Internet E-Mail, as most often seen, is "plain text". That is, a letter typewritten and easily readable as ASCII text. Of course, as soon as people found out how wonderful electronic mail was, they wondered if it was possible to mail programs, pictures, and other binary format files. Of course it is, through the use of encoding and the E-Mail attachment. You can send someone almost any kind of file in this manner, a binary executable program, a JPG picture, and even video and "movies". You can also send word processor and other files ("rich text") that are stored in a binary format. These are exactly the same as any other binary file, therefore, they must be specially encoded to be sent in a "plain text" mode.
If you operate a TCP/IP station, you probably already know that the mailer you use will take care of any special file types (at least most often). The information provided below is not so much for you, but for users who connect via AX.25 text mode to collect their mail from the gateway. Most TCP/IP users will have their mail automatically collected by your TCP/IP program. However, you may find the following information helpful, especially the information concerning file sizes.
There are various methods used to encode programs so that they can be mailed, among them UU, Base 64 and Bin2Hex. While this is no problem for the internet, where data rates reach astronomical speeds, they can represent a considerable challenge when collected by packet radio. There are a few things to consider if you decide to mail or receive a program encoded in this manner. The first thing to consider is the size of the file. It would be a lifelong endeavor to collect a 1-megabyte file at 1200 bps! You best recommend to anyone mailing you at a gateway to limit file sizes. Even a 10K file can try your patience at a typical LAN speed.
Also remember that sometimes an encoding program will double the size of the file! Before you send anything this way, encode the file and look at the file size. Anything that "bloats" a file is to be avoided (unless the file is a small one). In order for a lot of word-processor documents to be successfully transferred, you may need to convert these as well. Most of these kinds of files are a combination of plain text as well as odd control characters. In order for them to be safely transferred, they should be encoded prior to being sent.
HTML documents, on the other hand, do well via standard packet mail. HTML is a text-based programming language that is used extensively on the World-Wide Web. Of course any such document must be viewed with a Web Browser, but they can be transferred via packet mail, with no encoding necessary.
That being said, here's a special warning to users of Windows "Write!". Even if you tell this program to save the file in "plain ASCII text", it will add extraneous control characters to the file. Take note of this and either use a plain text editor, or use a different word processor that you are certain saves files as plain text.
Another method of file transfer via mailing is to use the UU encode and decode programs. These are stand-alone DOS programs that will encode or decode a binary-format file into a format that looks like plain text to the mail programs. When receiving a file like this, simply tell the UUDECODE program to decode it. You can then use the executable, or view a "rich text" format message or word processor document.
Either of these file conversion methods are likely to be decodable by mailers, or at least easily decodable with a stand-alone program. When in doubt about any such file exchange, think about the following:
- Will your correspondent be able to decode the message?
- Will you be able to decode the message?
- How big is the file?
Common sense says to keep any file under about 10K. - What is the content of the file? Remember, a picture file of inappropriate subject matter is just as illegal as any illegal wording. And one more thing to discuss.
Many of you have seen me use words like "Encode" and "Decode". Many astute observers will wonder if encoding a message sent via packet is legal. The phrase "Codes and Ciphers" in part 97 rings a bell with most people, but they often forget the "rest of the story". The full text of the rule in question should help to reassure you on this matter. This rule points to intent of the encoding more than anything else. Remember, it is illegal to code a message to hide it's meaning. It is OK to compress or encode a message if the intent of the encoding is to facilitate message exchange.
In other words, if you are using encoding to make a message transfer more efficient or even just plain possible, you are following the law. If you are using encoding simply to make it harder for someone to see your message, then you are outside of the law.
That's all for this time. In the next part of our series, we will continue to discover more of the features of the gateway.
On to Part 38 - Internet Gateway Q&A
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