Internet DRAFT - draft-ietf-drip-reqs
draft-ietf-drip-reqs
DRIP S. Card, Ed.
Internet-Draft A. Wiethuechter
Intended status: Informational AX Enterprize
Expires: 12 March 2022 R. Moskowitz
HTT Consulting
A. Gurtov
Linköping University
8 September 2021
Drone Remote Identification Protocol (DRIP) Requirements
draft-ietf-drip-reqs-18
Abstract
This document defines terminology and requirements for Drone Remote
Identification Protocol (DRIP) Working Group solutions to support
Unmanned Aircraft System Remote Identification and tracking (UAS RID)
for security, safety, and other purposes (e.g., initiation of
identity based network sessions supporting UAS applications). DRIP
will facilitate use of existing Internet resources to support RID and
to enable enhanced related services, and will enable online and
offline verification that RID information is trustworthy.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 12 March 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation and External Influences . . . . . . . . . . . 3
1.2. Concerns and Constraints . . . . . . . . . . . . . . . . 8
1.3. DRIP Scope . . . . . . . . . . . . . . . . . . . . . . . 10
1.4. Document Scope . . . . . . . . . . . . . . . . . . . . . 11
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 11
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 11
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 11
3. UAS RID Problem Space . . . . . . . . . . . . . . . . . . . . 20
3.1. Network RID . . . . . . . . . . . . . . . . . . . . . . . 22
3.2. Broadcast RID . . . . . . . . . . . . . . . . . . . . . . 25
3.3. USS in UTM and RID . . . . . . . . . . . . . . . . . . . 29
3.4. DRIP Focus . . . . . . . . . . . . . . . . . . . . . . . 29
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 31
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.1.1. Normative Requirements . . . . . . . . . . . . . . . 31
4.1.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 32
4.2. Identifier . . . . . . . . . . . . . . . . . . . . . . . 34
4.2.1. Normative Requirements . . . . . . . . . . . . . . . 34
4.2.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 35
4.3. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.3.1. Normative Requirements . . . . . . . . . . . . . . . 36
4.3.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 37
4.4. Registries . . . . . . . . . . . . . . . . . . . . . . . 37
4.4.1. Normative Requirements . . . . . . . . . . . . . . . 38
4.4.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 38
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
6. Security Considerations . . . . . . . . . . . . . . . . . . . 39
7. Privacy and Transparency Considerations . . . . . . . . . . . 40
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 41
8.1. Normative References . . . . . . . . . . . . . . . . . . 41
8.2. Informative References . . . . . . . . . . . . . . . . . 42
Appendix A. Discussion and Limitations . . . . . . . . . . . . . 46
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 47
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48
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1. Introduction
For any unfamiliar or _a priori_ ambiguous terminology herein, see
Section 2.
1.1. Motivation and External Influences
Many considerations (especially safety and security) necessitate
Unmanned Aircraft Systems (UAS) Remote Identification and tracking
(RID).
Unmanned Aircraft (UA) may be fixed wing, rotary wing (e.g.,
helicopter), hybrid, balloon, rocket, etc. Small fixed wing UA
typically have Short Take-Off and Landing (STOL) capability; rotary
wing and hybrid UA typically have Vertical Take-Off and Landing
(VTOL) capability. UA may be single- 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 Navigation Satellite System (GNSS)
waypoint to waypoint in a weak form of autonomy; stronger autonomy is
coming.
Small UA are "low observable" as they:
* typically have small radar cross sections;
* make noise quite noticeable at short ranges but difficult to
detect at distances they can quickly close (500 meters in under 13
seconds by the fastest consumer mass market drones available in
early 2021);
* typically fly at low altitudes (e.g., for those to which RID
applies in the US, under 400 feet Above Ground Level (AGL) as per
[Part107]);
* 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.
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Diverse other applications can be enabled or facilitated by RID.
Internet protocols typically start out with at least one entity
already knowing an identifier or locator of another; but an entity
(e.g., UAS or Observer device) encountering an _a priori_ unknown UA
in physical space has no identifier or logical space locator for that
UA, unless and until one is provided somehow. RID provides an
identifier, which, if well chosen, can facilitate use of a variety of
Internet family protocols and services to support arbitrary
applications, beyond the basic security functions of RID. For most
of these, some type of identifier is essential, e.g., Network Access
Identifier (NAI), Digital Object Identifier (DOI), Uniform Resource
Identifier (URI), domain name, or public key. DRIP motivations
include both the basic security and the broader application support
functions of RID. The general scenario is illustrated in Figure 1.
+-----+ +-----+
| UA1 | | UA2 |
+-----+ +-----+
+----------+ +----------+
| General | | Public |
| Public | | Safety |
| Observer o------\ /------o Observer |
+----------+ | | +----------+
| |
*************
+----------+ * * +----------+
| UA1 | * * | UA2 |
| Pilot/ o------* Internet *------o Pilot/ |
| Operator | * * | Operator |
+----------+ * * +----------+
*************
| | |
+----------+ | | | +----------+
| Public o---/ | \---o Private |
| Registry | | | Registry |
+----------+ | +----------+
+--o--+
| DNS |
+-----+
Figure 1: "General UAS RID Usage Scenario"
Figure 1 illustrates a typical case where there may be: multiple
Observers, some of them members of the general public, others
government officers with public safety/security responsibilities;
multiple UA in flight within observation range, each with its own
pilot/operator; at least one registry each for lookup of public and
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(by authorized parties only) private information regarding the UAS
and their pilots/operators; and in the DRIP vision, DNS resolving
various identifiers and locators of the entities involved.
Note the absence of any links to/from the UA in the figure; this is
because UAS RID and other connectivity involving the UA varies. Some
connectivity paths do or do not exist depending upon the scenario.
Command and Control (C2) from the GCS to the UA via the Internet
(e.g., using LTE cellular) is expected to become much more common as
Beyond Visual Line Of Sight (BVLOS) operations increase; in such a
case, there is typically not also a direct wireless link between the
GCS and UA. Conversely, if C2 is running over a direct wireless
link, then typically the GCS has but the UA lacks Internet
connectivity. Further, paths that nominally exist, such as between
an Observer device and the Internet, may be severely intermittent.
These connectivity constraints are likely to have an impact, e.g., on
how reliably DRIP requirements can be satisfied.
An Observer of UA may need to classify them, as illustrated
notionally in Figure 2, for basic airspace Situational Awareness
(SA). An Observer who classifies a UAS: as Taskable, can ask it to
do something useful; as Low Concern, can reasonably assume it is not
malicious and would cooperate with requests to modify its flight
plans for safety concerns that arise; as High Concern or
Unidentified, can focus surveillance on it.
xxxxxxx
x x No +--------------+
x ID? x+---->| Unidentified |
x x +--------------+
xxxxxxx
+
| Yes
v
xxxxxxx
x x
.---------+x Type? x+----------.
| x x |
| xxxxxxx |
| + |
v v v
+--------------+ +--------------+ +--------------+
| Taskable | | Low Concern | | High Concern |
+--------------+ +--------------+ +--------------+
Figure 2: "Notional UAS Classification"
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ASTM International, Technical Committee F38 (UAS), Subcommittee
F38.02 (Aircraft Operations), Work Item WK65041, developed the widely
cited Standard Specification for Remote ID and Tracking [F3411-19]:
the published standard is available for purchase from ASTM and as an
ASTM membership premium; early drafts are freely available as
[OpenDroneID] specifications. [F3411-19] is frequently referenced in
DRIP, where building upon its link layers and both enhancing support
for and expanding the scope of its applications are central foci.
In many applications, including UAS RID, identification and
identifiers are not ends in themselves; they exist to enable lookups
and provision of other services.
Using UAS RID to facilitate vehicular (V2X) communications and
applications such as Detect And Avoid (DAA), which would impose
tighter latency bounds than RID itself, is an obvious possibility,
explicitly contemplated in the United States (US) Federal Aviation
Administration (FAA) Remote Identification of Unmanned Aircraft rule
[FRUR]. However, usage of RID systems and information beyond mere
identification (primarily to hold operators accountable after the
fact), including DAA, have been declared out of scope in ASTM F38.02
WK65041, based on a distinction between RID as a security standard vs
DAA as a safety application. Aviation community Standards
Development Organizations (SDOs) generally set a higher bar for
safety than for security, especially with respect to reliability.
Each SDO has its own cultural set of connotations of safety vs
security; the denotative definitions of the International Civil
Aviation Organization (ICAO) are cited in Section 2.
[Opinion1] and [WG105] cite the Direct Remote Identification (DRI)
previously required and specified, explicitly stating that whereas
DRI is primarily for security purposes, the "Network Identification
Service" [Opinion1] (in the context of U-space [InitialView]) or
"Electronic Identification" [WG105] is primarily for safety purposes
(e.g., Air Traffic Management, especially hazards deconfliction) and
also is allowed to be used for other purposes such as support of
efficient operations. These emerging standards allow the security
and safety oriented systems to be separate or merged. In addition to
mandating both Broadcast and Network one-way to Observers, they will
use V2V to other UAS (also likely to and/or from some manned
aircraft). These reflect the broad scope of the European Union (EU)
U-space concept, as being developed in the Single European Sky ATM
Research (SESAR) Joint Undertaking, the U-space architectural
principles of which are outlined in [InitialView].
ASD-STAN is an Associated Body to CEN (European Committee for
Standardization) for Aerospace Standards. It is publishing an EU
standard "Aerospace series - Unmanned Aircraft Systems - Part 002:
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Direct Remote Identification; English version prEN 4709-002:2020" for
which a current (early 2021) informal overview is freely available in
[ASDRI]. It will provide compliance to cover the identical DRI
requirements applicable to drones of classes C1 - [Delegated] Part 2,
C2 - [Delegated] Part 3, C3 - [Delegated] Part 4, C5 - [Amended] Part
16, and C6 - [Amended] Part 17.
The standard contemplated in [ASDRI] will provide UA capability to be
identified in real time during the whole duration of the flight,
without specific connectivity or ground infrastructure link,
utilizing existing mobile devices within broadcast range. It will
use Bluetooth 4, Bluetooth 5, Wi-Fi Neighbor Awareness Networking
(NAN, also known as Wi-Fi Aware, [WiFiNAN]) and/or IEEE 802.11 Beacon
modes. The EU standard emphasis was compatibility with [F3411-19],
although there are differences in mandatory and optional message
types and fields.
The [ASDRI] contemplated DRI system will broadcast locally:
1. the UAS operator registration number;
2. the [CTA2063A] compliant unique serial number of the UA;
3. a time stamp, the geographical position of the UA, and its height
AGL or above its take-off point;
4. the UA ground speed and route course measured clockwise from true
north;
5. the geographical position of the remote pilot, or if that is not
available, the geographical position of the UA take-off point;
and
6. for Classes C1, C2, C3, the UAS emergency status.
Under the [ASDRI] contemplated standard, data will be sent in plain
text and the UAS operator registration number will be represented as
a 16-byte string including the (European) state code. The
corresponding private ID part will contain 3 characters that are not
broadcast but used by authorities to access regional registration
databases for verification.
ASD-STAN also contemplates corresponding Network Remote
Identification (NRI) functionality. The ASD-STAN RID target is to
revise their current standard with additional functionality (e.g.,
DRIP) to be published before 2022 [ASDRI].
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Security oriented UAS RID essentially has two goals: enable the
general public to obtain and record an opaque ID for any observed UA,
which they can then report to authorities; and enable authorities,
from such an ID, to look up information about the UAS and its
operator. Safety oriented UAS RID has stronger requirements.
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 regulations or international SDO technical specifications,
other than DRIP, known to the authors as of early 2021.
1.2. Concerns and Constraints
Disambiguation of multiple UA flying in close proximity may be very
challenging, even if each is reporting its identity, position, and
velocity as accurately as it can.
The origin of information in UAS RID and UAS Traffic Management (UTM)
generally is the UAS or its operator. Self-reports may be initiated
by the remote pilot at the console of the Ground Control Station
(GCS, the UAS subsystem used to remotely operate the UA), or
automatically by GCS software; in Broadcast RID, they typically would
be initiated automatically by a process on the UA. Data in the
reports may come from sensors available to the operator (e.g., radar
or cameras), the GCS (e.g., "dead reckoning" UA location, starting
from the takeoff location and estimating the displacements due to
subsequent piloting commands, wind, etc.), or the UA itself (e.g., an
on-board GNSS receiver); in Broadcast RID, all the data must be sent
proximately by, and most of the data comes ultimately from, the UA
itself. Whether information comes proximately from the operator, or
from automated systems configured by the operator, there are
possibilities not only of unintentional error in but also of
intentional falsification of this data. Mandating UAS RID,
specifying data elements required to be sent, monitoring compliance
and enforcing it (or penalizing non-compliance) are matters for Civil
Aviation Authorities (CAAs) et al; specifying message formats, etc.
to carry those data elements has been addressed by other SDOs;
offering technical means, as extensions to external standards, to
facilitate verifiable compliance and enforcement/monitoring, are
opportunities for DRIP.
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 in accordance with applicable policy.
The balance between privacy and transparency remains a subject for
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public debate and regulatory action; DRIP can only offer tools to
expand the achievable trade space and enable trade-offs within that
space. [F3411-19], the basis for most current (2021) thinking about
and efforts to provide UAS RID, 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 are
unspecified therein.
The need for nearly universal deployment of UAS RID is pressing:
consider how negligible the value of an automobile license plate
system would be if only 90% of the cars displayed plates. This
implies the need to support use by Observers of already ubiquitous
mobile devices (typically smartphones and tablets). Anticipating CAA
requirements to support legacy devices, especially in light of
[Recommendations], [F3411-19] specifies that any UAS sending
Broadcast RID over Bluetooth must do so over Bluetooth 4, regardless
of whether it also does so over newer versions; as UAS sender devices
and Observer receiver devices are unpaired, this implies extremely
short "advertisement" (beacon) frames.
Wireless data links to or from UA are challenging. Flight is often
amidst structures and foliage at low altitudes over varied terrain.
UA are constrained in both total energy and instantaneous power by
their batteries. Small UA imply small antennas. Densely populated
volumes will suffer from link congestion: even if UA in an airspace
volume are few, other transmitters nearby on the ground, sharing the
same license free spectral band, may be many. Thus air to air and
air to ground links will generally be slow and unreliable.
UAS Cost, Size, Weight, and Power (CSWaP) constraints are severe.
CSWaP is a burden not only on the designers of new UAS for sale, but
also on owners of existing UAS that must be retrofit. Radio
Controlled (RC) aircraft modelers, "hams" who use licensed amateur
radio frequencies to control UAS, drone hobbyists, and others who
custom build UAS, all need means of participating in UAS RID,
sensitive to both generic CSWaP and application-specific
considerations.
To accommodate the most severely constrained cases, all these
conspire to motivate system design decisions that complicate the
protocol design problem.
Broadcast RID uses one-way local data links. UAS may have Internet
connectivity only intermittently, or not at all, during flight.
Internet-disconnected operation of Observer devices has been deemed
by ASTM F38.02 too infrequent to address. However, the preamble to
[FRUR] cites "remote and rural areas that do not have reliable
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Internet access" as a major reason for requiring Broadcast rather
than Network RID, and states that "Personal wireless devices that are
capable of receiving 47 CFR part 15 frequencies, such as smart
phones, tablets, or other similar commercially available devices,
will be able to receive broadcast remote identification information
directly without reliance on an Internet connection". Internet-
disconnected operation presents challenges, e.g., for Observers
needing access to the [F3411-19] web based Broadcast Authentication
Verifier Service or needing to do external lookups.
As RID must often operate within these constraints, heavyweight
cryptographic security protocols or even simple cryptographic
handshakes are infeasible, yet trustworthiness of UAS RID information
is essential. Under [F3411-19], _even the most basic datum, the UAS
ID itself, can be merely an unsubstantiated claim_.
Observer devices being ubiquitous, thus popular targets for malware
or other compromise, cannot be generally trusted (although the user
of each device is compelled to trust that device, to some extent); a
"fair witness" functionality (inspired by [Stranger]) is desirable.
Despite work by regulators and SDOs, there are substantial gaps in
UAS standards generally and UAS RID specifically. [Roadmap] catalogs
UAS related standards, ongoing standardization activities and gaps
(as of 2020); Section 7.8 catalogs those related specifically to UAS
RID. DRIP will address the most fundamental of these gaps, as
foreshadowed above.
1.3. DRIP Scope
DRIP's initial charter 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. By "immediately actionable" is meant
information of sufficient precision, accuracy, timeliness, etc. for
an Observer to use it as the basis for immediate decisive action,
whether that be to trigger a defensive counter-UAS system, to attempt
to initiate communications with the UAS operator, to accept the
presence of the UAS in the airspace where/when observed as not
requiring further action, or whatever, with potentially severe
consequences of any action or inaction chosen based on that
information. For further explanation of the concept of immediate
actionability, see [ENISACSIRT].
Note that UAS RID must achieve nearly universal adoption, but DRIP
can add value even if only selectively deployed. Authorities with
jurisdiction over more sensitive airspace volumes may set a higher
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than generally mandated RID requirement for flight in such volumes.
Those with a greater need for high-confidence IFF can equip with
DRIP, enabling strong authentication of their own aircraft and allied
operators without regard for the weaker (if any) authentication of
others.
DRIP (originally 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,
and providing timely trustworthy identification data is also
prerequisite to identity-oriented networking, but the urgent
motivation and clear initial focus is UAS. Existing Internet
resources (protocol standards, services, infrastructure, and business
models) should be leveraged.
1.4. Document Scope
This document describes the problem space for UAS RID conforming to
proposed regulations and external technical standards, defines common
terminology, specifies numbered requirements for DRIP, identifies
some important considerations (IANA, security, privacy and
transparency), and discusses limitations.
A natural Internet-based approach to meet these requirements is
described in a companion architecture document [drip-architecture]
and elaborated in other DRIP documents.
2. Terms and Definitions
2.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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
This section defines a non-comprehensive set of terms expected to be
used in DRIP documents. This list is meant to be the DRIP
terminology reference; as such, some of the terms listed below are
not used in this document.
[RFC4949] provides a glossary of Internet security terms that should
be used where applicable.
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In the UAS community, the plural form of acronyms generally is the
same as the singular form, e.g., Unmanned Aircraft System (singular)
and Unmanned Aircraft Systems (plural) are both represented as UAS.
On this and other terminological issues, to encourage comprehension
necessary for adoption of DRIP by the intended user community, that
community's norms are respected herein, and definitions are quoted in
cases where they have been found in that community's documents. Most
of the listed terms are from that community (even if specific source
documents are not cited); any that are DRIP-specific or invented by
the authors of this document are marked "(DRIP)".
4-D
Four-dimensional. Latitude, Longitude, Altitude, Time. Used
especially to delineate an airspace volume in which an operation
is being or will be conducted.
AAA
Attestation, Authentication, Authorization, Access Control,
Accounting, Attribution, Audit, or any subset thereof (uses differ
by application, author, and context). (DRIP)
ABDAA
AirBorne DAA. Accomplished using systems onboard the aircraft
involved. Supports "self-separation" (remaining "well clear" of
other aircraft) and collision avoidance.
ADS-B
Automatic Dependent Surveillance - Broadcast. "ADS-B Out"
equipment obtains aircraft position from other on-board systems
(typically GNSS) and periodically broadcasts it to "ADS-B In"
equipped entities, including other aircraft, ground stations, and
satellite based monitoring systems.
AGL
Above Ground Level. Relative altitude, above the variously
defined local ground level, typically of a UA, measured in feet or
meters. Should be explicitly specified as either barometric
(pressure) or geodetic (GNSS) altitude.
ATC
Air Traffic Control. Explicit flight direction to pilots from
ground controllers. Contrast with ATM.
ATM
Air Traffic Management. A broader functional and geographic scope
and/or a higher layer of abstraction than ATC. "The dynamic,
integrated management of air traffic and airspace including air
traffic services, airspace management and air traffic flow
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management - safely, economically and efficiently - through the
provision of facilities and seamless services in collaboration
with all parties and involving airborne and ground-based
functions" [ICAOATM].
Authentication Message
[F3411-19] Message Type 2. Provides framing for authentication
data, only; the only message that can be extended in length by
segmenting it across more than one page.
Basic ID Message
[F3411-19] Message Type 0. Provides UA Type, UAS ID Type (and
Specific Session ID subtype if applicable), and UAS ID, only.
Broadcast Authentication Verifier Service
System component designed to handle any authentication of
Broadcast RID by offloading signature verification to a web
service [F3411-19].
BVLOS
Beyond Visual Line Of Sight. See VLOS.
byte
Used here in its now-customary sense as a synonym for "octet", as
"byte" is used exclusively in definitions of data structures
specified in [F3411-19]
CAA
Civil Aviation Authority of a regulatory jurisdiction. Often so
named, but other examples include the United States Federal
Aviation Administration (FAA) and the Japan Civil Aviation Bureau.
CSWaP
Cost, Size, Weight, and Power.
C2
Command and Control. Previously mostly used in military contexts.
Properly refers to a function, exercisable over arbitrary
communications; but in the small UAS context, often refers to the
communications (typically RF data link) over which the GCS
controls the UA.
DAA
Detect And Avoid, formerly Sense And Avoid (SAA). A means of
keeping aircraft "well clear" of each other and obstacles for
safety. "The capability to see, sense or detect conflicting
traffic or other hazards and take the appropriate action to comply
with the applicable rules of flight" [ICAOUAS].
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DRI (not to be confused with DRIP)
Direct Remote Identification. EU regulatory requirement for "a
system that ensures the local broadcast of information about a UA
in operation, including the marking of the UA, so that this
information can be obtained without physical access to the UA".
[Delegated] that presumably can be satisfied with appropriately
configured [F3411-19] Broadcast RID.
DSS
Discovery and Synchronization Service. The UTM system overlay
network backbone. Most importantly, it enables one USS to learn
which other USS have UAS operating in a given 4-D airspace volume,
for strategic deconfliction of planned operations and Network RID
surveillance of active operations. [F3411-19]
EUROCAE
European Organisation for Civil Aviation Equipment. Aviation SDO,
originally European, now with broader membership. Cooperates
extensively with RTCA.
GBDAA
Ground Based DAA. Accomplished with the aid of ground based
functions.
GCS
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 GNSS waypoints, or
otherwise directing its flight.
GNSS
Global Navigation Satellite System. Satellite based timing and/or
positioning with global coverage, often used to support
navigation.
GPS
Global Positioning System. A specific GNSS, but in the UAS
context, the term is typically misused in place of the more
generic term GNSS.
GRAIN
Global Resilient Aviation Interoperable Network. ICAO managed
IPv6 overlay internetwork based on IATF, dedicated to aviation
(but not just aircraft). Currently (2021) in design,
accommodating the proposed DRIP identifier.
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IATF
International Aviation Trust Framework. ICAO effort to develop a
resilient and secure by design framework for networking in support
of all aspects of aviation.
ICAO
International Civil Aviation Organization. A United Nations
specialized agency that develops and harmonizes international
standards relating to aviation.
IFF
Identification Friend or Foe. Originally, and in its narrow sense
still, a self-identification broadcast in response to
interrogation via radar, to reduce friendly fire incidents, which
led to military and commercial transponder systems such as ADS-B.
In the broader sense used here, any process intended to
distinguish friendly from potentially hostile UA or other entities
encountered.
LAANC
Low Altitude Authorization and Notification Capability. Supports
ATC authorization requirements for UAS operations: remote pilots
can apply to receive a near real-time authorization for operations
under 400 feet in controlled airspace near airports. FAA
authorized partial stopgap in the US until UTM comes.
Location/Vector Message
[F3411-19] Message Type 1. Provides UA location, altitude,
heading, speed, and status.
LOS
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 VLOS.
Message Pack
[F3411-19] Message Type 15. The framed concatenation, in message
type index order, of at most one message of each type of any
subset of the other types. Required to be sent in Wi-Fi NAN and
in Bluetooth 5 Extended Advertisements, if those media are used;
cannot be sent in Bluetooth 4.
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MSL
Mean Sea Level. Shorthand for relative altitude, above the
variously defined mean sea level, typically of a UA (but in [FRUR]
also for a GCS), measured in feet or meters. Should be explicitly
specified as either barometric (pressure) or geodetic (e.g., as
indicated by GNSS, referenced to the WGS84 ellipsoid).
Net-RID DP
Network RID Display Provider. [F3411-19] logical entity that
aggregates data from Net-RID SPs as needed in response to user
queries regarding UAS operating within specified airspace volumes,
to enable display by a user application on a user device.
Potentially could provide not only information sent via UAS RID
but also information retrieved from UAS RID registries or
information beyond UAS RID. Under superseded [NPRM], not
recognized as a distinct entity, but a service provided by USS,
including Public Safety USS that may exist primarily for this
purpose rather than to manage any subscribed UAS.
Net-RID SP
Network RID Service Provider. [F3411-19] logical entity that
collects RID messages from UAS and responds to NetRID-DP queries
for information on UAS of which it is aware. Under superseded
[NPRM], the USS to which the UAS is subscribed ("Remote ID USS").
Network Identification Service
EU regulatory requirement in [Opinion1] and [WG105] that
presumably can be satisfied with appropriately configured
[F3411-19] Network RID.
Observer
An entity (typically but not necessarily an individual human) who
has directly or indirectly observed a UA and wishes to know
something about it, starting with its ID. An Observer typically
is on the ground and local (within VLOS of an observed UA), but
could be remote (observing via Network RID or other surveillance),
operating another UA, aboard another aircraft, etc. (DRIP)
Operation
A flight, or series of flights of the same mission, by the same
UAS, separated by at most brief ground intervals. (Inferred from
UTM usage, no formal definition found)
Operator
"A person, organization or enterprise engaged in or offering to
engage in an aircraft operation" [ICAOUAS].
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Operator ID Message
[F3411-19] Message Type 5. Provides CAA issued Operator ID, only.
Operator ID is distinct from UAS ID.
page
Payload of a frame, containing a chunk of a message that has been
segmented, to allow transport of a message longer than can be
encapsulated in a single frame. [F3411-19]
PIC
Pilot In Command. "The pilot designated by the operator, or in
the case of general aviation, the owner, as being in command and
charged with the safe conduct of a flight" [ICAOUAS].
PII
Personally Identifiable Information. In the UAS RID context,
typically of the UAS Operator, Pilot In Command (PIC), or Remote
Pilot, but possibly of an Observer or other party. This specific
term is used primarily in the US; other terms with essentially the
same meaning are more common in other jurisdictions (e.g.,
"personal data" in the EU). Used herein generically to refer to
personal information, which the person might wish to keep private,
or may have a statutorily recognized right to keep private (e.g.,
under the EU [GDPR]), potentially imposing (legally or ethically)
a confidentiality requirement on protocols/systems.
Remote Pilot
A pilot using a GCS to exercise proximate control of a UA. Either
the PIC or under the supervision of the PIC. "The person who
manipulates the flight controls of a remotely-piloted aircraft
during flight time" [ICAOUAS].
RF
Radio Frequency. Adjective, e.g., "RF link", or noun.
RF LOS
RF Line Of Sight. Typically used in describing 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 VLOS.
RTCA
Radio Technical Commission for Aeronautics. US aviation SDO.
Cooperates extensively with EUROCAE.
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Safety
"The state in which risks associated with aviation activities,
related to, or in direct support of the operation of aircraft, are
reduced and controlled to an acceptable level." From Annex 19 of
the Chicago Convention, quoted in [ICAODEFS]
Security
"Safeguarding civil aviation against acts of unlawful
interference." From Annex 17 of the Chicago Convention, quoted in
[ICAODEFS]
Self-ID Message
[F3411-19] Message Type 3. Provides a 1 byte descriptor and 23
byte ASCII free text field, only. Expected to be used to provide
context on the operation, e.g., mission intent.
SDO
Standards Development Organization. ASTM, IETF, et al.
SDSP
Supplemental Data Service Provider. An entity that participates
in the UTM system, but provides services beyond those specified as
basic UTM system functions (e.g., weather data). [FAACONOPS]
System Message
[F3411-19] Message Type 4. Provides general UAS information,
including remote pilot location, multiple UA group operational
area, etc.
U-space
EU concept and emerging framework for integration of UAS into all
classes of airspace, specifically including high density urban
areas, sharing airspace with manned aircraft [InitialView].
UA
Unmanned Aircraft. In popular parlance, "drone". "An aircraft
which is intended to operate with no pilot on board" [ICAOUAS].
UAS
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 station
[F3411-19].
UAS ID
UAS identifier. Although called "UAS ID", it is actually unique
to the UA, neither to the operator (as some UAS registration
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numbers have been and for exclusively recreational purposes are
continuing to be assigned), nor to the combination of GCS and UA
that comprise the UAS. _Maximum length of 20 bytes_ [F3411-19].
If the UAS ID Type is 4, the proposed Specific Session ID, then
the 20 bytes includes the subtype index, leaving only 19 bytes for
the actual identifier.
UAS ID Type
UAS Identifier type index. 4 bits, see Section 3, Paragraph 6 for
currently defined values 0-3. [F3411-19]
UAS RID
UAS Remote Identification and tracking. System to enable
arbitrary Observers to identify UA during flight.
USS
UAS Service Supplier. "A USS is an entity that assists UAS
Operators with meeting UTM operational requirements that enable
safe and efficient use of airspace" and "... provide 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" [FAACONOPS].
UTM
UAS Traffic Management. "A specific aspect of air traffic
management which manages UAS operations safely, economically and
efficiently through the provision of facilities and a seamless set
of services in collaboration with all parties and involving
airborne and ground-based functions" [ICAOUTM]. In the US,
according to the FAA, a "traffic management" ecosystem for
"uncontrolled" low altitude UAS operations, separate from, but
complementary to, the FAA's ATC system for "controlled" operations
of manned aircraft.
V2V
Vehicle-to-Vehicle. Originally communications between
automobiles, now extended to apply to communications between
vehicles generally. Often, together with Vehicle-to-
Infrastructure (V2I) etc., generalized to V2X.
VLOS
Visual Line Of Sight. Typically used in describing operation of a
UA by a "remote" pilot who can clearly directly (without video
cameras or any 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.
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3. UAS RID Problem Space
CAAs worldwide are mandating UAS RID. The European Union Aviation
Safety Agency (EASA) has published [Delegated] and [Implementing]
Regulations. The US FAA has published a "final" rule [FRUR] and has
described the key role that UAS RID plays in UAS Traffic Management
(UTM) in [FAACONOPS] (especially Section 2.6). CAAs currently (2021)
promulgate performance-based regulations that do not specify
techniques, but rather cite industry consensus technical standards as
acceptable means of compliance.
The most widely cited such industry consensus technical standard for
UAS RID is [F3411-19], which defines two means of UAS RID:
Network RID defines a set of information for UAS to make available
globally indirectly via the Internet, through servers that can be
queried by Observers.
Broadcast RID defines a set of messages for UA to transmit locally
directly one-way over Bluetooth or Wi-Fi (without IP or any other
protocols between the data link and application layers), to be
received in real time by local Observers.
UAS using both means must send the same UAS RID application layer
information via each [F3411-19]. The presentation may differ, as
Network RID defines a data dictionary, whereas Broadcast RID defines
message formats (which carry items from that same data dictionary).
The interval (or rate) at which it is sent may differ, as Network RID
can accommodate Observer queries asynchronous to UAS updates (which
generally need be sent only when information, such as location,
changes), whereas Broadcast RID depends upon Observers receiving UA
messages at the time they are transmitted.
Network RID depends upon Internet connectivity in several segments
from the UAS to each Observer. Broadcast RID should need Internet
(or other Wide Area Network) connectivity only to retrieve UAS
registry information using the directly locally received UAS
Identifier (UAS ID) as the primary unique key for database lookup.
Broadcast RID does not assume IP connectivity of UAS; messages are
encapsulated by the UA _without IP_, directly in link layer frames
(Bluetooth 4, Bluetooth 5, Wi-Fi NAN, IEEE 802.11 Beacon, or in the
future perhaps others).
[F3411-19] specifies three UAS ID Type values and its currently
(August 2021) proposed revision adds a fourth:
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1 A static, manufacturer assigned, hardware serial number as defined
in ANSI/CTA-2063-A "Small Unmanned Aerial System Serial Numbers"
[CTA2063A].
2 A CAA assigned (generally static) ID, like the registration number
of a manned aircraft.
3 A UTM system assigned UUID [RFC4122], which can but need not be
dynamic.
4 A Specific Session ID, of any of an 8 bit range of subtypes
defined external to ASTM and registered with ICAO, for which
subtype 1 has been reserved by ASTM for the DRIP entity ID.
Per [Delegated], the EU allows only UAS ID Type 1. Under [FRUR], the
US allows types 1 and 3. [NPRM] proposed that a type 3 "Session ID"
would be "e.g., a randomly-generated alphanumeric code assigned by a
Remote ID UAS Service Supplier (USS) on a per-flight basis designed
to provide additional privacy to the operator", but given the
omission of Network RID from [FRUR], how this is to be assigned in
the US is still to be determined.
As yet apparently there are no CAA public proposals to use UAS ID
Type 2. In the preamble of [FRUR], the FAA argues that registration
numbers should not be sent in RID, insists that the capability of
looking up registration numbers from information contained in RID
should be restricted to FAA and other Government agencies, and
implies that Session ID would be linked to the registration number
only indirectly via the serial number in the registration database.
The possibility of cryptographically blinding registration numbers,
such that they can be revealed under specified circumstances, does
not appear to be mentioned in applicable regulations or external
technical standards.
Under [Delegated], the EU also requires an operator registration
number (an additional identifier distinct from the UAS ID) that can
be carried in an [F3411-19] optional Operator ID message.
[FRUR] allows RID requirements to be met by either the UA itself,
which is then designated a "standard remote identification unmanned
aircraft", or by an add-on "remote identification broadcast module".
Relative to a standard RID UA, the different requirements for a
module are that the latter: must transmit its own serial number
(neither the serial number of the UA to which it is attached, nor a
Session ID); must transmit takeoff location as a proxy for the
location of the pilot/GCS; need not transmit UA emergency status; and
is allowed to be used only for operations within VLOS of the remote
pilot.
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Jurisdictions may relax or waive RID requirements for certain
operators and/or under certain conditions. For example, [FRUR]
allows operators with UAS not equipped for RID to conduct VLOS
operations at counter-intuitively named "FAA-recognized
identification areas" (FRIA); radio controlled model aircraft flying
clubs and other eligible organizations can apply to the FAA for such
recognition of their operating areas.
3.1. Network RID
+-------------+ ******************
| UA | * Internet *
+--o-------o--+ * *
| | * *
| | * * +------------+
| '--------*--(+)-----------*-----o |
| * | * | |
| .--------*--(+)-----------*-----o NET-Rid SP |
| | * * | |
| | * .------*-----o |
| | * | * +------------+
| | * | *
| | * | * +------------+
| | * '------*-----o |
| | * * | NET-Rid DP |
| | * .------*-----o |
| | * | * +------------+
| | * | *
| | * | * +------------+
+--o-------o--+ * '------*-----o Observer's |
| GCS | * * | Device |
+-------------+ ****************** +------------+
Figure 3: "Network RID Information Flow"
Figure 3 illustrates Network RID information flows. Only two of the
three typically wireless links shown involving the UAS (UA-GCS, UA-
Internet, and GCS-Internet) need exist to support C2 and Network RID.
All three may exist, at the same or different times, especially in
BVLOS operations. There must be some information flow path (direct
or indirect) between the GCS and the UA, for the former to exercise
C2 over the latter. If this path is two-way (as increasingly it is,
even for inexpensive small UAS), the UA will also send its status
(and position, if suitably equipped, e.g., with GNSS) to the GCS.
There also must be some path between at least one subsystem of the
UAS (UA or GCS) and the Internet, for the former to send status and
position updates to its USS (serving _inter alia_ as a Net-RID SP).
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Direct UA-Internet wireless links are expected to become more common,
especially on larger UAS, but currently (2021) are rare. Instead,
the RID data flow typically originates on the UA and passes through
the GCS, or originates on the GCS. Network RID data makes three
trips through the Internet (GCS-SP, SP-DP, DP-Observer, unless any of
them are colocated), implying use of IP (and other middle layer
protocols, e.g., TLS/TCP or DTLS/UDP) on those trips. IP is not
necessarily used or supported on the UA-GCS link (if indeed that
direct link exists, as it typically does now, but in BVLOS operations
often will not).
Network RID is publish-subscribe-query. In the UTM context:
1. The UAS operator pushes an "operational intent" (the current term
in UTM corresponding to a flight plan in manned aviation) to the
USS (call it USS#1) that will serve that UAS (call it UAS#1) for
that operation, primarily to enable deconfliction with other
operations potentially impinging upon that operation's 4-D
airspace volume (call it Volume#1).
2. Assuming the operation is approved and commences, UAS#1
periodically pushes location/status updates to USS#1, which
serves _inter alia_ as the Network RID Service Provider (Net-RID
SP) for that operation.
3. When users of any other USS (whether they be other UAS operators
or Observers) develop an interest in any 4-D airspace volume
(e.g., because they wish to submit an operational intent or
because they have observed a UA), they query their own USS on the
volumes in which they are interested.
4. Their USS query, via the UTM Discovery and Synchronization
Service (DSS), all other USS in the UTM system, and learn of any
USS that have operations in those volumes (including any volumes
intersecting them); thus those USS whose query volumes intersect
Volume#1 (call them USS#2 through USS#n) learn that USS#1 has
such operations.
5. Interested parties can then subscribe to track updates on that
operation of UAS#1, via their own USS, which serve as Network RID
Display Providers (Net-RID DP) for that operation.
6. USS#1 (as Net-RID SP) will then publish updates of UAS#1 status
and position to all other subscribed USS in USS#2 through USS#n
(as Net-RID DP).
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7. All Net-RID DP subscribed to that operation of UAS#1 will deliver
its track information to their users who subscribed to that
operation of UAS#1 (via means unspecified by [F3411-19] etc., but
generally presumed to be web browser based).
Network RID has several connectivity scenarios:
_Persistently Internet connected UA_ can consistently directly
source RID information; this requires wireless coverage throughout
the intended operational airspace volume, plus a buffer (e.g.,
winds may drive the UA out of the volume).
_Intermittently Internet connected UA_, can usually directly
source RID information, but when offline (e.g., due to signal
blockage by a large structure being inspected using the UAS), need
the GCS to proxy source RID information.
_Indirectly connected UA_ lack the ability to send IP packets that
will be forwarded into and across the Internet, but instead have
some other form of communications to another node that can relay
or proxy RID information to the Internet; typically this node
would be the GCS (which to perform its function must know where
the UA is, although C2 link outages do occur).
_Non-connected UA_ have no means of sourcing RID information, in
which case the GCS or some other interface available to the
operator must source it. In the extreme case, this could be the
pilot or other agent of the operator using a web browser/
application to designate, to a USS or other UTM entity, a time-
bounded airspace volume in which an operation will be conducted.
This is referred to as a "non-equipped network participant"
engaging in "area operations". This may impede disambiguation of
ID if multiple UAS operate in the same or overlapping 4-D volumes.
In most airspace volumes, most classes of UA will not be permitted
to fly if non-connected.
In most cases in the near term (2021), the Network RID first hop data
link is likely to be cellular, which can also support BVLOS C2 over
existing large coverage areas, or Wi-Fi, which can also support
Broadcast RID. However, provided the data link can support at least
UDP/IP and ideally also TCP/IP, its type is generally immaterial to
higher layer protocols. The UAS, as the ultimate source of Network
RID information, feeds a Net-RID SP (typically the USS to which the
UAS operator subscribes), which proxies for the UAS and other data
sources. An Observer or other ultimate consumer of Network RID
information obtains it from a Net-RID DP (also typically a USS),
which aggregates information from multiple Net-RID SPs to offer
airspace Situational Awareness (SA) coverage of a volume of interest.
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Network RID Service and Display providers are expected to be
implemented as servers in well-connected infrastructure,
communicating with each other via the Internet, and accessible by
Observers via means such as web Application Programming Interfaces
(APIs) and browsers.
Network RID is the less constrained of the defined UAS RID means.
[F3411-19] specifies only Net-RID SP to Net-RID DP information
exchanges. It is presumed that IETF efforts supporting the more
constrained Broadcast RID (see next section) can be generalized for
Network RID and potentially also for UAS to USS or other UTM
communications.
3.2. Broadcast RID
+-------------------+
| Unmanned Aircraft |
+---------o---------+
|
|
|
| app messages directly over one-way RF data link
|
|
v
+------------------o-------------------+
| Observer's device (e.g., smartphone) |
+--------------------------------------+
Figure 4: "Broadcast RID Information Flow"
Figure 4 illustrates Broadcast RID information flow. Note the
absence of the Internet from the figure. This is because Broadcast
RID is one-way direct transmission of application layer messages over
a RF data link (without IP) from the UA to local Observer devices.
Internet connectivity is involved only in what the Observer chooses
to do with the information received, such as verify signatures using
a web-based Broadcast Authentication Verifier Service and look up
information in registries using the UAS ID as the primary unique key.
Broadcast RID is conceptually similar to Automatic Dependent
Surveillance - Broadcast (ADS-B). However, for various technical and
other reasons, regulators including the EASA have not indicated
intent to allow, and FAA has explicitly prohibited, use of ADS-B for
UAS RID.
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[F3411-19] specifies four Broadcast RID data links: Bluetooth 4.x,
Bluetooth 5.x with Extended Advertisements and Long Range Coded PHY
(S=8), Wi-Fi NAN at 2.4 GHz, and Wi-Fi NAN at 5 GHz. A UA must
broadcast (using advertisement mechanisms where no other option
supports broadcast) on at least one of these. If sending on
Bluetooth 5.x, it is also required concurrently to do so on 4.x
(referred to in [F3411-19] as Bluetooth Legacy); current (2021)
discussions in ASTM F38.02 on revising the standard, motivated by
European standards drafts, suggest that both Bluetooth versions will
be required. If broadcasting Wi-Fi NAN at 5 GHz, it is also required
concurrently to do so at 2.4 GHz; current discussions in F38.02
include relaxing this. Wi-Fi Beacons are also under consideration.
Future revisions of [F3411-19] may allow other data links.
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 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 31
byte payload limit of the Bluetooth 4.x "Broadcast Frame" transmitted
as an "advertisement" on beacon channels. After overheads, this
limits the RID message to 25 bytes and UAS ID string to a maximum
length of 20 bytes.
Length constraints also preclude a single Bluetooth 4.x frame
carrying not only the UAS ID but also position, velocity, and other
information that should be bound to the UAS ID, much less strong
authentication data. Messages that cannot be encapsulated in a
single frame (thus far, only the Authentication Message) must be
segmented into message "pages" (in the terminology of [F3411-19]).
Message pages must somehow be correlated as belonging to the same
message. Messages carrying position, velocity and other data must
somehow be correlated with the Basic ID message that carries the UAS
ID. This correlation is expected to be done on the basis of MAC
address: this may be complicated by MAC address randomization; not
all the common devices expected to be used by Observers have APIs
that make sender MAC addresses available to user space receiver
applications; and MAC addresses are easily spoofed. Data elements
are not so detached on other media (see Message Pack in the paragraph
after next).
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[F3411-19] Broadcast RID specifies several message types. The 4 bit
message type field in the header can index up to 16 types. Only 7
are currently defined. Only 2 are mandatory. All others are
optional, unless required by a jurisdictional authority, e.g., a CAA.
To satisfy both EASA and FAA rules, all types are needed, except
Self-ID and Authentication, as the data elements required by the
rules are scattered across several message types (along with some
data elements not required by the rules).
The Message Pack (type 0xF) is not actually a message, but the framed
concatenation of at most one message of each type of any subset of
the other types, in type index order. Some of the messages that it
can encapsulate are mandatory, others optional. The Message Pack
itself is mandatory on data links that can encapsulate it in a single
frame (Bluetooth 5.x and Wi-Fi).
+-----------------------+-----------------+-----------+-----------+
| Index | Name | Req | Notes |
+-----------------------+-----------------+-----------+-----------+
| 0x0 | Basic ID | Mandatory | - |
+-----------------------+-----------------+-----------+-----------+
| 0x1 | Location/Vector | Mandatory | - |
+-----------------------+-----------------+-----------+-----------+
| 0x2 | Authentication | Optional | paged |
+-----------------------+-----------------+-----------+-----------+
| 0x3 | Self-ID | Optional | free text |
+-----------------------+-----------------+-----------+-----------+
| 0x4 | System | Optional | - |
+-----------------------+-----------------+-----------+-----------+
| 0x5 | Operator | Optional | - |
+-----------------------+-----------------+-----------+-----------+
| 0xF | Message Pack | - | BT5 and |
| | | | Wi-Fi |
+-----------------------+-----------------+-----------+-----------+
| See Section 5.4.5 and | - | - | - |
| Table 3 of [F3411-19] | | | |
+-----------------------+-----------------+-----------+-----------+
Table 1: F3411-19 Message Types
[F3411-19] Broadcast RID specifies very few quantitative performance
requirements: static information must be transmitted at least once
per 3 seconds; dynamic information (the Location/Vector message) must
be transmitted at least once per second and be no older than one
second when sent. [FRUR] requires all information be sent at least
once per second.
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[F3411-19] Broadcast RID transmits all information as cleartext
(ASCII or binary), so static IDs enable trivial correlation of
patterns of use, unacceptable in many applications, e.g., package
delivery routes of competitors.
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 on the Broadcast RID data link, 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 and far too short for conventional
certificates (e.g., X.509). Fetching certificates via the Internet
is not always possible (e.g., Observers working in remote areas, such
as national forests), so devising a scheme whereby certificates can
be transported over Broadcast RID is necessary. 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). Without DRIP extensions to [F3411-19], 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.
In the currently (2021) proposed revision to ASTM [F3411-19], a new
Authentication Type 5 has been defined, "Specific Authentication
Method" (SAM), to enable SDOs other than ASTM to define
authentication payload formats. The first byte of the payload is the
SAM Type, used to demultiplex such variant formats. All formats for
other than private experimental use must be registered with ICAO,
which assigns the SAM Type. Any authentication message payload that
is to be sent in exactly the same form over all currently specified
Broadcast RID media is limited by lower layer constraints to a total
length of 201 bytes. For Authentication Type 5, expected to be used
by DRIP, the SAM Type byte consumes the first of these, limiting DRIP
authentication payload formats to a maximum of 200 bytes.
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3.3. USS in UTM and RID
UAS RID and UTM are complementary; Network RID is a UTM service. The
backbone of the UTM system is comprised of multiple USS: one or
several per jurisdiction; some limited to a single jurisdiction,
others spanning multiple jurisdictions. USS also serve as the
principal or perhaps the sole interface for operators and UAS into
the UTM environment. Each operator subscribes to at least one USS.
Each UAS is registered by its operator in at least one USS. Each
operational intent is submitted to one USS; if approved, that UAS and
operator can commence that operation. During the operation, status
and location of that UAS must be reported to that USS, which in turn
provides information as needed about that operator, UAS, and
operation into the UTM system and to Observers via Network RID.
USS provide services not limited to Network RID; indeed, the primary
USS function is deconfliction of airspace usage by different UAS and
other (e.g., manned aircraft, rocket launch) operations. Most
deconfliction involving a given operation is hoped to be completed
prior to commencing that operation, and is called "strategic
deconfliction". If that fails, "tactical deconfliction" comes into
play; ABDAA may not involve USS, but GBDAA likely will. Dynamic
constraints, formerly called UAS Volume Restrictions (UVR), can be
necessitated by local emergencies, extreme weather, etc., specified
by authorities on the ground, and propagated in UTM.
No role for USS in Broadcast RID is currently specified by regulators
or [F3411-19]. However, USS are likely to serve as registries (or
perhaps registrars) for UAS (and perhaps operators); if so, USS will
have a role in all forms of RID. Supplemental Data Service Providers
(SDSP) are also likely to find roles, not only in UTM as such but
also in enhancing UAS RID and related services. Whether USS, SDSP,
etc. are involved or not, RID services, narrowly defined, provide
regulator specified identification information; more broadly defined,
RID services may leverage identification to facilitate related
services or functions, likely beginning with V2X.
3.4. DRIP Focus
In addition to the gaps described above, there is a fundamental gap
in almost all current or proposed regulations and technical standards
for UAS RID. As noted above, ID is not an end in itself, but a
means. Protocols specified in [F3411-19] etc. provide limited
information potentially enabling, and no technical means 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. The System Message provides the location of the pilot/
GCS, so an Observer could physically go to the asserted location to
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look for the remote pilot; this is at best slow and may not be
feasible. What if the pilot is on the opposite rim of a canyon, or
there are multiple UAS operators to contact, whose GCS all lie in
different directions from the Observer? An Observer with Internet
connectivity and access privileges 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; this is at best unreliable and may not be prudent.
Should pilots be encouraged to answer phone calls while flying?
Internet technologies can do much better than this.
Thus complementing [F3411-19] with protocols enabling strong
authentication, preserving operator privacy while enabling immediate
use of information by authorized parties, is critical to achieve
widespread adoption of a RID system supporting safe and secure
operation of UAS. Just as [F3411-19] is expected to be approved by
regulators as a basic means of compliance with UAS RID regulations,
DRIP is expected likewise to be approved to address further issues,
starting with the creation and registration of Session IDs.
DRIP will focus on making information obtained via UAS RID
immediately usable:
1. by making it trustworthy (despite the severe constraints of
Broadcast RID);
2. by enabling verification that a UAS is registered for RID, 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. by facilitating independent reports of UA aeronautical data
(location, velocity, etc.) to confirm or refute the operator
self-reports upon which UAS RID and UTM tracking are based;
4. by enabling instant establishment, by authorized parties, of
secure communications with the remote pilot.
The foregoing considerations, beyond those addressed by baseline UAS
RID standards such as [F3411-19], imply the following requirements
for DRIP.
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4. Requirements
The following requirements apply to DRIP as a set of related
protocols, various subsets of which, in conjunction with other IETF
and external technical standards, may suffice to comply with the
regulations in any given jurisdiction or meet any given user need.
It is not intended that each and every DRIP protocol alone satisfy
each and every requirement. To satisfy these requirements, Internet
connectivity is required some of the time: e.g., to support DRIP
entity identifier creation/registration; but not all of the time,
e.g., authentication of an asserted DRIP entity identifier can be
achieved by a fully working and provisioned Observer device even when
that device is off-line so is required at all times.
4.1. General
4.1.1. Normative Requirements
GEN-1 Provable Ownership: DRIP MUST enable verification that the
asserted entity (typically UAS) ID is that of the actual
current sender (i.e., the entity ID in the DRIP authenticated
message set is not a replay attack or other spoof, e.g., by
verifying an asymmetric cryptographic signature using a
sender provided public key from which the asserted UAS ID can
be at least partially derived), even on an Observer device
lacking Internet connectivity at the time of observation.
GEN-2 Provable Binding: DRIP MUST enable the cryptographic binding
of all other [F3411-19] messages from the same actual current
sender to the UAS ID asserted in the Basic ID message.
GEN-3 Provable Registration: DRIP MUST enable cryptographically
secure verification that the UAS ID is in a registry and
identification of that registry, even on an Observer device
lacking Internet connectivity at the time of observation; the
same sender may have multiple IDs, potentially in different
registries, but each ID must clearly indicate in which
registry it can be found.
GEN-4 Readability: DRIP MUST enable information (regulation
required elements, whether sent via UAS RID or looked up in
registries) to be read and utilized by both humans and
software.
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GEN-5 Gateway: DRIP MUST enable Broadcast RID to Network RID
application layer gateways to stamp messages with precise
date/time received and receiver location, then relay them to
a network service (e.g., SDSP or distributed ledger) whenever
the gateway has Internet connectivity.
GEN-6 Contact: DRIP MUST enable dynamically establishing, with AAA,
per policy, strongly mutually authenticated, end-to-end
strongly encrypted communications with the UAS RID sender and
entities looked up from the UAS ID, including at least the
pilot (remote pilot or Pilot In Command), the USS (if any)
under which the operation is being conducted, and registries
in which data on the UA and pilot are held, whenever each
party to such desired communications has a currently usable
means of resolving the other party's DRIP entity identifier
to a locator (IP address) and currently usable bidirectional
IP (not necessarily Internet) connectivity with the other
party.
GEN-7 QoS: DRIP MUST enable policy based specification of
performance and reliability parameters.
GEN-8 Mobility: DRIP MUST support physical and logical mobility of
UA, GCS and Observers. DRIP SHOULD support mobility of
essentially all participating nodes (UA, GCS, Observers, Net-
RID SP, Net-RID DP, Private Registry, SDSP, and potentially
others as RID and UTM evolve).
GEN-9 Multihoming: DRIP MUST support multihoming of UA and GCS, for
make-before-break smooth handoff and resiliency against path/
link failure. DRIP SHOULD support multihoming of essentially
all participating nodes.
GEN-10 Multicast: DRIP SHOULD support multicast for efficient and
flexible publish-subscribe notifications, e.g., of UAS
reporting positions in designated airspace volumes.
GEN-11 Management: DRIP SHOULD support monitoring of the health and
coverage of Broadcast and Network RID services.
4.1.2. Rationale
Requirements imposed either by regulation or [F3411-19] are not
reiterated here, but drive many of the numbered requirements listed
here. The [FRUR] regulatory QoS requirement currently would be
satisfied by ensuring information refresh rates of at least 1 Hertz,
with latencies no greater than 1 second, at least 80% of the time,
but these numbers may vary between jurisdictions and over time. So
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instead the DRIP QoS requirement is that performance, reliability,
etc. parameters be user policy specifiable, which does not imply
satisfiable in all cases, but (especially together with the
management requirement) implies that when specifications are not met,
appropriate parties are notified.
The "provable ownership" requirement addresses the possibility that
the actual sender is not the claimed sender (i.e., is a spoofer).
The "provable binding" requirement addresses the MAC address
correlation problem of [F3411-19] noted above. The "provable
registration" requirement may impose burdens not only on the UAS
sender and the Observer's receiver, but also on the registry; yet it
cannot depend upon the Observer being able to contact the registry at
the time of observing the UA. The "readability" requirement pertains
to the structure and format of information at endpoints rather than
its encoding in transit, so may involve machine assisted format
conversions, e.g., from binary encodings, and/or decryption (see
Section 4.3).
The "gateway" requirement is in pursuit of three objectives: (1) mark
up a RID message with where and when it was actually received, which
may agree or disagree with the self-report in the set of messages;
(2) defend against replay attacks; and (3) support optional SDSP
services such as multilateration, to complement UAS position self-
reports with independent measurements. This is the only instance in
which DRIP transports [F3411-19] messages; most of DRIP pertains to
the authentication of such messages and identifiers carried in them.
The "contact" requirement allows any party that learns a UAS ID (that
is a DRIP entity identifier rather than another UAS ID Type) to
request establishment of a communications session with the
corresponding UAS RID sender and certain entities associated with
that UAS, but AAA and policy restrictions, _inter alia_ on resolving
the identifier to any locators (typically IP addresses), should
prevent unauthorized parties from distracting or harassing pilots.
Thus some but not all Observers of UA, receivers of Broadcast RID,
clients of Network RID, and other parties can become successfully
initiating endpoints for these sessions.
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The "QoS" requirement is only that performance and reliability
parameters can be _specified_ by policy, not that any such
specifications must be guaranteed to be met; any failure to meet such
would be reported under the "management" requirement. Examples of
such parameters are the maximum time interval at which messages
carrying required data elements may be transmitted, the maximum
tolerable rate of loss of such messages, and the maximum tolerable
latency between a dynamic data element (e.g., GNSS position of UA)
being provided to the DRIP sender and that element being delivered by
the DRIP receiver to an application.
The "mobility" requirement refers to rapid geographic mobility of
nodes, changes of their points of attachment to networks, and changes
to their IP addresses; it is not limited to micro-mobility within a
small geographic area or single Internet access provider.
4.2. Identifier
4.2.1. Normative Requirements
ID-1 Length: The DRIP entity identifier MUST NOT be longer than 19
bytes, to fit in the Specific Session ID subfield of the UAS ID
field of the Basic ID message of the currently (August 2021)
proposed revision of [F3411-19].
ID-2 Registry ID: The DRIP identifier MUST be sufficient to identify
a registry in which the entity identified therewith is listed.
ID-3 Entity ID: The DRIP identifier MUST be sufficient to enable
lookups of other data associated with the entity identified
therewith in that registry.
ID-4 Uniqueness: The DRIP identifier MUST be unique within the
applicable global identifier space from when it is first
registered therein until it is explicitly de-registered
therefrom (due to, e.g., expiration after a specified lifetime,
revocation by the registry, or surrender by the operator).
ID-5 Non-spoofability: The DRIP identifier MUST NOT be spoofable
within the context of a minimal Remote ID broadcast message set
(to be specified within DRIP to be sufficient collectively to
prove sender ownership of the claimed identifier).
ID-6 Unlinkability: The DRIP identifier MUST NOT facilitate
adversarial correlation over multiple operations. If this is
accomplished by limiting each identifier to a single use or
brief period of usage, the DRIP identifier MUST support well-
defined, scalable, timely registration methods.
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4.2.2. Rationale
The DRIP identifier can refer to various entities. In the primary
initial use case, the entity to be identified is the UA. Entities to
be identified in other likely use cases include but are not limited
to the operator, USS, and Observer. In all cases, the entity
identified must own (have the exclusive capability to use, such that
receivers can verify its ownership of) the identifier.
The DRIP identifier can be used at various layers. In Broadcast RID,
it would be used by the application running directly over the data
link. In Network RID, it would be used by the application running
over HTTPS (not required by DRIP but generally used by Network RID
implementations) and possibly other protocols. In RID initiated V2X
applications such as DAA and C2, it could be used between the network
and transport layers, e.g., with the Host Identity Protocol (HIP,
[RFC9063], [RFC7401], etc.), or between the transport and application
layers, e.g., with Datagram Transport Layer Security (DTLS,
[RFC6347]).
Registry ID (which registry the entity is in) and Entity ID (which
entity it is, within that registry) are requirements on a single DRIP
entity identifier, not separate (types of) ID. In the most common
use case, the entity will be the UA, and the DRIP identifier will be
the UAS ID; however, other entities may also benefit from having DRIP
identifiers, so the entity type is not prescribed here.
Whether a UAS ID is generated by the operator, GCS, UA, USS,
registry, or some collaboration thereamong, is unspecified; however,
there must be agreement on the UAS ID among these entities.
Management of DRIP identifiers is the primary function of their
registration hierarchies, from the root (presumably IANA), through
sector-specific and regional authorities (presumably ICAO and CAAs),
to the identified entities themselves.
While "uniqueness" might be considered an implicit requirement for
any identifier, here the point of the explicit requirement is not
just that it should be unique, but also where and when it should be
unique: global scope within a specified space, from registration to
deregistration.
While "non-spoofability" imposes requirements for and on a DRIP
authentication protocol, it also imposes requirements on the
properties of the identifier itself. An example of how the nature of
the identifier can support non-spoofability is embedding a hash of
both the registry ID and a public key of the entity in the entity
identifier, thus making it self-authenticating any time the entity's
corresponding private key is used to sign a message.
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While "unlinkability" is a privacy desideratum (see next section), it
imposes requirements on the DRIP identifier itself, as distinct from
other currently permitted choices for the UAS ID (including primarily
the static serial number of the UA or RID module).
4.3. Privacy
4.3.1. Normative Requirements
PRIV-1 Confidential Handling: DRIP MUST enable confidential handling
of private information (i.e., any and all information
designated by neither cognizant authority nor the information
owner as public, e.g., personal data).
PRIV-2 Encrypted Transport: DRIP MUST enable selective strong
encryption of private data in motion in such a manner that
only authorized actors can recover it. If transport is via
IP, then encryption MUST be end-to-end, at or above the IP
layer. DRIP MUST NOT encrypt safety critical data to be
transmitted over Broadcast RID in any situation where it is
unlikely that local Observers authorized to access the
plaintext will be able to decrypt it or obtain it from a
service able to decrypt it. DRIP MUST NOT encrypt data when/
where doing so would conflict with applicable regulations or
CAA policies/procedures, i.e., DRIP MUST support configurable
disabling of encryption.
PRIV-3 Encrypted Storage: DRIP SHOULD facilitate selective strong
encryption of private data at rest in such a manner that only
authorized actors can recover it.
PRIV-4 Public/Private Designation: DRIP SHOULD facilitate
designation, by cognizant authorities and information owners,
of which information is public and which is private. By
default, all information required to be transmitted via
Broadcast RID, even when actually sent via Network RID or
stored in registries, is assumed to be public; all other
information held in registries for lookup using the UAS ID is
assumed to be private.
PRIV-5 Pseudonymous Rendezvous: DRIP MAY enable mutual discovery of
and communications among participating UAS operators whose UA
are in 4-D proximity, using the UAS ID without revealing
pilot/operator identity or physical location.
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4.3.2. Rationale
Most data to be sent via Broadcast RID or Network RID is public, thus
the "encrypted transport" requirement for private data is selective,
e.g., for the entire payload of the Operator ID Message, but only the
pilot/GCS location fields of the System Message. Safety critical
data includes at least the UA location. Other data also may be
deemed safety critical, e.g., in some jurisdictions the pilot/GCS
location is implied to be safety critical.
UAS have several potential means of assessing the likelihood that
local Observers authorized to access the plaintext will be able to
decrypt it or obtain it from a service able to decrypt it. If the
UAS is not participating in UTM, an Observer would have no means of
obtaining a decryption key or decryption services from a cognizant
USS. If the UAS is participating in UTM, but has lost connectivity
with its USS, then an Observer within visual LOS of the UA is also
unlikely to be able to communicate with that USS (whether due to the
USS being offline or the UAS and Observer being in an area with poor
Internet connectivity). Either of these conditions (UTM non-
participation or USS unreachability) would be known to the UAS.
In some jurisdictions, the configurable enabling and disabling of
encryption may need to be outside the control of the operator.
[FRUR] mandates manufacturers design RID equipment with some degree
of tamper resistance; the preamble and other FAA commentary suggest
this is to reduce the likelihood that an operator, intentionally or
unintentionally, might alter the values of the required data elements
or disable their transmission in the required manner (e.g., as
cleartext).
How information is stored on end systems is out of scope for DRIP.
Encouraging privacy best practices, including end system storage
encryption, by facilitating it with protocol design reflecting such
considerations, is in scope. Similar logic applies to methods for
designating information as public or private.
The privacy requirements above are for DRIP, neither for [F3411-19]
(which requires obfuscation of location to any Network RID subscriber
engaging in wide area surveillance, limits data retention periods,
etc., in the interests of privacy), nor for UAS RID in any specific
jurisdiction (which may have its own regulatory requirements). The
requirements above are also in a sense parameterized: who are the
"authorized actors", how are they designated, how are they
authenticated, etc.?
4.4. Registries
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4.4.1. Normative Requirements
REG-1 Public Lookup: DRIP MUST enable lookup, from the UAS ID, of
information designated by cognizant authority as public, and
MUST NOT restrict access to this information based on identity
or role of the party submitting the query.
REG-2 Private Lookup: DRIP MUST enable lookup of private information
(i.e., any and all information in a registry, associated with
the UAS ID, that is designated by neither cognizant authority
nor the information owner as public), and MUST, according to
applicable policy, enforce AAA, including restriction of
access to this information based on identity or role of the
party submitting the query.
REG-3 Provisioning: DRIP MUST enable provisioning registries with
static information on the UAS and its operator, dynamic
information on its current operation within the U-space/UTM
(including means by which the USS under which the UAS is
operating may be contacted for further, typically even more
dynamic, information), and Internet direct contact information
for services related to the foregoing.
REG-4 AAA Policy: DRIP AAA MUST be specifiable by policies; the
definitive copies of those policies must be accessible in
registries; administration of those policies and all DRIP
registries must be protected by AAA.
4.4.2. Rationale
Registries are fundamental to RID. Only very limited information can
be Broadcast, but extended information is sometimes needed. The most
essential element of information sent is the UAS ID itself, the
unique key for lookup of extended information in registries. Beyond
designating the UAS ID as that unique key, the registry information
model is not specified herein, in part because regulatory
requirements for different registries (UAS operators and their UA,
each narrowly for UAS RID and broadly for U-space/UTM) and business
models for meeting those requirements are in flux. While it is
expected that registry functions will be integrated with USS, who
will provide them is not yet determined in most, and is expected to
vary between, jurisdictions. However this evolves, the essential
registry functions, starting with management of identifiers, are
expected to remain the same, so are specified herein.
While most data to be sent via Broadcast or Network RID is public,
much of the extended information in registries will be private. Thus
AAA for registries is essential, not just to ensure that access is
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granted only to strongly authenticated, duly authorized parties, but
also to support subsequent attribution of any leaks, audit of who
accessed information when and for what purpose, etc. As specific AAA
requirements will vary by jurisdictional regulation, provider
philosophy, customer demand, etc., they are left to specification in
policies, which should be human readable to facilitate analysis and
discussion, and machine readable to enable automated enforcement,
using a language amenable to both, e.g., XACML.
The intent of the negative and positive access control requirements
on registries is to ensure that no member of the public would be
hindered from accessing public information, while only duly
authorized parties would be enabled to access private information.
Mitigation of Denial of Service attacks and refusal to allow database
mass scraping would be based on those behaviors, not on identity or
role of the party submitting the query _per se_, but querant identity
information might be gathered (by security systems protecting DRIP
implementations) on such misbehavior.
By "Internet direct contact information" is meant a locator (e.g., IP
address), or identifier (e.g., FQDN) that can be resolved to a
locator, which would enable initiation of an end-to-end communication
session using a well known protocol (e.g., SIP).
5. IANA Considerations
This document does not make any IANA request.
6. Security Considerations
DRIP is all about safety and security, so content pertaining to such
is not limited to this section. This document does not define any
protocols, so security considerations of such are speculative.
Potential vulnerabilities of DRIP solutions to these requirements
include but are not limited to:
* Sybil attacks
* confusion created by many spoofed unsigned messages
* processing overload induced by attempting to verify many spoofed
signed messages (where verification will fail but still consume
cycles)
* malicious or malfunctioning registries
* interception by on-path attacker of (i.e., Man In The Middle
attacks on) registration messages
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* UA impersonation through private key extraction, improper key
sharing, or carriage of a small (presumably harmless) UA, i.e., as
a "false flag", by a larger (malicious) UA
It may be inferred from the general requirements (Section 4.1) for
provable ownership, provable binding, and provable registration,
together with the identifier requirements (Section 4.2), that DRIP
must provide:
* message integrity
* non-repudiation
* defense against replay attacks
* defense against spoofing
One approach to so doing involves verifiably binding the DRIP
identifier to a public key. Providing these security features,
whether via this approach or another, is likely to be especially
challenging for Observers without Internet connectivity at the time
of observation. For example, checking the signature of a registry on
a public key certificate received via Broadcast RID in a remote area
presumably would require that the registry's public key had been
previously installed on the Observer's device, yet there may be many
registries and the Observer's device may be storage constrained, and
new registries may come on-line subsequent to installation of DRIP
software on the Observer's device. See also Figure 1 and the
associated explanatory text, especially the second paragraph after
the figure. Thus there may be caveats on the extent to which
requirements can be satisfied in such cases, yet strenuous effort
should be made to satisfy them, as such cases, e.g., firefighting in
a national forest, are important. Each numbered requirement _a
priori_ expected to suffer from such limitations (General
requirements for Gateway and Contact functionality) contains language
stating when it applies.
7. Privacy and Transparency Considerations
Privacy and transparency are important for legal reasons including
regulatory consistency. [EU2018] states "harmonised and
interoperable national registration systems... should comply with the
applicable Union and national law on privacy and processing of
personal data, and the information stored in those registration
systems should be easily accessible."
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Privacy and transparency (where essential to security or safety) are
also ethical and moral imperatives. Even in cases where old
practices (e.g., automobile registration plates) could be imitated,
when new applications involving PII (such as UAS RID) are addressed
and newer technologies could enable improving privacy, such
opportunities should not be squandered. Thus it is recommended that
all DRIP work give due regard to [RFC6973] and more broadly
[RFC8280].
However, privacy and transparency are often conflicting goals,
demanding careful attention to their balance.
DRIP information falls into two classes: that which, to achieve the
purpose, must be published openly as cleartext, for the benefit of
any Observer (e.g., the basic UAS ID itself); 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).
How properly authorized parties are authorized, authenticated, etc.
are questions that extend beyond the scope of DRIP, but DRIP may be
able to provide support for such processes. Classification of
information as public or private must be made explicit and reflected
with markings, design, etc. 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. Details of the protection mechanisms will be provided
in other DRIP documents. Mitigation of adversarial correlation will
also be addressed.
8. References
8.1. Normative References
[F3411-19] ASTM International, "Standard Specification for Remote ID
and Tracking", February 2020,
<http://www.astm.org/cgi-bin/resolver.cgi?F3411>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
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8.2. Informative References
[Amended] European Union Aviation Safety Agency (EASA), "Commission
Delegated Regulation (EU) 2020/1058 of 27 April 2020
amending Delegated Regulation (EU) 2019/945", April 2020,
<https://eur-lex.europa.eu/legal-content/EN/
TXT/?uri=CELEX%3A32020R1058>.
[ASDRI] ASD-STAN, "Introduction to the European UAS Digital Remote
ID Technical Standard", January 2021, <https://asd-
stan.org/wp-content/uploads/ASD-STAN_DRI_Introduction_to_t
he_European_digital_RID_UAS_Standard.pdf>.
[CPDLC] Gurtov, A., Polishchuk, T., and M. Wernberg, "Controller-
Pilot Data Link Communication Security", MDPI
Sensors 18(5), 1636, 2018,
<https://www.mdpi.com/1424-8220/18/5/1636>.
[CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers",
September 2019, <https://shop.cta.tech/products/small-
unmanned-aerial-systems-serial-numbers>.
[Delegated]
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,
<https://eur-lex.europa.eu/eli/reg_del/2019/945/oj>.
[drip-architecture]
Card, S. W., Wiethuechter, A., Moskowitz, R., Zhao, S.,
and A. Gurtov, "Drone Remote Identification Protocol
(DRIP) Architecture", Work in Progress, Internet-Draft,
draft-ietf-drip-arch-15, 25 July 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-drip-
arch-15>.
[ENISACSIRT]
European Union Agency for Cybersecurity (ENISA),
"Actionable information for Security Incident Response",
November 2014, <https://www.enisa.europa.eu/topics/csirt-
cert-services/reactive-services/copy_of_actionable-
information>.
[EU2018] European Parliament and Council, "2015/0277 (COD) PE-CONS
2/18", February 2018,
<https://www.consilium.europa.eu/media/35805/easa-
regulation-june-2018.pdf>.
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[FAACONOPS]
FAA Office of NextGen, "UTM Concept of Operations v2.0",
March 2020, <https://www.faa.gov/uas/research_development/
traffic_management/media/UTM_ConOps_v2.pdf>.
[FR24] Flightradar24 AB, "Flightradar24 Live Air Traffic", May
2021, <https://www.flightradar24.com/about>.
[FRUR] Federal Aviation Administration, "Remote Identification of
Unmanned Aircraft", January 2021,
<https://www.federalregister.gov/
documents/2021/01/15/2020-28948/remote-identification-of-
unmanned-aircraft>.
[GDPR] European Parliament and Council, "General Data Protection
Regulation", April 2016,
<https://eur-lex.europa.eu/eli/reg/2016/679/oj>.
[I-D.ietf-raw-ldacs]
Maeurer, N., Graeupl, T., and C. Schmitt, "L-band Digital
Aeronautical Communications System (LDACS)", Work in
Progress, Internet-Draft, draft-ietf-raw-ldacs-08, 10 May
2021, <https://datatracker.ietf.org/doc/html/draft-ietf-
raw-ldacs-08>.
[ICAOATM] International Civil Aviation Organization, "Doc 4444:
Procedures for Air Navigation Services: Air Traffic
Management", November 2016, <https://store.icao.int/en/
procedures-for-air-navigation-services-air-traffic-
management-doc-4444>.
[ICAODEFS] International Civil Aviation Organization, "Defined terms
from the Annexes to the Chicago Convention and ICAO
guidance material", July 2017,
<https://www.icao.int/safety/cargosafety/Documents/
Draft%20Glossary%20of%20terms.docx>.
[ICAOUAS] International Civil Aviation Organization, "Circular 328:
Unmanned Aircraft Systems", February 2011,
<https://www.icao.int/meetings/uas/documents/
circular%20328_en.pdf>.
[ICAOUTM] International Civil Aviation Organization, "Unmanned
Aircraft Systems Traffic Management (UTM) - A Common
Framework with Core Principles for Global Harmonization,
Edition 3", October 2020,
<https://www.icao.int/safety/UA/Documents/
UTM%20Framework%20Edition%203.pdf>.
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[Implementing]
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,
<https://eur-lex.europa.eu/eli/reg_impl/2019/947/oj>.
[InitialView]
SESAR Joint Undertaking, "Initial view on Principles for
the U-space architecture", July 2019,
<https://www.sesarju.eu/sites/default/files/documents/u-
space/SESAR%20principles%20for%20U-
space%20architecture.pdf>.
[NPRM] United States Federal Aviation Administration (FAA),
"Notice of Proposed Rule Making on Remote Identification
of Unmanned Aircraft Systems", December 2019,
<https://www.federalregister.gov/
documents/2019/12/31/2019-28100/remote-identification-of-
unmanned-aircraft-systems>.
[OpenDroneID]
Intel Corp., "Open Drone ID", March 2019,
<https://github.com/opendroneid/specs>.
[OpenSky] OpenSky Network non-profit association, "The OpenSky
Network", May 2021,
<https://opensky-network.org/about/about-us>.
[Opinion1] European Union Aviation Safety Agency (EASA), "Opinion No
01/2020: High-level regulatory framework for the U-space",
March 2020, <https://www.easa.europa.eu/document-
library/opinions/opinion-012020>.
[Part107] United States Federal Aviation Administration, "Code of
Federal Regulations Part 107", June 2016,
<https://www.ecfr.gov/cgi-bin/text-idx?node=pt14.2.107>.
[Recommendations]
FAA UAS Identification and Tracking Aviation Rulemaking
Committee, "UAS ID and Tracking ARC Recommendations Final
Report", September 2017, <https://www.faa.gov/regulations_
policies/rulemaking/committees/documents/media/
UAS%20ID%20ARC%20Final%20Report%20with%20Appendices.pdf>.
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[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
[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,
<https://www.rfc-editor.org/info/rfc7401>.
[RFC8280] ten Oever, N. and C. Cath, "Research into Human Rights
Protocol Considerations", RFC 8280, DOI 10.17487/RFC8280,
October 2017, <https://www.rfc-editor.org/info/rfc8280>.
[RFC9063] Moskowitz, R., Ed. and M. Komu, "Host Identity Protocol
Architecture", RFC 9063, DOI 10.17487/RFC9063, July 2021,
<https://www.rfc-editor.org/info/rfc9063>.
[Roadmap] American National Standards Institute (ANSI) Unmanned
Aircraft Systems Standardization Collaborative (UASSC),
"Standardization Roadmap for Unmanned Aircraft Systems
draft v2.0", April 2020, <https://share.ansi.org/Shared
Documents/Standards Activities/UASSC/
UASSC_20-001_WORKING_DRAFT_ANSI_UASSC_Roadmap_v2.pdf>.
[Stranger] Heinlein, R.A., "Stranger in a Strange Land", June 1961.
[WG105] EUROCAE, "WG-105 draft ED-282 Minimum Operational
Performance Standards (MOPS) for Unmanned Aircraft System
(UAS) Electronic Identification", June 2020.
[WiFiNAN] Wi-Fi Alliance, "Wi-Fi Aware™ Specification Version 3.2",
October 2020, <https://www.wi-fi.org/downloads-registered-
guest/Wi-Fi_Aware_Specification_v3.2.pdf/29731>.
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Appendix A. Discussion and Limitations
This document is largely based on the process of one SDO, ASTM.
Therefore, it is tailored to specific needs and data formats of this
standard. Other organizations, for example in EU, do not necessarily
follow the same architecture.
The need for drone ID and operator privacy is an open discussion
topic. For instance, in the ground vehicular domain each car carries
a publicly visible plate number. In some countries, for nominal cost
or even for free, anyone can resolve the identity and contact
information of the owner. Civil commercial aviation and maritime
industries also have a tradition of broadcasting plane or ship ID,
coordinates, and even flight plans in plain text. Community networks
such as OpenSky [OpenSky] and Flightradar24 [FR24] use this open
information through ADS-B to deploy public services of flight
tracking. Many researchers also use these data to perform
optimization of routes and airport operations. Such ID information
should be integrity protected, but not necessarily confidential.
In civil aviation, aircraft identity is broadcast by a device known
as transponder. It transmits a four octal digit squawk code, which
is assigned by a traffic controller to an airplane after approving a
flight plan. There are several reserved codes such as 7600 which
indicate radio communication failure. The codes are unique in each
traffic area and can be re-assigned when entering another control
area. The code is transmitted in plain text by the transponder and
also used for collision avoidance by a system known as Traffic alert
and Collision Avoidance System (TCAS). The system could be used for
UAS as well initially, but the code space is quite limited and likely
to be exhausted soon. The number of UAS far exceeds the number of
civil airplanes in operation.
The ADS-B system is utilized in civil aviation for each "ADS-B Out"
equipped airplane to broadcast its ID, coordinates, and altitude for
other airplanes and ground control stations. If this system is
adopted for drone IDs, it has additional benefit with backward
compatibility with civil aviation infrastructure; then, pilots and
dispatchers will be able to see UA on their control screens and take
those into account. If not, a gateway translation system between the
proposed drone ID and civil aviation system should be implemented.
Again, system saturation due to large numbers of UAS is a concern.
The Mode S transponders used in all TCAS and most ADS-B Out
installations are assigned an ICAO 24 bit "address" (arguably really
an identifier rather than a locator) that is associated with the
aircraft as part of its registration. In the US alone, well over
2^20 UAS are already flying; thus, a 24 bit space likely would be
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rapidly exhausted if used for UAS (other than large UAS flying in
controlled airspace, especially internationally, under rules other
than those governing small UAS at low altitudes).
Wi-Fi and Bluetooth are two wireless technologies currently
recommended by ASTM specifications due to their widespread use and
broadcast nature. However, those have limited range (max 100s of
meters) and may not reliably deliver UAS ID at high altitude or
distance. Therefore, a study should be made of alternative
technologies from the telecom domain (WiMAX / IEEE 802.16, 5G) or
sensor networks (Sigfox, LoRa). Such transmission technologies can
impose additional restrictions on packet sizes and frequency of
transmissions, but could provide better energy efficiency and range.
In civil aviation, Controller-Pilot Data Link Communications (CPDLC)
is used to transmit command and control between the pilots and ATC.
It could be considered for UAS as well due to long range and proven
use despite its lack of security [CPDLC].
L-band Digital Aeronautical Communications System (LDACS) is being
standardized by ICAO and IETF for use in future civil aviation
[I-D.ietf-raw-ldacs]. It provides secure communication, positioning,
and control for aircraft using a dedicated radio band. It should be
analyzed as a potential provider for UAS RID as well. This will
bring the benefit of a global integrated system creating a global
airspace use awareness.
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 efforts. The work of Gabriel Cox, Intel
Corp., and their Open Drone ID collaborators opened UAS RID to a
wider community. 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
extensively reviewed or otherwise contributed to this document
include Amelia Andersdotter, Carsten Bormann, Toerless Eckert, Susan
Hares, Mika Jarvenpaa, Alexandre Petrescu, Saulo Da Silva and Shuai
Zhao. Thanks to Linda Dunbar for the Secdir review, Nagendra Nainar
for the Opsdir review and Suresh Krishnan for the Gen-ART review.
Thanks to IESG members Roman Danyliw, Erik Kline, Murray Kucherawy
and Robert Wilton for helpful and positive comments. Thanks to
chairs Daniel Migault and Mohamed Boucadair for direction of our team
of authors and editor, some of whom are newcomers to writing IETF
documents. Thanks especially to Internet Area Director Eric Vyncke
for guidance and support.
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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
Andrei Gurtov
Linköping University
IDA
SE-58183 Linköping
Sweden
Email: gurtov@acm.org
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