How to use an FTP Host as an Alternative EDI Network

Web site hosting services are very competative now. Easy to use and ever cheaper for both individuals and companies. These servers and systems can also easily provide FTP connections. Dozens of user logins and Giga bytes of storage can be had for an annual cost of less than the purchase price of a desktop computer. With the aid of some relatively simple scripts your computer system can reach out across the internet and use these as a stripped down, bargin basement, alternative EDI (Electronic Data Interchage) network. Here's how...

Create a folder for each partner. Within each folder create 2 sub-folders, inbox & outbox. See below

tom

tom\inbox

tom\outbox

dick

dick\inbox

dick\outbox

harry

harry\inbox

harry\outbox


You could call these sub folders something else, like upload & download, or simply in & out. However using the inbox/outbox terms helps to relate them to their function and models the familiar email arrangement.

Assign each partner a user id & password and set their "home" folder. When they log on they should only be able to access their own folder.

To send you a file, the partner will log on and "put" (in FTP terms) the file in the postbox folder. To receive any files from you they will list ("ls") the mailbox and "get" anything they find then "del".

To send a file to a partner, log on and "put" the file in the partner\mailbox folder for them to collect. remember as host you start from the root folder. To receive any files from your partners, list all outbox folders and "get" anything you find then "del".

This is a simple arrangement, but there are some suttle potential gotchas.

• All files sent and received should be have unique names. If you send a daily file (for example orders.csv) and the receiver doesn't pick it up before the next one is sent, it will get overwritten. To avoid this the sender keeps a counter updated on the generating system and the number is incorparated into the file name e.g. orders123.csv

• If both sender and receiver are logged on at the same time then it is possible to list a file that is only partly transmitted. To avoid receiving part files, the sender should "put" using a tempory name (typically with a .tmp extension), then "rename" it to its correct name. The receiver just egnores any listed .tmp file.

• The FTP protocol has 2 modes. ASCII & Binary. Most EDI files are text files. On Windows/Mac/Linux/Unix the end of a line (EOL) in a text file is marked by different characters. New lines, form feed etc. If sender and receiver have different EOL styles then this can cause problems. This is solved if the FTP is done in ASCII mode (which is usually the default). However for things like excel and jpeg's is would cause data curruption so binary mode must be used.

It doesn't really matter which party is the host. If you are at the client end of the relationship and have to deal with several different hosted sites, the overhead for each additional FTP connection and session is small. Address, username & password. No complicated configuration.

If Tom, Dick, Harry need to exchange files with each other, as well as yourself, then this can also be achieved. In traditional EDI the "to" & "from" envelope data is found by reading the beginning of the message. This method could be used but it would require each file to be moved to your system so it could be read and then imediately retured to the host server in the correct folder. A better way that does not restrict the files to formal EDI formats, is to require the file names to be in the form from-to-count.extn e.g. tom-dick-99.txt or harry-tom-321.xls