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for each data signalling rate should be chosen as follows:
Data signalling
rate Type of transmission
600 bitds Synchronous or asynchronous
serial transmission
1 200 bitsh Synchronous or asynchronous
serial transmission
2 400 birds Synchronous serial transmission
4 800 bits/s Synchronous serial rmnsmission
9 600 bits/s Synchronous serial transmission
7/11/96
No. 71
7/11/96
No. 71.
CHAPTER 7. SUBNETWORK INTERCONNECTION
[to be developed]
ANNEX 10 - VOLUME I11
CHAPTER 8. AFTN NETWORK
8.1 DEFINITIONS Medium modulation rates. Modulation rates above 300 and up
to and including 3 000 bauds.
Data signalling rate. Data signalling rate refers to the passage
of information per unit of time, and is expressed in
bits,second. Data sisalling rate is dven by the fornula: Modulation rute. The reciprocal of the unit interval measured
in seconds. This rate is expressed in bauds.
i x= m -1 logpi Note.- Telegraph signals are characterized by interi
- 1 Ti vals Qtime of duration equal to or longer than the shortest
or unit interval. The modulation rate Wrmerly telewhere
tn is the number of parallel channels, Ti is the graph speed) is therefore expressed as the inverse of the
minimum interval for the ith channel expressed in seconds, value of this unit interval. for example, the unit interval
n, is the number of significant conditions of the modu- is 20 milliseconds, the modulation rate is 50 bauds.
lation in the ith channel.
Synchronous operation. Operation in which the time interval
Note 1.- between code units is a constant.
a) For a single channel (serial trclnsmission) it
reduces to (1/T)log2n: with a two-condition modulatzo~
t (n = 21, it is 1K.
b) For a parallel transmission with equal minimum
intervals and equal number of significant conditions
on each channel, it is m(l/T)log2n (m(l/T) in
case of u two-condition modulation).
Note 2.- In the above definition, the tern >parallel
channels" is interpreted to mean; channels, each of which
carries an integral part of an information unit, e.g. the
parallel transmissio~z of bit$ forming a character: In the
case of a circuit cor?zprising a number of channels, each
of which carries infornzation "independently", with the
sole purpose of increasing the traffic handling capacity,
tlzese clzarznels are not to be regurded as parallel channels
in the context of this definition.
8.2 TECHNICAL PROVISIONS
RELATING TO TELETYPEWRITER
APPARATUS AND CIRCUITS
USED IN THE AFTN
8.2.1 In international teletypewriter circuits of the
AFTN, using a 5-unit code, the International Telegraph
Alphabet No. 2 (see Table 8-1) shall be used only to the
extent prescribed in 4.1.2 of Volume II.
8.2.2 Recornmendation.- The modulation rare should
be determined by bilateral or multilateral agreement between
ad~ninistrations concerned, taking into account primarily
trafic volume.
8.2.3 Recommendation.- The nonzinal duration of
the transmitting cycle should be at least 7.4 units (preferably
D e p e of standardized test distortion. The degee of distor- 7.51, the stop element lasting for at units
tion of the restitution measured during a specific period of (preferably 1.5).
time when the modulation is perfect and corresponds lo a
specific text.
8-2.3.1 Recommendation.- The receiver should be
Effective margin. That margin of an individual apparatus able to translate correctly in service the signals coming from
which could be measured undcr actual operating condi- a transmitter with a nominal transmitting cycle of 7 units.
tions.
8.2.4 Recommendation.- Apparatus in service shotild
Low3 m00o dbuauladtsi.o n rates. Modulation rates up to and including efSective margina insd neavdejur slreesds tihna snu 3c5h pae rm caennnt.e r net
Margin. The maximum degree of distortion of the circuit at
the end of which the apparatus is situated which is compa- 8.2.5 Recommendation.- The nirmber of chnrucfers
tiblc with the correct translation of all the signals which it which the textz4al line of the page-prznting apparatus rnay
may possibly receive. contairt should be fiKed ut 69.
ANNEX 10 - VOLUME 111
7/11/36
No. 71
Annex 10 - Aeronautical Telecommunications
Table 8-1. International Telegraph Alphabets No. 2 and No. 3
Sign 1 Closed circuit I Double current
A No curren~ Negative current
Z Positive current Positive current
Number of
signal
Volume III
Note 1. Used for answer-back facility.
Internutiom1
Code No. 2
1 A - A ZZAAA Z
2 B ? A ZAAZZ Z
3 C A AZZZA Z
4 D Note 1 A ZAAZA Z
5 E 3 A ZAAAA Z
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