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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'SAJ14' is mentioned on line 255, but not defined == Outdated reference: A later version (-05) exists of draft-thubert-raw-technologies-04 == Outdated reference: A later version (-04) exists of draft-bernardos-raw-use-cases-01 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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: 7 September 2020 C. Schmitt, Ed. 6 Research Institute CODE, UniBwM 7 6 March 2020 9 L-band Digital Aeronautical Communications System (LDACS) 10 draft-maeurer-raw-ldacs-01 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 7 September 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 . . . . . . . . . . . . . . . 5 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 . . . . . . . . . . . . . . . . . . 8 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 . . . . . . . . . . . . . . . . . 9 67 5.5.2. LDACS Mobility . . . . . . . . . . . . . . . . . . . 10 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 DetNet in this 114 document: 116 A/A Air-To-Air 117 AeroMACS Aeronautical Mobile Airport Communication System 118 A/G Air-To-Ground 119 AM(R)S Aeronautical Mobile (Route) Service 120 ANSP Air traffic Network Service Provider 121 AOC Aeronautical Operational Control 122 AS Aircraft Station 123 ATC Air-Traffic Control 124 ATM Air-Traffic Management 125 ATN Aeronautical Telecommunication Network 126 ATS Air Traffic Service 127 CCCH Common Control Channel 128 DCCH Dedicated Control Channel 129 DCH Data Channel 130 DLL Data Link Layer 131 DLS Data Link Service 132 DME Distance Measuring Equipment 133 DSB-AM Double Side-Band Amplitude Modulation 134 FAA Federal Aviation Administration 135 FCI Future Communication Infrastructure 136 FDD Frequency Division Duplex 137 FL Forward Link 138 GANP Global Air Navigation Plan 139 GNSS Global Navigation Satellite System 140 GS Ground Station 141 GSC Ground-Station Controller 142 HF High Frequency 143 ICAO International Civil Aviation Organization 144 IWF Interworking Function 145 kbit/s kilobit per secong 146 LDACS L-band Digital Aeronautical Communications System 147 LLC Logical Link Layer 148 LME LDACS Management Entity 149 MAC Medium Access Layer 150 MF Multi Frame 151 MIMO Multiple Input Multiple Output 152 OFDM Orthogonal Frequency-Division Multiplexing 153 OFDMA Orthogonal Frequency-Division Multiplexing Access 154 PDU Protocol Data Units 155 PHY Physical Layer 156 QoS Quality of Service 157 RL Reverse Link 158 SARPs Standards And Recommended Practices 159 SESAR Single European Sky ATM Research 160 SF Super-Frame 161 SNP Sub-Network Protocol 162 SSB-AM Single Side-Band Amplitude Modulation 163 SNDCF Sub-Network Dependent Convergence Function 164 TBO Trajectory-Based Operations 165 TDM Time Division Multiplexing 166 TDMA Time-Division Multiplexing-Access 167 VDL2 VHF Data Link mode 2 168 VHF Very High Frequency 169 VI Voice Interface 171 3. Motivation and Use Cases 173 Aircraft are currently connected to Air-Traffic Control (ATC) and 174 Airline Operational Control (AOC) via voice and data communications 175 systems through all phases of a flight. Within the airport terminal, 176 connectivity is focused on high bandwidth communications, while 177 during en-route high reliability, robustness, and range is the main 178 focus. Voice communications may use the same or different equipment 179 as data communications systems. In the following the main 180 differences between voice and data communications capabilities are 181 summarized. The assumed use cases for LDACS completes the list of 182 use cases stated in [RAW-USE-CASES] and the list of reliable and 183 available wireless technologies presented in [RAW-TECHNOS]. 185 3.1. Voice Communications Today 187 Voice links are used for Air-To-Ground (A/G) and Air-To-Air (A/A) 188 communications. The communication equipment is either ground-based 189 working in the High Frequency (HF) or Very High Frequency (VHF) 190 frequency band or satellite-based. All VHF and HF voice 191 communications is operated via open broadcast channels without any 192 authentication, encryption or other protective measures. The use of 193 well-proven communication procedures via broadcast channels helps to 194 enhance the safety of communications by taking into account that 195 other users may encounter communication problems and may be 196 supported, if required. The main voice communications media is still 197 the analogue VHF Double Side-Band Amplitude Modulation (DSB-AM) 198 communications technique, supplemented by HF Single Side-Band 199 Amplitude Modulation (SSB-AM) and satellite communications for remote 200 and oceanic areas. DSB-AM has been in use since 1948, works reliably 201 and safely, and uses low-cost communication equipment. These are the 202 main reasons why VHF DSB-AM communications is still in use, and it is 203 likely that this technology will remain in service for many more 204 years. This however results in current operational limitations and 205 becomes impediments in deploying new Air-Traffic Management (ATM) 206 applications, such as flight-centric operation with point-to-point 207 communications. 209 3.2. Data Communications Today 211 Like for voice, data communications into the cockpit is currently 212 provided by ground-based equipment operating either on HF or VHF 213 radio bands or by legacy satellite systems. All these communication 214 systems are using narrowband radio channels with a data throughput 215 capacity of some kilobits per second. While the aircraft is on 216 ground some additional communications systems are available, like 217 Aeronautical Mobile Airport Communication System (AeroMACS; as of now 218 not widely used) or public cellular networks, operating in the 219 Airport (APT) domain and able to deliver broadband communication 220 capability. 222 The data communication networks used for the transmission of data 223 relating to the safety and regularity of the flight must be strictly 224 isolated from those providing entertainment services to passengers. 225 This leads to a situation that the flight crews are supported by 226 narrowband services during flight while passengers have access to 227 inflight broadband services. The current HF and VHF data links 228 cannot provide broadband services now or in the future, due to the 229 lack of available spectrum. This technical shortcoming is becoming a 230 limitation to enhanced ATM operations, such as Trajectory-Based 231 Operations (TBO) and 4D trajectory negotiations. 233 Satellite-based communications are currently under investigation and 234 enhanced capabilities are under development which will be able to 235 provide inflight broadband services and communications supporting the 236 safety and regularity of flight. In parallel, the ground-based 237 broadband data link technology LDACS is being standardized by ICAO 238 and has recently shown its maturity during flight tests [SCH191]. 239 The LDACS technology is scalable, secure and spectrum efficient and 240 provides significant advantages to the users and service providers. 241 It is expected that both - satellite systems and LDACS - will be 242 deployed to support the future aeronautical communication needs as 243 envisaged by the ICAO Global Air Navigation Plan (GANP). 245 4. Provenance and Documents 247 The development of LDACS has already made substantial progress in the 248 Single European Sky ATM Research (SESAR) framework, and is currently 249 being continued in the follow-up program, SESAR2020 [RIH18]. A key 250 objective of the SESAR activities is to develop, implement and 251 validate a modern aeronautical data link able to evolve with aviation 252 needs over long-term. To this end, an LDACS specification has been 253 produced [GRA19] and is continuously updated; transmitter 254 demonstrators were developed to test the spectrum compatibility of 255 LDACS with legacy systems operating in the L-band [SAJ14]; and the 256 overall system performance was analyzed by computer simulations, 257 indicating that LDACS can fulfil the identified requirements [GRA11]. 259 LDACS standardization within the framework of the ICAO started in 260 December 2016. The ICAO standardization group has produced an 261 initial Standards and Recommended Practices (SARPs) document 262 [ICAO18]. The SARPs document defines the general characteristics of 263 LDACS. The ICAO standardization group plans to produce an ICAO 264 technical manual - the ICAO equivalent to a technical standard - 265 within the next years. Generally, the group is open to input from 266 all sources and develops LDACS in the open. 268 Up to now the LDACS standardization has been focused on the 269 development of the physical layer and the data link layer, only 270 recently have higher layers come into the focus of the LDACS 271 development activities. There is currently no "IPv6 over LDACS" 272 specification publicly available; however, SESAR2020 has started the 273 testing of IPv6-based LDACS testbeds. 275 The IPv6 architecture for the aeronautical telecommunication network 276 is called the Future Communications Infrastructure (FCI). FCI shall 277 support quality of service, diversity, and mobility under the 278 umbrella of the "multi-link concept". This work is conducted by ICAO 279 Communication Panel working group WG-I. 281 In addition to standardization activities several industrial LDACS 282 prototypes have been built. One set of LDACS prototypes has been 283 evaluated in flight trials confirming the theoretical results 284 predicting the system performance [GRA18] [SCH191]. 286 5. Characteristics 288 LDACS will become one of several wireless access networks connecting 289 aircraft to both Aeronautical Telecommunications Network (ATN, IPS as 290 well as OSI) and ACARS/FANS networks [FAN19]. 292 5.1. LDACS Sub-Network 294 An LDACS sub-network contains an Access Router (AR), a Ground-Station 295 Controller (GSC), and several Ground-Stations (GS), each of them 296 providing one LDACS radio cell serving up to 512 aircraft stations 297 (AS). User plane interconnection to the ATN is facilitated by the 298 Access Router (AR) peering with an Air/Ground Router (A/G Router) 299 connected to the ATN. It is up to implementor's choice to keep 300 Access Router and Air-Ground Router functions separated, or to merge 301 them. The internal control plane of an LDACS sub-network is managed 302 by the Ground-Station Controller (GSC). An LDACS sub-network is 303 illustrated in Figure 1. 305 wireless user 306 link plane 307 A--------------G-------------Access---A/G-----ATN 308 S..............S Router Router 309 . control . | 310 . plane . | 311 . . | 312 GSC.............. | 313 . | 314 . | 315 GS----------------+ 317 Figure 1: LDACS sub-network with two GSs and one AS 319 The LDACS wireless link protocol stack defines two layers, the 320 physical layer and the data link layer. 322 5.2. LDACS Physical Layer 324 The physical layer provides the means to transfer data over the radio 325 channel. The LDACS GS supports bi-directional links to multiple 326 aircraft under its control. The forward link direction (FL; ground- 327 to-air) and the reverse link direction (RL; air-to-ground) are 328 separated by frequency division duplex. Forward link and reverse 329 link use a 500 kHz channel each. The ground-station transmits a 330 continuous stream of Orthogonal Frequency-Division Multiplexing 331 (OFDM) symbols on the forward link. In the reverse link different 332 aircraft are separated in time and frequency using a combination of 333 Orthogonal Frequency-Division Multiple-Access (OFDMA) and Time- 334 Division Multiple-Access (TDMA). Aircraft thus transmit 335 discontinuously on the reverse link with radio bursts sent in 336 precisely defined transmission opportunities allocated by the ground- 337 station. 339 5.3. LDACS Data Link Layer 341 The data-link layer provides the necessary protocols to facilitate 342 concurrent and reliable data transfer for multiple users. The LDACS 343 data link layer is organized in two sub-layers: The medium access 344 sub-layer and the logical link control sub-layer. The medium access 345 sub-layer manages the organization of transmission opportunities in 346 slots of time and frequency. The logical link control sub-layer 347 provides acknowledged point-to-point logical channels between the 348 aircraft and the ground-station using an automatic repeat request 349 protocol. LDACS supports also unacknowledged point-to-point channels 350 and ground-to-air broadcast. 352 5.4. LDACS Data Rates 354 The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the 355 forward link, and 294 kbit/s to 1390 kbit/s on the reverse link, 356 depending on coding and modulation. 358 5.5. Reliability and Availability 360 LDACS has been designed with applications related to the safety and 361 regularity of flight in mind. It has therefore been designed as a 362 deterministic wireless data link (as far as possible). 364 5.5.1. LDACS Medium Access 366 LDACS medium access is always under the control of the ground-station 367 of a radio cell. Any medium access for the transmission of user data 368 has to be requested with a resource request message stating the 369 requested amount of resources and class of service. The ground- 370 station performs resource scheduling on the basis of these requests 371 and grants resources with resource allocation messages. Resource 372 request and allocation messages are exchanged over dedicated 373 contention-free control channels. 375 LDACS has two mechanisms to request resources from the scheduler in 376 the ground-station. 378 Resources can either be requested "on demand" with a given class of 379 service. On the forward link, this is done locally in the ground- 380 station, on the reverse link a dedicated contention-free control 381 channel is used called Dedicated Control Channel (DCCH; roughly 83 382 bit every 60 ms). A resource allocation is always announced in the 383 control channel of the forward link (Common Control Channel (CCCH); 384 variable sized). Due to the spacing of the reverse link control 385 channels every 60 ms, a medium access delay in the same order of 386 magnitude is to be expected. 388 Resources can also be requested "permanently". The permanent 389 resource request mechanism supports requesting recurring resources in 390 given time intervals. A permanent resource request has to be 391 canceled by the user (or by the ground-station, which is always in 392 control). 394 User data transmissions over LDACS are therefore always scheduled by 395 the ground-station, while control data uses statically (i.e. at cell 396 entry) allocated recurring resources (DCCH and CCCH). The current 397 specification documents specify no scheduling algorithm. However 398 performance evaluations so far have used strict priority scheduling 399 and round robin for equal priorities for simplicity. In the current 400 prototype implementations LDACS classes of service are thus realized 401 as priorities of medium access and not as flows. Note that this can 402 starve out low priority flows. However, this is not seen as a big 403 problem since safety related message always go first in any case. 404 Scheduling of reverse link resources is done in physical Protocol 405 Data Units (PDU) of 112 bit (or larger if more aggressive coding and 406 modulation is used). Scheduling on the forward link is done Byte- 407 wise since the forward link is transmitted continuously bythe ground- 408 station. 410 The LDACS data link layer protocol running on top of the medium 411 access sub-layer uses ARQ to provide reliable data transmission. 413 5.5.2. LDACS Mobility 415 The LDACS mobility service manages in the GSC and LME cell entry, 416 cell exit and handover between cells. 418 LDACS supports internal handovers to different RF channels. 419 Handovers may be initiated by the aircraft (break-before-make) or by 420 the ground- station (make-before-break). Make-before-break handovers 421 are only supported for ground-stations connected to the same ground- 422 station controller. 424 External handovers between non-connected LDACS deployments or 425 different aeronautical data links shall be handled by the FCI multi- 426 link concept. 428 5.5.3. LDACS Incremental Deployment 430 The LDACS data link provides enhanced capabilities to the future IPv6 431 based ATN enabling it to better support user needs and new 432 applications. The deployment scalability of LDACS allows its 433 implementation to start in areas where most needed to improve 434 immediately the performance of already fielded infrastructure. Later 435 the deployment is extended based on operational demand. 437 6. Protocol Stack 439 The protocol stack of LDACS is implemented in the AS, GS, and GSC: It 440 consists of the Physical Layer (PHY) with five major functional 441 blocks above it. Four are placed in the Data Link Layer (DLL) of the 442 AS and GS: (1) Medium Access Layer (MAC), (2) Voice Interface (VI), 443 (3) Data Link Service (DLS), (4) LDACS Management Entity (LME). The 444 last entity resides within the sub-network layer: Sub-Network 445 Protocol (SNP). The LDACS network is externally connected to voice 446 units, radio control units, and the ATN network layer. 448 Figure 2 shows the protocol stack of LDACS as implemented in the AS 449 and GS. 451 IPv6 network layer 452 | 453 | 454 +------------------+ +----+ 455 | SNP |--| | sub-network 456 | | | | layer 457 +------------------+ | | 458 | | LME| 459 +------------------+ | | 460 | DLS | | | logical link 461 | | | | control layer 462 +------------------+ +----+ 463 | | 464 DCH DCCH/CCCH 465 | RACH/BCCH 466 | | 467 +--------------------------+ 468 | MAC | medium access 469 | | layer 470 +--------------------------+ 471 | 472 +--------------------------+ 473 | PHY | physical layer 474 +--------------------------+ 475 | 476 | 477 ((*)) 478 FL/RL radio channels 479 separated by FDD 481 Figure 2: LDACS protocol stack in AS and GS 483 6.1. Medium Access Control (MAC) Entity Services 485 The MAC time framing service provides the frame structure necessary 486 to realize slot-based Time Division Multiplex (TDM) access on the 487 physical link. It provides the functions for the synchronization of 488 the MAC framing structure and the PHY layer framing. The MAC time 489 framing provides a dedicated time slot for each logical channel. 491 The MAC sub-layer offers access to the physical channel to its 492 service users. Channel access is provided through transparent 493 logical channels. The MAC sub-layer maps logical channels onto the 494 appropriate slots and manages the access to these channels. Logical 495 channels are used as interface between the MAC and LLC sub-layers. 497 The LDACS framing structure for FL and RL is based on Super-Frames 498 (SF) of 240 ms duration. Each SF corresponds to 2000 OFDM symbols. 499 The FL and RL SF boundaries are aligned in time (from the view of the 500 GS). 502 In the FL, an SF contains a Broadcast Frame of duration 6.72 ms (56 503 OFDM symbols) for the Broadcast Control Channel (BCCH), and four 504 Multi-Frames (MF), each of duration 58.32 ms (486 OFDM symbols). 506 In the RL, each SF starts with a Random Access (RA) slot of length 507 6.72 ms with two opportunities for sending reverse link random access 508 frames for the Random Access Channel (RACH), followed by four MFs. 509 These MFs have the same fixed duration of 58.32 ms as in the FL, but 510 a different internal structure 512 Figure 3 and Figure 2 illustrates the LDACS frame structure. 514 ^ 515 | +------+------------+------------+------------+------------+ 516 | FL | BCCH | MF | MF | MF | MF | 517 F +------+------------+------------+------------+------------+ 518 r <---------------- Super-Frame (SF) - 240ms ----------------> 519 e 520 q +------+------------+------------+------------+------------+ 521 u RL | RACH | MF | MF | MF | MF | 522 e +------+------------+------------+------------+------------+ 523 n <---------------- Super-Frame (SF) - 240ms ----------------> 524 c 525 y 526 | 527 ----------------------------- Time ------------------------------> 528 | 530 Figure 3: LDACS super-frame structure 532 ^ 533 | +-------------+------+-------------+ 534 | FL | DCH | CCCH | DCH | 535 F +-------------+------+-------------+ 536 r <---- Multi-Frame (MF) - 58.32ms --> 537 e 538 q +------+---------------------------+ 539 u RL | DCCH | DCH | 540 e +------+---------------------------+ 541 n <---- Multi-Frame (MF) - 58.32ms --> 542 c 543 y 544 | 545 ----------------------------- Time ------------------------------> 546 | 548 Figure 4: LDACS multi-frame (MF) structure 550 6.2. Data Link Service (DLS) Entity Services 552 The DLS provides acknowledged and unacknowledged (including broadcast 553 and packet mode voice) bi-directional exchange of user data. If user 554 data is transmitted using the acknowledged data link service, the 555 sending DLS entity will wait for an acknowledgement from the 556 receiver. If no acknowledgement is received within a specified time 557 frame, the sender may automatically try to retransmit its data. 558 However, after a certain number of failed retries, the sender will 559 suspend further retransmission attempts and inform its client of the 560 failure. 562 The data link service uses the logical channels provided by the MAC: 564 1. A ground-stations announces its existence and access parameters 565 in the Broadcast Channel (BC). 566 2. The Random Access Channel (RA) enables AS to request access to an 567 LDACS cell. 568 3. In the Forward Link (FL) the Common Control Channel (CCCH) is 569 used by the GS to grant access to data channel resources. 570 4. The reverse direction is covered by the Reverse Link (RL), where 571 aircraft-stations need to request resources before sending. This 572 happens via the Dedicated Common Control Channel (DCCH). 573 5. User data itself is communicated in the Data Channel (DCH) on the 574 FL and RL. 576 This is illustrated in Figure 2. 578 6.3. Voice Interface (VI) Services 580 The VI provides support for virtual voice circuits. Voice circuits 581 may either be set-up permanently by the GS (e.g. to emulate voice 582 party line) or may be created on demand. The creation and selection 583 of voice circuits is performed in the LME. The VI provides only the 584 transmission services. 586 6.4. LDACS Management Entity (LME) Services 588 The mobility management service in the LME provides support for 589 registration and de-registration (cell entry and cell exit), scanning 590 RF channels of neighbouring cells and handover between cells. In 591 addition, it manages the addressing of aircraft/ ASs within cells. 592 It is controlled by the network management service in the GSC. 594 The resource management service provides link maintenance (power, 595 frequency and time adjustments), support for adaptive coding and 596 modulation (ACM), and resource allocation. 598 6.5. Sub-Network Protocol (SNP) Services 600 The data link service provides functions required for the transfer of 601 user plane data and control plane data over the LDACS sub-network. 603 The security service provides functions for secure communication over 604 the LDACS sub-network. Note that the SNP security service applies 605 cryptographic measures as configured by the ground station 606 controller. 608 7. Security Considerations 610 Aviation will require secure exchanges of data and voice messages for 611 managing the air-traffic flow safely through the airspaces all over 612 the world. The main communication method for ATC today is still an 613 open analogue voice broadcast within the aeronautical VHF band. 614 Currently, the information security is purely procedural based by 615 using well-trained personnel and proven communications procedures. 616 This communication method has been in service since 1948. Future 617 digital communications waveforms will need additional embedded 618 security features to fulfill modern information security requirements 619 like authentication and integrity. These security features require 620 sufficient bandwidth which is beyond the capabilities of a VHF 621 narrowband communications system. For voice and data communications, 622 sufficient data throughput capability is needed to support the 623 security functions while not degrading performance. LDACS is a 624 mature data link technology with sufficient bandwidth to support 625 security. 627 Security considerations for LDACS are defined by the official ICAO 628 SARPS [ICAO18]: 630 1. LDACS shall provide a capability to protect the availability and 631 continuity of the system. 632 2. LDACS shall provide a capability including cryptographic 633 mechanisms to protect the integrity of messages in transit. 634 3. LDACS shall provide a capability to ensure the authenticity of 635 messages in transit. 636 4. LDACS should provide a capability for nonrepudiation of origin 637 for messages in transit. 638 5. LDACS should provide a capability to protect the confidentiality 639 of messages in transit. 640 6. LDACS shall provide an authentication capability. 641 7. LDACS shall provide a capability to authorize the permitted 642 actions of users of the system and to deny actions that are not 643 explicitly authorized. 644 8. If LDACS provides interfaces to multiple domains, LDACS shall 645 provide capability to prevent the propagation of intrusions within 646 LDACS domains and towards external domains. 648 The cybersecurity architecture of LDACS [ICAO18], [MAE18] and its 649 extensions [MAE191], [MAE192] regard all of the aforementioned 650 requirements, since LDACS has been mainly designed for air traffic 651 management communication. Thus it supports mutual entity 652 authentication, integrity and confidentiality capabilities of user 653 data messages and some control channel protection capabilities 654 [MAE192]. 656 8. Privacy Considerations 658 LDACS provides a Quality of Service (QoS), and the generic 659 considerations for such mechanisms apply. 661 9. IANA Considerations 663 This memo includes no request to IANA. 665 10. Acknowledgements 667 Thanks to all contributors to the development of LDACS and ICAO PT-T. 669 Thanks to Klaus-Peter Hauf, Bart Van Den Einden, and Pierluigi 670 Fantappie for further input to this draft. 672 Further, thanks to SBA Research Vienna for fruitful discussions on 673 aeronautical communications concerning security incentives for 674 industry and potential economic spillovers. 676 11. Normative References 678 12. Informative References 680 [MAE191] Maeurer, N., Graeupl, T., and C. Schmitt, "Evaluation of 681 the LDACS Cybersecurity Implementation", IEEE 38th Digital 682 Avionics Systems Conference (DACS), pp. 1-10, New York, 683 NY, USA , 2019. 685 [MAE192] Maeurer, N. and C. Schmitt, "Towards Successful 686 Realization of the LDACS Cybersecurity Architecture: An 687 Updated Datalink Security Threat- and Risk Analysis", IEEE 688 Integrated Communications, Navigation and Surveillance 689 Conference (ICNS), pp. 1-13, New York, NY, USA , 2019. 691 [GRA19] Graeupl, T., Rihacek, C., and B. Haindl, "LDACS A/G 692 Specification", German Aerospace Center (DLR), Germany, 693 SESAR2020 PJ14-02-01 D3.3.010 , 2017. 695 [FAN19] Pierattelli, S., Fantappie, P., Tamalet, S., van den 696 Einden, B., Rihacek, C., and T. Graeupl, "LDACS Deployment 697 Options and Recommendations", German Aerospace Center 698 (DLR), Germany, SESAR2020 PJ14-02-01 D3.4.020 , 2019. 700 [MAE18] Maeurer, N. and A. Bilzhause, "A Cybersecurity 701 Architecture for the L-band Digital Aeronautical 702 Communications System (LDACS)", IEEE 37th Digital Avionics 703 Systems Conference (DASC), pp. 1-10, New York, NY, USA , 704 2017. 706 [GRA11] Graeupl, T. and M. Ehammer, "L-DACS1 Data Link Layer 707 Evolution of ATN/IPS", 30th IEEE/AIAA Digital Avionics 708 Systems Conference (DASC), pp. 1-28, New York, NY, USA , 709 2011. 711 [GRA18] Graeupl, T., Schneckenburger, N., Jost, T., Schnell, M., 712 Filip, A., Bellido-Manganell, M.A., Mielke, D.M., Maeurer, 713 N., Kumar, R., Osechas, O., and G. Battista, "L-band 714 Digital Aeronautical Communications System (LDACS) flight 715 trials in the national German project MICONAV", Integrated 716 Communications, Navigation, Surveillance Conference 717 (ICNS), pp. 1-7, New York, NY, USA , 2018. 719 [SCH191] Schnell, M., "DLR Tests Digital Communications 720 Technologies Combined with Additional Navigation Functions 721 for the First Time", 2019. 723 [ICAO18] International Civil Aviation Organization (ICAO), "L-Band 724 Digital Aeronautical Communication System (LDACS)", 725 International Standards and Recommended Practices Annex 10 726 - Aeronautical Telecommunications, Vol. III - 727 Communication Systems , 2018. 729 [RIH18] Rihacek, C., Haindl, B., Fantappie, P., Pierattelli, S., 730 Graeupl, T., Schnell, M., and N. Fistas, "LDACS A/G 731 Specification", Integrated Communications Navigation and 732 Surveillance Conference (ICNS), pp. 1-8, New York, NY, 733 USA , 2018. 735 [RAW-TECHNOS] 736 Thubert, P., Cavalcanti, D., Vilajosana, X., and C. 737 Schmitt, "Reliable and Available Wireless Technologies", 738 Work in Progress, Internet-Draft, draft-thubert-raw- 739 technologies-04, 6 January 2020, 740 . 743 [RAW-USE-CASES] 744 Papadopoulos, G., Thubert, P., Theoleyre, F., and C. 745 Bernardos, "RAW use cases", Work in Progress, Internet- 746 Draft, draft-bernardos-raw-use-cases-01, 4 November 2019, 747 . 750 Authors' Addresses 752 Nils Maeurer (editor) 753 German Aerospace Center (DLR) 754 Muenchner Strasse 20 755 82234 Wessling 756 Germany 758 Email: Nils.Maeurer@dlr.de 760 Thomas Graeupl (editor) 761 German Aerospace Center (DLR) 762 Muenchner Strasse 20 763 82234 Wessling 764 Germany 766 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