Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4257

c) Tc seconds have elapsed since the last Comm-A segment with the same value of IIS was received (Table 5-1). 5.2.2.1.1.4.6 Segment cancellation. A received segment for an SLM frame shall be discarded if it is an intermediate or final segment and no initial segment has been received with the same value of IIS. 5.2.2.1.1.4.7 Segment duplication. If a received segment duplicates a currently received segment number with the same value of IIS, the new segment shall replace the currently received segment. Note.— The action of the Mode S subnetwork protocols may result in the duplicate delivery of Comm-A segments. 5.2.2.1.2 ELM frame. An uplink ELM frame shall consist of from 20 to 160 bytes and shall be transferred from the interrogator to the transponder using the protocol defined in 3.1.2.7 of Annex 10, Volume IV. The first 4 bits of each uplink ELM segment (MC field) shall contain the interrogator identifier (II) code of the Mode S interrogator transmitting the ELM. The ADLP shall check the II code of each segment of a completed uplink ELM. If all of the segments contain the same II code, the II code in each segment shall be deleted and the remaining message bits retained as user data for further processing. If all of the segments do not contain the same II code, the entire uplink ELM shall be discarded. Note.— An uplink ELM frame consists of two to sixteen associated Comm-C segments, each of which contains the 4-bit II code. Therefore, the capacity for packet transfer is 19 to 152 bytes per uplink ELM frame. 5.2.2.2 DOWNLINK FRAMES 5.2.2.2.1 SLM frame. A downlink SLM frame shall be composed of up to 4 Comm-B segments. The MB field of the first Comm-B segment of the frame shall contain a 2-bit linked Comm-B subfield (LBS, bits 1 and 2 of the MB field). This subfield shall be used to control linking of up to four Comm- B segments. Note.— The LBS uses the first 2-bit positions in the first segment of a multi or single segment downlink SLM frame. Hence, 54 bits are available for Mode S packet data in the first segment of a downlink SLM frame. The remaining segments of the downlink SLM frame, if any, have 56 bits available. 5.2.2.2.1.1 LBS coding. Linking shall be indicated by the coding of the LBS subfield of the MB field of the initial Comm-B segment of the SLM frame. The coding of LBS shall be as follows: LBS MEANING single segment initial segment of a two-segment SLM frame initial segment of a three-segment SLM frame initial segment of a four-segment SLM frame 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume III 5-6 28/11/02 No. 77 5.2.2.2.1.2 Linking protocol 5.2.2.2.1.2.1 In the Comm-B protocol, the initial segment shall be transmitted using the air-initiated or multisite-directed protocols. The LBS field of the initial segment shall indicate to the ground the number of additional segments to be transferred (if any). Before the transmission of the initial segment to the transponder, the remaining segments of the SLM frame (if any) shall be transferred to the transponder for transmission to the interrogator using the ground-initiated Comm-B protocol. These segments shall be accompanied by control codes that cause the segments to be inserted in groundinitiated Comm-B registers 2, 3 or 4, associated respectively with the second, third, or fourth segment of the frame. 5.2.2.2.1.2.2 Close-out of the air-initiated segment that initiated the protocol shall not be performed until all segments have been successfully transferred. Note.— The linking procedure including the use of the ground-initiated Comm-B protocol is performed by the ADLP. 5.2.2.2.1.3 Directing SLM frames. If the SLM frame is to be multisite-directed, the ADLP shall determine the II code of the Mode S interrogator or cluster of interrogators (5.2.8.1.3) that shall receive the SLM frame. 5.2.2.2.2 ELM FRAME Note.— A downlink ELM consists of one to sixteen associated Comm-D segments. 5.2.2.2.2.1 Procedure. Downlink ELM frames shall be used to deliver messages greater than or equal to 28 bytes and shall be formed using the protocol defined in 3.1.2.7 of Annex 10, Volume IV. 5.2.2.2.2.2 Directing ELM frames. If the ELM frame is to be multisite-directed, the ADLP shall determine the II code of the Mode S interrogator or cluster of interrogators (5.2.8.1.3) that shall receive the ELM frame. 5.2.2.3 XDLP frame processing. Frame processing shall be performed on all Mode S packets (except for the MSP packet) as specified in 5.2.2.3 to 5.2.2.5. Frame processing for Mode S specific services shall be performed as specified in 5.2.7. 5.2.2.3.1 Packet length. All packets (including a group of packets multiplexed into a single frame) shall be transferred in a frame consisting of the smallest number of segments needed to accommodate the packet. The user data field shall be an integral multiple of bytes in length. A 4-bit parameter (LV) shall be provided in the Mode S DATA, CALL REQUEST, CALL ACCEPT, CLEAR REQUEST and INTERRUPT packet headers so that during unpacking no additional bytes are added to the user data field. The LV field shall define the number of full bytes used in the last segment of a frame. During LV calculations, the 4-bit II code in the last segment of an uplink ELM message shall be (1) ignored for uplink ELM frames with an odd number of Comm-C segments and (2) counted for uplink ELM frames with an even number of Comm-C segments. The value contained in the LV field shall be ignored if the packet is multiplexed. Note.— A specific length field is used to define the length of each element of a multiplexed packet. Therefore the LV field value is not used. LV field error handling is described in Tables 5-16 and 5-19. 5.2.2.3.2 Multiplexing. When multiplexing multiple Mode S packets into single SLM on ELM frame, the following procedures shall be used. Multiplexing of the packets within the ADLP shall not be applied to packets associated with SVCs of different priorities. Note.— Multiplexing is not performed on MSP packets. 5.2.2.3.2.1 Multiplexing optimization Recommendation.— When multiple packets are awaiting transfer to the same XDLP, they should be multiplexed into a single frame in order to optimize throughput, provided that packets associated with SVCs of different priorities are not multiplexed together. 5.2.2.3.2.2 Structure. The structure of the multiplexed packets shall be as follows: Note.— A number in the field signifies the field length in bits; “v” signifies that the field is of variable length. 5.2.2.3.2.2.1 Multiplexing header. The header for the multiplexed packets shall be as follows: Where, Data packet type (DP) = 0 MSP packet type (MP) = 1 Supervisory packet (SP) = 3 Supervisory type (ST) = 2 Note.— See Figure 5-23 for a definition for the field structure used in the multiplexing header. 5.2.2.3.2.2.2 Length. This field shall contain the length of the following packet in bytes. Any error detected in a HEADER:6 or 8 LENGTH:8 1ST PACKET:v LENGTH:8 2ND PACKET:v DP:1 MP:1 SP:2 ST:2 FILL2:0 or 2 2007/70/II. szám Part I Annex 10 — Aeronautical Telecommunications 5-7 28/11/02 No. 77 multiplexed DATA packet, such as inconsistency between length as indicated in the LENGTH field and the length of the frame hosting that packet, shall result in the discarding of the packet unless the error can be determined to be limited to the LENGTH field, in which case a REJECT packet with the expected PS value can be sent. Recommendation.— For multiplex packets it is recommended that, if the entire packet cannot be de-multiplexed, then the first constituent packet be treated as a format error, and the remainder be discarded. 5.2.2.3.2.3 Termination. The end of a frame containing a sequence of multiplexed packets shall be determined by one of the following events:

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