation of the three interfaces in the MODERN problem

4.1.  Acquisition

   There are various scenarios for how TNs can be acquired by the
   relevant actors, that is, a CSP, Service Enabler, and a User.  There
   are three actors from which numbers can be acquired: a Registrar, a
   CSP and a User (presumably one who is delegating to another party).
   It is assumed that Registrars are either the same entity as
   Registries, or that Registrars have established business
   relationships with Registries that enable them to distribute the
   numbers that the Registries administer.  In these use cases, a User
   may acquire TNs either from a CSP or a Registry, or from an
   intermediate delegate.

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4.1.1.  Acquiring TNs from Registrar

   The most traditional number acquisition use case is one where a CSP,
   such as a carrier, requests a block of numbers from a Registrar to
   hold as inventory or assign to customers.

   Through some out-of-band business process, a CSP develops a
   relationship with a Registrar.  The Registrar maintains a profile of
   the CSP and assesses whether or not CSPs meet the policy restrictions
   for acquiring TNs.  The CSP may then request TNs from within a
   specific pool of numbers in the authority of the Registry; such as
   region, mobile, wireline, or freephone.  The Registrar must
   authenticate and authorize the CSP, and then either grant or deny a
   request.  When an assignment occurs, the Registry creates and stores
   administrative information related to the assignment such as TN
   status and Registrar contact information, and removes the specific
   TN(s) from the pool of those that are available for assignment.  As a
   part of the acquisition and assignment process, the Registry provides
   to the Registrar any tokens or other material needed by a Credential
   Authority to issue credentials (for example, STIR certificates [17])
   used to attest the assignment for future transactions.  Depending on
   the policies of the Numbering Authorities, Registrars may be required
   to log these operations.

   Before it is eligible to receive TN assignments, per the policy of a
   Numbering Authority, the CSP may need to have submitted (again,
   through some out-of-band process) additional qualifying information
   such as current utilization rate or a demand forecast.

   There are two scenarios under which a CSP requests resources; they
   are requesting inventory, or they are requesting for a specific User
   or delegate.  TNs assigned to a User are always considered assigned,
   not inventory.  The CSP will associate service information for that
   TN, e.g., service address, and make it available to other CSPs to
   enable interconnection.  The CSP may need to update the Registrar
   regarding this service activation; this is part of the "TN status"
   maintained by the Registrar.

   There are also use cases in which a User can acquire a TN directly
   from a Registrar.  Today, a user wishing to acquire a freephone
   number may browse the existing inventory through one or more
   Registrars, comparing their prices and services.  Each such Registrar
   either is a CSP, or has a business relationship with one or more CSPs
   to provide services for that freephone number.  In this case, the
   User must establish some business relationship directly with a
   Registrar, similarly to how such functions are conducted today when
   Users purchase domain names.  For the purpose of status information
   kept by the Registry, TNs assigned to a User are always considered

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   assigned, not inventory.In this use case, after receiving a number
   assignment from the Registrar, a User will then obtain communications
   service from a CSP, and provide to the CSP the TN to be used for that
   service.  The CSP will associate service information for that TN,
   e.g., service address, and make it available to other CSPs to enable
   interconnection.  The user will also need to inform the Registrar
   about this relationship.

4.1.2.  Acquiring TNs from CSPs

   Today, a User typically acquires a TN from CSP when signing up for
   communications service or turning on a new device.  In this use case,
   the User becomes the delegate of the CSP.  A reseller or a service
   bureau might also acquire a block of numbers from a CSP to be issued
   to Users.

   Consider a case where a User creates or has a relationship with the
   CSP, and subscribes to a communications service which includes the
   use of a TN.  The CSP collects and stores administrative data about
   the User.  The CSP then activates the User on their network and
   creates any necessary service data to enable connectivity with other
   CSPs.  The CSP could also update public or privileged databases
   accessible by other Actors.  The CSP provides any tokens or other
   material needed by a Credential Authority to issue credentials to the
   User (for example, a STIR certificate [17]) to prove the assignment
   for future transactions.  Such credentials could be delegated from
   the one provided by the Credential Authority to the CSP to continue
   the chain of assignment.  CSPs may be required to log such
   transactions, if required by the policy of the Numbering Authority.

   Virtually the same flow would work for a reseller: it would form a
   business relationship with the CSP, at which point the CSP would
   collect and store administrative data about the reseller and give the
   reseller any material needed for the reseller to acquire credentials
   for the numbers.  A user might then in turn acquire numbers from the
   reseller: in this case, the delegate re-delegating the TNs would be
   performing functions done by the CSP, e.g., providing any
   credentials, collecting administrative data, or creative service

   The CSP could assign a TN from its existing inventory or it could
   acquire a new TN from the Registrar as part of the assignment
   process.  If it assigns it from its existing inventory, it would
   remove the specific TN from the pool of those available for
   assignment.  It may also update the Registrar about the assignment so
   the Registrar has current assignment data.  If a reseller or delegate
   CSP is acquiring the numbers, it may have the same obligations to

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   provide utilization data to the Registry as the assignee, per
   Section 4.1.1.

4.2.  Management

   The management protocol mechanism is needed to associate
   administrative and service data with TNs, and may be used to refresh
   or rollover associated credentials.

4.2.1.  Management of Administrative Data

   Administrative data is primarily related to the status of the TN, its
   administrative contacts, and the actors involved in providing service
   to the TN.  Protocol interactions for administrative data will
   therefore predominantly occur between CSPs and Users to the
   Registrar, or between Users and delegate CSPs to the CSP.

   Some administrative data may be private, and would thus require
   special handling in a distributed data store model.  Access to it
   does not require real-time performance therefore local caches are not
   necessary.  And it will include sensitive information such as user
   and contact data.

   Some of the data could lend itself to being publicly available, such
   as CSP and TN assignment status.  In that case it would be deemed
   public information for the purposes of the retrieval interface.  Managing Data at a Registrar

   After a CSP acquires a TN or block of TNs from the Registrar (per
   Section 4.1.1 above), it then provides administrative data to the
   Registrar as a step in the acquisition process.  The Registrar will
   authenticate the CSP and determine if the CSP is authorized to
   provision the administrative data for the TNs in question.  The
   Registry will update the status of the TN, i.e., that it is
   unavailable for assignment.  The Registrar will also maintain
   administrative data provided by the CSP.

   Changes to this administrative data will not be frequent.  Examples
   of changes would be terminating service (see Section,
   changing the name or address of a User or organization, or changing a
   CSP or delegate.  Changes should be authenticated by a credential to
   prove administrative responsibility for the TN.

   In some cases, such as the freephone system in North America today,
   the User has a direct relationship with the Registrar.  Naturally,
   these users could provision administrative data associated with their
   TNs directly to the Registrar, just as a freephone provider today

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   maintains account and billing data.  While delegates may not
   ordinarily have a direct relationship to a Registrar, some
   environments as an optimization might want to support a model where
   the delegate updates the Registrar directly on changes, as opposed to
   sending that data to the CSP or through the CSP to the Registrar.  As
   stated already, the protocol should enable Users to acquire TNs
   directly from a Registrar, which Registrar may or may not also act as
   a CSP.  In these cases the updates would be similar to that described
   in Section

   In a distributed Registry model, TN status, e.g., allocated,
   assigned, available, unavailable, would need to be provided to other
   Registries in real-time.  Other administrative data could be sent to
   all Registries or other Registries could get a reference address to
   the host Registry's data store.  Mangaing Data at a CSP

   After a User acquires a TN or block of TNs from a CSP, the User will
   provide administrative data to the CSP.  The CSP commonly acts as a
   Registrar in this case, maintaining the administrative data and only
   notifies the Registry of the change in TN status.  In this case, the
   Registry maintains a reference address (see Section 2.3) to the CSP/
   Registrar's administrative data store so relevant actors have the
   ability to access the data.  Alternatively, a CSP could send the
   administrative data to an external Registrar to store.  If there is a
   delegate between the CSP and user, they will have to ensure there is
   a mechanism for the delegate to update the CSP as change occurs.

4.2.2.  Management of Service Data

   Service data is data required by an originating or intermediate CSP
   to enable communications service to a User: a SIP URI is an example
   of one service data element commonly used to route communications.
   CSPs typically create and manage service data, however, it is
   possible that delegates and Users could as well.  For most use cases
   involving individual Users, it is anticipated that lower-level
   service information changes (such as an end-user device receiving a
   new IP address) would be communicated to CSPs via existing protocols.
   For example, the baseline SIP REGISTER [2] method, even for bulk
   operations [13], would likely be used rather than through any new
   interfaces defined by MODERN.  CSP to other CSPs

   After a User enrolls for service with a CSP, in the case where the
   CSP was assigned the TN by a Registrar, the CSP will then create a
   service address such as a SIP URI and associate it with the TN.  The

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   CSP needs to update this data to enable service interoperability.
   There are multiple ways that this update can occur, though most
   commonly service data is exposed through the retrieval interface (see
   Section 4.3).  For certain deployment architectures, like a
   distributed data store model, CSPs may need to provision data
   directly to other CSPs.

   If the CSP is assigning a TN from its own inventory it may not need
   to perform service data updates as change occurs because the existing
   service data associated with inventory may be sufficient once the TN
   is put in service.  They would however likely update the Registry on
   the change in status.  User to CSP

   Users could also associate service data to their TNs at the CSP.  An
   example is a User acquires a TN from the Registrar (as described in
   Section 4.1.1) and wants to provide that TN to the CSP so the CSP can
   enable service.  In this case, once the user provides the number to
   the CSP, the CSP would update the Registry or other actors as
   outlined in Section

4.2.3.  Managing Change

   This section will address some special management use cases that were
   not covered above.  Changing the CSP for an Existing Service

   Consider the case where a User who subscribes to a communications
   service, and received their TN from that CSP, wishes to retain the
   same TN but move their service to a different CSP.

   In the simplest scenario, where there's an authoritative combined
   Registry/Registrar that maintains service data, the User could
   provide their credential to the new CSP and let the CSP initiate the
   change in service.  The new CSP could then provide the new service
   data with the User's credential to the Registry/Registrar, which then
   makes the change.  The old credential is revoked and a new one is
   provided.  The new CSP or the Registrar would send a notification to
   the old CSP, so they can disable service.  The old CSP will undo any
   delegations to the User, including contacting the Credential
   Authority to revoke any cryptographic credentials (e.g., STIR
   certificates [17]) previously granted to the User.  Any service data
   maintained by the CSP must be removed, and similarly, the CSP must
   delete any such information it provisioned in the Registry.

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   In a similar model to common practice in some environments today, the
   User could alternatively provide their credential to the old CSP, and
   the old CSP initiates the change in service.  Or, a User could go
   directly to a Registrar to initiate a port.  This framework should
   support all of these potential flows.

   Note that in cases with a distributed Registry that maintained
   service data, the Registry would also have to update the other
   Registries of the change.  Terminating a Service

   Consider a case where a user who subscribes to a communications
   service, and received their TN from the CSP, wishes to terminate
   their service.  At this time, the CSP will undo any delegations to
   the User, which may involve contacting the Credential Authority to
   revoke any cryptographic credentials (e.g., STIR certificates [17])
   previously granted to the User.  Any service data maintained by the
   CSP must be removed, and similarly, the CSP must delete any such
   information it provisioned in the Registrar.  However, per the policy
   of the Numbering Authority, Registrars and CSPs may be required to
   preserve historical data that will be accessible to Government
   Entities or others through audits, even if it is no longer
   retrievable through service interfaces.

   The TN will change state from assigned to unassigned, the CSP will
   update the Registry.  Depending on policies the TN could go back into
   the Registry, CSP, or delegate's pool of available TNs and would
   likely enter an ageing process.

   In an alternative use case, a User who received their own TN
   assignment directly from a Registrar terminates their service with a
   CSP.  At this time, the User might terminate their assignment from
   the Registrar, and return the TN to the Registry for re-assignment.
   Alternatively, they could retain the TN and elect to assign it to
   some other service at a later time.

4.3.  Retrieval

   Retrieval of administrative or service data will be subject to access
   restrictions based on the category of the specific data: public,
   semi-restricted or restricted.  Both administrative and service data
   can have data elements that fall into each of these categories.  It
   is expected that the majority of administrative will fall into the
   semi-restricted category: access to this information may require some
   form of authorization, though service data crucial to reachability
   will need to be accessible.  In some environments, it's possible that
   none of the service data necessary to initiate communications will be

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   useful to an entity on the public Internet, say, or that all that
   service data will have dependencies on .

   The retrieval protocol mechanism for semi-restricted and restricted
   data needs a way for the receiver of the request to identify the
   originator of the request and what is being requested.  The receiver
   of the request will process that request based on this information.

4.3.1.  Retrieval of Public Data

   Eithert administrative or service data may be made publicly available
   by the authority that generates and provisions it.  Under most
   circumstances, a CSP wants its communications service to be publicly
   reachable through TNs, so the retrieval interface supports public
   interfaces that permit clients to query for service data about a TN.
   Some service data may however require that the client be authorized
   to receive it, per the use case in Section 4.3.3 below.

   Public data can simply be posted on websites or made available
   through a publicly available API.  Public data hosted by a CSP may
   have a reference address at the Registry.

4.3.2.  Retrieval of Semi-restricted Administrative Data

   Consider a case in which a CSP is having service problems completing
   calls to a specific TN, so it wants to contact the CSP serving that
   TN.  The Registry authorizes the originating CSP to access this
   information.  It initiates a query to the Registry, the Registry
   verifies the requestor and the requested data and Registry responds
   with the serving CSP and contact data.  However, CSPs might not want
   to make those administrative contact points public data: they are
   willing to share them with other CSPs for troubleshooting purposes,
   but not to make them available to general communication.

   Alternatively that information could be part of a distributed data
   store and not stored at a monolithic Registry.  In that case, the CSP
   has the data in a local distributed data store and it initiates the
   query to the local data store.  The local data store responds with
   the CSP and contact data.  No verification is necessary because it
   was done when the CSP was authorized to receive the data store.

4.3.3.  Retrieval of Semi-restricted Service Data

   Consider a case where a User on a CSP's network calls a TN.  The CSP
   initiates a query for service data associated with the TN to complete
   the call, and will receive special service data because the CSP
   operates in a closed environment where different CSPs receive
   different responses, and only participating CSPs can initiate

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   communications.  This service data would be flagged as semi-
   restricted.  The query and response have real-time performance
   requirements in that environment.

   Semi-restricted service data also works in a distributed data store
   model, where each CSP distributes its updated service data to all
   other CSPs.  The originating CSP has the service data in its local
   data store and queries it.  The local data store responds with the
   service data.  The service data in the response can be a reference
   address to a data store maintained by the serving CSP, or it can be
   the service address itself.  In the case where the response gives a
   reference address, a subsequent query would go to the serving CSP,
   who would in turn authorize the requestor for the requested data and
   respond appropriate.  In the case where the original response
   contains the service address, the requestor would use that service
   address as the destination for the call.

   In some environments, aspects of the service data may reside at the
   Registry itself (for example, the assigned CSP for a TN), and thus
   the query may be sent to the Registry.  The Registry verifies the
   requestor and the requested data and responds with the service data,
   such as a SIP URI containing the domain of the assigned CSP.

4.3.4.  Retrieval of Restricted Data

   A Government Entity wishes to access information about a particular
   User, who subscribes to a communications service.  The entity that
   operates the Registry on behalf of the Numbering Authority in this
   case has some pre-defined relationship with the Government Entity.
   When the CSP acquired TNs from the Numbering Authority, it was a
   condition of that assignment that the CSP provide access for
   Government Entities to telephone numbering data when certain
   conditions apply.  The required data may reside either in the CSP or
   in the Registrar.

   For a case where the CSP delegates a number to the User, the CSP
   might provision the Registrar (or itself, if the CSP is composed with
   a Registrar) with information relevant to the User.  At such a time
   as the Government Entity needs information about that User, the
   Government Entity may contact the Registrar or CSP to acquire the
   necessary data.  The interfaces necessary for this will be the same
   as those described in Section 4.3; the Government Entity will be
   authenticated, and an authorization decision will be made by the
   Registrar or CSP under the policy dictates established by the
   Numbering Authority.

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5.  Acknowledgments

   We would like to thank Henning Schulzrinne and Adam Roach for their
   contributions to this problem statement and framework, and to thank
   Pierce Gorman for detailed comments.

6.  IANA Considerations

   This memo includes no instructions for the IANA.

7.  Security Considerations

   The acquisition, management, and retrieval of administrative and
   service data associated with telephone numbers raises a number of
   security issues.

   Any mechanism that allows an individual or organization to acquire
   telephone numbers will require a means of mutual authentication, of
   integrity protection, and of confidentiality.  A Registry as defined
   in this document will surely want to authenticate the source of an
   acquisition request as a first step in the authorization process to
   determine whether or not the resource will be granted.  Integrity of
   both the request and response is essential to ensuring that tampering
   does not allow attackers to block acquisitions, or worse, to
   commandeer resources.  Confidentiality is essential to preventing
   eavesdroppers from learning about allocations, including the
   personally identifying information associated with the administrative
   or technical contracts for allocations.

   A management interface for telephone numbers has similar
   requirements.  Without proper authentication and authorization
   mechanisms in place, an attack could use the management interface to
   disrupt service data or administrative data, which could deny service
   to users, enable new impersonation attacks, prevent billing systems
   from operating properly, and cause similar system failures.

   Finally, a retrieval interfaces has its own needs for mutual
   authentication, integrity protection, and for confidentiality.  Any
   CSP sending a request to retrieve service data associated with a
   number will want to know that it is reaching the proper authority,
   that the response from that authority has not been tampered with in
   transit, and in most cases the CSP will not want to reveal to
   eavesdroppers the number it is requesting or the response that it has
   received.  Similarly, any service answering such a query will want to
   have a means of authenticating the source of the query, and of
   protecting the integrity and confidentiality of its responses.

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8.  Informative References

   [1]        Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474,
              DOI 10.17487/RFC4474, August 2006,

   [2]        Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,

   [3]        Bradner, S., Conroy, L., and K. Fujiwara, "The E.164 to
              Uniform Resource Identifiers (URI) Dynamic Delegation
              Discovery System (DDDS) Application (ENUM)", RFC 6116,
              DOI 10.17487/RFC6116, March 2011,

   [4]        Channabasappa, S., Ed., "Data for Reachability of Inter-
              /Intra-NetworK SIP (DRINKS) Use Cases and Protocol
              Requirements", RFC 6461, DOI 10.17487/RFC6461, January
              2012, <>.

   [5]        Watson, M., "Short Term Requirements for Network Asserted
              Identity", RFC 3324, DOI 10.17487/RFC3324, November 2002,

   [6]        Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              DOI 10.17487/RFC3325, November 2002,

   [7]        Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <>.

   [8]        Elwell, J., "Connected Identity in the Session Initiation
              Protocol (SIP)", RFC 4916, DOI 10.17487/RFC4916, June
              2007, <>.

   [9]        Schulzrinne, H., "The tel URI for Telephone Numbers",
              RFC 3966, DOI 10.17487/RFC3966, December 2004,

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   [10]       Rosenberg, J. and C. Jennings, "The Session Initiation
              Protocol (SIP) and Spam", RFC 5039, DOI 10.17487/RFC5039,
              January 2008, <>.

   [11]       Peterson, J., Jennings, C., and R. Sparks, "Change Process
              for the Session Initiation Protocol (SIP) and the Real-
              time Applications and Infrastructure Area", BCP 67,
              RFC 5727, DOI 10.17487/RFC5727, March 2010,

   [12]       Newton, A. and S. Hollenbeck, "Registration Data Access
              Protocol (RDAP) Query Format", RFC 7482,
              DOI 10.17487/RFC7482, March 2015,

   [13]       Roach, A., "Registration for Multiple Phone Numbers in the
              Session Initiation Protocol (SIP)", RFC 6140,
              DOI 10.17487/RFC6140, March 2011,

   [14]       Hollenbeck, S., "Generic Registry-Registrar Protocol
              Requirements", RFC 3375, DOI 10.17487/RFC3375, September
              2002, <>.

   [15]       Daigle, L., "WHOIS Protocol Specification", RFC 3912,
              DOI 10.17487/RFC3912, September 2004,

   [16]       Peterson, J., "An Architecture and Information Model for
              Telephone-Related Information (TeRI)", draft-peterson-
              modern-teri-02 (work in progress), October 2016.

   [17]       Peterson, J. and S. Turner, "Secure Telephone Identity
              Credentials: Certificates", draft-ietf-stir-
              certificates-14 (work in progress), May 2017.

   [18]       Barnes, M., Jennings, C., Rosenberg, J., and M. Petit-
              Huguenin, "Verification Involving PSTN Reachability:
              Requirements and Architecture Overview", draft-jennings-
              vipr-overview-06 (work in progress), December 2013.

   [19]       Bellur, H. and C. Wendt, "Distributed Registry Protocol",
              draft-wendt-modern-drip-01 (work in progress), July 2016.

   [20]       Rosenberg, J. and H. Schulzrinne, "Session Initiation
              Protocol (SIP): Locating SIP Servers", RFC 3263,
              DOI 10.17487/RFC3263, June 2002,

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Authors' Addresses

   Jon Peterson
   Neustar, Inc.
   1800 Sutter St Suite 570
   Concord, CA  94520


   Tom McGarry
   Neustar, Inc.
   1800 Sutter St Suite 570
   Concord, CA  94520


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