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+
+Network Working Group                                          J. Postel
+Request for Comments: 769                                            ISI
+                                                       26 September 1980
+
+
+
+                   Rapicom 450 Facsimile File Format
+                   ---------------------------------
+
+Introduction:
+
+Several  organizations  in the ARPA Internet  community have RAPICOM 450
+facsimile   machines   interfaced   to  computers.   This  allows  these
+organizations  to enter a facsimile  representation  of a  page  into  a
+computer  file, and to produce a page from stored facsimile data.  These
+organizations  can exchange  stored facsimile data via file transfer and
+other protocols.   The purpose  of this note is to document  the  format
+used for  these  files  so  that  other  organizations  with  compatible
+facsimile devices can join in this information exchange procedure.
+
+The Rapicom 450:
+
+The Rapicom  450 has a built in encoding/decoding  scheme.   It produces
+data blocks  of 585 bits.   There are "set up" blocks and "data" blocks.
+The machine sends/receives several copies of the set up block, but since
+they are identical only one set up block is stored in the file.
+
+Records:
+
+Each 585 bit block  is placed  in a record  of 8-bit  bytes.  The record
+format is a length byte, a command byte and the data bytes.  Each record
+is an integral  number  of bytes.   The length value includes the length
+byte and the command  byte.   The command describes the data in the data
+field.
+
+                                    
+   0        1        2        3                              length 
+   +--------+--------+--------+--------+---//---+--------+--------+ 
+   | length | command|   data                                     | 
+   +--------+--------+--------+--------+---//---+--------+--------+ 
+
+                      Rapicom 450 Facsimile Record
+
+Commands:
+
+56 - SET-UP
+
+  The command code 56 (70 octal) indicates the following data field is a
+  set up block.
+
+
+
+
+
+Postel                                                          [page 1]
+
+
+                                                       26 September 1980
+Rapicom 450 Facsimile File Format                                RFC 769
+
+
+
+57 - DATA
+
+  The command code 57 (71 octal) indicates the following data field is a
+  data block.
+
+58 - END
+
+  The command  code 58 (72 octal) indicates that this is the last record
+  in the file.   In this case the length may be 2, indicating that there
+  is no data in this record.
+
+Conventions:
+
+In the files exchanged  to date,  each record  contains one block.  This
+means the data field is 74 bytes long  (585/8=73.125),  and  the  length
+field  has the value  76 (114 octal),  except  the last record which may
+carry no data and have a length of 2.
+
+The first  record  of a file is always  a SET UP record,  the  following
+records are DATA records, until the last record which is an END record.
+
+Details:
+
+The 585 bit data  block  is encoded by the Rapicom 450 and so can not be
+used a bit map unless the encoding/decoding procedure is known and used.
+
+The first 24 bits of the block is always a synchronization mark with the
+value 271 141 344 in octal or 101110010110000111100100 in binary.
+
+The low order  two bits of the  next  byte  contain  a  sequence  number
+(modulo 4).  The sequence number bits cycle in the order 11, 01, 10, 00,
+starting with the first DATA record (not the SET UP record).
+
+The line below represents  a DATA record,  where L represents  a  length
+bit,  C represents a command bit, M represents the synchronization mark,
+S represents  a  sequence  bit,  F  represents  a  fill  bit,  the  dash
+represents 68 other data octets, and an D represents a data bit.
+
+LLLLLLLLCCCCCCCCMMMMMMMMMMMMMMMMMMMMMMMMDDDDDDSSDDDDDDDD-DFFFFFFF
+
+In the line below  the normal values have been filled in for the length,
+the command, the synchronization mark and fill bits.
+
+0100110000111001101110010110000111100100DDDDDDSSDDDDDDDD-D0000000
+
+
+
+
+
+
+[page 2]                                                          Postel
+
+\ No newline at end of file