The University of Pennsylvania's Online Computing Magazine
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March 1992 - Volume 8:6 [Printout | Contents | Search ]
By Valerie Glauser Many of you may have heard of FTP, the high-speed file transfer protocol that allows you to copy all kinds of files from one computer to another on the Internet. Some of you may know people on campus who have used FTP in their work, possibly to get copies of computer programs or the results of database queries or statistical analyses. But what about the lyrics of songs by the Grateful Dead, David Bowie, or Depeche Mode, or, if your tastes run differently, Cole Porter or Alan Sherman? Or computer graphics images of M.C. Escher's works, a map of Israel, or listings of job opportunities in Germany and Hong Kong? Or a review of a book explaining Japanese idioms referring to parts of the body, the complete text of "Into the Woods," or a file that allows you to start up your Macintosh with the opening lines of the "Star Trek" theme music? All these files are available at no charge through the wonders of "anonymous FTP." Anonymous FTP allows you to log on as a "guest" to computers with files available to the Internet public, specifically for the purpose of transferring those files to your own machine or account. This article and the accompanying sidebars explain how anonymous FTP works and provide some pointers on getting started. Learning to traverse the Internet in search of largely uncharted FTP sites, however, often requires time and lessons from a seasoned Internet traveler, as well as an in-depth knowledge of different system directory structures and operating system commands. Thus, you should expect a relatively steep learning curve and some frustrations along the way.
FTP definedFTP, the technology that enables anonymous FTP, is an acronym for File Transfer Protocol, the Internet's standardized error-checking utility. It provides file transfer at speeds of 50 Kbytes to 1 Mbyte per second-many times faster than Kermit, its asynchronous counterpart, which transfers files at the rate of only 10 Kbytes per second.FTP works across dissimilar computers and operating systems. Provisions are made for automatic conversion of text across platforms and for file transfers between computers with different character sets, end of line conventions, etc. Security is handled by requiring the user to specify a user name and password for the other computer. FTP works on a "client/server" model, where one computer on the network plays the role of the "client," or active machine, that initiates the FTP session, and another computer on the network is the "server," or passive machine, accepting the commands sent by the client. There need not be a person working at the server; it need only be turned on and ready to accept FTP commands. Capabilities of FTP include moving around in, and generating lists of the contents of, permitted directories on a host computer; transferring individual or multiple text and binary (formatted) files from a server host computer to a client host computer ("getting") and vice versa ("putting"), regardless of the differences in system architecture between the sending and receiving machines; and archiving and compressing directory files to transfer copies of whole directory structures. FTP requires certain hardware, software, and network connections to work.
Anonymous FTPAn anonymous FTP server is a remote server that does not require an individual account and password for access to some files. Hundreds of anonymous FTP file servers across the Internet contain a wide variety of data and software that can be downloaded by anyone who logs on as a guest user.Just because you can log onto a server and transfer a file doesn't, however, mean you can use that file. You also have to know what application and platform (computer system) the file was written for and what type of compressor/archiver program(s) have transformed the file. Documents or directories with multiple files are often archived into one file for ease of transfer, and large archive files are often compressed to reduce the transfer time and disk space requirements. The stand-alone utilities Stuffit and PKZip/PKUnzip provide file archiving and compression for Macintosh and DOS computers respectively. Two built-in utilities, compress/uncompress and tar, provide the same capabilities in UNIX. You need a copy of the appropriate archiving/compressing software to "unarchive" or "uncompress" files after transferring them (see "Some popular anonymous FTP sites" at right for locations from which you can obtain stand-alone compressing and archiving software). Clues to the platform, application, and archiver or compressor often come from file name suffixes, called extensions, or from explanations in READ.ME files listed in the directory in which a file is stored. The following are a few of the most common extensions and the formats they represent:
txt ASCII text format zip DOS file archive hqx Macintosh BinHex file archive sit Macintosh StuffIt file archive ps Document in PostScript gif Graphic Interchange Format tar Unix archive file Z Unix Compressed formatIt also helps to know ahead of time who the target audience is for a given FTP server, and how server directories are organized. Common forms of directory organization are by platform and application (e.g., Mac/HyperCard), platform and purpose (e.g., DOS/games), medium/type ( e.g., graphics/gif), or topic/subtopic (e.g., music/folk/Dylan). Several important resources are readily available to help you track down a topic or determine if you are the audience for a file, group of files, or specific anonymous FTP file server. They are:
Anonymous FTP directories have historically been maintained almost entirely on a volunteer basis, often by experts for experts or for relatively few individuals. The result is that file organization is frequently incon-sistent and reflects the amount of effort expended by the volunteer. Searching for, finding, and identifying the files you want can be a tedious and frustrating process. If you are a novice, the resources posted on PennInfo will go a long way toward providing maps of where you want to go. In addition, to use FTP servers knowledgeably on a regular basis you need to know about the computing systems and directory and file structures of the host computers you are accessing. This article cannot begin to describe the various operating systems and directory structures of the dozens of different kinds of host computers you can access via anonymous FTP. However, a single suggestion is to get to know something about the UNIX operating system commands and directory structures; UNIX is the operating system that many anonymous FTP servers use.
Sidebar 1: FTP requirements To take advantage of anonymous FTP directly from your desktop computer or workstation, you need a computer with disk storage and an IP net-work connection. Some computers also require an Ethernet interface adapter and accompanying software to be installed. Common campus examples are
Sidebar 2: Anonymous FTP: how to get started. To start FTP on a UNIX workstation, type ftp followed by the full Internet name of the host you wish to reach at the system prompt. DOS users type ftp followed by the complete host name at the DOS prompt in the directory where the FTP program resides. Macintosh users must use a separate FTP client (see "FTP requirements" sidebar) and usually need only enter the complete host name. Log on as anonymous. If you are asked for a password, use either your complete user ID, e-mail address, or the word guest. Most sites prefer that you use your user ID so they can keep track of whom requests are coming from. You should now be connected to the remote machine and can use FTP commands to look at the directories and transfer files (if you are using a Mac client, you will probably use a combination of menu selections and FTP commands). Following is a list of basic FTP commands:
help or ? Generates a list of FTP
commands or consults
documentation
dir or ls Lists files and directories
in the current directory
cd <directory namegt Changes the directory to
the one named
get <filename> Transfers the specified
file to your local machine
quit Logs off the remote machine
and quits FTP
Sidebar 3: Some popular FTP sites The number of anonymous FTP sites available worldwide is enormous. Following are the preferred sites of some of the individuals who support computing and networking at Penn:
Hostname Audience -------- -------- wuarchive.wustl.edu DOS, Windows, games, GIF garbo.uwasa.fi DOS, Windows sumex.aim.stanford.edu Macintosh rascal.ics.utexas.edu Macintosh ftp.apple.com Apple news cs.orst.edu NeXT sonata.cc.purdue.edu NeXT nova.cc.purdue.edu NeXT june.cs.washington.edu TeXhax digest and TeX sources ames.arc.nasa.gov space-related GIF files VALERIE GLAUSER is a Senior Technical Writer for DCCS/UMIS Publications. |