Publication: Magyar Közlöny
Issue: MK-2009-104 (Year: 2009, Number: 104)
Era: 2004-2010
Section: 
Paragraph Index: 1999

k) A common ICAO data interchange network (CIDIN) switching centre is that part of an automatic AFTN switching centre which provides for the entry, relay, and exit centre functions using the bit-oriented link and CIDIN network Annex 10 — Aeronautical Communications Volume III 22/11/07 I-8-14 procedures specified in this section and includes the appropriate interface(s) with other parts of the AFTN and with other networks. 8.6.4.2 BIT-ORIENTED DATA LINK CONTROL PROCEDURES FOR POINT-TO-POINT, GROUND-GROUND DATA INTERCHANGE APPLICATIONS EMPLOYING SYNCHRONOUS TRANSMISSION FACILITIES Note.— The following link level procedures are the same as the LAPB link level procedures described in ITU CCITT Recommendation X.25, Section 2, Yellow Book (1981 version). Later versions of Recommendation X.25 will be reviewed as they are released to ascertain whether or not they should be adopted. 8.6.4.2.1 Frame format. Frames shall contain not less than 32 bits, excluding the opening and closing flags, and shall conform to the following format: FLAG F ADDRESS A CONTROL C INFORMATION I FCS FLAG F 8.6.4.2.1.1 A frame shall consist of an opening flag (F), an address field (A), a control field (C), an optional information field (I), a frame check sequence (FCS), and a closing flag sequence (F), and shall be transmitted in that order. Note.— In relation to CIDIN, the opening flag, the fields A and C, the FCS and the closing flag form together the Data Link Control Field (DLCF). The field I is denoted as the Link Data Field (LDF). 8.6.4.2.1.1.1 The flag (F) shall be the 8-bit sequence 01111110 which delimits the beginning and ending of each frame. It shall be permissible for the closing flag of a frame to also serve as the opening flag of the next frame. 8.6.4.2.1.1.2 The address (A) field shall consist of one octet, excluding 0 bits added to achieve transparent transmission, which shall contain the link address of the combined station. 8.6.4.2.1.1.3 The control (C) field shall consist of one octet, excluding 0 bits added to achieve transparent transmission, and shall contain the commands, responses, and frame sequence number components for the control of the data link. 8.6.4.2.1.1.4 The information (I) field shall contain digital data which may be presented in any code or sequence but shall not exceed a maximum of 259 octets, excluding 0 bits added to achieve transparent transmission. The I field shall always be a multiple of 8 bits in length. 8.6.4.2.1.1.5 The frame check sequence (FCS) shall consist of two octets, excluding 0 bits added to achieve transparent transmission, and shall contain the error detecting bits. 8.6.4.2.2 A frame check sequence (FCS) shall be included in each frame for the purpose of error checking. 8.6.4.2.2.1 The error checking algorithm shall be a cyclic redundancy check (CRC). 8.6.4.2.2.2 The CRC polynomial (P(x)) shall be x16 + x12 + x5 + 1. 8.6.4.2.2.3 The FCS shall be a 16-bit sequence. This FCS shall be the ones’ complement of the remainder, R(x), obtained from the modulo 2 division of x16[G(x)] + xK(x15 + x14 + x13 + ... + x2 + x1 + 1) Part I Annex 10 — Aeronautical Communications I-8-15 22/11/07 by the CRC polynomial, P(x). G(x) shall be the contents of the frame existing between, but including neither, the final bit of the opening flag nor the first bit of the FCS, excluding bits inserted for transparent transmission. K shall be the length of G(x) (number of bits). 8.6.4.2.2.4 The generation and checking of the FCS accumulation shall be as follows:

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