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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-05) exists of draft-thubert-raw-technologies-04 == Outdated reference: A later version (-04) exists of draft-bernardos-raw-use-cases-03 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RAW N. Maeurer, Ed. 3 Internet-Draft T. Graeupl, Ed. 4 Intended status: Informational German Aerospace Center (DLR) 5 Expires: 3 October 2020 C. Schmitt, Ed. 6 Research Institute CODE, UniBwM 7 1 April 2020 9 L-band Digital Aeronautical Communications System (LDACS) 10 draft-maeurer-raw-ldacs-02 12 Abstract 14 This document provides an overview of the architecture of the L-band 15 Digital Aeronautical Communications System (LDACS), which provides a 16 secure, scalable and spectrum efficient terrestrial data link for 17 civil aviation. LDACS is a scheduled, reliable multi-application 18 cellular broadband system with support for IPv6. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on 3 October 2020. 37 Copyright Notice 39 Copyright (c) 2020 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 44 license-info) in effect on the date of publication of this document. 45 Please review these documents carefully, as they describe your rights 46 and restrictions with respect to this document. Code Components 47 extracted from this document must include Simplified BSD License text 48 as described in Section 4.e of the Trust Legal Provisions and are 49 provided without warranty as described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2.1. Terms used in this document . . . . . . . . . . . . . . . 3 56 3. Motivation and Use Cases . . . . . . . . . . . . . . . . . . 4 57 3.1. Voice Communications Today . . . . . . . . . . . . . . . 4 58 3.2. Data Communications Today . . . . . . . . . . . . . . . . 5 59 4. Provenance and Documents . . . . . . . . . . . . . . . . . . 6 60 5. Characteristics . . . . . . . . . . . . . . . . . . . . . . . 7 61 5.1. LDACS Sub-Network . . . . . . . . . . . . . . . . . . . . 7 62 5.2. LDACS Physical Layer . . . . . . . . . . . . . . . . . . 7 63 5.3. LDACS Data Link Layer . . . . . . . . . . . . . . . . . . 8 64 5.4. LDACS Data Rates . . . . . . . . . . . . . . . . . . . . 8 65 5.5. Reliability and Availability . . . . . . . . . . . . . . 8 66 5.5.1. LDACS Medium Access . . . . . . . . . . . . . . . . . 8 67 5.5.2. LDACS Mobility . . . . . . . . . . . . . . . . . . . 9 68 5.5.3. LDACS Incremental Deployment . . . . . . . . . . . . 10 69 6. Protocol Stack . . . . . . . . . . . . . . . . . . . . . . . 10 70 6.1. Medium Access Control (MAC) Entity Services . . . . . . . 11 71 6.2. Data Link Service (DLS) Entity Services . . . . . . . . . 13 72 6.3. Voice Interface (VI) Services . . . . . . . . . . . . . . 14 73 6.4. LDACS Management Entity (LME) Services . . . . . . . . . 14 74 6.5. Sub-Network Protocol (SNP) Services . . . . . . . . . . . 14 75 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 76 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 15 77 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 78 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 79 11. Normative References . . . . . . . . . . . . . . . . . . . . 16 80 12. Informative References . . . . . . . . . . . . . . . . . . . 16 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 83 1. Introduction 85 One of the main pillars of the modern Air Traffic Management (ATM) 86 system is the existence of a communication infrastructure that 87 enables efficient aircraft control and safe separation in all phases 88 of flight. Current systems are technically mature but suffering from 89 the VHF band's increasing saturation in high-density areas and the 90 limitations posed by analogue radio communications. Therefore, 91 aviation globally and the European Union (EU) in particular, strives 92 for a sustainable modernization of the aeronautical communication 93 infrastructure. 95 In the long-term, ATM communication shall transition from analogue 96 VHF voice and VDL2 communication to more spectrum efficient digital 97 data communication. The European ATM Master Plan foresees this 98 transition to be realized for terrestrial communications by the 99 development (and potential implementation) of the L-band Digital 100 Aeronautical Communications System (LDACS). LDACS shall enable IPv6 101 based air- ground communication related to the aviation safety and 102 regularity of flight. The particular challenge is that no additional 103 spectrum can be made available for terrestrial aeronautical 104 communication. It was thus necessary to develop co-existence 105 mechanism/procedures to enable the interference free operation of 106 LDACS in parallel with other aeronautical services/systems in the 107 same frequency band. 109 2. Terminology 111 2.1. Terms used in this document 113 The following terms are used in the context of RAW in this document: 115 A/A Air-To-Air 116 AeroMACS Aeronautical Mobile Airport Communication System 117 A/G Air-To-Ground 118 AM(R)S Aeronautical Mobile (Route) Service 119 ANSP Air traffic Network Service Provider 120 AOC Aeronautical Operational Control 121 AS Aircraft Station 122 ATC Air-Traffic Control 123 ATM Air-Traffic Management 124 ATN Aeronautical Telecommunication Network 125 ATS Air Traffic Service 126 CCCH Common Control Channel 127 DCCH Dedicated Control Channel 128 DCH Data Channel 129 DLL Data Link Layer 130 DLS Data Link Service 131 DME Distance Measuring Equipment 132 DSB-AM Double Side-Band Amplitude Modulation 133 FAA Federal Aviation Administration 134 FCI Future Communication Infrastructure 135 FDD Frequency Division Duplex 136 FL Forward Link 137 GANP Global Air Navigation Plan 138 GNSS Global Navigation Satellite System 139 GS Ground Station 140 GSC Ground-Station Controller 141 HF High Frequency 142 ICAO International Civil Aviation Organization 143 kbit/s kilobit per second 144 LDACS L-band Digital Aeronautical Communications System 145 LLC Logical Link Layer 146 LME LDACS Management Entity 147 MAC Medium Access Layer 148 MF Multi Frame 149 OFDM Orthogonal Frequency-Division Multiplexing 150 OFDMA Orthogonal Frequency-Division Multiplexing Access 151 PDU Protocol Data Units 152 PHY Physical Layer 153 QoS Quality of Service 154 RL Reverse Link 155 SARPs Standards And Recommended Practices 156 SESAR Single European Sky ATM Research 157 SF Super-Frame 158 SNP Sub-Network Protocol 159 SSB-AM Single Side-Band Amplitude Modulation 160 TBO Trajectory-Based Operations 161 TDM Time Division Multiplexing 162 TDMA Time-Division Multiplexing-Access 163 VDL2 VHF Data Link mode 2 164 VHF Very High Frequency 165 VI Voice Interface 167 3. Motivation and Use Cases 169 Aircraft are currently connected to Air-Traffic Control (ATC) and 170 Airline Operational Control (AOC) via voice and data communications 171 systems through all phases of a flight. Within the airport terminal, 172 connectivity is focused on high bandwidth communications, while 173 during en-route high reliability, robustness, and range is the main 174 focus. Voice communications may use the same or different equipment 175 as data communications systems. In the following the main 176 differences between voice and data communications capabilities are 177 summarized. The assumed use cases for LDACS completes the list of 178 use cases stated in [RAW-USE-CASES] and the list of reliable and 179 available wireless technologies presented in [RAW-TECHNOS]. 181 3.1. Voice Communications Today 183 Voice links are used for Air-To-Ground (A/G) and Air-To-Air (A/A) 184 communications. The communication equipment is either ground-based 185 working in the High Frequency (HF) or Very High Frequency (VHF) 186 frequency band or satellite-based. All VHF and HF voice 187 communications is operated via open broadcast channels without any 188 authentication, encryption or other protective measures. The use of 189 well-proven communication procedures via broadcast channels helps to 190 enhance the safety of communications by taking into account that 191 other users may encounter communication problems and may be 192 supported, if required. The main voice communications media is still 193 the analogue VHF Double Side-Band Amplitude Modulation (DSB-AM) 194 communications technique, supplemented by HF Single Side-Band 195 Amplitude Modulation (SSB-AM) and satellite communications for remote 196 and oceanic areas. DSB-AM has been in use since 1948, works reliably 197 and safely, and uses low-cost communication equipment. These are the 198 main reasons why VHF DSB-AM communications is still in use, and it is 199 likely that this technology will remain in service for many more 200 years. This however results in current operational limitations and 201 becomes impediments in deploying new Air-Traffic Management (ATM) 202 applications, such as flight-centric operation with point-to-point 203 communications. 205 3.2. Data Communications Today 207 Like for voice, data communications into the cockpit is currently 208 provided by ground-based equipment operating either on HF or VHF 209 radio bands or by legacy satellite systems. All these communication 210 systems are using narrowband radio channels with a data throughput 211 capacity of some kilobits per second. While the aircraft is on 212 ground some additional communications systems are available, like 213 Aeronautical Mobile Airport Communication System (AeroMACS; as of now 214 not widely used) or public cellular networks, operating in the 215 Airport (APT) domain and able to deliver broadband communication 216 capability. 218 The data communication networks used for the transmission of data 219 relating to the safety and regularity of the flight must be strictly 220 isolated from those providing entertainment services to passengers. 221 This leads to a situation that the flight crews are supported by 222 narrowband services during flight while passengers have access to 223 inflight broadband services. The current HF and VHF data links 224 cannot provide broadband services now or in the future, due to the 225 lack of available spectrum. This technical shortcoming is becoming a 226 limitation to enhanced ATM operations, such as Trajectory-Based 227 Operations (TBO) and 4D trajectory negotiations. 229 Satellite-based communications are currently under investigation and 230 enhanced capabilities are under development which will be able to 231 provide inflight broadband services and communications supporting the 232 safety and regularity of flight. In parallel, the ground-based 233 broadband data link technology LDACS is being standardized by ICAO 234 and has recently shown its maturity during flight tests [SCH191]. 235 The LDACS technology is scalable, secure and spectrum efficient and 236 provides significant advantages to the users and service providers. 237 It is expected that both - satellite systems and LDACS - will be 238 deployed to support the future aeronautical communication needs as 239 envisaged by the ICAO Global Air Navigation Plan (GANP). 241 4. Provenance and Documents 243 The development of LDACS has already made substantial progress in the 244 Single European Sky ATM Research (SESAR) framework, and is currently 245 being continued in the follow-up program, SESAR2020 [RIH18]. A key 246 objective of the SESAR activities is to develop, implement and 247 validate a modern aeronautical data link able to evolve with aviation 248 needs over long-term. To this end, an LDACS specification has been 249 produced [GRA19] and is continuously updated; transmitter 250 demonstrators were developed to test the spectrum compatibility of 251 LDACS with legacy systems operating in the L-band [SAJ14]; and the 252 overall system performance was analyzed by computer simulations, 253 indicating that LDACS can fulfil the identified requirements [GRA11]. 255 LDACS standardization within the framework of the ICAO started in 256 December 2016. The ICAO standardization group has produced an 257 initial Standards and Recommended Practices (SARPs) document 258 [ICAO18]. The SARPs document defines the general characteristics of 259 LDACS. The ICAO standardization group plans to produce an ICAO 260 technical manual - the ICAO equivalent to a technical standard - 261 within the next years. Generally, the group is open to input from 262 all sources and develops LDACS in the open. 264 Up to now the LDACS standardization has been focused on the 265 development of the physical layer and the data link layer, only 266 recently have higher layers come into the focus of the LDACS 267 development activities. There is currently no "IPv6 over LDACS" 268 specification publicly available; however, SESAR2020 has started the 269 testing of IPv6-based LDACS testbeds. 271 The IPv6 architecture for the aeronautical telecommunication network 272 is called the Future Communications Infrastructure (FCI). FCI shall 273 support quality of service, diversity, and mobility under the 274 umbrella of the "multi-link concept". This work is conducted by ICAO 275 Communication Panel working group WG-I. 277 In addition to standardization activities several industrial LDACS 278 prototypes have been built. One set of LDACS prototypes has been 279 evaluated in flight trials confirming the theoretical results 280 predicting the system performance [GRA18] [SCH191]. 282 5. Characteristics 284 LDACS will become one of several wireless access networks connecting 285 aircraft to both Aeronautical Telecommunications Network (ATN, IPS as 286 well as OSI) and ACARS/FANS networks [FAN19]. 288 5.1. LDACS Sub-Network 290 An LDACS sub-network contains an Access Router (AR), a Ground-Station 291 Controller (GSC), and several Ground-Stations (GS), each of them 292 providing one LDACS radio cell serving up to 512 aircraft stations 293 (AS). User plane interconnection to the ATN is facilitated by the 294 Access Router (AR) peering with an Air/Ground Router (A/G Router) 295 connected to the ATN. It is up to implementer's choice to keep 296 Access Router and Air-Ground Router functions separated, or to merge 297 them. The internal control plane of an LDACS sub-network is managed 298 by the Ground-Station Controller (GSC). An LDACS sub-network is 299 illustrated in Figure 1. 301 wireless user 302 link plane 303 A--------------G-------------Access---A/G-----ATN 304 S..............S Router Router 305 . control . | 306 . plane . | 307 . . | 308 GSC..............| 309 . | 310 . | 311 GS---------------+ 313 Figure 1: LDACS sub-network with two GSs and one AS 315 The LDACS wireless link protocol stack defines two layers, the 316 physical layer and the data link layer. 318 5.2. LDACS Physical Layer 320 The physical layer provides the means to transfer data over the radio 321 channel. The LDACS GS supports bi-directional links to multiple 322 aircraft under its control. The forward link direction (FL; ground- 323 to-air) and the reverse link direction (RL; air-to-ground) are 324 separated by frequency division duplex. Forward link and reverse 325 link use a 500 kHz channel each. The ground-station transmits a 326 continuous stream of Orthogonal Frequency-Division Multiplexing 327 (OFDM) symbols on the forward link. In the reverse link different 328 aircraft are separated in time and frequency using a combination of 329 Orthogonal Frequency-Division Multiple-Access (OFDMA) and Time- 330 Division Multiple-Access (TDMA). Aircraft thus transmit 331 discontinuously on the reverse link with radio bursts sent in 332 precisely defined transmission opportunities allocated by the ground- 333 station. 335 5.3. LDACS Data Link Layer 337 The data-link layer provides the necessary protocols to facilitate 338 concurrent and reliable data transfer for multiple users. The LDACS 339 data link layer is organized in two sub-layers: The medium access 340 sub-layer and the logical link control sub-layer. The medium access 341 sub-layer manages the organization of transmission opportunities in 342 slots of time and frequency. The logical link control sub-layer 343 provides acknowledged point-to-point logical channels between the 344 aircraft and the ground-station using an automatic repeat request 345 protocol. LDACS supports also unacknowledged point-to-point channels 346 and ground-to-air broadcast. 348 5.4. LDACS Data Rates 350 The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the 351 forward link, and 294 kbit/s to 1390 kbit/s on the reverse link, 352 depending on coding and modulation. 354 5.5. Reliability and Availability 356 LDACS has been designed with applications related to the safety and 357 regularity of flight in mind. It has therefore been designed as a 358 deterministic wireless data link (as far as possible). 360 5.5.1. LDACS Medium Access 362 LDACS medium access is always under the control of the ground-station 363 of a radio cell. Any medium access for the transmission of user data 364 has to be requested with a resource request message stating the 365 requested amount of resources and class of service. The ground- 366 station performs resource scheduling on the basis of these requests 367 and grants resources with resource allocation messages. Resource 368 request and allocation messages are exchanged over dedicated 369 contention-free control channels. 371 LDACS has two mechanisms to request resources from the scheduler in 372 the ground-station. 374 Resources can either be requested "on demand" with a given class of 375 service. On the forward link, this is done locally in the ground- 376 station, on the reverse link a dedicated contention-free control 377 channel is used called Dedicated Control Channel (DCCH; roughly 83 378 bit every 60 ms). A resource allocation is always announced in the 379 control channel of the forward link (Common Control Channel (CCCH); 380 variable sized). Due to the spacing of the reverse link control 381 channels every 60 ms, a medium access delay in the same order of 382 magnitude is to be expected. 384 Resources can also be requested "permanently". The permanent 385 resource request mechanism supports requesting recurring resources in 386 given time intervals. A permanent resource request has to be 387 canceled by the user (or by the ground-station, which is always in 388 control). 390 User data transmissions over LDACS are therefore always scheduled by 391 the ground-station, while control data uses statically (i.e. at cell 392 entry) allocated recurring resources (DCCH and CCCH). The current 393 specification documents specify no scheduling algorithm. However 394 performance evaluations so far have used strict priority scheduling 395 and round robin for equal priorities for simplicity. In the current 396 prototype implementations LDACS classes of service are thus realized 397 as priorities of medium access and not as flows. Note that this can 398 starve out low priority flows. However, this is not seen as a big 399 problem since safety related message always go first in any case. 400 Scheduling of reverse link resources is done in physical Protocol 401 Data Units (PDU) of 112 bit (or larger if more aggressive coding and 402 modulation is used). Scheduling on the forward link is done Byte- 403 wise since the forward link is transmitted continuously by the 404 ground-station. 406 The LDACS data link layer protocol running on top of the medium 407 access sub-layer uses ARQ to provide reliable data transmission. 409 5.5.2. LDACS Mobility 411 The LDACS mobility service manages in the GSC and LME cell entry, 412 cell exit and handover between cells. 414 LDACS supports internal handovers to different RF channels. 415 Handovers may be initiated by the aircraft (break-before-make) or by 416 the ground- station (make-before-break). Make-before-break handovers 417 are only supported for ground-stations connected to the same ground- 418 station controller. 420 External handovers between non-connected LDACS deployments or 421 different aeronautical data links shall be handled by the FCI multi- 422 link concept. 424 5.5.3. LDACS Incremental Deployment 426 The LDACS data link provides enhanced capabilities to the future IPv6 427 based ATN enabling it to better support user needs and new 428 applications. The deployment scalability of LDACS allows its 429 implementation to start in areas where most needed to improve 430 immediately the performance of already fielded infrastructure. Later 431 the deployment is extended based on operational demand. 433 6. Protocol Stack 435 The protocol stack of LDACS is implemented in the AS, GS, and GSC: It 436 consists of the Physical Layer (PHY) with five major functional 437 blocks above it. Four are placed in the Data Link Layer (DLL) of the 438 AS and GS: (1) Medium Access Layer (MAC), (2) Voice Interface (VI), 439 (3) Data Link Service (DLS), (4) LDACS Management Entity (LME). The 440 last entity resides within the sub-network layer: Sub-Network 441 Protocol (SNP). The LDACS network is externally connected to voice 442 units, radio control units, and the ATN network layer. 444 Figure 2 shows the protocol stack of LDACS as implemented in the AS 445 and GS. 447 IPv6 network layer 448 | 449 | 450 +------------------+ +----+ 451 | SNP |--| | sub-network 452 | | | | layer 453 +------------------+ | | 454 | | LME| 455 +------------------+ | | 456 | DLS | | | logical link 457 | | | | control layer 458 +------------------+ +----+ 459 | | 460 DCH DCCH/CCCH 461 | RACH/BCCH 462 | | 463 +--------------------------+ 464 | MAC | medium access 465 | | layer 466 +--------------------------+ 467 | 468 +--------------------------+ 469 | PHY | physical layer 470 +--------------------------+ 471 | 472 | 473 ((*)) 474 FL/RL radio channels 475 separated by FDD 477 Figure 2: LDACS protocol stack in AS and GS 479 6.1. Medium Access Control (MAC) Entity Services 481 The MAC time framing service provides the frame structure necessary 482 to realize slot-based Time Division Multiplex (TDM) access on the 483 physical link. It provides the functions for the synchronization of 484 the MAC framing structure and the PHY layer framing. The MAC time 485 framing provides a dedicated time slot for each logical channel. 487 The MAC sub-layer offers access to the physical channel to its 488 service users. Channel access is provided through transparent 489 logical channels. The MAC sub-layer maps logical channels onto the 490 appropriate slots and manages the access to these channels. Logical 491 channels are used as interface between the MAC and LLC sub-layers. 493 The LDACS framing structure for FL and RL is based on Super-Frames 494 (SF) of 240 ms duration. Each SF corresponds to 2000 OFDM symbols. 495 The FL and RL SF boundaries are aligned in time (from the view of the 496 GS). 498 In the FL, an SF contains a Broadcast Frame of duration 6.72 ms (56 499 OFDM symbols) for the Broadcast Control Channel (BCCH), and four 500 Multi-Frames (MF), each of duration 58.32 ms (486 OFDM symbols). 502 In the RL, each SF starts with a Random Access (RA) slot of length 503 6.72 ms with two opportunities for sending reverse link random access 504 frames for the Random Access Channel (RACH), followed by four MFs. 505 These MFs have the same fixed duration of 58.32 ms as in the FL, but 506 a different internal structure 508 Figure 3 and Figure 4 illustrates the LDACS frame structure. 510 ^ 511 | +------+------------+------------+------------+------------+ 512 | FL | BCCH | MF | MF | MF | MF | 513 F +------+------------+------------+------------+------------+ 514 r <---------------- Super-Frame (SF) - 240ms ----------------> 515 e 516 q +------+------------+------------+------------+------------+ 517 u RL | RACH | MF | MF | MF | MF | 518 e +------+------------+------------+------------+------------+ 519 n <---------------- Super-Frame (SF) - 240ms ----------------> 520 c 521 y 522 | 523 ----------------------------- Time ------------------------------> 524 | 526 Figure 3: LDACS super-frame structure 528 ^ 529 | +-------------+------+-------------+ 530 | FL | DCH | CCCH | DCH | 531 F +-------------+------+-------------+ 532 r <---- Multi-Frame (MF) - 58.32ms --> 533 e 534 q +------+---------------------------+ 535 u RL | DCCH | DCH | 536 e +------+---------------------------+ 537 n <---- Multi-Frame (MF) - 58.32ms --> 538 c 539 y 540 | 541 ----------------------------- Time ------------------------------> 542 | 544 Figure 4: LDACS multi-frame (MF) structure 546 6.2. Data Link Service (DLS) Entity Services 548 The DLS provides acknowledged and unacknowledged (including broadcast 549 and packet mode voice) bi-directional exchange of user data. If user 550 data is transmitted using the acknowledged data link service, the 551 sending DLS entity will wait for an acknowledgement from the 552 receiver. If no acknowledgement is received within a specified time 553 frame, the sender may automatically try to retransmit its data. 554 However, after a certain number of failed retries, the sender will 555 suspend further retransmission attempts and inform its client of the 556 failure. 558 The data link service uses the logical channels provided by the MAC: 560 1. A ground-stations announces its existence and access parameters 561 in the Broadcast Channel (BC). 562 2. The Random Access Channel (RA) enables AS to request access to an 563 LDACS cell. 564 3. In the Forward Link (FL) the Common Control Channel (CCCH) is 565 used by the GS to grant access to data channel resources. 566 4. The reverse direction is covered by the Reverse Link (RL), where 567 aircraft-stations need to request resources before sending. This 568 happens via the Dedicated Common Control Channel (DCCH). 569 5. User data itself is communicated in the Data Channel (DCH) on the 570 FL and RL. 572 6.3. Voice Interface (VI) Services 574 The VI provides support for virtual voice circuits. Voice circuits 575 may either be set-up permanently by the GS (e.g., to emulate voice 576 party line) or may be created on demand. The creation and selection 577 of voice circuits is performed in the LME. The VI provides only the 578 transmission services. 580 6.4. LDACS Management Entity (LME) Services 582 The mobility management service in the LME provides support for 583 registration and de-registration (cell entry and cell exit), scanning 584 RF channels of neighboring cells and handover between cells. In 585 addition, it manages the addressing of aircraft/ ASs within cells. 586 It is controlled by the network management service in the GSC. 588 The resource management service provides link maintenance (power, 589 frequency and time adjustments), support for adaptive coding and 590 modulation (ACM), and resource allocation. 592 6.5. Sub-Network Protocol (SNP) Services 594 The data link service provides functions required for the transfer of 595 user plane data and control plane data over the LDACS sub-network. 597 The security service provides functions for secure communication over 598 the LDACS sub-network. Note that the SNP security service applies 599 cryptographic measures as configured by the ground station 600 controller. 602 7. Security Considerations 604 Aviation will require secure exchanges of data and voice messages for 605 managing the air-traffic flow safely through the airspaces all over 606 the world. The main communication method for ATC today is still an 607 open analogue voice broadcast within the aeronautical VHF band. 608 Currently, the information security is purely procedural based by 609 using well-trained personnel and proven communications procedures. 610 This communication method has been in service since 1948. Future 611 digital communications waveforms will need additional embedded 612 security features to fulfill modern information security requirements 613 like authentication and integrity. These security features require 614 sufficient bandwidth which is beyond the capabilities of a VHF 615 narrowband communications system. For voice and data communications, 616 sufficient data throughput capability is needed to support the 617 security functions while not degrading performance. LDACS is a 618 mature data link technology with sufficient bandwidth to support 619 security. 621 Security considerations for LDACS are defined by the official ICAO 622 SARPS [ICAO18]: 624 1. LDACS shall provide a capability to protect the availability and 625 continuity of the system. 626 2. LDACS shall provide a capability including cryptographic 627 mechanisms to protect the integrity of messages in transit. 628 3. LDACS shall provide a capability to ensure the authenticity of 629 messages in transit. 630 4. LDACS should provide a capability for nonrepudiation of origin 631 for messages in transit. 632 5. LDACS should provide a capability to protect the confidentiality 633 of messages in transit. 634 6. LDACS shall provide an authentication capability. 635 7. LDACS shall provide a capability to authorize the permitted 636 actions of users of the system and to deny actions that are not 637 explicitly authorized. 638 8. If LDACS provides interfaces to multiple domains, LDACS shall 639 provide capability to prevent the propagation of intrusions within 640 LDACS domains and towards external domains. 642 The cybersecurity architecture of LDACS [ICAO18], [MAE18] and its 643 extensions [MAE191], [MAE192] regard all of the aforementioned 644 requirements, since LDACS has been mainly designed for air traffic 645 management communication. Thus it supports mutual entity 646 authentication, integrity and confidentiality capabilities of user 647 data messages and some control channel protection capabilities 648 [MAE192]. 650 8. Privacy Considerations 652 LDACS provides a Quality of Service (QoS), and the generic 653 considerations for such mechanisms apply. 655 9. IANA Considerations 657 This memo includes no request to IANA. 659 10. Acknowledgements 661 Thanks to all contributors to the development of LDACS and ICAO PT-T. 663 Thanks to Klaus-Peter Hauf, Bart Van Den Einden, and Pierluigi 664 Fantappie for further input to this draft. 666 Thanks to SBA Research Vienna for fruitful discussions on 667 aeronautical communications concerning security incentives for 668 industry and potential economic spillovers. 670 11. Normative References 672 12. Informative References 674 [MAE191] Maeurer, N., Graeupl, T., and C. Schmitt, "Evaluation of 675 the LDACS Cybersecurity Implementation", IEEE 38th Digital 676 Avionics Systems Conference (DACS), pp. 1-10, San Diego, 677 CA, USA , 2019. 679 [MAE192] Maeurer, N. and C. Schmitt, "Towards Successful 680 Realization of the LDACS Cybersecurity Architecture: An 681 Updated Datalink Security Threat- and Risk Analysis", IEEE 682 Integrated Communications, Navigation and Surveillance 683 Conference (ICNS), pp. 1-13, Herndon, VA, USA , 2019. 685 [GRA19] Graeupl, T., Rihacek, C., and B. Haindl, "LDACS A/G 686 Specification", SESAR2020 PJ14-02-01 D3.3.030 , 2019. 688 [FAN19] Pierattelli, S., Fantappie, P., Tamalet, S., van den 689 Einden, B., Rihacek, C., and T. Graeupl, "LDACS Deployment 690 Options and Recommendations", SESAR2020 PJ14-02-01 691 D3.4.020 , 2019. 693 [MAE18] Maeurer, N. and A. Bilzhause, "A Cybersecurity 694 Architecture for the L-band Digital Aeronautical 695 Communications System (LDACS)", IEEE 37th Digital Avionics 696 Systems Conference (DASC), pp. 1-10, London, UK , 2017. 698 [GRA11] Graeupl, T. and M. Ehammer, "L-DACS1 Data Link Layer 699 Evolution of ATN/IPS", 30th IEEE/AIAA Digital Avionics 700 Systems Conference (DASC), pp. 1-28, Seattle, WA, USA , 701 2011. 703 [GRA18] Graeupl, T., Schneckenburger, N., Jost, T., Schnell, M., 704 Filip, A., Bellido-Manganell, M.A., Mielke, D.M., Maeurer, 705 N., Kumar, R., Osechas, O., and G. Battista, "L-band 706 Digital Aeronautical Communications System (LDACS) flight 707 trials in the national German project MICONAV", Integrated 708 Communications, Navigation, Surveillance Conference 709 (ICNS), pp. 1-7, Herndon, VA, USA , 2018. 711 [SCH191] Schnell, M., "DLR Tests Digital Communications 712 Technologies Combined with Additional Navigation Functions 713 for the First Time", 2019. 715 [ICAO18] International Civil Aviation Organization (ICAO), "L-Band 716 Digital Aeronautical Communication System (LDACS)", 717 International Standards and Recommended Practices Annex 10 718 - Aeronautical Telecommunications, Vol. III - 719 Communication Systems , 2018. 721 [SAJ14] Haindl, B., Meser, J., Sajatovic, M., Mueller, S., 722 Arthaber, H., Faseth, T., and M. Zaisberger, "LDACS1 723 Conformance and Compatibility Assessment", IEEE/AIAA 33rd 724 Digital Avionics Systems Conference (DASC), pp. 1-11, 725 Colorado Springs, CO, USA , 2014. 727 [RIH18] Rihacek, C., Haindl, B., Fantappie, P., Pierattelli, S., 728 Graeupl, T., Schnell, M., and N. Fistas, "L-band Digital 729 Aeronautical Communications System (LDACS) Activities in 730 SESAR2020", Integrated Communications Navigation and 731 Surveillance Conference (ICNS), pp. 1-8, Herndon, VA, 732 USA , 2018. 734 [RAW-TECHNOS] 735 Thubert, P., Cavalcanti, D., Vilajosana, X., and C. 736 Schmitt, "Reliable and Available Wireless Technologies", 737 Work in Progress, Internet-Draft, draft-thubert-raw- 738 technologies-04, 6 January 2020, 739 . 742 [RAW-USE-CASES] 743 Papadopoulos, G., Thubert, P., Theoleyre, F., and C. 744 Bernardos, "RAW use cases", Work in Progress, Internet- 745 Draft, draft-bernardos-raw-use-cases-03, 8 March 2020, 746 . 749 Authors' Addresses 751 Nils Maeurer (editor) 752 German Aerospace Center (DLR) 753 Muenchner Strasse 20 754 82234 Wessling 755 Germany 757 Email: Nils.Maeurer@dlr.de 759 Thomas Graeupl (editor) 760 German Aerospace Center (DLR) 761 Muenchner Strasse 20 762 82234 Wessling 763 Germany 765 Email: Thomas.Graeupl@dlr.de 767 Corinna Schmitt (editor) 768 Research Institute CODE, UniBwM 769 Werner-Heisenberg-Weg 28 770 85577 Neubiberg 771 Germany 773 Email: corinna.schmitt@unibw.de