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FTP Server

Overview

FTP (File Transfer Protocol) is a standard Ethernet protocol for transferring files between computers. It is based on TCP/IP and is defined in the standard RFC 959. The PreciseFlex™ Controller software includes a FTP server that implements much (but not all) of this standard and is compatible with most FTP clients.

Whenever a PreciseFlex™ Controller is active, it automatically listens on the standard FTP port (port 21) for incoming connection requests.

The FTP server supports a limited level of security based on specifying an unencrypted user name and password. See DataID 427 "FTP user name and password" for information on defining these values.

The FTP server can be directly accessed from a host computer using a FTP client and is utilized by the PreciseFlex™ web-based operator interface for the “Backup and Restore” and “System Upgrade” utility functions.

FTP Clients

There are numerous FTP client applications available that are compatible with this FTP server. Most web browsers include FTP clients that may be accessed by specifying "ftp://" followed by the IP address of the PreciseFlex™ Controller. For example, if your PreciseFlex™ Controller is configured with the standard IP address, you can connect to its FTP server by entering the following into Internet Explorer, Safari or Firefox:

ftp://192.168.0.1

Restrictions

The following restrictions apply to the built in FTP server:

1. A maximum of 4 simultaneous connections are allowed. If a connection is inactive for 3 minutes, it is automatically closed to prevent unclosed orphan connections from blocking FTP access.
   
2. The FTP server does not support "wild-card" specifications for file directory requests. That means the FTP client must perform wild-card screening of directory listings. If your client does not do that, some client commands such as "mget" may not work with the PreciseFlex™ controller.
   
3. The FTP server does not support encryption of files, user names, or passwords. Therefore, you should only use this server on a secure network.
   
4. Some FTP clients cache the files that are transferred. It is possible that even though a file has been changed locally on the PreciseFlex™ Controller, the FTP client will return the contents of a previous version of that file that is held in the client’s cache. To avoid this confusion:
   
• Make sure the date and time on your PreciseFlex™ Controller match the date and time on your FTP client.
• Press the refresh button on your FTP client window before attempting to copy files to or from the PreciseFlex™ Controller.
• When updating a file on a PreciseFlex™ Controller, first delete the file, and then copy the new file. Do not simply overwrite the old file.
• In extreme situations, stopping and re-launching the browser should always correct this problem.
5. File names may be from 1 to 43 characters in length and may contain any printable ASCII character other than "/" or a leading ".". No blanks are allowed. Upper and lower case letters are considered to be different, so files names are case sensitive. It is recommended, but not required, that file names be valid GPL symbol names: they should start with an alphabetic character or "_," should not be a single "_," and the remaining characters should be alphanumeric characters or "_".

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