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RFC804.TXT
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- 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
- 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
- (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.
- Format: 000000000001 ... ... ... ... 000000000001
- (total of 6 times)
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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.
