

MMM-6







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.





.

