RFC 468 (rfc468) - Page 1 of 7

FTP data compression

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Network Working Group                                         R.  Braden
Request for Comment: 468                                        UCLA/CCN
NIC: 14742                                                 March 8, 1973


                          FTP DATA COMPRESSION

I.  INTRODUCTION

APOLOGIA

   Major design objectives of the proposed File Transfer Protocol (FTP)
   are reliability and efficiency for transmission of large files.
   Efficiency has two faces: efficiency of the host CPU's, and efficient
   use of the Network bandwidth.  Block mode is intended to minimize CPU
   overhead for bandwidth efficiency, there is a mode called "HASP" in
   RFC 454.  The "HASP" mode of FTP is really transmission with data
   compression, i.e., an encoding scheme to reduce the information
   redundancy in the messages.

   RFC 454 contains no explicit definition of the "HASP" or compressed
   mode, but instead notes that a future RFC by yours truly will define
   the mode.  Students of FTP may find this scarcely credible, but you
   are now reading the promised RFC.  It turned out to be much farther
   in the future than any of us expected.  Mea Culpa.

GENERAL CONSIDERATIONS

   In the early years of the Network, its major uses have been remote
   terminal interactions and the small-to-medium-sized file transmission
   typical of remote job entry.  As facilities such as the Illiac IV and
   the Data Machine become operational on the Network, and the Network
   community begins to include users with heavy data transmission
   requirements, large file transmission will become a major mode of
   Network use.  For example, one user of CCN expects to send 2 x 10**8
   bits of data _each_ _day_ over the Network.

   Local byte compression of the type proposed here is particular
   effective for reducing the size of "printer" files such as those
   transmitted under the Network RJE protocol.  Experience with CCN's
   RJS service has shown a typical compression of print files by a
   factor of between two and three.  Since FTP was intended to contain
   the data transfer part of Network RJE protocol as a subset, it is
   appropriate to include a print file compression mechanism in FTP.
   These considerations led the FTP committee to include a compressed
   mode within FTP.





Braden
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