DRIP                                                        S. Card, Ed.
Internet-Draft                                           A. Wiethuechter
Intended status: Informational                             AX Enterprize
Expires: 27 November 26 December 2020                                   R. Moskowitz
                                                          HTT Consulting
                                                                 S. Zhao
                                                             26 May
                                                               A. Gurtov
                                               Linköping University
                                                            24 June 2020

        Drone Remote Identification Protocol (DRIP) Architecture


   This document defines an architecture for protocols and services to
   support Unmanned Aircraft System Remote Identification and tracking
   (UAS RID), plus RID-related communications, including required
   architectural building blocks and their interfaces.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3   2
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   5
     2.2.  Additional Definitions  . . . . . . . . . . . . . . . . .   6   5
   3.  Entities and their Interfaces . . . . . . . . . . . . . . . .   6
     3.1.  Private Information Registry  . . . . . . . . . . . . . .   6
       3.1.1.  Background  . . . . . . . . . . . . . . . . . . . . .   6
       3.1.2.  Proposed Approach . . . . . . . . . . . . . . . . . .   6
     3.2.  Public Information Registry . . . . . . . . . . . . . . .   7
       3.2.1.  Background  . . . . . . . . . . . . . . . . . . . . .   7
       3.2.2.  Proposed Approach . . . . . . . . . . . . . . . . . .   7
     3.3.  CS-RID concept  . . . . . . . . . . . . . . . . . . . . .   7
       3.3.1.  Proposed optional CS-RID SDSP . . . . . . . . . . . .   8   7
       3.3.2.  Proposed optional CS-RID Finder . . . . . . . . . . .   8
   4.  Identifiers . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Background  . . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Proposed Approach . . . . . . . . . . . . . . . . . . . .   9
   5.  DRIP Transactions enabling Trustworthy UAS RID  . . . . . . .  10   9
   6.  Privacy for Broadcast PII . . . . . . . . . . . . . . . . . .  10
   7.  Architectural implications of EASA requirements . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  12
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  12
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     9.2.  12
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11  12
   Appendix A.  Overview of Unmanned Aircraft Systems (UAS) Traffic
           Management (UTM)  . . . . . . . . . . . . . . . . . . . .  13  14
     A.1.  Operation Concept . . . . . . . . . . . . . . . . . . . .  14
     A.2.  UAS Service Supplier (USS)  . . . . . . . . . . . . . . .  14  15
     A.3.  UTM Use Cases for UAS Operations  . . . . . . . . . . . .  15
     A.4.  Overview UAS Remote ID (RID) and RID Standardization  . .  15  16
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   This document describes a natural Internet based architecture for
   Unmanned Aircraft System Remote Identification and tracking (UAS
   RID), conforming to proposed regulations and external technical
   standards, satisfying the requirements listed in the companion
   requirements document [I-D.ietf-drip-reqs].  The requirements
   document also provides an extended introduction to the problem space,
   use cases, etc.  Only a brief summary of that introduction will be
   restated here as context, with reference to the general architecture
   shown in Figure 1 below.

      General      x                           x     Public
      Public     xxxxx                       xxxxx   Safety
      Observer     x                           x     Observer
                   x                           x
                  x x ---------+  +---------- x x
                 x   x         |  |          x   x
                               |  |
                               +  +
                           x          x
               +----------+x Internet x+------------+
               |           x          x             |
    UA1      x |            xxxxxxxxxx              | x    UA2
    Pilot  xxxxx               + + +                xxxxx  Pilot
   Operator  x                 | | |                  x  Operator
             x                 | | |                  x
            x x                | | |                 x x
           x   x               | | |                x   x
                               | | |
             +----------+      | | |       +----------+
             |          |------+ | +-------|          |
             | Public   |        |         | Private  |
             | Registry |     +-----+      | Registry |
             |          |     | DNS |      |          |
             +----------+     +-----+      +----------+

                                  Figure 1

   Many considerations (especially safety) dictate that UAS be remotely
   identifiable.  Civil Aviation Authorities (CAAs) worldwide are
   mandating Unmanned Aircraft Systems (UAS) Remote Identification
   (RID).  CAAs currently (2020) promulgate performance-based
   regulations that do not specify techniques, but rather cite industry
   consensus technical standards as acceptable means of compliance.

   ASTM International, Technical Committee F38 (UAS), Subcommittee
   F38.02 (Aircraft Operations), Work Item WK65041, developed the new
   ASTM [F3411-19] Standard Specification for Remote ID and Tracking.
   It defines one set of RID information and two means of communicating
   it.  If a UAS uses both communication methods, generally the same
   information must provided via both means.  While hybrids are possible
   (and indeed one is proposed as an optional DRIP service), the two
   basic methods are defined as follows:

      Network RID defines a RID data dictionary and data flow: from a
      UAS via unspecified means to a Network Remote ID Service Provider
      (Net-RID SP); from the Net-RID SP to an integrated, or over the
      Internet to a separate, Network Remote ID Display Provider (Net-
      RID DP); from the Net-RID DP via the Internet to Network Remote ID
      clients in response to their queries (expected typically, but not
      specified exclusively, to be web based) specifying airspace
      volumes of interest.  Network RID depends upon connectivity, in
      several segments, via the Internet, from the UAS to the Observer.

      Broadcast RID defines a set of RID messages and how the UA
      transmits them locally directly one-way, over Bluetooth or Wi-Fi.
      Broadcast RID should need Internet (or other Wide Area Network)
      connectivity only for UAS registry information lookup using the
      locally directly received UAS ID as a key.  Broadcast RID should
      be functionally usable in situations with no Internet

   The less constrained but more complex case of Network RID is
   illustrated in Figure 2 below.

             x x  UA
            xxxxx       ********************
             |         *              ------*---+------------+
             |        *              /       *  | NET_Rid_DP |
             |        * ------------/    +---*--+------------+
             | RF     */                 |   *
             |        *      INTERNET    |   *  +------------+
             |       /*                  +---*--| NET_Rid_SP |
             |      / *                 +----*--+------------+
             +     /   *                |   *
              x   /     ****************|***      x
            xxxxx                       |       xxxxx
              x                         +-------  x
              x                                   x
             x x   Operator (GCS)     Observer   x x
            x   x                               x   x

                                  Figure 2

   Via the direct Radio Frequency (RF) link between the UA and GCS:
   Command and Control (C2) flows from the GCS to the UA; for all but
   the simplest hobby aircraft, position and status flow from the UA to
   the GCS.  Via the Internet, through three distinct segments, Network
   RID information flows from the UAS (comprising the UA and its GCS) to
   the Observer.

   Other Standards Development Organizations (SDOs, e.g., 3GPP,
   Appendix A.4) may define their own communication methods for both
   Network and Broadcast RID.  The CAAs expect any additional methods to
   maintain consistency of the RID messages.

   DRIP will enable leveraging existing Internet resources (standard
   protocols, services, infrastructure and business models) to meet UAS
   RID and closely related needs.  DRIP will specify how to apply IETF
   standards, complementing [F3411-19] and other external standards, to
   satisfy UAS RID requirements.  DRIP will update existing and develop
   new protocol standards as needed to accomplish the foregoing.

   This document will outline the UAS RID architecture into which DRIP
   must fit, and an architecture for DRIP itself.  This includes
   presenting the gaps between the CAAs' Concepts of Operations and
   [F3411-19] as it relates to use of Internet technologies and UA
   direct RF communications.  Issues include, but are not limited to:

   *  Trustworthy Remote ID and trust in RID messages

   *  Privacy in RID messages (PII protection)

   *  UA -> Ground communications including Broadcast RID

   *  Broadcast RID 'harvesting' and secure forwarding into the UTM

   *  Secure UAS -> Net-RID SP communications

   *  Secure Observer -> Pilot communications

2.  Terms and Definitions

2.1.  Requirements Terminology

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

2.2.  Additional Definitions

   This document uses terms defined in [I-D.ietf-drip-reqs].

3.  Entities and their Interfaces

   Any DRIP solutions for UAS RID must fit into the UTM (or U-space)
   system.  This implies interaction with entities including UA, GCS,
   USS, Net-RID SP, Net-RID DP, Observers, Operators, Pilots In Command,
   Remote Pilots, possibly SDSP, etc.  The only additional entities
   introduced in this document are registries, required but not
   specified by the regulations and [RFC7401], and optionally CS-RID
   SDSP and Finder nodes.

   UAS registries hold both public and private UAS information.  The
   public information is primarily pointers to the repositories of, and
   keys for looking up, the private information.  Given these different
   uses, and to improve scalability, security and simplicity of
   administration, the public and private information can be stored in
   different registries, indeed different types of registry.

3.1.  Private Information Registry

3.1.1.  Background

   The private information required for UAS RID is similar to that
   required for Internet domain name registration.  Thus a DRIP RID
   solution can leverage existing Internet resources: registration
   protocols, infrastructure and business models, by fitting into an ID
   structure compatible with DNS names.  This implies some sort of
   hierarchy, for scalability, and management of this hierarchy.  It is
   expected that the private registry function will be provided by the
   same organizations that run USS, and likely integrated with USS.

3.1.2.  Proposed Approach

   A DRIP UAS ID MUST be amenable to handling as an Internet domain name
   (at an arbitrary level in the hierarchy), MUST be registered in at
   least a pseudo-domain (e.g. .ip6 for reverse lookup), and MAY be
   registered as a sub-domain (for forward lookup).

   A DRIP private information registry MUST support essential Internet
   domain name registry operations (e.g. add, delete, update, query)
   using interoperable open standard protocols.  It SHOULD support the
   Extensible Provisioning Protocol (EPP) and the Registry Data Access
   Protocol (RDAP) with access controls.  It MAY use XACML to specify
   those access controls.  It MUST be listed in a DNS: that DNS MAY be
   private; but absent any compelling reasons for use of private DNS,
   SHOULD be the definitive public Internet DNS hierarchy.  The DRIP
   private information registry in which a given UAS is registered MUST
   be locatable, starting from the UAS ID, using the methods specified
   in [RFC7484].

3.2.  Public Information Registry

3.2.1.  Background

   The public information required to be made available by UAS RID is
   transmitted as cleartext to local observers in Broadcast RID and is
   served to a client by a Net-RID DP in Network RID.  Therefore, while
   IETF can offer e.g.  [RFC6280] as one way to implement Network RID,
   the only public information required to support essential DRIP
   functions for UAS RID is that required to look up Internet domain
   hosts, services, etc.

3.2.2.  Proposed Approach

   A DRIP public information registry MUST be a standard DNS server, in
   the definitive public Internet DNS hierarchy.  It MUST support NS,
   MX, SRV, TXT, AAAA, PTR, CNAME and HIP RR (the last per [RFC8005])

3.3.  CS-RID concept

   ASTM anticipated that regulators would require both Broadcast RID and
   Network RID for large UAS, but allow RID requirements for small UAS
   to be satisfied with the operator's choice of either Broadcast RID or
   Network RID.  The EASA initially specified Broadcast RID for UAS of
   essentially all UAS and is now considering Network RID also.  The FAA
   NPRM requires both for Standard RID and specifies Broadcast RID only
   for Limited RID.  One obvious opportunity is to enhance the
   architecture with gateways from Broadcast RID to Network RID.  This
   provides the best of both and gives regulators and operators
   flexibility.  Such gateways could be pre-positioned (e.g. around
   airports and other sensitive areas) and/or crowdsourced (as nothing
   more than a smartphone with a suitable app is needed).  Gateways can
   also perform multilateration to provide independent measurements of
   UA position, which is otherwise entirely operator self-reported in
   UAS RID and UTM.  CS-RID would be an option, beyond baseline DRIP
   functionality; if implemented, it adds 2 more entity types.

3.3.1.  Proposed optional CS-RID SDSP

   A CS-RID SDSP MUST appear (i.e. present the same interface) to a Net-
   RID SP as a Net-RID DP.  A CS-RID SDSP MUST appear to a Net-RID DP as
   a Net-RID SP.  A CS-RID SDSP MUST NOT present a standard GCS-facing
   interface as if it were a Net-RID SP.  A CS-RID SDSP MUST NOT present
   a standard client-facing interface as if it were a Net-RID DP.  A CS-
   RID SDSP MUST present a TBD interface to a CS-RID Finder; this
   interface SHOULD be based upon but readily distinguishable from that
   between a GCS and a Net-RID SP.

3.3.2.  Proposed optional CS-RID Finder

   A CS-RID Finder MUST present a TBD interface to a CS-RID SDSP; this
   interface SHOULD be based upon but readily distinguishable from that
   between a GCS and a Net-RID SP.  A CS-RID Finder must implement,
   integrate, or accept outputs from, a Broadcast RID receiver.  A CS-
   RID Finder MUST NOT interface directly with a GCS, Net-RID SP, Net-
   RID DP or Network RID client.

4.  Identifiers

4.1.  Background

   A DRIP UA ID needs to be "Trustworthy".  This means that within the
   framework of the RID messages, an observer can establish that the RID
   used does uniquely belong to the UA.  That the only way for any other
   UA to assert this RID would be to steal something from within the UA.
   The RID is self-generated by the UAS (either UA or GCS) and
   registered with the USS.

   Within the limitations of Broadcast RID, this is extremely
   challenging as:

   *  An RID can at most be 20 characters

   *  The ASTM Basic RID message (the message containing the RID) is 25
      characters; only 3 characters are currently unused

   *  The ASTM Authentication message, with some changes from [F3411-19]
      can carry 224 bytes of payload.

   Standard approaches like X.509 and PKI will not fit these
   constraints, even using the new EdDSA algorithm.  An example of a
   technology that will fit within these limitations is an enhancement
   of the Host Identity Tag (HIT) of HIPv2 [RFC7401] introducing
   hierarchy as defined in HHIT [I-D.moskowitz-hip-hierarchical-hit];
   using Hierarchical HITs for UAS RID is outlined in HHIT based UAS RID
   [I-D.moskowitz-drip-uas-rid].  As PKI with X.509 is being used in
   other systems with which UAS RID must interoperate (e.g. the UTM
   Discovery and Synchronization Service and the UTM InterUSS protocol)
   mappings between the more flexible but larger X.509 certificates and
   the HHIT based structures must be devised.

   By using the EdDSA HHIT suite, self-assertions of the RID can be done
   in as little as 84 bytes.  Third-party assertions can be done in 200
   bytes.  An observer would need Internet access to validate a self-
   assertion claim.  A third-party assertion can be validated via a
   small credential cache in a disconnected environment.  This third-
   party assertion is possible when the third-party also uses HHITs for
   its identity and the UA has the public key for that HHIT.

4.2.  Proposed Approach

   A DRIP UAS ID MUST be a HHIT.  It SHOULD be self-generated by the UAS
   (either UA or GCS) and MUST be registered with the Private
   Information Registry identified in its hierarchy fields.  Each UAS ID
   HHIT MUST NOT be used more than once, with one exception as follows.

   Each UA MAY be assigned, by its manufacturer, a single HI and derived
   HHIT encoded as a hardware serial number per [CTA2063A].  Such a
   static HHIT SHOULD be used only to bind one-time use UAS IDs (other
   HHITs) to the unique UA.  Depending upon implementation, this may
   leave a HI private key in the possession of the manufacturer (see
   Security Considerations).

   Each UA equipped for Broadcast RID MUST be provisioned not only with
   its HHIT but also with the HI public key from which the HHIT was
   derived and the corresponding private key, to enable message
   signature.  Each UAS equipped for Network RID MUST be provisioned
   likewise; the private key SHOULD reside only in the ultimate source
   of Network RID messages (i.e. on the UA itself if the GCS is merely
   relaying rather than sourcing Network RID messages).  Each observer
   device MUST be provisioned with public keys of the UAS RID root
   registries and MAY be provisioned with public keys or certificates
   for subordinate registries.

   Operators and Private Information Registries MUST possess and other
   UTM entities MAY possess UAS ID style HHITs.  When present, such
   HHITs SHOULD be used with HIP to strongly mutually authenticate and
   optionally encrypt communications.

5.  DRIP Transactions enabling Trustworthy UAS RID

   Each Operator MUST generate a "HIo" and derived "HHITo", register
   them with a Private Information Registry along with whatever Operator
   data (inc.  PII) is required by the cognizant CAA and the registry,
   and obtain a certificate "Cro" signed with "HIr(priv)" proving such

   To add an UA, an Operator MUST generate a "HIa" and derived "HHITa",
   create a certificate "Coa" signed with "HIo(priv)" to associate the
   UA with its Operator, register them with a Private Information
   Registry along with whatever UAS data is required by the cognizant
   CAA and the registry, obtain a certificate "Croa" signed with
   "HIr(priv)" proving such registration, and obtain a certificate "Cra"
   signed with "HIr(priv)" proving UA registration in that specific
   registry while preserving Operator privacy.  The operator then MUST
   provision the UA with "HIa", "HIa(priv)", "HHITa" and "Cra".

   UA engaging in Broadcast RID MUST use "HIa(priv)" to sign Auth
   Messages and MUST periodically broadcast "Cra".  UAS engaging in
   Network RID MUST use "HIa(priv)" to sign Auth Messages.  Observers
   MUST use "HIa" from received "Cra" to verify received Broadcast RID
   Auth messages.  Observers without Internet connectivity MAY use "Cra"
   to identify the trust class of the UAS based on known registry
   vetting.  Observers with Internet connectivity MAY use "HHITa" to
   perform lookups in the Public Information Registry and MAY then query
   the Private Information Registry, which MUST enforce AAA policy on
   Operator PII and other sensitive information.

6.  Privacy for Broadcast PII

   Broadcast RID messages may contain PII.  This may be information
   about the UA such as its destination or Operator information such as
   GCS location.  There is no absolute "right" in hiding PII, as there
   will be times (e.g., disasters) and places (buffer zones around
   airports and sensitive facilities) where policy may mandate all
   information be sent as cleartext.  Otherwise, the modern general
   position (consistent with, e.g., the EU General Data Protection
   Regulation) is to hide PII unless otherwise instructed.  While some
   have argued that a system like that of automobile registration plates
   should suffice for UAS, others have argued persuasively that each
   generation of new identifiers should take advantage of advancing
   technology to protect privacy, to the extent compatible with the
   transparency needed to protect safety.

   A viable architecture for PII protection would be symmetric
   encryption of the PII using a key known to the UAS and a USS service.
   An authorized Observer may send the encrypted PII along with the
   Remote ID (to their UAS display service) to get the plaintext.  The
   authorized Observer may send the Remote ID (to their UAS display
   service) and receive the key to directly decrypt all PII content from
   the UA.

   PII is protected unless the UAS is informed otherwise.  This may come
   from operational instructions to even permit flying in a space/time.
   It may be special instructions at the start or during a mission.  PII
   protection should not be used if the UAS loses connectivity to the
   USS.  The USS always has the option to abort the mission if PII
   protection is disallowed.

   An authorized Observer may instruct a UAS via the USS that conditions
   have changed mandating no PII protection or land the UA.

7.  Architectural implications of EASA requirements

   According to EASA, in EU broadcasting drone identification will be
   mandatory from July 2020.  Following info should be sent in plaintext
   over Wifi or Bluetooth.  In real time during the whole duration of
   the flight, the direct periodic broadcast from the UA using an open
   and documented transmission protocol, of the following data, in a way
   that they can be received directly by existing mobile devices within
   the broadcasting range:

   i) the UAS operator registration number;

   ii) the unique physical serial number of the UA compliant with
   standard ANSI/CTA2063;

   iii) the geographical position of the UA and its height above the
   surface or take-off point;

   iv) the route course measured clockwise from true north and ground
   speed of the UA; and

   v) the geographical position of the remote pilot or, if not
   available, the take-off point;

   The architecture proposed in this document partially satisfies EASA
   requirements.  In particular, i) is included to Operator-ID Message
   as optional. ii) cannot be directly supported due to its heavy
   privacy implications.  A cryptographic identifier that needs to be
   resolved is proposed instead. iii) and iv) are included into
   Location/Vector Message. v) is included into a System Message

8.  IANA Considerations

   This document does not make any request to IANA.


9.  Security Considerations

   DRIP is all about safety and security, so content pertaining to such
   is not limited to this section.  The security provided by asymmetric
   cryptographic techniques depends upon protection of the private keys.
   A manufacturer that embeds a private key in an UA may have retained a
   copy.  A manufacturer whose UA are configured by a closed source
   application on the GCS which communicates over the Internet with the
   factory may be sending a copy of a UA or GCS self-generated key back
   to the factory.  Compromise of a registry private key could do
   widespread harm.  Key revocation procedures are as yet to be
   determined.  These risks are in addition to those involving Operator
   key management practices.


10.  References


10.1.  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,

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


10.2.  Informative References

              ATIS, "Report on UAS in 3GPP",

   [CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers",
              September 2019.

              European Union Aviation Safety Agency (EASA), "EU
              Commission Delegated Regulation 2019/945 of 12 March 2019
              on unmanned aircraft systems and on third-country
              operators of unmanned aircraft systems", March 2019.

   [F3411-19] ASTM, "Standard Specification for Remote ID and Tracking",
              December 2019.

              Card, S., Wiethuechter, A., Moskowitz, R., and A. Gurtov,
              "Drone Remote Identification Protocol (DRIP)
              Requirements", Work in Progress, Internet-Draft, draft-
              ietf-drip-reqs-01, 25 May 2020,

              Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
              "UAS Remote ID", Work in Progress, Internet-Draft, draft-
              moskowitz-drip-uas-rid-01, 5
              moskowitz-drip-uas-rid-02, 28 May 2020,

              Moskowitz, R., Card, S., and A. Wiethuechter,
              "Hierarchical HITs for HIPv2", Work in Progress, Internet-
              Draft, draft-moskowitz-hip-hierarchical-hit-05, 13 May
              2020, <https://tools.ietf.org/html/draft-moskowitz-hip-

              European Union Aviation Safety Agency (EASA), "EU
              Commission Implementing Regulation 2019/947 of 24 May 2019
              on the rules and procedures for the operation of unmanned
              aircraft", May 2019.

   [LANNC]    United States Federal Aviation Administration (FAA), "Low
              Altitude Authorization and Notification Capability",

   [NPRM]     United States Federal Aviation Administration (FAA),
              "Notice of Proposed Rule Making on Remote Identification
              of Unmanned Aircraft Systems", December 2019.

   [RFC6280]  Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
              Tschofenig, H., and H. Schulzrinne, "An Architecture for
              Location and Location Privacy in Internet Applications",
              BCP 160, RFC 6280, DOI 10.17487/RFC6280, July 2011,

   [RFC7401]  Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
              Henderson, "Host Identity Protocol Version 2 (HIPv2)",
              RFC 7401, DOI 10.17487/RFC7401, April 2015,

   [RFC7484]  Blanchet, M., "Finding the Authoritative Registration Data
              (RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March
              2015, <https://www.rfc-editor.org/info/rfc7484>.

   [RFC8005]  Laganier, J., "Host Identity Protocol (HIP) Domain Name
              System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005,
              October 2016, <https://www.rfc-editor.org/info/rfc8005>.

              3GPP, "UAS RID requirement study",

              3GPP, "UAV service in the LTE network",

   [U-Space]  European Organization for the Safety of Air Navigation
              (EUROCONTROL), "U-space Concept of Operations", October

Appendix A.  Overview of Unmanned Aircraft Systems (UAS) Traffic
             Management (UTM)

A.1.  Operation Concept

   The National Aeronautics and Space Administration (NASA) and FAAs'
   effort of integrating UAS's operation into the national airspace
   system (NAS) leads to the development of the concept of UTM and the
   ecosystem around it.  The UTM concept was initially presented in
   2013.  The eventual development and implementation are conducted by
   the UTM research transition team which is the joint workforce by FAA
   and NASA.  World efforts took place afterward.  The Single European
   Sky ATM Research (SESAR) started the CORUS project to research its
   UTM counterpart concept, namely [U-Space].  This effort is led by the
   European Organization for the Safety of Air Navigation (Eurocontrol).

   Both NASA and SESAR have published the UTM concept of operations to
   guide the development of their future air traffic management (ATM)
   system and make sure safe and efficient integrations of manned and
   unmanned aircraft into the national airspace.

   The UTM composes of UAS operation infrastructure, procedures and
   local regulation compliance policies to guarantee UAS's safe
   integration and operation.  The main functionality of a UTM includes,
   but is not limited to, providing means of communication between UAS
   operators and service providers and a platform to facilitate
   communication among UAS service providers.

A.2.  UAS Service Supplier (USS)

   A USS plays an important role to fulfill the key performance
   indicators (KPIs) that a UTM has to offer.  Such Entity acts as a
   proxy between UAS operators and UTM service providers.  It provides
   services like real-time UAS traffic monitor and planning,
   aeronautical data archiving, airspace and violation control,
   interacting with other third-party control entities, etc.  A USS can
   coexist with other USS(s) to build a large service coverage map which
   can load-balance, relay and share UAS traffic information.

   The FAA works with UAS industry shareholders and promotes the Low
   Altitude Authorization and Notification Capability [LANNC] program
   which is the first implementation to realize UTM's functionality.
   The LAANC program can automate the UAS's fly plan application and
   approval process for airspace authorization in real-time by checking
   against multiple aeronautical databases such as airspace
   classification and fly rules associated with it, FAA UAS facility
   map, special use airspace, Notice to airman (NOTAM) and Temporary
   flight rule (TFR).

A.3.  UTM Use Cases for UAS Operations

   This section illustrates a couple of use case scenarios where UAS
   participation in UTM has significant safety improvement.

   1.  For a UAS participating in UTM and takeoff or land in a
       controlled airspace (e.g., Class Bravo, Charlie, Delta and Echo
       in United States), the USS where UAS is currently communicating
       with is responsible for UAS's registration, authenticating the
       UAS's fly plan by checking against designated UAS fly map
       database, obtaining the air traffic control (ATC) authorization
       and monitor the UAS fly path in order to maintain safe boundary
       and follow the pre-authorized route.

   2.  For a UAS participating in UTM and take off or land in an
       uncontrolled airspace (ex.  Class Golf in the United States),
       pre-fly authorization must be obtained from a USS when operating
       beyond-visual-of-sight (BVLOS) operation.  The USS either accepts
       or rejects received intended fly plan from the UAS.  Accepted UAS
       operation may share its current fly data such as GPS position and
       altitude to USS.  The USS may keep the UAS flight status near
       real-time and may keep it as a record for overall airspace air
       traffic monitor.

A.4.  Overview UAS Remote ID (RID) and RID Standardization

   A RID is an application enabler for a UAS to be identified by a UTM/
   USS or third parties entities such as law enforcement.  Many safety
   and other considerations dictate that UAS be remotely identifiable.
   CAAs worldwide are mandating UAS RID.  The European Union Aviation
   Safety Agency (EASA) has published [Delegated] and [Implementing]
   Regulations.  The FAA has published a Notice of Proposed Rule Making
   [NPRM].  CAAs currently promulgate performance-based regulations that
   do not specify techniques, but rather cite industry consensus
   technical standards as acceptable means of compliance.

   3GPP provides UA service in the LTE network since release 15 in
   published technical specification [TS-36.777].  Start from its
   release 16, it completed the UAS RID requirement study in [TS-22.825]
   and proposed use cases in the mobile network and the services that
   can be offered based on RID and ongoing release 17 specification
   works on enhanced UAS service requirement and provides the protocol
   and application architecture support which is applicable for both 4G
   and 5G network.  ATIS's recent report [ATIS-I-0000074] proposes
   architecture approaches for the 3GPP network to support UAS and one
   of which is put RID in higher 3GPP protocol stack such as using ASTM
   remote ID [F3411-19].


   The work of the FAA's UAS Identification and Tracking (UAS ID)
   Aviation Rulemaking Committee (ARC) is the foundation of later ASTM
   and proposed IETF DRIP WG efforts.  The work of ASTM F38.02 in
   balancing the interests of diverse stakeholders is essential to the
   necessary rapid and widespread deployment of UAS RID.  IETF
   volunteers who have contributed to this draft include Amelia
   Andersdotter and Mohamed Boucadair.

Authors' Addresses

   Stuart W. Card (editor)
   AX Enterprize
   4947 Commercial Drive
   Yorkville, NY 13495
   United States of America

   Email: stu.card@axenterprize.com

   Adam Wiethuechter
   AX Enterprize
   4947 Commercial Drive
   Yorkville, NY 13495
   United States of America

   Email: adam.wiethuechter@axenterprize.com

   Robert Moskowitz
   HTT Consulting
   Oak Park, MI 48237
   United States of America

   Email: rgm@labs.htt-consult.com

   Shuai Zhao
   United States of America

   Email: shuaiizhao@tencent.com

   Andrei Gurtov
   Link&#246;ping University
   SE-58183 Link&#246;ping

   Email: gurtov@acm.org