Network Virtual Terminal (NVT)

Telnet is designed for terminal to terminal communication and distributed computer processing. Each host sets up a Network Virtual Terminal (NVT) and a host at one end assumes that an NVT has been set up at the other end. The NVT defines a set of rules for how information is formatted and sent, such as character set, line termination, and how information about the Telnet session itself is sent.There is the mechanism to negotiate options so that the hosts can operate a more elaborate interface at each end using different fonts etc. than the NVT. The User Host is the one that initiates a conversation whilst the Server Host is the one that is providing services.

The Network Virtual Terminal (NVT) is a bi-directional character device. The NVT has a printer and a keyboard. The printer responds to incoming data and the keyboard produces outgoing data which is sent over the TELNET connection and, if echoes are desired, to the NVT's printer as well. Any code conversion and timing considerations are local problems and do not affect the NVT.

Brief NVT description

- NVT comands are inserted to the data stream via TCP/IP before sending to the TCP/IP connection.
- Every NVT command is prefixed by character "0xFF".
- There are some basic commands with 2 byte interpretation only (EOF, ABORT, BRK, AYT, NOP, EC), and others with defined start ( = 0xFF 0xFA) and defined end ( = 0xFF 0xF0) commands.
- The TCP/IP device separates NVT commands and processes them without delay, while the data stream stores to the output stack.
- The NVT commands can't be found in the serial port data, if the device is Serial / TCP/IP converter.
- If you are sending character "0xFF" (255), the PC will just double it, because in NVT "0xFFFF" means send character "0xFF" to the output.
- NVT uses a negotiation process. It's a way of testing if terminals on the opposite side use ECHO or not ar if there are specific terminals etc.

FTP - File Transfer Protocol

- File Transfer Protocol (FTP), a standard Internet protocol, is the simplest way to exchange files between computers on the Internet.
- FTP is an application protocol that uses the Internets TCP/IP protocols.
- FTP is commonly used to transfer Web page files from their creator to the computer that acts as their server for everyone on the Internet.
- FTP is also commonly used to download programs and other files to your computer from other servers.
- Web browser can also make FTP requests to download programs you select from a Web page.
- FTP can also be used to update (delete, rename, move, and copy) files at a server.
- FTP can be run in active mode or passive mode, which control how the second connection is opened.
- In active mode the client sends the server, the IP address port number, that the client will use for the data connection, and the server opens the connection.
- Passive mode was devised for use where the client is behind a firewall and unable to accept incoming TCP connections.

The objectives of FTP are :
- to promote sharing of files (computer programs and/or data),
- to encourage indirect or implicit (via programs) use of remote computers,
- to shield a user from variations in file storage systems among hosts, and
- to transfer data reliably and efficiently.

Anonymous FTP

Thousands of hosts on the Internet run ftp servers that permit guests to login. Such servers usually contain data and software of interest to the general public. They are often called anonymous ftp servers because the guest login name is anonymous. To login to an anonymous ftp server, enter the name anonymous when prompted for a username or userid. When prompted for a password, enter your full e-mail address, unless the on-screen instructions specify an alternative guest password.

FTP Software & Anonymous FTP Servers

FTP Software
Depending on what you are planning to do with your FTP software you should pick different ones. There are hundreds of free pieces of software so there is a very good choice. The three software packages are:

- Cute FTP : It used to be the best shareware FTP program around. It is easy to use and has many functions. Unfortunately, because it has become so popular, the latest version only allows you to transfer one file at a time unless you register. If you can find a copy of version 2.6.* it is an excellent program.

- FTP Explorer : It is not such a good program as Cute FTP but it is freeware so there are no annoying nag-screens. It can be downloaded here.

- Elite FTP : It is not such a good program for uploading standard files it works better if you are working with CGI as you can send commands to the server by typing them in.

Anonymous FTP Servers
A host that provides an FTP service may additionally provide anonymous FTP access. Users typically login to the service with an 'anonymous' account when prompted for user name. Although users are commonly asked to send their email address in lieu of a password, little to no verification is actually performed on the supplied data.
The login id for the public accounts on most anonymous FTP servers is anonymous, and guest is also common. The password can be anything, but most anonymous FTP service machines will ask you to enter your complete email address as your password.

Overview Of File Transfer Protocol

File Transfer Protocol (FTP) is a standard network protocol used to exchange and manipulate files over a TCP/IP based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server applications.

The objectives of FTP are :
* To promote sharing of files (computer programs and/or data).
* To encourage indirect or implicit use of remote computers.
* To shield a user from variations in file storage systems among different hosts.
* To transfer data reliably, and efficiently.

What FTP does ?
It works by establishing a connection between one computer (for example, your PC) and another (for example, your Web server). To do this, you need to know the host name (e.g."webserver.example.com") or IP address (e.g. "12.34.56.78") of your Web server. Your FTP program will allow you to enter lots of different servers if you want (by host name or IP address), and usually you can double-click on one of them to connect to it.
- Logging in
Once connected, the Web server usually asks you for your user name and password.
- Transferring files
You're then logged in to your Web server. Once you're logged in, you can start moving files about. On most FTP programs, this works a lot like Windows Explorer or other similar file managers.
- The home directory
When you first log in, you will be viewing your home directory on your Web server. This will be the directory that contains your website, amongst other files.
- Going dotty
Some FTP programs will show two extra entries in the folder display - a single dot and a pair of dots. The single dot means "this directory" and usually does nothing, but the pair of dots mean "the directory above".