RFC 804 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.