RFC 804
CCITT draft recommendation T.4
RFC 804: CCITT Draft Recommendation T.4 ✨
okay bestie, title block tea 🫖 this is RFC 804, and its title is CCITT Draft Recommendation T.4. It's As Defined In: CCITT STUDY GROUP XIV, CONTRIBUTION No.25-E 📄. The SOURCE is the DRAFTING GROUP ON DRAFT RECOMMENDATION T.4 💜. The TITLE (as amended and agreed by Working Party XIV/2) is DRAFT RECOMMENDATION T.4 - STANDARDIZATION OF GROUP 3 FACSIMILE APPARATUS FOR DOCUMENT TRANSMISSION 🎀.
STANDARDIZATION OF GROUP 3 FACSIMILE APPARATUS FOR DOCUMENT TRANSMISSION 📠🌈
The CCITT, considering 🌸
- a. okay so Recommendation T.2 covers Group 1 type apparatus for ISO A4 document transmission over a telephone-type circuit, taking about six minutes 🐢
- b. Recommendation T.3 covers Group 2 type apparatus for ISO A4 document transmission over a telephone-type circuit, taking about three minutes 🏃♀️
- c. there's demand for Group 3 apparatus that can send an ISO A4 document over a telephone-type circuit in about one minute ⚡
- d. for a big pile of applications, black and white reproduction is enough 🖤🤍
- e. this service can be requested either alongside a phone conversation, or when either or both stations aren't attended. In both cases the facsimile operation follows Recommendation T.30 📞💅
(unanimously) declares the vibe 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 the receiver. Look at the message area in a vertical plane, and the scanning direction should go from left to right, with each subsequent scan sitting adjacent to and below the previous one 🦋
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 keep 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 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 works like this 💅
a. DATA
A line of data is made up of a series of variable length code words. Each code word represents a run length of either all white or all black, and white runs and black runs alternate. A total of 1728 picture elements represent one horizontal scanning line of the document of standard A4 size. To make sure the receiver keeps color synchronization, all DATA lines begin with a white run length code word. If the actual scanning line begins with a black run, a white run length of zero is 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 come in 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's 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 for the run length that is equal to or shorter than what's required. That's followed by the Terminating Code word for the difference between the required run length and the run length the Make Up Code represents 🧠✨
b. END OF LINE (EOL)
This code word follows each line of DATA. It's a unique code word that can never be found within a valid line of DATA, so resynchronization after an error burst is possible 🔥
This signal also occurs before the first DATA line of a page.
Format: 000000000001
c. FILL
A pause can 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 so 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.
part 2 is next bestie, stay tuned 🦋💖
d. RETURN TO CONTROL (RTC) 🎀
okay so the end of a document transmission is marked by sending six consecutive EOL's 🧚. Once that RTC signal goes out, the transmitter sends the post message commands in the standard T.30 blocked format at the data rate. iconic, right? 💅
Format: 000000000001 ... ... ... ... 000000000001
(total of 6 times)Now the lookup tables, bestie. These are the terminating white codes ⬜✨
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 63And the make up white codes 🍓
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 1728Next up, the terminating black codes 🖤 (the black side of the table, bestie, so pay attention 🙈)
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 63And the matching make up black codes 🌈
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 1728Note: 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: 👀
For those wider machines, here are the extended make up codes (black and white) 📏✨
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 2560The choice between the standard code table and the extended code table is made in the pre-message (Phase B) portion of the T.30 control procedures, so that's where the decision happens 🧠💖
4.2 Two dimensional coding scheme 🦋
The one-dimensional coding scheme from 4.1 may be extended as an option to a two-dimensional scheme. ngl this part is still giving "to be studied later" 🫶 It 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. Main character energy 👑
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. 💜
📦 where this page comes from
- ietf: rfc804 1981-01
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms