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From: BILLW%sri-kl@sri-unix.UUCP
Newsgroups: net.micro
Subject: Re: FTP help?
Message-ID: <3976@sri-arpa.UUCP>
Date: Mon, 8-Aug-83 12:43:00 EDT
Article-I.D.: sri-arpa.3976
Posted: Mon Aug  8 12:43:00 1983
Date-Received: Thu, 11-Aug-83 15:55:15 EDT
Lines: 51

Well, you see,  on a real network (In this case, the ARPANet/Internet),
you are able to transfer files directly between arbitary hosts on the
internet, using something called the "File Tranfer Protocol" (FTP).
To get a file from, say, the CPM library at Simtel20 to my home system
(SRI-KL), I log in on SRI-KL, run the FTP program and ask it to
connect me to Simtel20.  FTP uses the lower level reliable
transmission protocols for the actual data transfer, but the user
program (along with a server program on the other computer) takes care
of things like accounting, access control, file format conversion (eg
text, 8bit, 36bit, page, etc), etc. FTP uses multiple "connections" so
that data transfers can be interupted, for example.

A representative set of low level commands used in the FTP protocol
is USER, PASSWORD, ACCOUNT, STRUCTURE, MODE, TYPE, RETREIVE, STORE,
ALLOCATE, APPEND, DELETE, ABORT, LIST, CHANGE DIRECTORY, STATUS.

The following picture is taken from RFC765 - The FTP protocol specification.

                                            -------------
                                            |/---------\|
                                            ||   User  ||    --------
                                            ||Interface|<--->| User |
                                            |\----:----/|    --------
                  ----------                |     V     |
                  |/------\|  FTP Commands  |/---------\|
                  ||Server|<---------------->|   User  ||
                  ||  PI  ||   FTP Replies  ||    PI   ||
                  |\--:---/|                |\----:----/|
                  |   V    |                |     V     |
      --------    |/------\|      Data      |/---------\|    --------
      | File |<--->|Server|<---------------->|  User   |<--->| File |
      |System|    || DTP  ||   Connection   ||   DTP   ||    |System|
      --------    |\------/|                |\---------/|    --------
                  ----------                -------------

                  Server-FTP                   User-FTP

      NOTES: 1. The data connection may be used in either direction.
             2. The data connection need not exist all of the time.
	     3. PI = Protocol interpreter
	     4. DTP = Data transfer process

If you think of FTP as a real-time, interactively driven UUCP designed
with transferring files between systems running arbitrary Operating systems
with arbirary file systems, You'll have about the right idea.  Some files
mad available for FTP make it to net.sources, however since FTP data rates
vary from about 8K bps accross the country to people on very-distant-host
adaptors or ecus (eg: rutgers), to 300K bps over local ethernets, it isnt
partical to make everything available for FTPing also available for UUCPing.

Bill Westfield