RFC 804
CCITT Draft Recommendation T.4
As Defined In: CCITT STUDY GROUP XIV, CONTRIBUTION No.25-E
SOURCE: DRAFTING GROUP ON DRAFT RECOMMENDATION T.4
TITLE: DRAFT RECOMMENDATION T.4 - STANDARDIZATION OF GROUP 3
FACSIMILE APPARATUS FOR DOCUMENT TRANSMISSION (as
amended and agreed by Working Party XIV/2)
Draft Recommendation T.4
STANDARDIZATION OF GROUP 3 FACSIMILE APPARATUS FOR DOCUMENT
TRANSMISSION
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 vertical plane, the scanning direction
should be from left to right and subsequent scans should be
adjacent and below the previous scan.
2. Dimensions of apparatus
CCITT Draft Recommendation T.4 PAGE 2
The following dimensions should be used:
a. A normal definition standard and an optional higher
definition standard of 3.85 and 7.7 line/mm respectively
in vertical direction;
b. 1728 black and white picture elements along the scanned
line;
c. A scanning line length of 215 mm. Other scanning line
lengths may be employed in which case the scanning
density should be changed to maintain the correct
picture proportions;
d. Input documents up to a minimum of ISO A4 size should be
accepted.
3. Transmission time per scanning line
A total scanning line is defined as the sum of DATA
bits plus any required FILL bits plus the EOL bits. The
minimum transmission times of the total scanning line should
conform to the following:
a. 20 milliseconds recommended standard with an optional
fall-back to the 40 milliseconds option;
b. 10 milliseconds recognized option with a mandatory
fall-back to the 20 milliseconds standard;
c. 5 milliseconds recognized option with a mandatory
fall-back to the 10 milliseconds option and the 20
milliseconds standard;
d. 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 the T.30 control procedure. The maximum
transmission time of any total scanning line should be less
than 5 seconds.
4. Coding scheme
The one-dimensional run length encoding scheme
recommended for Group 3 apparatus is as follows:
a. 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 scanning line of the document
of standard A4 size. In order to insure that the
receiver maintains color synchronization, all DATA lines
will begin with a white run length code word. If the
actual scanning 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 scanning line
CCITT Draft Recommendation T.4 PAGE 3
(1728 picture elements or pels) are defined by the code
words in Tables 1 and 2. The code words are of two
types: Terminating Code words and Make Up Code words.
Each run length is represented by either one Terminating
Code word or 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 different 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 Terminating Code word
representing the difference between the required run
length and the run length represented by the Make Up
Code.
b. 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; therefore, resynchronization after an
error burst is possible.
In addition, this signal will occur prior to the first
DATA line of a page.
Format: 000000000001
c. 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 insure that each line of DATA,
FILL, and EOL exceeds the minimum transmission time of a
total scanning line established in the premessage
control procedure. The maximum length for a single line
of FILL is 5 seconds, after which the receiver may
disconnect.
Format: variable length string of 0's.
d. RETURN TO CONTROL (RTC)
The end of a document transmission is indicated by
sending six consecutive EOL's. Following the RTC
signal, the transmitter will send the post message
commands in the standard T.30 blocked format at the data
rate.
CCITT Draft Recommendation T.4 PAGE 4
Format: 000000000001 ... ... ... ... 000000000001
(total of 6 times)
CCITT Draft Recommendation T.4 PAGE 5
Table 1a. Terminating White Codes
Code Lng Run
---------------------------
00110101 8 0
000111 6 1
0111 4 2
1000 4 3
1011 4 4
1100 4 5
1110 4 6
1111 4 7
10011 5 8
10100 5 9
00111 5 10
01000 5 11
001000 6 12
000011 6 13
110100 6 14
110101 6 15
101010 6 16
101011 6 17
0100111 7 18
0001100 7 19
0001000 7 20
0010111 7 21
0000011 7 22
0000100 7 23
0101000 7 24
0101011 7 25
0010011 7 26
0100100 7 27
0011000 7 28
00000010 8 29
00000011 8 30
00011010 8 31
00011011 8 32
00010010 8 33
00010011 8 34
00010100 8 35
00010101 8 36
00010110 8 37
00010111 8 38
00101000 8 39
00101001 8 40
00101010 8 41
00101011 8 42
00101100 8 43
00101101 8 44
00000100 8 45
00000101 8 46
00001010 8 47
00001011 8 48
01010010 8 49
CCITT Draft Recommendation T.4 PAGE 6
01010011 8 50
01010100 8 51
01010101 8 52
00100100 8 53
00100101 8 54
01011000 8 55
01011001 8 56
01011010 8 57
01011011 8 58
01001010 8 59
01001011 8 60
00110010 8 61
00110011 8 62
00110100 8 63
CCITT Draft Recommendation T.4 PAGE 7
Table 1b. Make Up White Codes
Code Lng Run
---------------------------
11011 5 64
10010 5 128
010111 6 192
0110111 7 256
00110110 8 320
00110111 8 384
01100100 8 448
01100101 8 512
01101000 8 576
01100111 8 640
011001100 9 704
011001101 9 768
011010010 9 832
011010011 9 896
011010100 9 960
011010101 9 1024
011010110 9 1088
011010111 9 1152
011011000 9 1216
011011001 9 1280
011011010 9 1344
011011011 9 1408
010011000 9 1472
010011001 9 1536
010011010 9 1600
011000 6 1664
010011011 9 1728
CCITT Draft Recommendation T.4 PAGE 8
Table 2a. Terminating Black Codes
Code Lng Run
---------------------------
0000110111 10 0
010 3 1
11 2 2
10 2 3
011 3 4
0011 4 5
0010 4 6
00011 5 7
000101 6 8
000100 6 9
0000100 7 10
0000101 7 11
0000111 7 12
00000100 8 13
00000111 8 14
000011000 9 15
0000010111 10 16
0000011000 10 17
0000001000 10 18
00001100111 11 19
00001101000 11 20
00001101100 11 21
00000110111 11 22
00000101000 11 23
00000010111 11 24
00000011000 11 25
000011001010 12 26
000011001011 12 27
000011001100 12 28
000011001101 12 29
000001101000 12 30
000001101001 12 31
000001101010 12 32
000001101011 12 33
000011010010 12 34
000011010011 12 35
000011010100 12 36
000011010101 12 37
000011010110 12 38
000011010111 12 39
000001101100 12 40
000001101101 12 41
000011011010 12 42
000011011011 12 43
000001010100 12 44
000001010101 12 45
000001010110 12 46
000001010111 12 47
000001100100 12 48
000001100101 12 49
CCITT Draft Recommendation T.4 PAGE 9
000001010010 12 50
000001010011 12 51
000000100100 12 52
000000110111 12 53
000000111000 12 54
000000100111 12 55
000000101000 12 56
000001011000 12 57
000001011001 12 58
000000101011 12 59
000000101100 12 60
000001011010 12 61
000001100110 12 62
000001100111 12 63
CCITT Draft Recommendation T.4 PAGE 10
Table 2b. Make Up Black Codes
Code Lng Run
---------------------------
0000001111 10 64
000011001000 12 128
000011001001 12 192
000001011011 12 256
000000110011 12 320
000000110100 12 384
000000110101 12 448
0000001101100 13 512
0000001101101 13 576
0000001001010 13 640
0000001001011 13 704
0000001001100 13 768
0000001001101 13 832
0000001110010 13 896
0000001110011 13 960
0000001110100 13 1024
0000001110101 13 1088
0000001110110 13 1152
0000001110111 13 1216
0000001010010 13 1280
0000001010011 13 1344
0000001010100 13 1408
0000001010101 13 1472
0000001011010 13 1536
0000001011011 13 1600
0000001100100 13 1664
0000001100101 13 1728
CCITT Draft Recommendation T.4 PAGE 11
Note: It is recognized that machines exist which accommodate
larger paper widths whilst maintaining the standard
horizontal resolution. This option has been provided for by
the addition of the Make Up Code Set defined as follows:
Table 3. Extended Make Up Codes (Black and White)
Code Lng Run
---------------------------
00000001000 11 1792
00000001100 11 1856
00000001101 11 1920
000000010010 12 1984
000000010011 12 2048
000000010100 12 2112
000000010101 12 2176
000000010110 12 2240
000000010111 12 2304
000000011100 12 2368
000000011101 12 2432
000000011110 12 2496
000000011111 12 2560
The identification and choice of either the standard
code table or the extended code table is to be made in the
pre-message (Phase B) portion of the T.30 control
procedures.
4.2 Two dimensional coding scheme
The one-dimensional coding scheme defined in 4.1 may be
extended as an option to a two-dimensional scheme. This is
the subject of further study.
5. Modulation and demodulation method
It is provisionally agreed that Group 3 apparatus
operating on the general switched telephone network shall
utilize the modulation scrambler, equalization and timing
signals defined in Recommendation V.27ter, specifically in
the preamble and 2, 3, 6, 7, 9 and 10.
The data signalling rates to be used are those
recommended in Recommendation V.27ter, i.e. 4800 and 2400
bit/s.
Note 1: Some administrations pointed out that it would not
be possible to guarantee the service at a data signalling
rate higher than 2400 bit/s.
Note 2: It should be noted that there are equipments in
service using, inter alia, other modulation methods. The
CCITT Draft Recommendation T.4 PAGE 12
arrangement of interworking between equipment conforming to
Recommendation T.4 and these existing equipments is subject
to further study.
Note 3: For higher speed operation, such as may be possible
on leased circuits, it is provisionally agreed that Group 3
apparatus may utilize the signals specifically defined in 1,
2, 3, 4, 7, 8, 9, 11, and 12 of Recommendation V.29.