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FASCICLE VII.3
Recommendations T.0-T.63
TERMINAL EQUIPMENT AND PROTOCOLS
FOR TELEMATIC SERVICES
Blanc
MONTAGE: PAGE 2 = PAGE BLANCHE
"Telematic services" is used provisionally and includes such
services as Videotex, Teletex, facsimile, etc.
COLLABORATION WITH OTHER |
INTERNATIONAL ORGANIZATIONS
ON CCITT-DEFINED TELEMATIC SERVICES
Recommendation A.21 published in Volume I is reproduced
below for the convenience of the reader.
Recommendation A.21
COLLABORATION WITH OTHER INTERNATIONAL ORGANIZATIONS
ON CCITT-DEFINED TELEMATIC SERVICES
(Geneva, 1980, amended at Malaga-Torremolinos, 1984)
The CCITT,
considering
(a) that, according to Article 1 of the agreement between the
United Nations and the International Telecommunication Union, the
United Nations recognizes the International Telecommunication Union
as the specialized agency responsible for taking such action as may
be appropriate under its basic instrument for the accomplishment of
the purposes set forth therein;
(b) that Article 4 of the International Telecommunication Con-
vention | (Nairobi, 1982) states that the purposes of the Union
are:
"a) to maintain and extend international cooperation
between all Members of the Union for the improvement and rational
use of telecommunications of all kinds, as well as to promote and
to offer technical assistance to developing countries in the field
of telecommunications;
" b) to promote the development of technical facili-
ties and their most efficient operation with a view to improving
the efficiency of telecommunication services, increasing their use-
fulness and making them, as far as possible, generally available to
the public;
" c) to harmonize the actions of nations in the
attainment of those ends.";
(c) that Article 40 of the Convention states that "in further-
ance of complete international coordination on matters affecting
telecommunication, the Union shall cooperate with international
organizations having related interests and activities";
(d) that this cooperation has to recognize the advisory capa-
city of organizations participating in the work of CCITT;
(e) that, in the study of terminals for new CCITT-defined
telematic services (e.g. for Teletex , Telefax , Datafax ,
Bureaufax , Videotex services), ISO in particular is invited to
give advice to CCITT based on their work on data systems and data
communications;
(f ) that this cooperation has to be organized in a manner
that will avoid duplication of work and of decisions that would be
contrary to the principles set out above;
recognizes the following principles
(1) It is the responsibility of the CCITT alone to make the
decisions regarding the operational, technical (including factors
needed to ensure international interworking) and tariff principles
of the CCITT-defined services.
(2) While the CCITT will define many of the relevant factors
for the CCITT-defined telematic services, other international
organizations will be invited to give specialist advice to CCITT on
subjects that are of mutual interest, such as:
- character sets and coding;
- end-to-end control procedures including error
protection;
- interfaces between terminals and circuit ter-
minating equipment;
- terminal transmitter distortion and receiver mar-
gin;
- paper sizes and text formatting.
(3) Standardization, if required, of hardware and software
implementation of terminals, such as printing systems, paper feed,
character type fonts, paper characteristics, etc., are outside the
scope of CCITT.
Recommendation A.22
COLLABORATION WITH OTHER INTERNATIONAL ORGANIZATIONS
ON INFORMATION TECHNOLOGY
(Melbourne, 1988)
The CCITT,
considering
(a) that the purposes of the International Telecommunication
Union and the recognition of CCITT relations with other organiza-
tions were given in 1964 and later, in CCITT Recommendation A.20
which concerns data transmission;
(b) that the principles of responsibility in regard to
CCITT-defined Telematic services were given in 1980 and later, in
Recommendation A.21 which mentions some subjects of mutual
interest;
(c) that CCITT Resolution No. 7 in 1984 further recognized
common interests with ISO and IEC concerning Information Technology
and cooperation with them by appropriate means,
recognizes the following principles
(1) that in accordance with CCITT Recommendations A.20 and
A.21 and Resolution No. 7, every effort should be made in estab-
lishing respective study programmes to identify overlapping studies
with a view to avoiding duplication of work;
(2) that where subjects are identified in which coordination
seems desirable, text should be drawn up mutually and kept aligned;
(3) that in carrying on the respective programmes of Informa-
tion Technology studies, collaborative meetings at appropriate lev-
els should be scheduled, where necessary. In drafting aligned text,
it is necessary to take into account the respective timing for
approvals and publication, particularly with the ISO/IEC Joint
Technical Committee 1 (JTC1) on Information Technology;
(4) that commonality of text with ISO/IEC and cross-references
is considered desirable in certain areas of mutual interest, such
as:
- Message Handling Systems,
- Directory Systems,
- Open Systems Interconnection (OSI) architecture -
service definitions and protocol specifications,
- certain areas of Interworking,
- certain aspects of Telematic Services,
- Document Architecture,
- certain aspects of ISDN.
Recommendation T.0
CLASSIFICATION OF FACSIMILE APPARATUS FOR DOCUMENT |
TRANSMISSION
OVER THE PUBLIC NETWORKS
(Geneva, 1976; amended at Geneva, 1980;
Malaga-Torremolinos, 1984 and Melbourne, 1988)
1 For document facsimile transmission by international commun-
ications carried on the public networks there is a need for provid-
ing sufficient operating speeds to meet users' requirements.
2 Users' requirements may best be served at the present time
by classifying the following four basic categories of document fac-
simile apparatus.
2.1 Apparatus for use over the public telephone network
Group 1 (see Note 1)
Apparatus which uses double sideband modulation without any
special measures to compress the bandwidth of the transmitted sig-
nal and which is suitable for the transmission of documents of
ISO A4 size at nominally 4 lines per mm in about six minutes via a
telephone-type circuit.
Apparatus in this group may be designed to operate at a lower
definition suitable for the transmission of documents of ISO A4
size in a time between three and six minutes.
Group 2 (see Note 2)
Apparatus which exploits bandwidth compression techniques in
order to achieve a transmission time of about three minutes for the
transmission of an ISO A4 size document at nominally 4 lines
per mm via a telephone-type circuit. Bandwidth compression in this
context includes encoding and/or vestigial sideband working but
excludes processing of the document signal to reduce redundancy.
Group 3 (see Note 3)
Apparatus which incorporates means for reducing the redundant
information in the document signal prior to the modulation process
and which can achieve a transmission time of about 1 minute for a
typical typescript document of ISO A4 size via a telephone-type
circuit. The apparatus may incorporate bandwidth compression of the
line signal.
2.2 Apparatus for use over the public data networks
Group 4 (see Note 4)
Apparatus which incorporates means for reducing the redundant
information in the document signal prior to transmission mainly via
public data networks (PDNs). The apparatus will utilize procedures
applicable to the PDN and will assure an essentially error-free
reception of the document. The apparatus may also be used on the
public telephone network where an appropriate modulation process
will be utilized.
3 The users will choose among this apparatus, in accordance
with their needs and the facilities afforded by the connection and
the network.
4 Procedures for Groups 1, 2 and 3 document facsimile
transmission in the public switched telephone network should be in
accordance with Recommendation T.30.
5 Procedures for Group 4 document facsimile transmission
should be in accordance with Recommendations T.62, T.62 | fIbis ,
and T.70.
Note 1 - This apparatus has been standardized in
Recommendation T.2.
Note 2 - This apparatus has been standardized in
Recommendation T.3.
Note 3 - This apparatus has been standardized in
Recommendation T.4.
Note 4 - This apparatus has been standardized in
Recommendations T.6, T.503, T.521 and T.563.
6 Annex A contains definitions for terms used in the T-series
Recommendations applicable to facsimile apparatus.
ANNEX A
(to Recommendation T.0)
Definitions for terms used in the T-series Recommendations
applicable to fascimile apparatus
The following definitions apply to Recommendations T.1, T.2,
T.3 and T.4:
A.1 dead sector (Recommendations T.1, T.2)
In drum apparatus, that portion of the drum surface the scan-
ning time of which cannot be used for picture signal transmission.
A.2 drum factor (Recommendation T.1)
In drum apparatus, the ratio of the usable scanning length of
the drum to its diameter.
A.3 facsimile (Series T)
The process of scanning a document (page), converting the
image scanned into electrical signals for transmission to a remote
receiver and the conversion of the received signals to produce a
copy of the image originally scanned.
A.4 factor of cooperation (Recommendation T.1)
The product of the total scanning line length and the scanning
density.
A.5 flat-bed transmitter (Recommendation T.1)
Apparatus in which the original document is placed flat and
scanned line by line.
A.6 index of cooperation (Recommendations T.1, T.2, T.3)
Quotient of the factor of cooperation divided by the quan-
tity ~~. In the case of a drum apparatus, the index of cooperation
is also equal to the product of the drum diameter and the scanning
density.
A.7 judder, longitudinal (Recommendation T.1)
Effect due to the irregular rotation of the drum or helix
causing, on the reproduced picture, slight waviness or breaks in
lines that are regular on the original document.
A.8 judder, transverse (Recommendation T.1)
Effect due to irregularity of the scanning pitch resulting in
concurrent overlapping and underlapping in the reproduced picture.
A.9 lost time (Recommendation T.3)
The portion of the scanning line period which cannot be used
for picture signal transmission.
Note - In the case of drum apparatus, this is the same as the
dead sector scanning time.
A.10 nominal black (white) (Recommendation T.1)
Level or frequency of the signal corresponding to a pure black
(white).
A.11 pel (Series T)
A contraction of "picture element".
A.12 phasing (Recommendations T.1, T.2, T.3)
At the receiver, ensuring the exact coincidence of the mid-
point of the scanning field, with the corresponding point at the
transmitter so as to ensure the correct positioning of the picture
on the recording medium.
A.13 phasing signal (Recommendations T.1, T.2, T.3)
A signal sent by the transmitter for phasing purposes.
Note - Phasing is known as "phase white (black)" if the phas-
ing signal is a black (white) signal of which a short interruption
corresponding to the white (black) is sent during the lost time.
A.14 phototelegraphy (Recommendation T.1)
Method of reception of facsimile telegraphy which is chiefly
intended for the reproduction of graded tonal densities and in
which a photographic process is used at the receiver.
A.15 picture element (Recommendations T.3, T.4)
a) at transmission:
The part of the area of the original document which coincides
with the scanning spot at a given instant and which is of one
intensity only, with no distinction of the details that may be
included.
b) at reception:
The area of the finest detail that can be effectively
reproduced on the recording medium.
A.16 reproduction ratio (Recommendation T.1)
The ratio of the linear dimensions of the reproduced document
to the corresponding dimensions of the original document.
A.17 resolution (Series T)
A measure of the capability for delineating picture detail. In
Group 3 and Group 4 facsimile transmission resolution is expressed
as picture elements or pels per mm (horizontal resolution) and
lines per mm (vertical resolution).
A.18 scanning density (Recommendations T.1, T.2, T.3)
Number of scanning pitches per unit length.
A.19 scanning line (Recommendations T.1, T.2, T.3)
The area explored by the scanning spot in one sweep from one
side to the other of the scanning field.
A.20 scanning pitch (Recommendation T.1)
The distance between the corresponding edges of two consecu-
tive scanning lines.
A.21 skew (Recommendation T.3)
A defect in reproduction in which lines that should be at
right-angles to the scanning direction are inclined to it, owing to
a difference between the scanning speeds at transmission and recep-
tion.
A.22 synchronization (Recommendation T.1)
The establishment of equal scanning line frequencies at the
transmitter and receiver.
Recommendation T.1
STANDARDIZATION OF PHOTOTELEGRAPH APPARATUS
(former CCIT Recommendation D.1; amended at
New Delhi, 1960; Geneva, 1964; Mar del Plata, 1968;
Malaga-Torremolinos, 1984 and Melbourne, 1988)
The CCITT,
considering
that the transmission of pictures is possible only if certain
characteristics of the transmitting and receiving equipments are
identical,
unanimously declares the view
that phototelegraph apparatus and the associated modulating
and demodulating equipment should be constructed and employed
according to the following standards:
1 Scanning track
At the transmitting apparatus the message area should be
scanned in a "negative" direction. The orientation of the document
in relation to the scanning plane will depend upon its dimensions
and is of no consequence.
At the receiving apparatus scanning takes place in a "nega-
tive" direction for "positive" reception and in a "positive" direc-
tion for "negative" reception.
2 Index of cooperation
The normal index is 352 (corresponds to a factor of coopera-
tion of 1105).
The preferred alternative index, for use when less dense scan-
ning is required, or when the characteristics of circuits (and par-
ticularly combined radio and metallic circuits) so demand, is 264
(a factor of cooperation of 829). The admissible tolerances on the
above-mentioned values are _ | %.
3 Dimensions of apparatus
3.1 Apparatus with drum scanning
The most currently used drum diameters are 66, 70 and 88 mm.
The drum factor of the sending apparatus shall not be more
than 2.4.
The drum factor of the receiving apparatus shall not be less
than 2.4.
The width of the picture-retaining device (dead sector) may
not exceed 15 mm. An allowance of 3% of the total length of a scan-
ning line is also made for phasing. Thus, since the total cir-
cumference of a drum of the diameter of 66 mm is about 207 mm, the
usable circumference will be at least 186 mm.
3.2 Apparatus with flat-bed scanning
The total lengths of the most current scanning lines are 207,
220 and 276 mm of which 15 mm are not used for effective transmis-
sion, because of the possibility that the receiving station may use
a drum apparatus.
Before transmitting a picture to a receiving station using a
drum apparatus, it is necessary to ensure that the value of ratio:
otal length of a scanning line
____________________________________ x ~~
is less or at most equal to the drum factor of the receiver used.
3.3 Table 1/T.1 gives corresponding values of index of
cooperation M , factor of cooperation C , drum diameter D , total
length of scanning line L , scanning pitch P and scanning density F
for apparatus in most common use.
H.T. [T1.1]
TABLE 1/T.1
_________________________
Measured in the direction perpendicular to the scanning
line.
_________________________________________________________
M C D (mm) L (mm) P (mm) F (lines/mm)
_________________________________________________________
264 829 66 207 1/4.77 4.77
264 829 70 220 1/3.77 3.77
264 829 88 276 1/3.77 3.77
350 1099 70 220 1/5.77 5.77
352 1105 66 207 3/16 7 16/3
352 1105 88 276 1/4.77 4.77
_________________________________________________________
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Note - The maximum dimensions of the pictures to be transmitted
result from the parameters given in the table.
Tableau 1/T.1 [T1.1], p.
4 Reproduction ratio
In the case where apparatus working with different lengths of
scanning line (but with the same index of cooperation) are inter-
connected, there will be a slight change in size and the reproduc-
tion will bear the same proportion as the original, the ratio being
that of the total lengths of the scanning lines.
5 Drum rotation speed - scanning line frequency
5.1 Table 2/T.1 gives the normal and approved alternative com-
binations of drum rotation speeds or of scanning line frequencies
and indices of cooperation.
H.T. [T2.1]
TABLE 2/T.1
______________________________________________________________________________________________
Metallic circuits {
{
______________________________________________________________________________________________
Normal conditions 60 90 352 352 264
______________________________________________________________________________________________
{
Alternatives for use when the phototelegraph
apparatus and metallic circuits are suitable
} 90 120 150 {
264 and 352
264 and 352
264
}
______________________________________________________________________________________________
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Note 1 - In the case of transmitters operating on metallic cir-
cuits, the index 264 is not intended to be used with an 88-mm drum.
In the case of transmitters operating on combined metallic and
radio circuits, the index 264 associated with a drum diameter
of 88-mm is intended to be used only exceptionally.
Note 2 - The provisions given in the table are not intended to
require the imposition of such standards on users who use their own
equipment for the transmission of pictures over leased circuits.
However, the characteristics of the apparatus used should be compa-
tible with the characteristics of the circuits used.
Tableau 2/T.1 [T2.1], p.
5.2 The speed of transmitters must be maintained as nearly as
possible to the nominal speed and in any case within _ | 0 parts
in 106 of the nominal speed. The speed of receivers must be adju-
stable and the range of adjustment should be at least _ | 0 parts
in 106 from the nominal speed. After regulation, the speeds of the
transmitting and receiving sets should not differ by more than
10 parts in 106.
6 Judder
The stability of the speed during one rotation should be such
that the maximum shift of the drum surface from the average posi-
tion should not exceed one quarter of the scanning pitch P at nor-
mal index 352, which means that the maximum angle of the oscilla-
tions should not exceed 0.08 degree measured from the average posi-
tion.
7 Synchronization
When phototelegraph stations have available a standard of fre-
quency which is better than _ | parts in 106, verification of the
synchronism between the two stations may be dispensed with. In view
of the saving of time, this method should be adopted wherever pos-
sible.
To compare the speeds of a transmitter and a receiver, an
alternating current whose frequency bears an unvarying relationship
to the transmitter speed and has a nominal value of 1020 Hz is
used.
Where there is the possibility that the transmitter and
receiver may be connected by a circuit liable to introduce fre-
quency drifts, for example, by a carrier telephone circuit, the use
of the simple 1020-Hz synchronizing tone is unsatisfactory. The
preferred method of overcoming this difficulty is to transmit the
phototelegraph carrier (of about 1900 Hz) modulated by the 1020-Hz
synchronizing tone.
At the receiving end, the 1020-Hz synchronizing frequency is
restored by detection and can then be used in the normal manner.
8 Phasing
Phasing is performed after the speeds of the transmitter and
receiver drums have been equalized.
For phasing purposes, the transmitter sends a series of alter-
nating white and black signals in such a way that the black
lasts 95% and the white 5% of the total scanning line period
(admissible tolerance: _ | .5% of the total duration of a scanning
line). The apparatus must be so adjusted that the pulses
corresponding to the signal for white are transmitted:
- during scanning of the " dead sector ", when drum
apparatus is used,
- during "lost time", when flat-bed apparatus is
used,
and that they are placed at the middle of the dead sector (or of
the interval corresponding to the lost time ).
(Tolerance admitted in the position of the "white" pulses:
__E = _ 1% of a "total scanning line length".)
At the receiving station, phasing signals are used to start
the apparatus so that short white pulses occur in the middle of the
"lost time" (tolerance admitted: __R = _ 2% of a "total scanning
line length").
Note - These tolerances allow for the fact that the restitu-
tion of the original may deviate from its nominal position by 3% of
a "total scanning line length", when the sending and receiving sta-
tions are operating with the maximum authorized drift in the same
direction.
9 Contrast
The transmitter must transmit the original document without
changing the contrast of the tone scales of the picture to be
transmitted.
10 Modulation and demodulation equipment
10.1 Amplitude modulation
Phototelegraph equipment shall normally provide for transmis-
sion and reception of an amplitude modulated audio-frequency car-
rier, which is the normal mode of transmission for international
metallic circuits.
The level of the output signal of the transmitter shall be
greatest for white and least for black. It is desirable that the
ratio of nominal white signal to nominal black signal should be
approximately 30 decibels.
To simplify multi-destination operation and AM/FM conversion
for radio operation it is desirable that the amplitude of the
transmitted signal should vary linearly with the photocell voltage
and that no corrections for tone scale should be made at the photo-
telegraph transmitting station.
For audio-frequency telephone circuits, the frequency of the
picture carrier-current is fixed at about 1300 Hz. This frequency
gives the least delay distortion on lightly loaded underground
cables.
In the case of carrier telephone circuits providing a
transmission band from 300 to 3400 Hz, a carrier-current frequency
of about 1900 Hz is recommended.
10.2 Frequency modulation
Preferably phototelegraph apparatus should also provide for
transmission and reception of a frequency-modulated audio-frequency
carrier for use when necessary:
a) on combined metallic and radio circuits;
b) on wholly metallic circuits.
In such a case, the characteristics of the frequency-modulated
output should be: mean frequency 1900 Hz
white frequency 1500 Hz
black frequency 2300 Hz
The deviation of frequency should vary linearly with photocell
voltage or, in the case of conversion from amplitude modulation to
frequency modulation, with the amplitude of the amplitude-modulated
carrier.
The stability of the transmission must be such that the
frequency corresponding to a given tone does not vary by more than
8 Hz in a period of 1 second and by more than 16 Hz in a period of
15 minutes.
The receiving apparatus must be capable of operating correctly
when the drift of black and white frequencies received does not
exceed their nominal value by more than _ | 2 Hz.
Note - It is recognized that there are difficulties operating
with these frequency limits on the public switched telephone net-
work (PSTN) where certain types of signalling equipment are used.
By prior agreement between users on the PSTN, alternative frequen-
cies of 1300 Hz for white and 2100 Hz for black may be used.
11 Positive or negative reception
Selection of positive or negative reception should be made by
adjustment at the receiver. The adaptation of the transmitted sig-
nals to the characteristics of the photographic materials must also
be effected at the receiving end according to the type of reproduc-
tion, negative or positive.
12 Colour transmission (optional)
12.1 Phototelegraphy apparatus constructed in accordance with
this Recommendation can be used in colour phototelegraphy by split-
ting the spectrum of light reflected from the picture elements into
three basic colours and transmitting the three resulting signals
sequentially. Then each signal can be treated and transmitted as a
phototelegraphy signal as specified in this Recommendation above.
12.2 The splitting of light reflected from picture element
into three spectral components should be performed simultaneously.
Thus synchro and phase coincidence and electronic colour correction
can be achieved.
12.3 The triad RGB (red, green, blue) shall be used as a basis
of main colours. The red colour shall be in range of 575-700 nm,
green 485-575 nm, blue 400-485 nm.
Note - For the high quality reproduction of art images by
means of graphic facilities, transmission of fourth components
(i.e. black overtone) is desirable.
12.4 The order of signal transmission shall be as follows:
red, green, blue. In the case of negative reproduction the order of
colour separated signals transmission is reversed.
12.5 The speeds of the transmitting and receiving sets should
not differ by more than 1 part in 107.
Recommendation T.2
STANDARDIZATION OF GROUP 1 FACSIMILE APPARATUS
FOR DOCUMENT TRANSMISSION
(Mar del Plata, 1968; amended at Geneva, 1972 and 1976)
The CCITT,
considering
(a) that there is a requirement for Group 1 facsimile
apparatus which enables an ISO A4 document to be transmitted over a
telephone-type circuit in approximately six minutes;
(b) that document facsimile transmission may be requested
alternately with telephone conversation or when either or both sta-
tions are unattended; in both cases the facsimile operation should
conform to Recommendation T.30,
unanimously declares the view
that Group 1 facsimile apparatus for use on the general
switched telephone network and international leased circuits should
be designed and operated according to the following standards:
1 Scanning track
The message area should be scanned in the same direction in
the transmitter and receiver. Viewing the message area in a verti-
cal plane, the scanning direction should be from left to right, and
subsequent scans should be adjacent and below the previous scan.
2 Index of cooperation
The nominal index of cooperation is 264. In cases where a
lower vertical resolution is acceptable, and by agreement between
the users, an optional index of cooperation of 176 may be used.
These values should be observed with a nominal tolerance of _
| % for each equipment.
3 Dimensions of apparatus
3.1 The apparatus should accept documents up to a minimum of
ISO A4 size (nominally 210 mm x 297 mm).
3.2 The total scanning line length ( active sector plus dead
sector) should be nominally 215 mm. Nominally 200 mm should be
available for scanning or recording, the remainder being the dead
sector
3.3 For any one document the nominal number of scans should
be 1144 for an index of cooperation of 264 (762 scans for an index
of 176). The receiver should be capable of recording nominally
1144 scans per document for an index of cooperation of 264 (or
762 scans for an index of 176).
3.4 Apparatus with other dimensions may be used provided that
the index of cooperation is respected, that the total scanning line
length lies between 210 and 250 mm and the usable recording line
length retains the same ratio to the total scanning line length.
4 Scanning density
Scanning density is normally 3.85 lines per mm.
5 Scanning line frequency
In the subscriber-to-subscriber service via the general
switched telephone network, the scanning line frequency should be
180 lines per minute (see Note).
For leased circuits operation the best line frequency, which
may be higher or lower than 180 lines per minute, may be chosen
according to the circuit characteristics.
The scanning line frequency during the transmission should be
kept within _ | 0 parts in 106 of the nominal value.
Note - With manual control at the two ends of connection set
up over the general switched telephone network, another scanning
line frequency (e.g. 240 per minute) may be chosen by agreement
between the two operators.
6 Phasing
The duration of the phasing signal for transmitters should be
15 _ 1 seconds.
In a preferred method of phasing (see Note 1), the transmitter
sends a series of alternating white and black signals in such a way
that the white pulse (phasing pulse) is 4 to 6% of the total scan-
ning line length and the leading edge is 2 to 3% in advance of the
middle of the dead sector.
Receiving apparatus should synchronize the middle of its dead
sector 0.5 to 4.5% lagging the leading edge of the received phasing
pulse (see Note 2).
Note 1 - In a permitted method of phasing for present genera-
tion machines, the transmitter sends a series of white and black
signals in such a way that the white pulse is 2 to 12% of the total
scanning line length and the leading edge is 2 to 3% in advance of
the middle of the dead sector.
Note 2 - Maximum reduction of recorded scanning line length
due to synchronizing misalignment should not exceed 3% of total
scanning line length. Maximum reduction of recorded scanning line
length due to the combined effect of deviations of the transmitter
and receiver scanning line frequencies should not exceed 4% of
total scanning line length. The effect of these reductions of
recorded scanning line length may cause it to be less than the nom-
inal 200 mm.
7 Modulation and demodulation equipments
7.1 Amplitude modulation | (for leased circuits only)
The facsimile signal level is higher for black and lower for
white.
The carrier frequency should range between 1300 and 1900 Hz
and will depend upon the characteristics of the circuits used.
7.2 Frequency modulation | (for leased circuits and for
switched connections)
The frequency corresponding to black will normally
be f0 + 400 Hz and the frequency corresponding to white will nor-
mally be f0 - 400 Hz (see Note).
For switched connections f0 = 1700 Hz (provisional). For
leased circuits f0should range between 1300 and 1900 Hz: the choice
of the centre frequency f0will depend upon the circuit characteris-
tics. However, if the user, in some cases, wishes to use the
apparatus on switched connections, f0 = 1700 Hz.
The stability of the transmitter must be such that the signi-
ficant frequencies do not vary by more than 32 Hz from their nomi-
nal value in a period of 15 minutes.
Note - Attention is drawn to the fact that there are some
equipments currently in operation for which black and white ele-
ments are represented in the opposite sense, but the preferred
standard for new equipment is as indicated above.
7.3 Power at the transmitter output
When amplitude modulation is used, the power of black at the
transmitter output must be able to be adjusted between -7 dBm and
0 dBm. The white level must be approximately 15 dB below the black
level.
In frequency-modulated systems, the level at the output of the
facsimile apparatus must be able to be adjusted between -15 dBm and
0 dBm.
The equipment should be so designed that there is no possibil-
ity of this adjustment being tampered with by an operator.
7.4 Power at the receiver input
The facsimile receiver must be so designed that it functions
correctly when the input power ranges between 0 dBm and -40 dBm,
the latter value being considered provisional. In the case of
amplitude modulation, this concerns the power of the black signal.
No control of receiver sensitivity should be provided for operator
use.
Recommendation T.3
STANDARDIZATION OF GROUP 2 FACSIMILE APPARATUS |
FOR DOCUMENT TRANSMISSION
(Geneva, 1976; amended at Geneva, 1980)
The CCITT,
considering
(a) that Recommendation T.2 refers to Group 1 type apparatus
for ISO A4 document transmission in approximately six minutes;
(b) that there is a demand for Group 2 apparatus which enables
an ISO A4 document to be transmitted over a telephone-type circuit
in approximately three minutes;
(c) that the Group 2 apparatus reproduces document quality
similar to Group 1 apparatus;
(d) that such a service may be requested either alternatively
with telephone conversation, or when either or both stations are
not attended; in both cases, the facsimile operation will follow
Recommendation T.30;
(e) interconnection between two machines of different designs,
both conforming to Recommendation T.3 as published in the
Orange Book may give a lower guaranteed reproducible area in cer-
tain cases;
unanimously declares the view
that Group 2 facsimile apparatus for use on the general
switched telephone network and international leased circuits shall,
in future, be designed and operated in accordance with this Recom-
mendation. Apparatus conforming to Recommendation T.3 of the
Orange Book may continue in service.
1 Scanning track
The message area should be scanned in the same direction in
the transmitter and receiver. Viewing the message area in a verti-
cal plane, the scanning direction should be from left to right and
subsequent scans should be adjacent and below the previous scan.
In order to avoid loss of information, users should insert
documents so that the scanning direction is from the wider to the
narrower margin.
2 Dimensions of apparatus
The following dimensions are recommended but apparatus with
other dimensions may be used provided that the factor of coopera-
tion is respected and that the total scanning line length lies
between 215 and 222 mm.
Factor of cooperation (FOC) 829 _ 1%
Total scanning line-length (TLL) 215 mm
Usable scanning line-length (ULL) 205 mm minimum
The end of ULL shall lie between 0 and 1 mm within
the nominal position of the right hand edge of an ISO A4 size docu-
ment.
Input document size Up to a minimum of ISO A4 size
(nominally 210 x 297 mm)
The foregoing dimensions give rise to the following approxi-
mate secondary dimensions.
Index of cooperation (IOC) 264
Scanning density 3.85 line/mm
Number of scanning lines in a document 297 mm long
1145
3 Scanning line frequency
3.1 The scanning line frequency should be 360 lines per
minute.
Note - Another scanning line frequency (e.g. 300 lines per
minute) may be chosen by agreement between the two stations.
3.2 The scanning line frequency during the transmission should
be kept within _ | parts in 106 of the nominal value.
4 Phasing
For phasing prior to transmission of document information the
transmitter sends a signal as shown in Figure 1/T.3. The start of
the carrier indicates the end of the lost time time to the start of
carrier should be _ | .5% of TLL. The receiver should phase its
reference point with an accuracy of _ | % of TLL to this start of
the carrier. The reference point should be 209 mm before the end of
ULL (see Figure 2/T.3).
Note - In the case of the multiple page transmission the
phasing procedure may need to be repeated between pages.
Figure 1/T.3, (M) p.
Figure 2/T.3, (M) p.
5 Document transmission
5.1 During transmission of document information the
transmitter should transmit full amplitude carrier during the lost
time for at least 4% of the transmission time for TLL. The phase of
the carrier may be reversed at the end of this signal.
Following the lost time the information transmitted to the
receiver is the one contained in ULL. The value of ULL is defined
in S 2.
The receiver must be able to reproduce at least ULL on the
reproduction media after the end of the lost time.
5.2 This signal may be used at the receiver as an amplitude
reference independent of the document signal and also to indicate
to the receiver that document transmission is still in progress.
6 Paper alignment
All types of apparatus should be designed to ensure that paper
is positioned within _ | .5 mm of nominal in the horizontal direc-
tion. In the vertical direction it must be ensured that paper is
positioned in such a way that scanning and recording start not more
than 4 mm down the document from the top edge.
7 Modulation and demodulation
7.1 Equivalent modulated waveforms with vestigial sideband
amplitude modulation - phase modulation characteristics should be
used for Group 2 apparatus operated on leased circuits and on the
general switched telephone network. The carrier frequency should be
2100 _ 10 Hz (see Note). A white signal should be represented by
maximum carrier and a black signal by minimum (at least 26 dB below
white) or no carrier. The phase of the carrier representing white
may be reversed after each transition through black.
Note - It should be noted that there are equipments in ser-
vice using, inter alia, a carrier frequency of 2048 Hz.
7.2 The facsimile transmission could contain a limited range
of half-tones represented by a carrier amplitude less than that
sent during the lost time.
7.3 A vestigial sideband filter symmetrical about the 2100-Hz
carrier frequency should be provided at the transmitter. The
response of this filter should conform to Figure 3/T.3. The accu-
racy of this filter is not critical but the relative transmittance
at the carrier frequency should be 0.5 with a tolerance of _ | .05
and the characteristic should be sensibly symmetrical about the
carrier frequency.
Figure 3/T.3, (M) p.
7.4 The receiving apparatus must be capable of operating
correctly when the drift of carrier frequency does not exceed its
nominal value by more than _ | 6 Hz.
7.5 A fixed compromise equalizer, an automatic equalizer or an
adaptive equalizer may be provided in the receiver but this should
be a matter for further study.
8 Power at the transmitter output
The power of the white signal should be adjustable from
-15 dBm to 0 dBm but the equipment should be so designed that there
is no possibility of this adjustment being tampered with by an
operator. The black level should be at least 26 dB below the white
level.
9 Power at the receiver input
The receiving apparatus should be capable of functioning
correctly when the received signal level for white is within the
range 0 dBm to -40 dBm, the latter value being considered provi-
sional. No control of receiver sensitivity should be provided for
operator use.
APPENDIX I
(to Recommendation T.3)
Guaranteed
reproducible area for Group 2 machines
conforming to Recommendation T.3
Figure I-1/T.3, (M), p.6
I.1 Horizontal loss
Figure I-2/T.3, (M), p.7
H.T. [T1.3]
TABLE I-1/T/3
Results
_____________________________________________________________
Left margin (mm) Right margin (mm)
Horizontal losses 205 210 205 210
_____________________________________________________________
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Transmitter a _0.5% 1.11 1.11 1.11 1.11
Phasing Receiver b _1.0% 2.22 2.22 2.22|
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2.22
_________________________________________________________________________________
Skew c {
_5 x 10 | uDlF2616
} 2.46 2.46 2.46 2.46
_________________________________________________________________________________
Enlarging d - - 6.46 6.62
_________________________________________________________________________________
Paper insertion f 1.50 1.50 1.50 1.50
_________________________________________________________________________________
Min. x - - 1.00 1.00
Lost time Max. x 5.00 - - -
_________________________________________________________________________________
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Tableau I-1/T.3 [T1.3], p.8
I.2 Vertical loss
Figure I-3/T.3, (M), p.9
H.T. [T2.3]
TABLE I-2/T.3
___________________________________________________
Top (mm) Bottom (mm)
___________________________________________________
Gripping loss g 4.0 4.0
___________________________________________________
Paper insertion h
___________________________________________________
Enlarging + FOC i - 15.15
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Tableau I-2/T.3 [T2.3], p.10
Recommendation T.4
STANDARDIZATION OF GROUP 3 FACSIMILE APPARATUS
FOR DOCUMENT TRANSMISSION
(Geneva, 1980, amended at Malaga-Torremolinos, 1984 and Melbourne,
1988)
The CCITT,
considering
(a) that Recommendation T.2 refers to Group 1 type apparatus
for ISO A4 document transmission over a telephone-type circuit in
approximately six minutes;
(b) that Recommendation T.3 refers to Group 2 type apparatus
for ISO A4 document transmission over a telephone-type circuit in
approximately three minutes;
(c) that there is a demand for Group 3 apparatus which enables
an ISO A4 document to be transmitted over a telephone-type circuit
in approximately one minute;
(d) that for a large number of applications black and white
reproduction is sufficient;
(e) that such a service may be requested either alternatively
with telephone conversation, or when either or both stations are
not attended; in both cases, the facsimile operation will follow
Recommendation T.30;
unanimously declares the view
that Group 3 facsimile apparatus for use on the general
switched telephone network and international leased circuits should
be designed and operated according to the following standards:
1 Scanning track
The message area should be scanned in the same direction in
the transmitter and receiver. Viewing the message area in a verti-
cal plane, the picture elements should be processed as if the scan-
ning direction were from left to right with subsequent scans adja-
cent and below the previous scan.
2 Dimensions of apparatus
Note - The tolerances on the factors of cooperation are
subject to further study.
2.1 The following dimensions should be used:
a) a standard resolution and an optional higher
resolution of 3.85 line/mm _ 1% and 7.7 line/mm _ 1% respectively
in vertical direction,
b) 1728 black and white picture elements along the
standard scan line length of 215 mm _ 1%,
c) optionally, 2048 black and white picture ele-
ments along a scan line length of 255 mm _ 1%,
d) optionally, 2432 black and white picture ele-
ments along a scan line length of 303 mm _ 1%,
and, for equipment which provides A5 and/or A6 facilities:
e) optionally, 864 black and white picture elements
along a scan line length of 107 mm _ | %,
f ) optionally, 1216 black and white picture ele-
ments along a scan line length of 151 mm _ | %,
g) Optionally, 1728 black and white picture ele-
ments along a scan line length of 107 mm _ | %,
h) Optionally, 1728 black and white picture ele-
ments along a scan line length of 151 mm _ | %.
The normal method of interworking when transmitting from an A5
or A6 machine to an A4 machine not signalling such capabilities, is
that the A5 or A6 content will be enlarged to fill the A4 page (see
also Note 3). This means that if the document is then retransmit-
ted, or if it has been stored for later retransmission, it will be
received without additional reduction.
Where the full image contents being received from an A4
machine need to be maintained, g) or h) respectively should be
used.
Interworking between equipments with A5/A6 and A4 facilities
and between equipments with combinations of these facilities is
shown in Annex C.
Note 1 - Cases e) to h) describe equipments which may be
implemented singly or in any combination and would not, for A5/A6
facsimile equipments, require implementation of a) or b). These
equipments may be implemented with cases different for sending and
receiving.
Note 2 - In cases e) to h), 1728 pels will always be provided
to the coder (see Annex C).
In cases e) and f ), the additional pels required are produced
by pel processing (i.e., either by picture processing or by adding
white pels on each side of the central picture information) prior
to coding.
Note 3 - It could be possible, by a setting on the A5/A6
transmitting machine, to send the document so that it is received
equal size on an A4 machine not signalling such capabilities. In
this case the vertical resolution will be 3.85 (or 7.7) line/mm.
The user should be made aware that in this particular equal size
case if the received copy is transmitted back to the A5/A6 machine
the subsequent copy will be reduced.
Note 4 - Some Administrations may require that equipments
using e) or f ) dimensions, when working with a receiver not sig-
nalling such capabilities, insert a message e.g., "ISO A6" or
"ISO A5", as the case may be, into the picture at the transmitting
side.
2.2 Input documents up to a minimum of ISO A4 size should be
accepted.
Note - The size of the guaranteed reproducible area is shown
in Appendix I.
3 Transmission time per total coded scan line
The total coded scan line is defined as the sum of DATA bits
plus any required FILL bits plus the end-of-line (EOL) bits.
For the optional two-dimensional coding scheme as described in
S 4.2, the total coded scan line is defined as the sum of DATA bits
plus any required FILL bits plus the EOL bits plus a tag bit.
To handle various printing methods, several optional minimum
total coded scan line times are possible in addition to the 20 mil-
liseconds standard.
3.1 The minimum transmission times of the total coded scan
line should conform to the following:
1) Alternative 1, where the minimum transmission
time of the total coded scan line is the same both for the standard
resolution and for the optional higher resolution:
a) 20 milliseconds recommended standard,
b) 10 milliseconds recognized option with a manda-
tory fall-back to the 20 milliseconds standard,
c) 5 milliseconds recognized option with a manda-
tory fall-back to the 10 milliseconds option and the 20 mil-
liseconds standard,
d) 0 millisecond recognized option with a mandatory
fall-back to the 5 milliseconds option, the 10 milliseconds option
and the 20 milliseconds standard, and an optional fall-back to the
40 milliseconds option,
e) 40 milliseconds recognized option.
2) Alternative 2, where the minimum transmission
time of the total coded scan line for the optional higher resolu-
tion is half of that for the standard resolution (see Note). These
figures refer to the standard resolution:
a) 10 milliseconds recognized option with a manda-
tory fall-back to the 20 milliseconds standard,
b) 20 milliseconds recommended standard,
c) 40 milliseconds recognized option.
The identification and choice of this minimum transmission
time is to be made in the pre-message (phase B) portion of
Recommendation T.30 control procedure.
Note - Alternative 2 applies to equipment with printing
mechanisms which achieve the standard vertical resolution by print-
ing two consecutive, identical higher resolution lines. In this
case, the minimum transmission time of the total coded scan line
for the standard resolution is double the minimum transmission time
of the total coded scan line for the higher resolution.
3.2 The maximum transmission time of any total coded scan line
should be less than 5 seconds. When this transmission time exceeds
5 seconds, the receiver must proceed to disconnect the line.
3.3 Error correction mode
For the optional error correction mode, an HDLC frame struc-
ture is utilized to transmit the total coded scan line. This error
correction mode is defined in Annex A.
4 Coding scheme
4.1 One-dimensional coding scheme
The one-dimensional run length coding scheme recommended for
Group 3 apparatus is as follows:
4.1.1 Data
A line of Data is composed of a series of variable length code
words. Each code word represents a run length of either all white
or all black. White runs and black runs alternate. A total of
1728 picture elements represent one horizontal scan line of 215 mm
length.
In order to ensure that the receiver maintains colour syn-
chronization, all Data lines will begin with a white run length
code word. If the actual scan line begins with a black run, a white
run length of zero will be sent. Black or white run lengths, up to
a maximum length of one scan line (1728 picture elements or pels )
are defined by the code words in Tables 1/T.4 and 2/T.4. The code
words are of two types: Terminating code words and Make-up code
words one Make-up code word followed by a Terminating code word.
Run lengths in the range of 0 to 63 pels are encoded with
their appropriate Terminating code word. Note that there is a dif-
ferent list of code words for black and white run lengths.
Run lengths in the range of 64 to 1728 pels are encoded first
by the Make-up code word representing the run length which is equal
to or shorter than that required. This is then followed by the Ter-
minating code word representing the difference between the required
run length and the run length represented by the Make-up code
4.1.2 End-of-line (EOL)
This code word follows each line of Data. It is a unique code
word that can never be found within a valid line of Data; there-
fore, resynchronization after an error burst is possible.
In addition, this signal will occur prior to the first Data
line of a page.
Format: 000000000001
4.1.3 Fill
A pause may be placed in the message flow by transmitting
Fill. Fill may be inserted between a line of Data and an EOL, but
never within a line of Data. Fill must be added to ensure that the
transmission time of Data, Fill and EOL is not less than the
minimum transmission time of the total coded scan line established
in the pre-message control procedure.
Format: variable length string of 0s.
H.T. [T1.4]
TABLE 1/T.4
Terminating codes
________________________________________________________________
White run length Code word Black run length Code word
________________________________________________________________
0 00110101 0 0000110111
1 000111 1 010
2 0111 2 11
3 1000 3 10
4 1011 4 011
5 1100 5 0011
6 1110 6 0010
7 1111 7 00011
8 10011 8 000101
9 10100 9 000100
10 00111 10 0000100
11 01000 11 0000101
12 001000 12 0000111
13 000011 13 00000100
14 110100 14 00000111
15 110101 15 000011000
16 101010 16 0000010111
17 101011 17 0000011000
18 0100111 18 0000001000
19 0001100 19 00001100111
20 0001000 20 00001101000
21 0010111 21 00001101100
22 0000011 22 00000110111
23 0000100 23 00000101000
24 0101000 24 00000010111
25 0101011 25 00000011000
26 0010011 26 000011001010
27 0100100 27 000011001011
28 0011000 28 000011001100
29 00000010 29 000011001101
30 00000011 30 000001101000
31 00011010 31 000001101001
32 00011011 32 000001101010
33 00010010 33 000001101011
34 00010011 34 000011010010
35 00010100 35 000011010011
36 00010101 36 000011010100
37 00010110 37 000011010101
38 00010111 38 000011010110
39 00101000 39 000011010111
40 00101001 40 000001101100
41 00101010 41 000001101101
42 00101011 42 000011011010
43 00101100 43 000011011011
44 00101101 44 000001010100
45 00000100 45 000001010101
46 00000101 46 000001010110
47 00001010 47 000001010111
48 00001011 48 000001100100
49 01010010 49 000001100101
50 01010011 50 000001010010
51 01010100 51 000001010011
52 01010101 52 000000100100
53 00100100 53 000000110111
54 00100101 54 000000111000
55 01011000 55 000000100111
56 01011001 56 000000101000
57 01011010 57 000001011000
58 01011011 58 000001011001
59 01001010 59 000000101011
60 01001011 60 000000101100
61 00110010 61 000001011010
62 00110011 62 000001100110
63 00110100 63 000001100111
________________________________________________________________
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Tableau 1/T.4 [T1.4],p.11
H.T. [T2.4]
TABLE 2/T.4
Make-up codes