DRIP                                                             S. Card
Internet-Draft                                           A. Wiethuechter
Intended status: Informational                             AX Enterprize
Expires: 25 September 2020                                  R. Moskowitz
                                                          HTT Consulting
                                                           24 March 2020

        Drone Remote Identification Protocol (DRIP) Requirements


   This document defines the requirements for Drone Remote
   Identification Protocol (DRIP) Working Group protocols and services
   to support Unmanned Aircraft System Remote Identification (UAS RID).

   Objectives include: complementing external technical standards as
   regulator-accepted means of compliance with UAS RID regulations;
   facilitating use of existing Internet resources to support UAS RID
   and to enable enhanced related services; and enabling verification
   that UAS RID information is trustworthy (to some extent, even in the
   absence of Internet connectivity at the receiving node).

Status of This Memo

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

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   This Internet-Draft will expire on 25 September 2020.

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/

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   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   4
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  UAS RID Problem Space . . . . . . . . . . . . . . . . . . . .   8
     3.1.  Network RID . . . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  Broadcast RID . . . . . . . . . . . . . . . . . . . . . .   9
     3.3.  DRIP Focus  . . . . . . . . . . . . . . . . . . . . . . .  10
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.2.  UAS Identifier  . . . . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Many safety and other considerations dictate that UAS be remotely
   identifiable.  Civil Aviation Authorities (CAAs) worldwide are
   mandating UAS RID.  The European Union Aviation Safety Agency (EASA)
   has published [Delegated] and [Implementing] Regulations.  The United
   States (US) Federal Aviation Administration (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.

   ASTM International, Technical Committee F38 (UAS), Subcommittee
   F38.02 (Aircraft Operations), Work Item WK65041, developed new ASTM
   F3411-19 [F3411-19] Standard Specification for Remote ID and
   Tracking.  It defines 2 means of UAS RID.  Network RID defines a set
   of information for UAS to make available globally indirectly via the
   Internet.  Broadcast RID defines a set of messages for Unmanned
   Aircraft (UA) to transmit locally directly one-way over Bluetooth or
   Wi-Fi.  Network RID depends upon Internet connectivity, in several

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   segments, from the UAS to the observer.  Broadcast RID should need
   Internet (or other Wide Area Network) connectivity only for UAS
   registry information lookup using the directly locally received UAS
   ID as a key.

   [F3411-19] specifies 3 UAS ID types.  Type 1 is a static,
   manufacturer assigned, hardware serial number per ANSI/CTA-2063-A
   "Small Unmanned Aerial System Serial Numbers" [CTA2063A].  Type 2 is
   a CAA assigned (presumably static) ID.  Type 3 is a UAS Traffic
   Management (UTM) system assigned UUID [RFC4122], which can but need
   not be dynamic.  The EU allows only Type 1; the US allows Types 1 and
   3, but requires Type 3 IDs (if used) each to be used only once.
   [F3411-19] Broadcast RID transmits all information in the clear as
   plaintext, so Type 1 static IDs enable trivial correlation of
   patterns of use, unacceptable in many applications, e.g. package
   delivery routes of competitors.

   An ID is not an end in itself; it exists to enable lookups and
   provision of services complementing mere identification.

   Minimal specified information must be made available to the public;
   access to other data, e.g.  UAS operator Personally Identifiable
   Information (PII), must be limited to strongly authenticated
   personnel, properly authorized per policy.  [F3411-19] specifies only
   how to get the UAS ID to the observer; how the observer can perform
   these lookups, and how the registries first can be populated with
   information, is unspecified.

   Although using UAS RID to facilitate related services, such as Detect
   And Avoid (DAA) and other applications of Vehicle to Vehicle or
   Vehicle to Infrastructure (V2V, V2I, collectively V2X)
   communications, is an obvious application (explicitly contemplated in
   the FAA NPRM), it has been omitted from [F3411-19] (explicitly
   declared out of scope in the ASTM working group discussions based on
   a distinction between RID as a security standard vs DAA as a safety
   application).  Although dynamic establishment of secure
   communications between the observer and the UAS pilot seems to have
   been contemplated by the FAA UAS ID and Tracking Aviation Rulemaking
   Committee (ARC) in their [Recommendations], it is not addressed in
   any of the subsequent proposed regulations or technical

   The need for near-universal deployment of UAS RID is pressing.  This
   implies the need to support use by observers of already ubiquitous
   mobile devices (smartphones and tablets).  UA onboard RID devices are
   severely constrained in Size, Weight and Power (SWaP).  Cost is a
   significant impediment to the necessary near-universal adoption of
   UAS send and observer receive RID capabilities.  To accommodate the

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   most severely constrained cases, all these conspire to motivate
   system design decisions, especially for the Broadcast RID data link,
   which complicate the protocol design problem: one-way links;
   extremely short packets; and Internet-disconnected operation of UA
   onboard devices.  Internet-disconnected operation of observer devices
   has been deemed by ASTM F38.02 too infrequent to address, but for
   some users is important and presents further challenges.  Heavyweight
   security protocols are infeasible, yet trustworthiness of UAS RID
   information is essential.  Under [F3411-19], even the most basic
   datum, the UAS ID string (typically number) itself can be merely an
   unsubstantiated claim.

   DRIP's goal is to make RID immediately actionable, in both Internet
   and local-only connected scenarios (especially emergencies), in
   severely constrained UAS environments, balancing legitimate (e.g.
   public safety) authorities' Need To Know trustworthy information with
   UAS operators' privacy.  To accomplish this, DRIP WG will liaise with
   SDOs and complement their standards with IETF work to meet this
   urgent need.  An Applicability Statement RFC for UAS RID, showing how
   to use IETF standardized technologies for this purpose, will be a
   central work product.  Technical Specification RFCs will address any
   necessary enhancements of specific supporting protocols.  DRIP
   (originally called Trustworthy Multipurpose Remote Identification,
   TM-RID) potentially could be applied to verifiably identify other
   types of registered things reported to be in specified physical
   locations, but the urgent motivation and clear initial focus is UAS.
   Existing Internet resources (business models, infrastructure and
   protocol standards) should be leveraged.  A natural Internet
   architecture for UAS RID conforming to proposed regulations and
   external technical standards will be described in a companion DRIP
   Architecture document; this document describes only requirements.

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.  Definitions

      Cost, Size, Weight and Power.

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      Attestation, Authentication, Authorization, Access Control,
      Accounting, Attribution, Audit.

      AirBorne DAA.  Also known as "self-separation".

      Above Ground Level.  Relative altitude, above the variously
      defined local ground level, typically of an UA, typically measured
      in feet.

      Civil Aviation Authority.  An example is the Federal Aviation
      Administration (FAA) in the United States of America.

      Command and Control.  A set of organizational and technical
      attributes and processes that employs human, physical, and
      information resources to solve problems and accomplish missions.
      Mainly used in military contexts.

      Detect And Avoid, formerly Sense And Avoid (SAA).  A means of
      keeping aircraft "well clear" of each other for safety.

      End to End.

      Ground Based DAA.

      Ground Control Station.  The part of the UAS that the remote pilot
      uses to exercise C2 over the UA, whether by remotely exercising UA
      flight controls to fly the UA, by setting GPS waypoints, or
      otherwise directing its flight.

      Global Positioning System.  In this context, misused in place of
      Global Navigation Satellite System (GNSS) or more generally SATNAV
      to refer generically to satellite based timing and/or positioning.

   Limited RID
      Per the FAA NPRM, a mode of operation that must use Network RID,
      must not use Broadcast RID, and must provide pilot/GCS location
      only (not UA location).  This mode is only allowed for UA that
      neither require (due to e.g. size) nor are equipped for Standard

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      RID, operated within V-LOS and within 400 feet of the pilot, below
      400 feet AGL, etc.

      Line Of Sight.  An adjectival phrase describing any information
      transfer that travels in a nearly straight line (e.g.
      electromagnetic energy, whether in the visual light, RF or other
      frequency range) and is subject to blockage.  A term to be avoided
      due to ambiguity, in this context, between RF-LOS and V-LOS.

      Mean Sea Level.  Relative altitude, above the variously defined
      mean sea level, typically of an UA (but in FAA NPRM Limited RID
      for a GCS), typically measured in feet.

      UAS RID Display Provider.  System component that requests data
      from one or more NETSP and aggregates them to display to a user
      application on a device.  Often an USS.

      UAS RID Service Provider.  System component that compiles
      information from various sources (and methods) in its given
      service area.  Usually an USS.

      Referred to in other UAS RID documents as a "user", but there are
      also other classes of UAS RID users, so we prefer "observer" to
      denote an individual who has observed an UA and wishes to know
      something about it, starting with its ID.

      Personally Identifiable Information.  In this context, typically
      of the UAS operator, Pilot In Command (PIC) or remote pilot, but
      possibly of an observer or other party.

      Radio Frequency.  May be used as an adjective or as a noun; in the
      latter case, typically means Radio Frequency energy.

      RF LOS.  Typically used in describing operation of a direct radio
      link between a GCS and the UA under its control, potentially
      subject to blockage by foliage, structures, terrain or other
      vehicles, but less so than V-LOS.

   Standard RID
      Per the FAA NPRM, a mode of operation that must use both Network

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      RID (if Internet connectivity is available at the time in the
      operating area) and Broadcast RID (always and everywhere), and
      must provide both pilot/GCS location and UA location.  This mode
      is required for UAS that exceed the allowed envelope (e.g. size,
      range) of Limited RID and for all UAS equipped for Standard RID
      (even if operated within parameters that would otherwise permit
      Limited RID).

      Unmanned Aircraft.  Typically a military or commercial "drone" but
      can include any and all aircraft that are unmanned.

      Unmanned Aircraft System.  Composed of UA, all required on-board
      subsystems, payload, control station, other required off-board
      subsystems, any required launch and recovery equipment, all
      required crew members, and C2 links between UA and control

      Unique UAS identifier.  Per [F3411-19], maximum length of 20

   UAS ID Type
      Identifier type index.  Per [F3411-19], 4 bits, values 0-3 already

      UAS Remote Identification.  System for identifying UA during
      flight by other parties.

   UAS RID Verification Service
      System component designed to handle the authentication
      requirements of RID by offloading verification to a web hosted

      UAS Service Supplier.  Provide UTM services to support the UAS
      community, to connect Operators and other entities to enable
      information flow across the USS network, and to promote shared
      situational awareness among UTM participants.  (From FAA UTM
      ConOps V1, May 2018).

      UAS Traffic Management.  A "traffic management" ecosystem for
      "uncontrolled" UAS operations separate from, but complementary to,
      the FAA's Air Traffic Management (ATM) system for "controlled"
      operations of manned aircraft.

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      Visual LOS.  Typically used in describing operation of an UA by a
      "remote" pilot who can clearly directly (without video cameras or
      any other aids other than glasses or under some rules binoculars)
      see the UA and its immediate flight environment.  Potentially
      subject to blockage by foliage, structures, terrain or other
      vehicles, more so than RF-LOS.

3.  UAS RID Problem Space

   UA may be fixed wing Short Take-Off and Landing (STOL), rotary wing
   (e.g. helicopter) Vertical Take-Off and Landing (VTOL), or hybrid.
   They may be single engine or multi engine.  The most common today are
   multicopters: rotary wing, multi engine.  The explosion in UAS was
   enabled by hobbyist development, for multicopters, of advanced flight
   stability algorithms, enabling even inexperienced pilots to take off,
   fly to a location of interest, hover, and return to the take-off
   location or land at a distance.  UAS can be remotely piloted by a
   human (e.g. with a joystick) or programmed to proceed from Global
   Positioning System (GPS) waypoint to waypoint in a weak form of
   autonomy; stronger autonomy is coming.  UA are "low observable": they
   typically have a small radar cross section; they make noise quite
   noticeable at short range but difficult to detect at distances they
   can quickly close (500 meters in under 17 seconds at 60 knots); they
   typically fly at low altitudes (for the small UAS to which RID
   applies in the US, under 400 feet AGL); they are highly maneuverable
   so can fly under trees and between buildings.

   UA can carry payloads including sensors, cyber and kinetic weapons,
   or can be used themselves as weapons by flying them into targets.
   They can be flown by clueless, careless or criminal operators.  Thus
   the most basic function of UAS RID is "Identification Friend or Foe"
   (IFF) to mitigate the significant threat they present.  Numerous
   other applications can be enabled or facilitated by RID: consider the
   importance of identifiers in many Internet protocols and services.

   Network RID from the UA itself (rather than from its GCS) and
   Broadcast RID require one or more wireless data links from the UA,
   but such communications are challenging due to $SWaP constraints and
   low altitude flight amidst structures and foliage over terrain.

3.1.  Network RID

   Network RID has several variants.  The UA may have persistent onboard
   Internet connectivity, in which case it can consistently source RID
   information directly over the Internet.  The UA may have intermittent
   onboard Internet connectivity, in which case the GCS must source RID
   information whenever the UA itself is offline.  The UA may not have

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   Internet connectivity of its own, but have instead some other form of
   communications to another node that can relay RID information to the
   Internet; this would typically be the GCS (which to perform its
   function must know where the UA is).  The UA may have no means of
   sourcing RID information, in which case the GCS must source it; this
   is typical in FAA NPRM Limited RID, which only needs to provide the
   location of the GCS (not that of the UA).  In the extreme case, this
   could be the pilot using a web browser to designate, to an UAS
   Service Supplier (USS) or other UTM entity, a time-bounded airspace
   volume in which an operation will be conducted; this may impede
   disambiguation of ID if multiple UAS operate in the same or
   overlapping spatio-temporal volumes.

   In most cases in the near term, if the RID information is fed to the
   Internet directly by the UA or GCS, the first hop data links will be
   cellular Long Term Evolution (LTE) or WiFi, but provided the data
   link can support at least IP and ideally TCP, its type is generally
   immaterial to the higher layer protocols.  An UAS or other ultimate
   source of Network RID information feeds an USS acting as a Network
   RID Service Provider (NETSP), which essentially proxies for that and
   other sources; an observer or other ultimate consumer of Network RID
   information obtains it from a Network RID Display Provider (NETDP),
   which aggregates information from multiple NETSPs to offer coverage
   of an airspace volume of interest.

   Network RID is the more flexible and less constrained of the defined
   UAS RID means, but is only partially specified in [F3411-19].  It is
   presumed that IETF efforts supporting Broadcast RID (see next
   section) can be easily generalized for Network RID.

3.2.  Broadcast RID

   [F3411-19] specifies 3 Broadcast RID data links: Bluetooth 4.X;
   Bluetooth 5.X Long Range; and WiFi with Neighbor Awareness Networking
   (NAN).  For compliance with this standard, an UA must broadcast
   (using advertisement mechanisms where no other option supports
   broadcast) on at least one of these; if broadcasting on Bluetooth
   5.x, it is also required concurrently to do so on 4.x (referred to in
   [F3411-19] as Bluetooth Legacy).

   The selection of the Broadcast media was driven by research into what
   is commonly available on 'ground' units (smartphones and tablets) and
   what was found as prevalent or 'affordable' in UA.  Further, there
   must be an Application Programming Interface (API) for the observer's
   receiving application to have access to these messages.  As yet only
   Bluetooth 4.X support is readily available, thus the current focus is
   on working within the 26 byte limit of the Bluetooth 4.X "Broadcast
   Frame" transmitted on beacon channels.

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   Finally, the 26 byte limit of the Bluetooth 4.1 "Broadcast Frame",
   after nominal overheads, limits the UAS ID string to a maximum length
   of 20 bytes.

3.3.  DRIP Focus

   DRIP WG will focus on making information obtained via UAS RID
   immediately usable:

   1.  first by making it trustworthy (despite the severe constraints of
       Broadcast RID);

   2.  second by enabling verification that an UAS is registered, and if
       so, in which registry (for classification of trusted operators on
       the basis of known registry vetting, even by observers lacking
       Internet connectivity at observation time);

   3.  third by enabling instant establishment, by authorized parties,
       of secure communications with the remote pilot.

   Any UA can assert any ID using the [F3411-19] required Basic ID
   message, which lacks any provisions for verification.  The Position/
   Vector message likewise lacks provisions for verification, and does
   not contain the ID, so must be correlated somehow with a Basic ID
   message: the developers of [F3411-19] have suggested using the MAC
   addresses, but these may be randomized by the operating system stack
   to avoid the adversarial correlation problems of static identifiers.
   The [F3411-19] optional Authentication Message specifies framing for
   authentication data, but does not specify any authentication method,
   and the maximum length of the specified framing is too short for
   conventional digital signatures, much less certificates.  The one-way
   nature of Broadcast RID precludes challenge-response security
   protocols (e.g. observers sending nonces to UA, to be returned in
   signed messages).  An observer would be seriously challenged to
   validate the asserted UAS ID or any other information about the UAS
   or its operator looked up therefrom.

   Further, [F3411-19] provides very limited choices for an observer to
   communicate with the pilot, e.g.  to request further information on
   the UAS operation or exit from an airspace volume in an emergency.
   An observer could physically go to the asserted GCS location to look
   for the remote pilot.  An observer with Internet connectivity could
   look up operator PII in a registry, then call a phone number in hopes
   someone who can immediately influence the UAS operation will answer
   promptly during that operation.

   Thus complementing [F3411-19] with protocols enabling strong
   authentication, preserving operator privacy while enabling immediate

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   use of information by authorized parties, is critical to achieve
   widespread adoption of a RID system supporting safe and secure
   operation of UAS.

4.  Requirements

4.1.  General

   The general DRIP requirements are to:

   1.  verify that messages originated from the claimed sender;

   2.  verify that the UAS ID is in a registry and identify which one;

   3.  lookup, from the UAS ID, public information;

   4.  lookup, with AAA, private information, per policy;

   5.  structure information for both human and machine readability;

   6.  provision registries with static information on the UAS and its
       operator, dynamic information on its current operation within the
       UTM, and Internet direct contact information for services related
       to the foregoing;

   7.  close the AAA-policy registry loop by governing AAA per
       registered policies and administering policies only via AAA;

   8.  dynamically establish, with AAA, per policy, E2E strongly
       encrypted communications with the UAS RID sender and entities
       looked up from the UAS ID, including the remote pilot and USS.

   It is highly desirable that Broadcast RID receivers be able to stamp
   messages with accurate date/time received and receiver location, then
   relay them to a network service (e.g. distributed ledger), inter alia
   for correlation to assess sender and receiver veracity.

4.2.  UAS Identifier


   1.  20 bytes or smaller;

   2.  sufficient to identify a registry in which the UAS is listed;

   3.  sufficient to enable lookup of other data in that registry;

   4.  unique within a to-be-defined scope;

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   5.  non-spoofable within the context of Remote ID broadcast messages
       (some collection of messages provides proof of UA ownership of

   A DRIP UAS ID MUST NOT facilitate adversarial correlation of UAS
   operational patterns; this may be accomplished e.g. by limiting each
   identifier to a single use, but if so, the UAS ID MUST support
   defined scalable timely registration methods.

   Mechanisms standardized in DRIP WG MUST be capable of proving
   ownership of a claimed UAS ID, and SHOULD be capable of doing so
   immediately on an observer device lacking Internet connectivity at
   the time of observation.

   Mechanisms standardized in DRIP WG MUST be capable of verifying that
   messages claiming to have been sent from a UAS with a given UAS ID
   indeed came from the claimed sender.

5.  IANA Considerations

   It is likely that an IPv6 prefix or other namespace will be needed;
   this will be specified in other documents.

6.  Security Considerations

   DRIP is all about safety and security, so content pertaining to such
   is not limited to this section.  DRIP information must be divided
   into 2 classes: that which, to achieve the purpose, must be published
   openly in clear plaintext, for the benefit of any observer; and that
   which must be protected (e.g.  PII of pilots) but made available to
   properly authorized parties (e.g. public safety personnel who
   urgently need to contact pilots in emergencies).  Details of the
   protection mechanisms will be provided in other documents.
   Classifying the information will be addressed primarily in external
   standards; herein it will be regarded as a matter for CAA, registry
   and operator policies, for which enforcement mechanisms will be
   defined within the scope of DRIP WG and offered.  Mitigation of
   adversarial correlation will also be addressed.

7.  Acknowledgments

   The work of the FAA's UAS Identification and Tracking (UAS ID)
   Aviation Rulemaking Committee (ARC) is the foundation of later ASTM
   [F3411-19] and 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.

8.  References

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8.1.  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>.

8.2.  Informative References

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

              European Union Aviation Safety Agency (EASA), "Commission
              Delegated Regulation (EU) 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.

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

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

              FAA UAS Identification and Tracking Aviation Rulemaking
              Committee, "UAS ID and Tracking ARC Recommendations Final
              Report", September 2017.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,

Authors' Addresses

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Internet-Draft                  DRIP Reqs                     March 2020

   Stuart W.   Card
   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

Card, et al.            Expires 25 September 2020              [Page 14]