Publication: Magyar Közlöny
Issue: MK-2009-104 (Year: 2009, Number: 104)
Era: 2004-2010
Section: 
Paragraph Index: 1810

c) non-use, or restricted use, of remote access to ATN ground end system, intermediate systems and SM workstations. 3.9.2 ATN security policy Note.— Communication monitoring and third party traffic analysis do not constitute safety hazards and are not considered security threats for the ATSC. However, some ATS and/or non-ATS users and applications may have local, or Part I Annex 10 — Aeronautical Communications I-3-15 22/11/07 organizational, policies wherein communication monitoring and third party traffic analysis would be considered security threats based on other concerns, such as economic considerations. 3.9.2.1 ATS messages shall be protected from masquerade, modification and replay. Note 1. — This means that for data messages exchanged among ATN entities there will be a high level of assurance that a message comes from where it claims, has not been tampered with, and is not a repeat of an obsolete message. Note 2. — The level of protection may vary by the type of security threat and by the level of ATN security service selected by the user or application process. 3.9.2.2 A request for protection of ATS messages shall be honoured. Note.— A request for non-use of protection may be honoured. This means that the use of security is the default and negotiation to non-use is based on local policy. 3.9.2.3 The ATN services that support messages to and from the aircraft shall be protected against denial of service attacks to a level of probability consistent with the required application service availability as determined by local policies. Note 1.— The term “denial of service” describes a condition where legitimate access to information or other ATN resources is deliberately impeded. Note 2.— This may mean having alternative communications paths available in case one path is subject to denial of service. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-3-16 TABLES FOR CHAPTER 3 Table 3-1. Transit delays for ATSC classes Maximum one-way ATN end-to-end transit delay at 95% probability (seconds) ATSC class Reserved A 4.5 B 7.2 C 13.5 D E F G H No value specified no preference Note 1.— The value for the ATN end-to-end transit delay represents approximately 90% of the value for the total end-to-end transit delay between the ultimate users of the system. Note 2.— The 95% probability is based on the availability of a route conforming to the requested ATSC class. Part I Annex 10 — Aeronautical Communications I-3-17 22/11/07 Table 3-2. Mapping of ATN communication priorities Corresponding protocol priority Message categories ATN application Transport layer priority Network layer priority Network/systems management SM Distress communications Urgent communications High-priority flight safety messages CPDLC, ADS Normal-priority flight safety messages AIDC, ATIS Meteorological communications METAR Flight regularity communications CM, ATSMHS Aeronautical information service messages Network/systems administration SM, DIR Aeronautical administrative messages <unassigned> Urgent-priority administrative and U.N. Charter communications High-priority administrative and State/Government communications Normal-priority administrative communications Low-priority administrative communications and aeronautical passenger communications Note.— The network layer priorities shown in the table apply only to connectionless network priority and do not apply to subnetwork priority. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-3-18 Table 3-3. Mapping of ATN network priority to mobile subnetwork priority Corresponding mobile subnetwork priority (see Note 4) Message categories ATN network layer priority AMSS VDL Mode 2 VDL Mode 3 VDL Mode 4 (see Note 5) SSR Mode S HFDL Network/systems management see Note 1 high high Distress communications see Note 1 high high Urgent communications see Note 1 high high High-priority flight safety messages see Note 1 high high Normal-priority flight safety messages see Note 1 high high Meteorological communications see Note 1 medium low Flight regularity communications see Note 1 medium low Aeronautical information service messages see Note 1 medium low Network/systems administration see Note 1 medium low Aeronautical administrative messages not allowed not allowed not allowed not allowed not allowed <unassigned> unassigned unassigned unassigned unassigned unassigned unassigned Urgent-priority administrative and U.N. Charter communications not allowed not allowed not allowed not allowed not allowed High-priority administrative and State/Government communications not allowed not allowed not allowed not allowed not allowed Normal-priority administrative communications not allowed not allowed not allowed not allowed not allowed Low-priority administrative communications and aeronautical passenger communications not allowed not allowed not allowed not allowed not allowed Note 1.— VDL Mode 2 has no specific subnetwork priority mechanisms. Note 2.— The AMSS SARPs specify mapping of message categories to subnetwork priority without explicitly referencing ATN network layer priority. Note 3.— The term “not allowed” means that only communications related to safety and regularity of flight are authorized to pass over this subnetwork as defined in the subnetwork SARPs. Note 4.— Only those mobile subnetworks are listed for which subnetwork SARPs exist and for which explicit support is provided by the ATN boundary intermediate system (BIS) technical provisions. Note 5.— The VDL Mode 4 subnetwork provides support for surveillance applications (e.g. ADS). Part I Annex 10 — Aeronautical Communications I-3-19 22/11/07 FIGURE FOR CHAPTER 3 Note 1.— Shading indicates elements outside the scope of these SARPs. User requirements define the interface between the application entity and the user and ensure the functionality and interoperability of the ATN. Note 2.— The figure represents a simplified model of the ATN and does not depict all of its capabilities (e.g. the store and forward capability which is provided for ATS message handling service). Note 3.— Various end-to-end points have been defined within the ATN to specify certain end-to-end performance requirements. It may be necessary, however, to define different end-to-end points to facilitate the qualification of implementations to those performance requirements. In such cases, the end-to-end points should be clearly defined and correlated with the end-to-end points shown in the figure. Note 4.— An IS is a conceptual representation of functionality and does not correspond precisely to a router. A router which implements the system management application requires the protocols of an end system and when using the system management application is also acting as an end system. Figure 3-1. Conceptual model of the ATN ___________________ Application process End system (ES) Application entity Upper layers communications service Internet communications service ATN end-to-end ATN communication services end-to-end ATN Internet communications service end-to-end Intermediate system (IS) Intermediate system (IS) Application process Application entity Upper layers communications service Internet communications service Subnetwork Subnetwork Subnetwork End system (ES) ANNEX 10 — VOLUME III I-4-1 22/11/07 CHAPTER 4. AERONAUTICAL MOBILE-SATELLITE (ROUTE) SERVICE (AMS(R)S) Note 1.— This chapter contains Standards and Recommended Practices applicable to the use of Aeronautical Mobile- Satellite (R) Service communications technologies. The Standards and Recommended Practices in this chapter are serviceand performance-oriented and are not tied to a specific technology or technique. Note 2.— Detailed Technical Specifications of AMS(R)S Systems are contained in the manual on AMS(R)S. This document also provides a detailed description of the AMS(R)S, including details on the Standards and Recommended Practices below. 4.1 DEFINITIONS Connection establishment delay. Connection establishment delay, as defined in ISO 8348, includes a component, attributable to the called subnetwork (SN) service user, which is the time between the SN-CONNECT indication and the SN-CONNECT response. This user component is due to actions outside the boundaries of the satellite subnetwork and is therefore excluded from the AMS(R)S specifications. Data transfer delay (95th percentile). The 95th percentile of the statistical distribution of delays for which transit delay is the average. Data transit delay. In accordance with ISO 8348, the average value of the statistical distribution of data delays. This delay represents the subnetwork delay and does not include the connection establishment delay. Network (N). The word “network” and its abbreviation “N” in ISO 8348 are replaced by the word “subnetwork” and its abbreviation “SN”, respectively, wherever they appear in relation to the subnetwork layer packet data performance. Residual error rate. The ratio of incorrect, lost and duplicate subnetwork service data units (SNSDUs) to the total number of SNSDUs that were sent. Spot beam. Satellite antenna directivity whose main lobe encompasses significantly less than the earth’s surface that is within line-of-sight view of the satellite. May be designed so as to improve system resource efficiency with respect to geographical distribution of user earth stations. Subnetwork (SN). See Network (N). Subnetwork service data unit (SNSDU). An amount of subnetwork user data, the identity of which is preserved from one end of a subnetwork connection to the other. Total voice transfer delay. The elapsed time commencing at the instant that speech is presented to the AES or GES and concluding at the instant that the speech enters the interconnecting network of the counterpart GES or AES. This delay includes vocoder processing time, physical layer delay, RF propagation delay and any other delays within an AMS(R)S subnetwork. Note.— The following terms used in this chapter are defined in Annex 10 as follows: Annex 10 — Aeronautical Communications Volume III 22/11/07 I-4-2 • Aeronautical telecommunication network (ATN): Volume III, Chapter 1. • Aeronautical mobile-satellite (route) service (AMS(R)S): Volume II, Chapter 1.1. • Aircraft earth station (AES): Volume III, Chapter 1. • Ground earth station (GES): Volume III, Chapter 1. • Subnetwork layer: Volume III, Chapter 6.1. 4.2 GENERAL 4.2.1 Any mobile-satellite system intended to provide AMS(R)S shall conform to the requirements of this chapter. 4.2.1.1 An AMS(R)S system shall support packet data service, or voice service, or both. 4.2.2 Requirements for mandatory carriage of AMS(R)S system equipment including the level of system capability shall be made on the basis of regional air navigation agreements which specify the airspace of operation and the implementation timescales for the carriage of equipment. A level of system capability shall include the performance of the AES, the satellite and the GES. 4.2.3 The agreements indicated in 4.2.2 shall provide at least two years’ notice of mandatory carriage of airborne systems. 4.2.4 Recommendation.— Civil aviation authorities should coordinate with national authorities and service providers those implementation aspects of an AMS(R)S system that will permit its worldwide interoperability and optimum use, as appropriate. 4.3 RF CHARACTERISTICS 4.3.1 Frequency bands Note.— ITU Radio Regulations permit systems providing mobile-satellite service to use the same spectrum as AMS(R)S without requiring such systems to offer safety services. This situation has the potential to reduce the spectrum available for AMS(R)S. It is critical that States consider this issue in frequency planning and in the establishment of national or regional spectrum requirements. 4.3.1.1 When providing AMS(R)S communications, an AMS(R)S system shall operate only in frequency bands which are appropriately allocated to AMS(R)S and protected by the ITU Radio Regulations. 4.3.2 Emissions 4.3.2.1 The total emissions of the AES necessary to meet designed system performance shall be controlled to avoid harmful interference to other systems necessary to support safety and regularity of air navigation, installed on the same or other aircraft. Note 1.— Harmful interference can result from radiated and/or conducted emissions that include harmonics, discrete spurious, intermodulation product and noise emissions, and are not necessarily limited to the “transmitter on” state. Part I Annex 10 — Aeronautical Communications I-4-3 22/11/07 Note 2.— Protection requirements for GNSS are contained in Annex 10, Volume I. 4.3.2.2 INTERFERENCE TO OTHER AMS(R)S EQUIPMENT 4.3.2.2.1 Emissions from an AMS(R)S system AES shall not cause harmful interference to an AES providing AMS(R)S on a different aircraft. Note.— One method of complying with 4.3.2.2.1 is by limiting emissions in the operating band of other AMS(R)S equipment to a level consistent with the intersystem interference requirements such as contained in RTCA document DO-215. RTCA and EUROCAE may establish new performance standards for future AMS(R)S which may describe methods of compliance with this requirement. 4.3.3 Susceptibility 4.3.3.1 The AES equipment shall operate properly in an interference environment causing a cumulative relative change in its receiver noise temperature (ΔT/T) of 25 per cent. 4.4 PRIORITY AND PRE-EMPTIVE ACCESS 4.4.1 Every aircraft earth station and ground earth station shall be designed to ensure that messages transmitted in accordance with Annex 10, Volume II, 5.1.8, including their order of priority, are not delayed by the transmission and/or reception of other types of messages. If necessary, as a means to comply with the above requirement, message types not defined in Annex 10, Volume II, 5.1.8 shall be terminated even without warning, to allow Annex 10, Volume II, 5.1.8 type messages to be transmitted and received. 4.4.2 All AMS(R)S data packets and all AMS(R)S voice calls shall be identified as to their associated priority. 4.4.3 Within the same message category, the system shall provide voice communications priority over data communications. 4.5 SIGNAL ACQUISITION AND TRACKING 4.5.1 The AES, GES and satellites shall properly acquire and track service link signals when the aircraft is moving at a ground speed of up to 1 500 km/h (800 knots) along any heading. 4.5.1.1 Recommendation.— The AES, GES and satellites should properly acquire and track service link signals when the aircraft is moving at a ground speed of up to 2 800 km/h (1 500 knots) along any heading. 4.5.2 The AES, GES and satellites shall properly acquire and track service link signals when the component of the aircraft acceleration vector in the plane of the satellite orbit is up to 0.6 g. 4.5.2.1 Recommendation.— The AES, GES and satellites should properly acquire and track service link signals when the component of the aircraft acceleration vector in the plane of the satellite orbit is up to 1.2 g. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-4-4 4.6 PERFORMANCE REQUIREMENTS 4.6.1 Designated operational coverage 4.6.1.1 An AMS(R)S system shall provide AMS(R)S throughout its designated operational coverage (DOC). 4.6.2 Failure notification 4.6.2.1 In the event of a service failure, an AMS(R)S system shall provide timely predictions of the time, location and duration of any resultant outages until full service is restored. Note.— Service outages may, for example, be caused by the failure of a satellite, satellite spot beam, or GES. The geographic areas affected by such outages may be a function of the satellite orbit and system design, and may vary with time. 4.6.2.2 The system shall annunciate a loss of communications capability within 30 seconds of the time when it detects such a loss. 4.6.3 AES requirements 4.6.3.1 The AES shall meet the relevant performance requirements contained in 4.6.4 and 4.6.5 for aircraft in straight and level flight throughout the designated operational coverage of the satellite system. 4.6.3.1.1 Recommendation.— The AES should meet the relevant performance requirements contained in 4.6.4 and 4.6.5 for aircraft attitudes of +20/-5 degrees of pitch and +/-25 degrees of roll throughout the DOC of the satellite system. 4.6.4 Packet data service performance 4.6.4.1 If the system provides AMS(R)S packet data service, it shall meet the standards of the following subparagraphs. Note.— System performance standards for packet data service may also be found in RTCA Document DO-270. 4.6.4.1.1 An AMS(R)S system providing a packet data service shall be capable of operating as a constituent mobile subnetwork of the ATN. Note.— In addition, an AMS(R)S may provide non-ATN data functions. 4.6.4.1.2 DELAY PARAMETERS Note.— The term “highest priority service” denotes the priority which is reserved for distress, urgency and certain infrequent network system management messages. The term “lowest priority service” denotes the priority used for regularity of flight messages. All delay parameters are under peak-hour traffic loading conditions. 4.6.4.1.2.1 Connection establishment delay. Connection establishment delay shall not be greater than 70 seconds. 4.6.4.1.2.1.1 Recommendation.— Connection establishment delay should not be greater than 50 seconds. 4.6.4.1.2.2 In accordance with ISO 8348, data transit delay values shall be based on a fixed subnetwork service data unit (SNSDU) length of 128 octets. Data transit delays shall be defined as average values. Part I Annex 10 — Aeronautical Communications I-4-5 22/11/07 4.6.4.1.2.3 Data transit delay, from-aircraft, highest priority. From-aircraft data transit delay shall not be greater than 40 seconds for the highest priority data service. 4.6.4.1.2.3.1 Recommendation.— Data transit delay, from-aircraft, highest priority. From-aircraft data transit delay should not be greater than 23 seconds for the highest priority data service. 4.6.4.1.2.3.2 Recommendation.— Data transit delay, from-aircraft, lowest priority. From-aircraft data transit delay should not be greater than 28 seconds for the lowest priority data service. 4.6.4.1.2.4 Data transit delay, to-aircraft, highest priority. To-aircraft data transit delay shall not be greater than 12 seconds for the highest priority data service. 4.6.4.1.2.4.1 Recommendation.— Data transit delay, to-aircraft, lowest priority. To-aircraft data transit delay should not be greater than 28 seconds for the lowest priority data service. 4.6.4.1.2.5 Data transfer delay (95th percentile), from-aircraft, highest priority. From-aircraft data transfer delay (95th percentile), shall not be greater than 80 seconds for the highest priority data service. 4.6.4.1.2.5.1 Recommendation.— Data transfer delay (95th percentile), from-aircraft, highest priority. From-aircraft data transfer delay (95th percentile), should not be greater than 40 seconds for the highest priority data service. 4.6.4.1.2.5.2 Recommendation.— Data transfer delay (95th percentile), from-aircraft, lowest priority. From-aircraft data transfer delay (95th percentile), should not be greater than 60 seconds for the lowest priority data service. 4.6.4.1.2.6 Data transfer delay (95th percentile), to-aircraft, highest priority. To-aircraft data transfer delay (95th percentile), shall not be greater than 15 seconds for the highest priority data service. 4.6.4.1.2.6.1 Recommendation.— Data transfer delay (95th percentile), to-aircraft, lowest priority. To-aircraft data transfer delay (95th percentile), should not be greater than 30 seconds for the lowest priority data service. 4.6.4.1.2.7 Connection release delay (95th percentile). The connection release delay (95th percentile) shall not be greater than 30 seconds in either direction. 4.6.4.1.2.7.1 Recommendation.— The connection release delay (95th percentile) should not be greater than 25 seconds in either direction. 4.6.4.1.3 INTEGRITY 4.6.4.1.3.1 Residual error rate, from-aircraft. The residual error rate in the from-aircraft direction shall not be greater than 10-4 per SNSDU. 4.6.4.1.3.1.1 Recommendation.— The residual error rate in the from-aircraft direction should not be greater than 10-6 per SNSDU. 4.6.4.1.3.2 Residual error rate, to-aircraft. The residual error rate in the to-aircraft direction shall not be greater than 10-6 per SNSDU. 4.6.4.1.3.3 Connection resilience. The probability of a subnetwork connection (SNC) provider-invoked SNC release shall not be greater than 10-4 over any one-hour interval. Note.— Connection releases resulting from GES-to-GES handover, AES log-off or virtual circuit pre-emption are excluded from this specification. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-4-6 4.6.4.1.3.4 The probability of an SNC provider-invoked reset shall not be greater than 10-1 over any one-hour interval. 4.6.5 Voice service performance 4.6.5.1 If the system provides AMS(R)S voice service, it shall meet the requirements of the following subparagraphs. Note.— ICAO is currently considering these provisions in the light of the introduction of new technologies. 4.6.5.1.1 CALL PROCESSING DELAY 4.6.5.1.1.1 AES origination. The 95th percentile of the time delay for a GES to present a call origination event to the terrestrial network interworking interface after a call origination event has arrived at the AES interface shall not be greater than 20 seconds. 4.6.5.1.1.2 GES origination. The 95th percentile of the time delay for an AES to present a call origination event at its aircraft interface after a call origination event has arrived at the terrestrial network interworking interface shall not be greater than 20 seconds. 4.6.5.1.2 VOICE QUALITY 4.6.5.1.2.1 The voice transmission shall provide overall intelligibility performance suitable for the intended operational and ambient noise environment. 4.6.5.1.2.2 The total allowable transfer delay within an AMS(R)S subnetwork shall not be greater than 0.485 seconds. 4.6.5.1.2.3 Recommendation.— Due account should be taken of the effects of tandem vocoders and/or other analog/digital conversions. 4.6.5.1.3 VOICE CAPACITY 4.6.5.1.3.1 The system shall have sufficient available voice traffic channel resources such that an AES- or GESoriginated AMS(R)S voice call presented to the system shall experience a probability of blockage of no more than 10-2. Note.— Available voice traffic channel resources include all pre-emptable resources, including those in use by non- AMS(R)S communications. 4.6.6 Security 4.6.6.1 The system shall provide features for the protection of messages in transit from tampering. 4.6.6.2 The system shall provide features for protection against denial of service, degraded performance characteristics, or reduction of system capacity when subjected to external attacks. Note.— Possible methods of such attack include intentional flooding with spurious messages, intentional corruption of system software or databases, or physical destruction of the support infrastructure. 4.6.6.3 The system shall provide features for protection against unauthorized entry. Note.— These features are intended to provide protection against spoofing and “phantom controllers”. Part I Annex 10 — Aeronautical Communications I-4-7 22/11/07 4.7 SYSTEM INTERFACES 4.7.1 An AMS(R)S system shall allow subnetwork users to address AMS(R)S communications to specific aircraft by means of the ICAO 24-bit aircraft address. Note.— Provisions on the allocation and assignment of ICAO 24-bit addresses are contained in the Appendix to Chapter 9. 4.7.2 Packet data service interfaces 4.7.2.1 If the system provides AMS(R)S packet data service, it shall provide an interface to the ATN. Note.— The detailed technical specifications related to provisions of the ATN-compliant subnetwork service are contained in Section 5.2.5 and Section 5.7.2 of Doc 9880 — Manual on Detailed Technical Specifications for the Aeronautical Telecommunication Network (ATN) (in preparation). 4.7.2.2 If the system provides AMS(R)S packet data service, it shall provide a connectivity notification (CN) function. ___________________ ANNEX 10 — VOLUME III I-5-1 22/11/07 CHAPTER 5. SSR MODE S AIR-GROUND DATA LINK Note.— The SSR Mode S air-ground data link is also referred to as the Mode S subnetwork in the context of the aeronautical telecommunication network (ATN). 5.1 DEFINITIONS RELATING TO THE MODE S SUBNETWORK Aircraft. The term aircraft may be used to refer to Mode S emitters (e.g. aircraft/vehicles), where appropriate. Aircraft address. A unique combination of 24 bits available for assignment to an aircraft for the purpose of air-ground communications, navigation and surveillance. Aircraft data circuit-terminating equipment (ADCE). An aircraft specific data circuit-terminating equipment that is associated with an airborne data link processor (ADLP). It operates a protocol unique to Mode S data link for data transfer between air and ground. Aircraft data link processor (ADLP). An aircraft-resident processor that is specific to a particular air-ground data link (e.g. Mode S) and which provides channel management, and segments and/or reassembles messages for transfer. It is connected to one side of aircraft elements common to all data link systems and on the other side to the air-ground link itself. Aircraft/vehicle. May be used to describe either a machine or device capable of atmospheric flight, or a vehicle on the airport surface movement area (i.e. runways and taxiways). Air-initiated protocol. A procedure initiated by a Mode S aircraft installation for delivering a standard length or extended length downlink message to the ground. BDS Comm-B Data Selector. The 8-bit BDS code determines the register whose contents are to be transferred in the MB field of a Comm-B reply. It is expressed in two groups of 4 bits each, BDS1 (most significant 4 bits) and BDS2 (least significant 4 bits). Broadcast. The protocol within the Mode S system that permits uplink messages to be sent to all aircraft in coverage area, and downlink messages to be made available to all interrogators that have the aircraft wishing to send the message under surveillance. Capability report. Information identifying whether the transponder has a data link capability as reported in the capability (CA) field of an all-call reply or squitter transmission (see “data link capability report”). Close-out. A command from a Mode S interrogator that terminates a Mode S link layer communication transaction. Cluster of interrogators. Two or more interrogators with the same interrogator identifier (II) code, operating cooperatively to ensure that there is no interference to the required surveillance and data link performance of each of the interrogators, in areas of common coverage. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-5-2 Comm-A. A 112-bit interrogation containing the 56-bit MA message field. This field is used by the uplink standard length message (SLM) and broadcast protocols. Comm-B. A 112-bit reply containing the 56-bit MB message field. This field is used by the downlink SLM, ground-initiated and broadcast protocols. Comm-C. A 112-bit interrogation containing the 80-bit MC message field. This field is used by the uplink extended length message (ELM) protocol. Comm-D. A 112-bit reply containing the 80-bit MD message field. This field is used by the downlink ELM protocol. Connection. A logical association between peer-level entities in a communication system. Data link capability report. Information in a Comm-B reply identifying the complete Mode S communications capabilities of the aircraft installation. Downlink. A term referring to the transmission of data from an aircraft to the ground. Mode S air-to-ground signals are transmitted on the 1 090 MHz reply frequency channel. Extended length message (ELM). A series of Comm-C interrogations (uplink ELM) transmitted without the requirement for intervening replies, or a series of Comm-D replies (downlink ELM) transmitted without intervening interrogations. Uplink ELM (UELM). A term referring to extended length uplink communication by means of 112-bit Mode S Comm-C interrogations, each containing the 80-bit Comm-C message field (MC). Downlink ELM (DELM). A term referring to extended length downlink communication by means of 112-bit Mode S Comm-D replies, each containing the 80-bit Comm-D message field (MD). Frame. The basic unit of transfer at the link level. In the context of Mode S subnetwork, a frame can include from one to four Comm-A or Comm-B segments, from two to sixteen Comm-C segments, or from one to sixteen Comm-D segments. General formatter/manager (GFM). The aircraft function responsible for formatting messages to be inserted in the transponder registers. It is also responsible for detecting and handling error conditions such as the loss of input data. Ground data circuit-terminating equipment (GDCE). A ground specific data circuit-terminating equipment associated with a ground data link processor (GDLP). It operates a protocol unique to Mode S data link for data transfer between air and ground. Ground data link processor (GDLP). A ground-resident processor that is specific to a particular air-ground data link (e.g. Mode S), and which provides channel management, and segments and/or reassembles messages for transfer. It is connected on one side (by means of its DCE) to ground elements common to all data link systems, and on the other side to the air-ground link itself. Ground-initiated Comm-B (GICB). The ground-initiated Comm-B protocol allows the interrogator to extract Comm-B replies containing data from a defined source in the MB field. Ground-initiated protocol. A procedure initiated by a Mode S interrogator for delivering standard length or extended length messages to a Mode S aircraft installation. Mode S air-initiated Comm-B (AICB) protocol. A procedure initiated by a Mode S transponder for transmitting a single Comm-B segment from the aircraft installation. Part I Annex 10 — Aeronautical Communications I-5-3 22/11/07 Mode S broadcast protocols. Procedures allowing standard length uplink or downlink messages to be received by more than one transponder or ground interrogator respectively. Mode S ground-initiated Comm-B (GICB) protocol. A procedure initiated by a Mode S interrogator for eliciting a single Comm-B segment from a Mode S aircraft installation, incorporating the contents of one of 255 Comm-B registers within the Mode S transponder. Mode S multisite-directed protocol. A procedure to ensure that extraction and close-out of a downlink standard length or extended length message is affected only by the particular Mode S interrogator selected by the aircraft. Mode S packet. A packet conforming to the Mode S subnetwork standard, designed to minimize the bandwidth required from the air-ground link. ISO 8208 packets may be transformed into Mode S packets and vice-versa. Mode S specific protocol (MSP). A protocol that provides restricted datagram service within the Mode S subnetwork. Mode S specific services. A set of communication services provided by the Mode S system which are not available from other air-ground subnetworks, and therefore not interoperable. Mode S specific services entity (SSE). An entity resident within an XDLP to provide access to the Mode S specific services. Packet. The basic unit of data transfer among communication devices within the network layer (e.g. an ISO 8208 packet or a Mode S packet). Segment. A portion of a message that can be accommodated within a single MA/MB field in the case of a standard length message, or MC/MD field in the case of an extended length message. This term is also applied to the Mode S transmissions containing these fields. Standard length message (SLM). An exchange of digital data using selectively addressed Comm-A interrogations and/or Comm-B replies (see “Comm-A” and “Comm-B”). Subnetwork. An actual implementation of a data network that employs a homogeneous protocol and addressing plan, and is under the control of a single authority. Subnetwork management entity (SNME). An entity resident within a GDLP that performs subnetwork management and communicates with peer entities in intermediate or end-systems. Timeout. The cancellation of a transaction after one of the participating entities has failed to provide a required response within a pre-defined period of time. Uplink. A term referring to the transmission of data from the ground to an aircraft. Mode S ground-to-air signals are transmitted on the 1 030 MHz interrogation frequency channel. XDCE. A general term referring to both the ADCE and the GDCE. XDLP. A general term referring to both the ADLP and the GDLP. Annex 10 — Aeronautical Communications Volume III 22/11/07 I-5-4 5.2 MODE S CHARACTERISTICS 5.2.1 General provisions Note 1.— Reference ISO document. When the term “ISO 8208” is referred to in this standard, it means the ISO Standard “Information technology — Data communications — X.25 Packet Layer Protocol for Data Terminal Equipment, Reference Number ISO/IEC 8208: 1990(E)”. Note 2.— The overall architecture of the Mode S subnetwork is presented in the diagram on the following page. Note 3.— The processing splits into three different paths. The first consists of the processing of switched virtual circuits (SVCs), the second consists of the processing of Mode S specific services, and the third consists of the processing of subnetwork management information. SVCs utilize the reformatting process and the ADCE or GDCE function. Mode S specific services utilize the Mode S specific services entity (SSE) function. 5.2.1.1 Message categories. The Mode S subnetwork shall only carry aeronautical communications classified under categories of flight safety and flight regularity as specified in Annex 10, Volume II, Chapter 5, 5.1.8.4 and 5.1.8.6. 5.2.1.2 Signals in space. The signal-in-space characteristics of the Mode S subnetwork shall conform to the provisions contained in Annex 10, Volume IV, Chapter 3, 3.1.2. 5.2.1.3 Code and byte independency. The Mode S subnetwork shall be capable of code and byte independent transmission of digital data. 5.2.1.4 Data transfer. Data shall be conveyed over the Mode S data link in segments using either standard length message (SLM) protocols or extended length message (ELM) protocols as defined in 3.1.2.6.11 and 3.1.2.7 of Annex 10, Volume IV. Note 1.— An SLM segment is the contents of one 56-bit MA or MB field. An ELM segment is the contents of one 80-bit MC or MD field. Note 2.— An SLM frame is the contents of up to four linked MA or MB fields. An ELM frame is the contents of 2 to 16 MC or 1 to 16 MD fields. 5.2.1.5 Bit numbering. In the description of the data exchange fields, the bits shall be numbered in the order of their transmission, beginning with bit 1. Bit numbers shall continue through the second and higher segments of multi-segment frames. Unless otherwise stated, numerical values encoded by groups (fields) of bits shall be encoded using positive binary notation and the first bit transmitted shall be the most significant bit (MSB) (3.1.2.3.1.3 of Annex 10, Volume IV). 5.2.1.6 Unassigned bits. When the length of the data is not sufficient to occupy all bit positions within a message field or subfield, the unassigned bit positions shall be set to 0. 5.2.2 Frames 5.2.2.1 UPLINK FRAMES 5.2.2.1.1 SLM frame. An uplink SLM frame shall be composed of up to four selectively addressed Comm-A segments. Part I Annex 10 — Aeronautical Communications I-5-5 22/11/07 Functional elements of the Mode S subnetwork Key : physical (RF) connection : peer level association : interfaces Notes:

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