Drone Remote Identification Protocol (DRIP) Architecture

Internet-Draft	DRIP Architecture	December 2021
Card, et al.	Expires 17 June 2022	[Page]

Abstract

This document describes an architecture for protocols and services to support Unmanned Aircraft System Remote Identification and tracking (UAS RID), plus RID-related communications. This architecture adheres to the requirements listed in the DRIP Requirements document.¶

1. Introduction

This document describes an architecture for protocols and services to support Unmanned Aircraft System Remote Identification and tracking (UAS RID), plus RID-related communications. The architecture takes into account both current (including proposed) regulations and non-IETF technical standards.¶

The architecture adheres to the requirements listed in the DRIP Requirements document [I-D.ietf-drip-reqs]. The requirements document provides an extended introduction to the problem space and use cases.¶

1.1. Overview of Unmanned Aircraft System (UAS) Remote ID (RID) and Standardization

UAS Remote Identification (RID) is an application enabler for a UAS to be identified by Unmanned Aircraft Systems Traffic Management (UTM) and UAS Service Supplier (USS) (Appendix A) or third parties entities such as law enforcement. Many considerations (e.g., safety) dictate that UAS be remotely identifiable.¶

Civil Aviation Authorities (CAAs) worldwide are mandating UAS RID. CAAs currently promulgate performance-based regulations that do not specify techniques, but rather cite industry consensus technical standards as acceptable means of compliance.¶

Federal Aviation Administration (FAA)¶

The FAA published a Notice of Proposed Rule Making [NPRM] in 2019 and thereafter published a "Final Rule" in 2021 [FAA_RID], imposing requirements on UAS manufacturers and operators, both commercial and recreational. The rule clearly states that Automatic Dependent Surveillance Broadcast (ADS-B) Out and transponders cannot be used to satisfy the RID requirements on UAS to which the rule applies (see Appendix B).¶

European Union Aviation Safety Agency (EASA)¶

The EASA published a [Delegated] regulation in 2019 imposing requirements on UAS manufacturers and third-country operators, including but not limited to RID requirements. The EASA also published in 2019 an [Implementing] regulation laying down detailed rules and procedures for UAS operations and operating personnel.¶

American Society for Testing and Materials (ASTM)¶

ASTM International, Technical Committee F38 (UAS), Subcommittee F38.02 (Aircraft Operations), Work Item WK65041, developed the ASTM [F3411] Standard Specification for Remote ID and Tracking.¶

ASTM defines one set of RID information and two means, MAC-layer broadcast and IP-layer network, of communicating it. If an UAS uses both communication methods, the same information must be provided via both means. [F3411] is cited by FAA in its RID final rule [FAA_RID] as "a potential means of compliance" to a Remote ID rule.¶

The 3rd Generation Partnership Project (3GPP)¶

With release 16, the 3GPP completed the UAS RID requirement study [TS-22.825] and proposed a set of use cases in the mobile network and the services that can be offered based on RID. Release 17 specification focuses on enhanced UAS service requirements and provides the protocol and application architecture support that will be applicable for both 4G and 5G networks. The study of Further Architecture Enhancement for Uncrewed Aerial Vehicles (UAV) and Urban Air Mobility (UAM) [FS_AEUA] in release 18 further enhances the communication mechanism between UAS and USS/UTM. The RID discussed in Section 3 may be used as the 3GPP CAA-level ID for Remote Identification purposes.¶

1.2. Overview of Types of UAS Remote ID

1.2.1. Broadcast RID

[F3411] defines a set of RID messages for direct, one-way, broadcast transmissions from the UA over Bluetooth or Wi-Fi. These are currently defined as MAC-Layer messages. Internet (or other Wide Area Network) connectivity is only needed for UAS registry information lookup by Observers using the directly received UAS ID. Broadcast RID should be functionally usable in situations with no Internet connectivity.¶

The minimum Broadcast RID data flow is illustrated in Figure 1.¶

                  +------------------------+
                  | Unmanned Aircraft (UA) |
                  +-----------o------------+
                              |
                              |
                              |
                              | app messages directly over
                              | one-way RF data link (no IP)
                              |
                              |
                              v
           +------------------o-------------------+
           | Observer's device (e.g., smartphone) |
           +--------------------------------------+

Figure 1

Broadcast RID provides information only about unmanned aircraft (UA) within direct RF LOS, typically similar to visual Light-Of-Sight (LOS), with a range up to approximately 1 km. This information may be 'harvested' from received broadcasts and made available via the Internet, enabling surveillance of areas too large for local direct visual observation or direct RF link based ID (see Section 6).¶

1.2.2. Network RID

[F3411], using the same data dictionary that is the basis of Broadcast RID messages, defines a Network Remote Identification (Net-RID) data flow as follows.¶

The information to be reported via RID is generated by the UAS (typically some by the UA and some by the GCS, e.g. their respective GNSS derived locations).¶
The information is sent by the UAS (UA or GCS) via unspecified means to the cognizant Network Remote Identification Service Provider (Net-RID SP), typically the USS under which the UAS is operating if participating in UTM.¶
The Net-RID SP publishes via the Discovery and Synchronization Service (DSS) over the Internet that it has operations in various 4-D airspace volumes, describing the volumes but not the operations.¶
An Observer's device, expected typically but not specified to be web based, queries a Network Remote Identification Display Provider (Net-RID DP), typically also a USS, about any operations in a specific 4-D airspace volume.¶
Using fully specified web based methods over the Internet, the Net-RID DP queries all Net-RID SP that have operations in volumes intersecting that of the Observer's query for details on all such operations.¶
The Net-RID DP aggregates information received from all such Net-RID SP and responds to the Observer's query.¶

The minimum Net-RID data flow is illustrated in Figure 2:¶

     +-------------+     ******************
     |     UA      |     *    Internet    *
     +--o-------o--+     *                *
        |       |        *                *
        |       |        *                *     +------------+
        |       '--------*--(+)-----------*-----o            |
        |                *   |            *     |            |
        |       .--------*--(+)-----------*-----o NET-RID SP |
        |       |        *                *     |            |
        |       |        *         .------*-----o            |
        |       |        *         |      *     +------------+
        |       |        *         |      *
        |       |        *         |      *     +------------+
        |       |        *         '------*-----o            |
        |       |        *                *     | NET-RID DP |
        |       |        *         .------*-----o            |
        |       |        *         |      *     +------------+
        |       |        *         |      *
        |       |        *         |      *     +------------+
     +--o-------o--+     *         '------*-----o Observer's |
     |     GCS     |     *                *     | Device     |
     +-------------+     ******************     +------------+

Figure 2

Command and Control (C2) must flow from the GCS to the UA via some path, currently (in the year of 2021) typically a direct RF link, but with increasing beyond Visual Line of Sight (BVLOS) operations expected often to be wireless links at either end with the Internet between.¶

Telemetry (at least UA's position and heading) flows from the UA to the GCS via some path, typically the reverse of the C2 path. Thus, RID information pertaining to both the GCS and the UA can be sent, by whichever has Internet connectivity, to the Net-RID SP, typically the USS managing the UAS operation.¶

The Net-RID SP forwards RID information via the Internet to subscribed Net-RID DP, typically USS. Subscribed Net-RID DP forward RID information via the Internet to subscribed Observer devices. Regulations require and [F3411] describes RID data elements that must be transported end-to-end from the UAS to the subscribed Observer devices.¶

[F3411] prescribes the protocols between the Net-RID SP, Net-RID DP, and the Discovery and Synchronization Service (DSS). It also prescribes data elements (in JSON) between Observer and Net-RID DP. DRIP could address standardization of secure protocols between the UA and GCS (over direct wireless and Internet connection), between the UAS and the Net-RID SP, and/or between the Net-RID DP and Observer devices.¶

- Informative note: Neither link layer protocols nor the use of links (e.g., the link often existing between the GCS and the UA) for any purpose other than carriage of RID information is in the scope of [F3411] Network RID.¶

1.3. Overview of USS Interoperability

With Net-RID, there is direct communication between each UAS and its USS. Multiple USS exchange information with the assistance of a Discovery and Synchronization Service (DSS) so all USS collectively have knowledge about all activities in a 4D airspace.¶

The interactions among an Observer, multiple UAS, and their USS are shown in Figure 3.¶

            +------+     +----------+     +------+
            | UAS1 |     | Observer |     | UAS2 |
            +----o-+     +-----o----+     +-o----+
                  |             |            |
                  |             |            |
            ******|*************|************|******
            *     |             |            |     *
            *     |         +---o--+         |     *
            *     |  .------o USS3 o------.  |     *
            *     |  |      +--o---+      |  |     *
            *     |  |         |          |  |     *
            *   +-o--o-+    +--o--+     +-o--o-+   *
            *   |      o----o DSS o-----o      |   *
            *   | USS1 |    +-----+     | USS2 |   *
            *   |      o----------------o      |   *
            *   +------+                +------+   *
            *                                      *
            *               Internet               *
            ****************************************

Figure 3

1.4. Overview of DRIP Architecture

Figure 4 illustrates the general UAS RID usage scenario. Broadcast RID links are not shown as they reach from any UA to any listening receiver in range and thus would obscure the intent of the figure. Figure 4 shows, as context, some entities and interfaces beyond the scope of DRIP (as currently (2022) chartered).¶

***************                                        ***************
*    UAS1     *                                        *     UAS2    *
*             *                                        *             *
* +--------+  *                 DAA/V2V                *  +--------+ *
* |   UA   o--*----------------------------------------*--o   UA   | *
* +--o--o--+  *                                        *  +--o--o--+ *
*    |  |     *   +------+      Lookups     +------+   *     |  |    *
*    |  |     *   | GPOD o------.    .------o PSOD |   *     |  |    *
*    |  |     *   +------+      |    |      +------+   *     |  |    *
*    |  |     *                 |    |                 *     |  |    *
* C2 |  |     *     V2I      ************     V2I      *     |  | C2 *
*    |  '-----*--------------*          *--------------*-----'  |    *
*    |        *              *          *              *        |    *
*    |        o====NetRID====*          *====NetRID====o        |    *
* +--o--+     *              * Internet *              *     +--o--+ *
* | GCS o-----*--------------*          *--------------*-----o GCS | *
* +-----+     * Registration *          * Registration *     +-----+ *
*             * (and UTM)    *          * (and UTM)    *             *
***************              ************              ***************
                               |  |  |
                +----------+   |  |  |   +----------+
                | Public   o---'  |  '---o Private  |
                | Registry |      |      | Registry |
                +----------+      |      +----------+
                               +--o--+
                               | DNS |
                               +-----+

GPOD: General Public Observer Device (for brevity in this figure)
PSOD: Public Safety Observer Device (for brevity in this figure)

Figure 4

DRIP is meant to leverage existing Internet resources (standard protocols, services, infrastructures, and business models) to meet UAS RID and closely related needs. DRIP will specify how to apply IETF standards, complementing [F3411] and other external standards, to satisfy UAS RID requirements.¶

This document outlines the DRIP architecture in the context of the UAS RID architecture. This includes presenting the gaps between the CAAs' Concepts of Operations and [F3411] as it relates to the use of Internet technologies and UA direct RF communications. Issues include, but are not limited to:¶

- - Design of trustworthy remote identifiers (Section 3).¶

- Mechanisms to leverage Domain Name System (DNS [RFC1034]), Extensible Provisioning Protocol (EPP [RFC5731]) and Registration Data Access Protocol (RDAP) ([RFC7482]) for publishing public and private information (see Section 4.1 and Section 4.2).¶

- Specific authentication methods and message payload formats to enable verification that Broadcast RID messages were sent by the claimed sender (Section 5) and that sender is in the claimed registry (Section 4 and Section 5).¶

- Harvesting broadcast RID messages for UTM inclusion (Section 6).¶

- Methods for instantly establishing secure communications between an Observer and the pilot of an observed UAS (Section 7).¶

- Privacy in RID messages (PII protection) (Section 10).¶

3. HHIT as the DRIP Entity Identifier

This section describes the DRIP architectural approach to meeting the basic requirements of a DRIP entity identifier within external technical standard ASTM [F3411] and regulatory constraints. It justifies and explains the use of Hierarchical Host Identity Tags (HHITs) as self-asserting IPv6 addresses suitable as a UAS ID type and more generally as trustworthy multipurpose remote identifiers.¶

Self-asserting in this usage is given the Host Identity (HI), the HHIT ORCHID construction and a signature of the HHIT by the HI can both be validated. The explicit registration hierarchy within the HHIT provides registry discovery (managed by a Registrar) to either yield the HI for 3rd-party (who is looking for ID attestation) validation or prove the HHIT and HI have uniquely been registered.¶

3.1. UAS Remote Identifiers Problem Space

A DRIP entity identifier needs to be "Trustworthy" (See DRIP Requirement GEN-1, ID-4 and ID-5 in [I-D.ietf-drip-reqs]). This means that given a sufficient collection of RID messages, an Observer can establish that the identifier claimed therein uniquely belongs to the claimant: that the only way for any other entity to prove ownership of that identifier would be to obtain information that ought to be available only to the legitimate owner of the identifier (e.g., a cryptographic private key).¶

To satisfy DRIP requirements and maintain important security properties, the DRIP identifier should be self-generated by the entity it names (e.g., a UAS) and registered (e.g., with a USS, see Requirements GEN-3 and ID-2).¶

Broadcast RID, especially its support for Bluetooth 4, imposes severe constraints. ASTM RID [F3411] allows a UAS ID of types 1, 2 and 3 of 20 bytes; a revision to [F3411], currently in balloting (as of Oct 2021), adds type 4, Session IDs, to be standardized by IETF and other standard development organizations (SDOs) as extensions to ASTM RID, consumes one of those bytes to index the sub-type, leaving only 19 for the identifier (see DRIP Requirement ID-1). Likewise, the maximum ASTM RID [F3411] Authentication Message payload is 201 bytes for most authentication types, but for type 5, also added in this revision, for IETF and other SDOs to develop Specific Authentication Methods as extensions to ASTM RID, one byte is consumed to index the sub-type, leaving only 200 for DRIP authentication payloads, including one or more DRIP entity identifiers and associated authentication data.¶

3.2. HHIT as A Trustworthy DRIP Entity Identifier

A Remote ID that can be trustworthily used in the RID Broadcast mode can be built from an asymmetric keypair. Rather than using a key signing operation to claim ownership of an ID that does not guarantee name uniqueness, in this method the ID is cryptographically derived directly from the public key. The proof of ID ownership (verifiable attestation, versus mere claim) is guaranteed by signing this cryptographic ID with the associated private key. The association between the ID and the private key is ensured by cryptographically binding the public key with the ID, more specifically the ID results from the hash of the public key. It is statistically hard for another entity to create a public key that would generate (spoof) the ID.¶

The basic HIT is designed statistically unique through the cryptographic hash feature of second-preimage resistance. The cryptographically-bound addition of the Hierarchy and an HHIT registration process (e.g. based on Extensible Provisioning Protocol, [RFC5730]) provide complete, global HHIT uniqueness. This registration forces the attacker to generate the same public key rather than a public key that generates the same HHIT. This is in contrast to general IDs (e.g. a UUID or device serial number) as the subject in an X.509 certificate.¶

A DRIP identifier can be assigned to a UAS as a static HHIT by its manufacturer, such as a single HI and derived HHIT encoded as a hardware serial number per [CTA2063A]. Such a static HHIT SHOULD only be used to bind one-time use DRIP identifiers to the unique UA. Depending upon implementation, this may leave a HI private key in the possession of the manufacturer (more details in Section 9).¶

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

HHITs can also be used throughout the USS/UTM system. The Operators, Private Information Registries, as well as other UTM entities, can use HHITs for their IDs. Such HHITs can facilitate DRIP security functions such as used with HIP to strongly mutually authenticate and encrypt communications.¶

A self-attestation of a HHIT used as a UAS ID can be done in as little as 84 bytes, by avoiding an explicit encoding technology like ASN.1 or Concise Binary Object Representation (CBOR [RFC8949]). This attestation consists of only the HHIT, a timestamp, and the EdDSA signature on them.¶

In general, Internet access may be needed to validate Attestations or Certificates. This may be obviated in the most common cases (e.g. attestation of the UAS ID), even in disconnected environments, by prepopulating small caches on Observer devices with Registry public keys and a chain of Attestations or Certificates (tracing a path through the Registry tree). This is assuming all parties on the trust path also use HHITs for their identities.¶

3.3. HHIT for DRIP Identifier Registration and Lookup

Remote ID needs a deterministic lookup mechanism that rapidly provides actionable information about the identified UA. Given the size constraints imposed by the Bluetooth 4 broadcast media, the UAS ID itself needs to be a non-spoofable inquiry input into the lookup.¶

A DRIP registration process based on the explicit hierarchy within a HHIT provides manageable uniqueness of the HI for the HHIT. This is the defense against a cryptographic hash second pre-image attack on the HHIT (e.g. multiple HIs yielding the same HHIT, see Requirement ID-3). A lookup of the HHIT into this registration data provides the registered HI for HHIT proof. A first-come-first-serve registration for a HHIT provides deterministic access to any other needed actionable information based on inquiry access authority (more details in Section 4.2).¶

3.4. HHIT as a Cryptographic Identifier

The only (known to the authors at the time of this writing) extant types of IP address compatible identifiers cryptographically derived from the public keys of the identified entities are Cryptographically Generated Addresses (CGAs) [RFC3972] and Host Identity Tags (HITs) [RFC7401]. CGAs and HITs lack registration/retrieval capability. To provide this, each HHIT embeds plaintext information designating the hierarchy within which is registered and a cryptographic hash of that information concatenated with the entity's public key, etc. Although hash collisions may occur, the registrar can detect them and reject registration requests rather than issue credentials, e.g., by enforcing a first-claimed, first-attested policy. Pre-image hash attacks are also mitigated through this registration process, locking the HHIT to a specific HI¶

4. DRIP Identifier Registration and Registries

DRIP registries hold both public and private UAS information resulting from the DRIP identifier registration process. Given these different uses, and to improve scalability, security, and simplicity of administration, the public and private information can be stored in different registries. This section introduces the public and private information registries for DRIP identifiers. This DRIP Identifier registration process satisfies the following DRIP requirements defined in [I-D.ietf-drip-reqs]: GEN-3, GEN-4, ID-2, ID-4, ID-6, PRIV-3, PRIV-4, REG-1, PRG-2, REG-3 and REG-4.¶

4.1. Public Information Registry

4.1.1. Background

The public registry provides trustable information such as attestations of RID ownership and registration with the HDA (Hierarchical HIT Domain Authority). Optionally, pointers to the registries for the HDA and RAA (Registered Assigning Authority)implicit in the RID can be included (e.g., for HDA and RAA HHIT|HI used in attestation signing operations). This public information will be principally used by Observers of Broadcast RID messages. Data on UAS that only use Network RID, is available via an Observer's Net-RID DP that would tend to directly provide all public registry information. The Observer may visually "see" these Net-RID UAS, but they may be silent to the Observer. The Net-RID DP is the only source of information based on a query for an airspace volume.¶

4.1.2. DNS as the Public DRIP Identifier Registry

A DRIP identifier SHOULD be registered as an Internet domain name (at an arbitrary level in the hierarchy, e.g. in .ip6.arpa). Thus DNS can provide all the needed public DRIP information. A standardized HHIT FQDN (Fully Qualified Domain Name) can deliver the HI via a HIP RR (Resource Record) [RFC8005] and other public information (e.g., RRA and HDA PTRs, and HIP RVS (Rendezvous Servers) [RFC8004]). These public information registries can use secure DNS transport (e.g. DNS over TLS) to deliver public information that is not inherently trustable (e.g. everything other than attestations).¶

4.2. Private Information Registry

4.2.1. Background

The private information required for DRIP identifiers is similar to that required for Internet domain name registration. A DRIP identifier solution can leverage existing Internet resources: registration protocols, infrastructure, and business models, by fitting into an ID structure compatible with DNS names. The HHIT hierarchy can provide the needed scalability and management structure. It is expected that the private registry function will be provided by the same organizations that run a USS, and likely integrated with a USS. The lookup function may be implemented by the Net-RID DPs.¶

4.2.2. EPP and RDAP as the Private DRIP Identifier Registry

A DRIP private information registry supports essential registry operations (e.g. add, delete, update, query) using interoperable open standard protocols. It can accomplish this by using the Extensible Provisioning Protocol (EPP [RFC5730]) and the Registry Data Access Protocol (RDAP RFC7480] [RFC7482] [RFC7483]). The DRIP private information registry in which a given UAS is registered needs to be findable, starting from the UAS ID, using the methods specified in [RFC7484].¶

4.2.3. Alternative Private DRIP Registry methods

A DRIP private information registry might be an access controlled DNS (e.g. via DNS over TLS). Additionally, WebFinger [RFC7033] can be deployed. These alternative methods may be used by Net-RID DP with specific customers.¶

6. Harvesting Broadcast Remote ID messages for UTM Inclusion

ASTM anticipated that regulators would require both Broadcast RID and Network RID for large UAS, but allow RID requirements for small UAS to be satisfied with the operator's choice of either Broadcast RID or Network RID. The EASA initially specified Broadcast RID for UAS of essentially all UAS and is now also considering Network RID. The FAA RID Final Rules [FAA_RID] permit only Broadcast RID for rule compliance, but still encourage Network RID for complementary functionality, especially in support of UTM.¶

One obvious opportunity is to enhance the architecture with gateways from Broadcast RID to Network RID. This provides the best of both and gives regulators and operators flexibility. It offers advantages over either form of RID alone: greater fidelity than Network RID reporting of planned area operations; surveillance of areas too large for local direct visual observation and direct RF-LOS link based Broadcast RID (e.g., a city or a national forest).¶

These gateways could be pre-positioned (e.g. around airports, public gatherings, and other sensitive areas) and/or crowd-sourced (as nothing more than a smartphone with a suitable app is needed). As Broadcast RID media have limited range, gateways receiving messages claiming locations far from the gateway can alert authorities or a SDSP to the failed sanity check possibly indicating intent to deceive. Surveillance SDSPs can use messages with precise date/time/position stamps from the gateways to multilaterate UA location, independent of the locations claimed in the messages, which are entirely operator self-reported in UAS RID and UTM, and thus are subject not only to natural time lag and error but also operator misconfiguration or intentional deception.¶

Further, gateways with additional sensors (e.g. smartphones with cameras) can provide independent information on the UA type and size, confirming or refuting those claims made in the RID messages. This Crowd Sourced Remote ID (CS-RID) would be a significant enhancement, beyond baseline DRIP functionality; if implemented, it adds two more entity types.¶

This approach satisfies the following DRIP requirements defined in [I-D.ietf-drip-reqs]: GEN-5, GEN-11, and REG-1.¶

6.1. The CS-RID Finder

A CS-RID Finder is the gateway for Broadcast Remote ID Messages into the UTM. It performs this gateway function via a CS-RID SDSP. A CS-RID Finder could implement, integrate, or accept outputs from, a Broadcast RID receiver. However, it should not depend upon a direct interface with a GCS, Net-RID SP, Net-RID DP or Network RID client. It would present a TBD interface to a CS-RID SDSP, similar to but readily distinguishable from that between a GCS and a Net-RID SP.¶

6.2. The CS-RID SDSP

A CS-RID SDSP aggregates and processes (e.g., estimates UA location using including using multilateration when possible) information collected by CS-RID Finders. A CS-RID SDSP should appear (i.e. present the same interface) to a Net-RID SP as a Net-RID DP.¶

7. DRIP Contact

One of the ways in which DRIP can enhance [F3411] with immediately actionable information is by enabling an Observer to instantly initiate secure communications with the UAS remote pilot, Pilot In Command, operator, USS under which the operation is being flown, or other entity potentially able to furnish further information regarding the operation and its intent and/or to immediately influence further conduct or termination of the operation (e.g., land or otherwise exit an airspace volume). Such potentially distracting communications demand strong "AAA" (Authentication, Attestation, Authorization, Access Control, Accounting, Attribution, Audit) per applicable policies (e.g., of the cognizant CAA).¶

A DRIP entity identifier based on a HHIT as outlined in Section 3 embeds an identifier of the registry in which it can be found (expected typically to be the USS under which the UAS is flying) and the procedures outlined in Section 5 enable Observer verification of that relationship. A DRIP entity identifier with suitable records in public and private registries as outlined in Section 5 can enable lookup not only of information regarding the UAS but also identities of and pointers to information regarding the various associated entities (e.g., the USS under which the UAS is flying an operation), including means of contacting those associated entities (i.e., locators, typically IP addresses). An Observer equipped with HIP can initiate a Base Exchange (BEX) and establish a Bound End to End Tunnel (BEET) protected by IPsec Encapsulating Security Payload (ESP) encryption to a likewise equipped and identified entity: the UA itself, if operating autonomously; the GCS, if the UA is remotely piloted and the necessary records have been populated in DNS; likewise the USS, etc. Certain preconditions are necessary: each party to the communication needs a currently usable means (typically DNS) of resolving the other party's DRIP entity identifier to a currently usable locator (IP address); and there must be currently usable bidirectional IP (not necessarily Internet) connectivity between the parties. Given a BEET, arbitrary standard higher layer protocols can then be used for Observer to Pilot (O2P) communications (e.g., SIP [RFC3261] et seq), V2X communications (e.g., [MAVLink]), etc. This approach satisfies DRIP requirement GEN-6 Contact, supports satisfaction of requirements [I-D.ietf-drip-reqs] GEN-8, GEN-9, PRIV-2, PRIV-5 and REG-3, and is compatible with all other DRIP requirements.¶

11. References

11.1. Normative References

[I-D.ietf-drip-reqs]: Card, S. W., Wiethuechter, A., Moskowitz, R., and A. Gurtov, "Drone Remote Identification Protocol (DRIP) Requirements", Work in Progress, Internet-Draft, draft-ietf-drip-reqs-18, 8 September 2021, <https://www.ietf.org/archive/id/draft-ietf-drip-reqs-18.txt>.
[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>.

11.2. Informative References

[CTA2063A]: ANSI, "Small Unmanned Aerial Systems Serial Numbers", 2019.
[Delegated]: European Union Aviation Safety Agency (EASA), "EU Commission Delegated Regulation 2019/945 of 12 March 2019 on unmanned aircraft systems and on third-country operators of unmanned aircraft systems", 2019.
[F3411]: ASTM International, "Standard Specification for Remote ID and Tracking", February 2020, <http://www.astm.org/cgi-bin/resolver.cgi?F3411>.
[FAA_RID]: United States Federal Aviation Administration (FAA), "Remote Identification of Unmanned Aircraft", 2021, <https://www.govinfo.gov/content/pkg/FR-2021-01-15/pdf/2020-28948.pdf>.
[FAA_UAS_Concept_Of_Ops]: United States Federal Aviation Administration (FAA), "Unmanned Aircraft System (UAS) Traffic Management (UTM) Concept of Operations (V2.0)", 2020, <https://www.faa.gov/uas/research_development/traffic_management/media/UTM_ConOps_v2.pdf>.
[FS_AEUA]: "Study of Further Architecture Enhancement for UAV and UAM", 2021, <https://www.3gpp.org/ftp/tsg_sa/WG2_Arch/TSGS2_147E_Electronic_2021-10/Docs/S2-2107092.zip>.
[Implementing]: European Union Aviation Safety Agency (EASA), "EU Commission Implementing Regulation 2019/947 of 24 May 2019 on the rules and procedures for the operation of unmanned aircraft", 2019.
[LAANC]: United States Federal Aviation Administration (FAA), "Low Altitude Authorization and Notification Capability", n.d., <https://www.faa.gov/uas/programs_partnerships/data_exchange/>.
[MAVLink]: "Micro Air Vehicle Communication Protocol", 2021, <http://mavlink.io/>.
[NPRM]: United States Federal Aviation Administration (FAA), "Notice of Proposed Rule Making on Remote Identification of Unmanned Aircraft Systems", 2019.
[RFC1034]: Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, <https://www.rfc-editor.org/info/rfc1034>.
[RFC3261]: Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, June 2002, <https://www.rfc-editor.org/info/rfc3261>.
[RFC3972]: Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, DOI 10.17487/RFC3972, March 2005, <https://www.rfc-editor.org/info/rfc3972>.
[RFC5730]: Hollenbeck, S., "Extensible Provisioning Protocol (EPP)", STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009, <https://www.rfc-editor.org/info/rfc5730>.
[RFC5731]: Hollenbeck, S., "Extensible Provisioning Protocol (EPP) Domain Name Mapping", STD 69, RFC 5731, DOI 10.17487/RFC5731, August 2009, <https://www.rfc-editor.org/info/rfc5731>.
[RFC7033]: Jones, P., Salgueiro, G., Jones, M., and J. Smarr, "WebFinger", RFC 7033, DOI 10.17487/RFC7033, September 2013, <https://www.rfc-editor.org/info/rfc7033>.
[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>.
[RFC7482]: Newton, A. and S. Hollenbeck, "Registration Data Access Protocol (RDAP) Query Format", RFC 7482, DOI 10.17487/RFC7482, March 2015, <https://www.rfc-editor.org/info/rfc7482>.
[RFC7483]: Newton, A. and S. Hollenbeck, "JSON Responses for the Registration Data Access Protocol (RDAP)", RFC 7483, DOI 10.17487/RFC7483, March 2015, <https://www.rfc-editor.org/info/rfc7483>.
[RFC7484]: Blanchet, M., "Finding the Authoritative Registration Data (RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March 2015, <https://www.rfc-editor.org/info/rfc7484>.
[RFC7519]: Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, <https://www.rfc-editor.org/info/rfc7519>.
[RFC8004]: Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) Rendezvous Extension", RFC 8004, DOI 10.17487/RFC8004, October 2016, <https://www.rfc-editor.org/info/rfc8004>.
[RFC8005]: Laganier, J., "Host Identity Protocol (HIP) Domain Name System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005, October 2016, <https://www.rfc-editor.org/info/rfc8005>.
[RFC8392]: Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8949]: Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, December 2020, <https://www.rfc-editor.org/info/rfc8949>.
[TS-22.825]: 3GPP, "Study on Remote Identification of Unmanned Aerial Systems (UAS)", n.d., <https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=3527>.
[U-Space]: European Organization for the Safety of Air Navigation (EUROCONTROL), "U-space Concept of Operations", 2019, <https://www.sesarju.eu/sites/default/files/documents/u-space/CORUS%20ConOps%20vol2.pdf>.

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

A.1. Operation Concept

The National Aeronautics and Space Administration (NASA) and FAA's effort of integrating UAS's operation into the national airspace system (NAS) led to the development of the concept of UTM and the ecosystem around it. The UTM concept was initially presented in 2013 and version 2.0 was published in 2020 [FAA_UAS_Concept_Of_Ops].¶

The eventual concept refinement, initial prototype implementation, and testing were conducted by the UTM research transition team which is the joint workforce by FAA and NASA. World efforts took place afterward. The Single European Sky ATM Research (SESAR) started the CORUS project to research its UTM counterpart concept, namely [U-Space]. This effort is led by the European Organization for the Safety of Air Navigation (Eurocontrol).¶

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

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

A.2. UAS Service Supplier (USS)

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

The FAA works with UAS industry shareholders and promotes the Low Altitude Authorization and Notification Capability [LAANC] program which is the first system to realize some of the UTM envisioned functionality. The LAANC program can automate the UAS operational intent (flight plan) submission and application for airspace authorization in real-time by checking against multiple aeronautical databases such as airspace classification and operating rules associated with it, FAA UAS facility map, special use airspace, Notice to Airmen (NOTAM), and Temporary Flight Restriction (TFR).¶

A.3. UTM Use Cases for UAS Operations

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

For a UAS participating in UTM and taking off or landing in a controlled airspace (e.g., Class Bravo, Charlie, Delta, and Echo in the United States), the USS under which the UAS is operating is responsible for verifying UA registration, authenticating the UAS operational intent (flight plan) by checking against designated UAS facility map database, obtaining the air traffic control (ATC) authorization, and monitoring the UAS flight path in order to maintain safe margins and follow the pre-authorized sequence of authorized 4-D volumes (route).¶
For a UAS participating in UTM and taking off or landing in uncontrolled airspace (ex. Class Golf in the United States), pre-flight authorization must be obtained from a USS when operating beyond-visual-of-sight (BVLOS). The USS either accepts or rejects the received operational intent (flight plan) from the UAS. Accepted UAS operation may share its current flight data such as GPS position and altitude to USS. The USS may keep the UAS operation status near real-time and may keep it as a record for overall airspace air traffic monitoring.¶