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8.6.5.1.4.2 CIDIN packets of one CIDIN message shall
be relayed independently via predetermined routes through the
network thus allowing alternative routing on a CIDIN packet
basis as necessary.
8,6.5.1.4.3 The CIDIN packet header shall contain
information to enable relay cenlres to handle CIDIN packets
in the order of priority, to transmit the CIDIN packets on the
proper outgoing circuit(s) and to duplicate or multiplicate
CIDLN packets when required for multiple dissemination
purposes. Tlie information shall be sufficient to apply address
stripping on the exit addresses as well as on the addressee
indicators of messages in AFTN format.
Note.- Guidance material on address stripping in the
CIDIN is contained in the Manual on the Planning and
Engineering of the Aeronautical Fixed Telecommunication
Network (Doc 8259).
8.6.5.1.4.4 The CDLN packet procedures shall be as
described in 8.6.6.3 below.
8.6.5.1.5 THE TRANSPORT PROTOCOL LEVEL
8.6.5.1.5.1 hformation exchanged over the CIDIN shall
be transmitted as CIDIN messages.
8.6.5.1.5.2 The length of a CIDIN message shall be
defined by the CIDIN packet sequence number (CPSN). The
maximum permissible length is 215 packets which in effect
results jn no practical limitation.
8.6.5.1.5.3 If the length of a CIDIN message and its
transport and packet headers (as defined below) exceeds 256
octets the message shall be divided into segments and placed
in the CIDIN user dala field of CIDIN packets. Each segment
shall be preceded by a transport header containing information
to enable the re-assembly of the CIDIN message at the exit
centre(s) from individually received segments and to determine
further handling of the received complete CIDIN messagc.
8.6.5.1.5.4 All segments of one CIDIN message shall he
provided with the same message identification infonnation in
the transport header. Only the CPSN and final CWW packet
(FCP) indicator shall be different.
7/11/96
No. 71
Part I Annex 10 - Aeronautical Telecommunications
8.6.5.1.5.5 Recovery of messages shall be performed at
the transport level.
8.6.6.2.2.1.1 Data packct (Figure 8-3), comprising:
a) the general formal identifier;
8.6.5.1.5.6 Recommendation.- When an entry centre
or station has to rnake separate transmissions of the same
message to more than one exit centre or station, the same
message identijication number (MIN) should be used for each
transmission.
b) the logical channel identifier, comprising a logical
channel group number and a logical channel number:
C) the packet type identifier, including the packet receive
sequence number P(R), the packet send sequence
number P(S), and the more data bit M which has no
8.6.5.1.5.7 The transport protocol shall be as described significance on CIDIN circuits and shall be set to zero;
in 8.6.6.4 below.
d) the user data field, comprising up to 256 octets and
ending on an integral octet boundary.
8.6.6 CIDIN procedures
Note.- Datu networks operating in the packet mode and
connected with CIDIN using procedures described in ITU
CCIli" Recommendution X.25-I981 that limit the user data
Jield to not more than I28 octets may require the use of the
M bit. Later versions of Recornmendation X.25 will be
reviewed as they are released to ascertain whether or not they
should be adopted.
8.6.6.1 THE DATA LINK PROCEDURES
8.6.6.1.1 The data link procedures shall be as described
in 8.6.4 above.
8.6.6.2 THE X.25 PACKET PROCEDURES FOR
PERMANENT VIRTUAL CIRCUITS 8.6.6.2.2.1.2 RECETVEREADY packet (RR) (Figure 8-4),
comprising:
8.6.6.2.1 The following descriptions shall apply to the
packet level procedures for permanent virtual circuits: a) the general format identifier;
a) A permanent virtual circuit (PVC) is a logical path
which conveys data solely from one PVC termination
centre, optionally through PVC transit centres to a
single distant PVC termination centre via an assigned
logical channel on each of one or more data links.
b) the logical channel identifier, comprising a logical
channel group number and a logical channel number;
c) the packet type identifier, including P(R).
8.6.6.2.2.1.3 RECEIVE NOT READY packet (RNR)
b) A PVC termination centre is a centre which introduces (Figure 8-5), comprising:
data into, and receives data from, a PVC.
a) the general format identifier;
c) A PVC transit centre is a ccntre which relays data for
a PVC from one assigned logical channel on one data
link to another assigned logical channel on another
data link.
b) the logical channel identifier, comprising a logical
 
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