FTP Protocol

Posted by : Unknown Monday, July 1, 2013

HIGH-SPEED FILE EXCHANGE

Introduction:

Lick an ice cream, munch on some wafers, dig into some chocolate and at the same time upgrade your computer software from the comfort of your chair. Who said dreams don’t come true? The Net has made our lives so much easier that getting hold of the day’s stocks or even the complete works of Shakespeare is not a big deal. Just connect and download the information you want.

It’s as simple as data, which has to be transferred from one computer to another over a network. This is where FTP steps in. In its simplest form, FTP allows the sending and receiving of files between computers. FTP, or File Transfer Protocol, at the crudest level is a standard using which you can upload or download files on the Internet.

The term protocol suggests standardization. It is a set of rules defining a format. To say it in a slightly different way, a network protocol describes how computer systems communicate with each other at a unit level. This is what allows you to exchange files globally. To make it clearer, let’s say you have a friend and you want to ask her to come over for dinner. How do you do that? You call her up and tell her to come over for dinner! This very simple process involves the use of speech over language. Language is the protocol here, which you and your friend understand. What if your friend were Hungarian? You would have to probably look up a dictionary and formulate the appropriate sentences so that she understands that you are calling her for dinner, not asking her out ice-skating! Since the Internet understands a definite language for transferring file, it makes it easier for you to exchange information with others.

HTTP (Hyper Text Transfer Protocol) is the protocol used by Web browsers to communicate with Web servers. A Web browser is an Internet client application and the Web server is an Internet server application.

HTTP has the ability to transfer Web pages, graphics, and any other type of media that is used on the Web. The client (browser) makes a request to the server, which serves the files (Web pages) to it. Similarly, FTP follows the same architecture – and FTP client connects to an FTP server and downloads or uploads file to or from it.

Technically, FTP can be used as part of any application on the Internet, since it is a basic file transfer method. However, in some cases it may be too limited or inappropriate. However, a few key uses of FTP can be outlined. It can be used to share files such as software or data. It can also be used for indirect or implicit use of remote computers (via programs). If a remote control displays the remote screen on the local machine, it is essentially transferring image files. This can easily be handled by FTP and the program can then process the images. It can also be used to standardize file transfer methods over an intranet or extranet. This means that you can use FTP’s inherent security measures and not bother with having to set up another security system for file sharing.

Why FTP?

Whether we use FTP or any other method, it is transfer of data over a large network that we need to achieve. With the evolution of the Internet, other standards of file transfer have been developed too. In fact, many of these were designed to be user-friendlier than FTP and are widely used today.

As we have already seen, HTTP does pretty much the same thing as FTP. A browser requests a file and the Web server sends it to the browser. This can work the other way too, with the browser uploading a file to the Web server. Most users use e-mail as a means of transferring files. It is extremely simple to attach files to a message and send it to a recipient who simply has to check his or her e-mail to download the file. So why not use any of these or other methods of uploading or downloading files?

With FTP, you can queue files for upload or download, whereas you cannot do so over HTTP. File transfers over FTP can always be resumed. The server would specifically need to support this capability in case of HTTP. Also, security over FTP is much more manageable than HTTP. With FTP, security restrictions can cascade down folders with specific rights on all of them, much as on a file server over a LAN. Uploading files over FTP, too, is much easier than over HTTP.

E-mail attachments (using Simple Mail Transfer Protocol or SMTP) have lots of drawbacks. The e-mail service has the least priority on the server if it runs multiple services, such as Web services, FTP services, etc., which means it is the slowest means of transfer. Most e-mail service providers allocate restricted amounts of space to each user and sending huge files would mean clogging up someone’s account – often the files may even bounce back! For the recipient, most e-mail sites do not support resuming, which means that if the connection breaks, he would have to download it all over again. Also, different e-mail clients or providers may encode attachments in different ways, for each of which the recipient would require a decoding mechanism. Most importantly, e-mail attachments take up exactly double the amount of space that a file would otherwise. This is because e-mail can be sent only as text over the Internet. Most users and providers have standardized on MIME (Multipurpose Internet Mail Extensions) as the encoding format for attachments. Here, every byte in the file is represented by two ASCII (text) characters. This doubles the size of the file.

The FTP Server:

An FTP server is like a large filing cabinet. With a traditional filing cabinet, the person who does the filing has the option to label and organize the files. They also decide which files to keep locked and which remain public. It is the same with an FTP site. To use an analogy, if you wanted to pass a book to another person you put the book in his hands.

Conversely, if you want to take it back, you get the book from his hands. In this case, if he does not allow you to take the book, you cannot. This is the same principle behind FTP. The FTP server is a computer waiting for someone to put a file onto it or get a file from it.

The FTP server maintains the files on it, the users who can access them, the amount of control each user has over the files and the number of people who can log on simultaneously to it. A person can have any combination of read, write and delete options over each file or folder. This means that a person can either read or retrieve a file, change or upload a file or delete an existing file. Most FTP servers maintain an anonymous login by which anyone can access to publicly available files on the server without having to provide a password. In an anonymous FTP session, the user provides the generic username ‘anonymous’. As a password, you would typically use your e-mail address. Anonymous users usually have very limited access privileges. For example, they may only have access to one or two directories and may be able to copy but not delete files. Other users are assigned a custom username and password so they can access private directories.

The FTP Client:

To make a connection to an FTP server, you have to use an FTP client – software that can communicate with the server using the FTP protocol. Most Web browsers now incorporate FTP into the browser itself. Hence, you can use Internet Explorer or Netscape as your FTP client. However, it is easier to use dedicated FTP software. Even the older DOS and Unix systems have FTP clients with them. Dedicated FTP clients allow you more control over your FTP session, as you are able to carry out every action that is possible on the server. This is because they are command based. Browsers, on the contrary, do not allow you to do much more than downloading or uploading files. The most immediate advantage of an FTP client you will notice is the Resume feature. It can start transfers of broken downloads from the point where it disconnected so that you do not have to download the entire file again.

Let’s take a look at some popular FTP clients.

BulletProof FTP:

Bulletproof FTP (BPFTP) delivers a wide range of traditional FTP features as well as several unique ones. Its best feature is its ability to reconnect automatically and resume terminated file transfers. Another useful feature is the Leech mode option, which is not available in any of its competitors. Some FTP servers restrict the number of downloads in one session – BPFTP will automatically disconnect when you reach the maximum number of downloads, reconnect and resume downloading again. It also has clipboard-monitoring support for both, FTP and HTTP links.

Additional features of BPFTP include firewall and proxy support, remote mirroring capabilities, HTTP downloading with support for redirected URLs, capability to periodically send a random command to prevent the server from disconnecting and recursive uploading and downloading of directories. It can also import all site listings and passwords from CuteFTP, FTP Explorer and WS-FTP. It caches remote file listings, allowing faster browsing. It also has basic scheduling capabilities and the ability to queue multiple file transfers.

BPFTP works a bit differently compared to most FTP clients. After selecting a file operation, BPFTP first enters the commands in a queue. When ready, you just have to click once and BPFTP takes you through each of the tasks. Such batch transfer jobs can be carried out in different directories and even on different sites.

CuteFTP:

One of the oldest FTP clients to become popular, CuteFTP is packed with plenty of features and configuration options. It works on any Windows platform. Ever since its arrival in the market, two features that stand out are the Stop command, which allows you to stop any operation in progress while the connection is still maintained and the Keep alive command that helps in transfer of data without interruptions.

Apart from this, CuteFTP blends the file listing process with file descriptions obtained from index files found at many anonymous FTP sites. One normally faces cryptic file names on FTP sites and this feature is helpful in deciphering them. CuteFTP also caches recently visited directories, making browsing through them faster.

Other features include comprehensive login listings, customizable colours, the ability to download and upload complete directory trees and the ability to sent multiple files at a time. Recent updates have a sleek new design and improved drag-and-droop functionality, automatic resuming for interrupted transfers, directory comparison capabilities, a file transfer queue, support for macro scripting, remote file editing custom commands, automatic renaming and a quick-save command for remote and local default directories.

Also included is an MP3 and file search feature, an integrated CuteHTML Lite client, site-to-site file transfer capabilities, URL parsing, clipboard monitoring, an improved site manager and scheduling.

FTP Voyager:

This is a pretty good FTP client that sports an interface similar to that of Windows Explorer. It also incorporates useful features from Explorer such as multiple file listing display, quick sorting, content menus and drag-and-drop capabilities. Apart from this, Voyager offers many critical file transfer features o fits own. These include Folder shortcuts, file filtering capabilities, an instant Stop feature and quick searching capabilities. You can easily crate special folders that can be accessed from the root even when the link could be a directory that’s much deeper.

Voyager offers buttons that can connect to specific FTP sites automatically, launch Windows Explorer for quick file transfers between two clients or automatically sending a group of files upon connection. Folder synchronization tools provide a simple solution for backups or Web site maintenance. Another very useful feature is the capability to edit remote files.

Additional new features include firewall and proxy support, an online help system, retry and resume support, automatic rename capabilities, extensive configuration options, an impressive site manager, and an improved list of common FTP sites. The latest versions also include a scheduler that allows scheduled file and folder uploads, a transfer queue that performs file uploads and downloads sequentially, as well as clipboard monitoring support.

WS-FTP:

WS-FTP is an award-winning FTP client from RhinoSoft.com. It is a simple program with an Internet Explorer-like interface. Its features include several alternative screen layouts, the ability to associate remote files with local programs, automatic logging, extension conversion on transfer, force lower case on transfer and quick screen sizing. WS-FTP also comes pre-configured with an extensive array of FTP sites to check out. Multiple copies of the program can be launched to download multiple files.

WS-FTP Limited Edition (WS-FTP LE) is a restricted freeware version of WS-FTP. This release lacks several features in Pro version. The Windows Explorer FTP shell extension support, which allows you to connect to FTP sites and upload or download files using Windows Explorer, is one of the features that’s missing. WS-FTP Professional Edition (WS-FTP Pro) costs, but has useful additional features. These include automatic resume capability for file transfers, a network utilities package (ping, trace route, finger, whois and nslookup clients), support for multiple file transfers, scheduling and file transfer queuing. You can even run scripts developed with the scripting utility at set intervals. Support for SSL (Secure Sockets Layer) encryption protects your valuable information when you connect to an SSL FTP server. It also has enhanced firewall support that allows quicker connections by storing multiple firewall settings.

File Transfer:

Files can be transferred in either ASCII or binary modes. Text files (rather, text-based files) should be transferred in ASCII mode, since this ensures that the document is translated into a format that is suitable for reading on your computer. Keep in mind that this translation is only useful for text-based files and it usually makes other files unusable.

Binary files, such as executable programs and compressed archives, require Binary mode transfer. This mode transfers an exact copy of the original file. FTP does not translate any data from the file. It simply reads the bytes from one computer and writes them out in the same sequence on the other.

Once you have navigated the remote host’s directories and found the file(s) that you wish to retrieve, it is necessary to determine the file type. By default, FTP uses ASCII mode to transfer files. Most files can be reliability transferred using the binary mode. However, text documents, postscript documents and Uuencoded files are some of the text-based files that should be transferred using the ASCII mode. This is because FTP copies the data across, not the bytes, hence making the file compatible across platforms.

FTP Commands:

With the number of FTP clients available, you will never need to know any FTP commands. Also, if you are only bothered about uploading and downloading your files, you can use just your browser -- either of these would take care of the file formats and transfer modes, too. However, it is always better to know the FTP commands, just so that you know what you can and cannot do during an FTP session.

When an FTP server is waiting for user actions, the prompt ftp> is provided where you can type commands. Commands are always entered in upper case, though most servers now accept either upper or lower case commands. The following list of commands is applicable across all FTP servers. Servers on different platforms may have extended features, too. These can be taken advantage of by using the REMOTEHELP command.

Command	Syntax	Result
!	! [command [args]]	Switch to the command prompt at the local machine while keeping the FTP session alive. If there are arguments, the first is taken to be a command to execute directly, with the rest of the arguments as its arguments.
?	? [command]	Print help about a command. If no argument is given, FTP prints a list of known commands.
APPEND	APPEND local-file [remote-file]	Append local-file to a file on the server. If remote-file is unspecified, the local file name is used for the remote file.
ASCII	ASCII	Set the file transfer type to ASCII. This is the default type.
BELL	BELL	Toggle settings for a beep after each file transfer is completed.
BYE	BYE	Set the file transfer type to binary.
CD	CD remote-directory	Change the working directory on the server to remote-directory.
CLOSE	CLOSE
Command	Syntax	Result
DELETE	DELETE remote-file	Delete remote-file on the server.
DIR	DIR [remote-directory] [local-file]	Print a listing of the directory contents in remote-directory and, optionally, placing the output in local-file. If no remote-directory is specified, the current working directory on the server is used.
DISCONNECT	DISCONNECT	Terminate the FTP session with the server and return to the FTP command interpreter.
GET	GET remote-file [local-file]	Retrieve remote-file and store it on the local machine. If the local filename is not specified, the filename on the server is used.
GLOB	GLOB	Toggle filename expansion for MADELTE, MGET and MPUT. If globbing is turned off, the filename arguments are taken literally and not expanded.
HASH	HASH	Toggle printing of the hash (#) symbol for each data block transferred. The size of a data block is 1024 bytes.
HELP	HELP [command]	Print help about a command. If no argument is given, FTP prints a list of known commands.
LCD	LCD [directory]	Change the working directory on the local machine. If directory is not specified, the user’s home directory is used.
LS	LS [remote-directory] [local-file]	Print a listing of the directory contents in remote-directory and, optionally, placing the output in local-file. If no remote-directory is specified, the current working directory on the server is used. The listing includes nay system-dependent information that the server chooses to include.
MDELETE	MDELETE [remote-files]	Delete remote-files on the server. Can be used with wildcards to delete e multiple files if GLOB is off.
MDIR	MDIR remote-files local-file	Like DIR, except multiple remote directories may be specified.
Command	Syntax	Result
MGET	MGET remote-files	Retrieve remote-file and store it on the local machine. Can be used with wildcards to retrieve multiple files if GLOB is off.
MKDIR	MKDIR directory-name	Make a directory on the server.
MLS	MLS remote-files local-file	Like LIST, except multiple remote directories may be specified.
MPUT	MPUT local-files	Store a local file on the server. If remote-file is unspecified, the local file name is used. Can be used with wildcards to store multiple files if GLOB is off.
OPEN	OPEN host [port]	Establish a connection to host. If port is specified, FTP will attempt to contact an FTP server at that port.
PASS	PASS password	Sends a user’s password to the server.
PROMPT	PROMPT	Toggle interactive prompting. Interactive prompting occurs during multiple file transfers to allow the user to selectively retrieve or store files. If prompting is turned off (default is on), mget or mput will transfer all files, and mdelete will delete all files.
PUT	PUT local-file [remote-file]	Store a local file on the server. If remote-file is unspecified, the local file name is used.
PWD	PWD	Print the name of the current working directory on the server.
QUIT	QUIT	Terminate the FTP session and exit FTP.
QUOTE	QUOTE arg1 arg2 …	The arguments are sent as a server command directly to the FTP server on the remote system.
RECV	RECV remote-file [local-file]	Retrieve remote-file and store it on the local machine. If the local file name is not specified, the filename on the server is used.
REMOTEHELP	REMOTEHELP [command-name]	Request help from the remote FTP server. If command-name is specified, help on that command is printed.
Command	Syntax	Result
RENAME	RENAME original-name new-name	Rename the file original-name on the server, to the file new-name.
RMDIR	RMDIR directory-name	Delete a directory on the server.
SEND	SEND local-file [remote-file]	Store a local file on the server. If remote-file is unspecified, the local file name is used.
STATUS	STATUS	Show the current status of FTP.
TRACE	TRACE	Toggle packet tracing.
TYPE	TYPE [type-name]	Set the file transfer type to type-name. If no type is specified, the current type is printed.
USER	USER user-name password	Identify yourself to the remote FTP server. If password is not specified and the server requires it, FTP will prompt you for it.
VERBOSE	VERBOSE	Toggle verbose mode. In verbose mode, all responses from the FTP server are displayed to the user. In addition, if verbose is on, when a file transfer completes, statistics of the transfer are reported. By default, verbose is on.

Conclusion:

Probably one of the oldest protocols on the Internet to still remain alive, FTP, or File Transfer Protocol, is the most efficient means of transferring files over the Internet. FTP is the Internet standard for file transfer. Unlike most other TCP applications, it uses two TCP connections between the client and server – a control connection that is left up for the duration of the client-server session, and a data connection that is created and deleted as necessary. The file transfer provided by FTP copies a complete file from one system to another system. To use FTP we need an account to login to on the server, or we need to use it with a server that allows anonymous FTP.