The concepts used in BBS mail forwarding might be a little foreign to most people, and one can easily "upturn the apple cart" if you do not know how the system works. For that reason, we will explore a bit of how BBS mail gets from point A to point B. This will help you to understand how your TNC will interact with the BBS network, and help stop problems before they start.
First, we'll talk about how a BBS gets packet mail and flood messages, and what it does with these messages once it has them. Notice that you may see messages from all over the country, maybe even all over the world on your local BBS. They arrive through the store-and-forward system. This system is simple enough in concept. Messages are stored on a BBS, and sent to the next BBS down the line in a large group or batch. One BBS will automatically connect to another to establish a forwarding session when messages are exchanged. When the sending BBS is through with it's work, the it asks "Do you have anything for me?". If so, messages are reverse-forwarded to the originator of the forwarding session.
Messages are stored on the BBS, and the next BBS down the line does the same thing until it gets to the last BBS in the line. While this seems simple enough, there are a large number of packet radio BBS's present world-wide and a large number of paths to get to a BBS. This means that there is a possibility of a message reaching a BBS through mulitiple forwarding routes. How does your local BBS know not to accept a duplicate message?
Each message has a unique Message Identification Number called a MID, or a Bulletin Identifier called a BID. This is sort of a unique serial number that accomanies a message. It is generated by the originating BBS or TNC when the message is created. Your local BBS keeps a list of these BIDs and compares what the BBS is proposed to receive during a forwarding session to what it already has. If it sees that unique BID on a message it already has, it refuses that message and asks for the next one in the batch to be forwarded.
If you've been a regular reader of this series, you already know about the hierarchial addressing scheme that BBS's use world-wide. If you do not, please consult Part 15 of "Using the Wisconsin Network" before proceeding. This is very important, and cannot be overlooked. If you're not familiar with the casual operation of your TNC's mailbox, and how to command your TNC, stop right here and either read up on this, or obtain the help of an experienced operator. Mistakes made here can show up world-wide, and may cause you to be the recipient of some unfriendly advice.
Once you are at the stage where you are comfortable with these concepts, you can proceed. You will also need the following to properly set up your TNC:
1) The permission and participation of your local BBS Sysop.
2) To know if your TNC's mailbox supports forwarding and reverse forwarding.
3) Knowledge of the size of your TNC's mailbox. How much can it hold?
4) Your packet station to be "on the air" when you expect to participate in a forwarding session.
5) Knowlege of the times that your LAN frequency is least busy.
6) The call-sign of the BBS you intend to exchange mail with. This should be your "home" BBS.
7) The path you use to connect to it, and the command you use
to connect to your BBS through a node,
if you use one when accessing your local BBS.
8) Knowledge of your home BBS's hierarchical address.
Now the "why" of all of this.
You need the permission and participation of your local BBS Sysop because he or she has to set up the BBS both originate a forwarding session and to accept a proposed forwarding session from your station. Keep in mind that some BBS's are set up with limited capabilities and a big upgrade may be in order to accomadate your request.
Obviously, you need to know if your packet TNC can forward. Most will accept a reverse forward. You can often find information concerning this in the "PBBS Sysop" section of your TNC's commands manual.
You need to know how big your mailbox size is in bytes because this has a direct bearing on how much incoming mail you can receive. You can usually find this out by logging onto your mailbox when it is empty. It will tell you how many bytes are "free". Keep in mind that a typical typewritten page formatted at 80 columns by 54 lines is between 2000 and 3000 bytes. If you expect to accept mail in any quantity, make sure your TNC's mailbox is sufficiently large to accept what you want to get. Remember to keep your mailbox clean of old messages. Otherwise it will take multiple forwarding sessions to get your messages. This also has a direct bearing on whether you will tell your TNC to kill off any messages that have been forwarded.
Likewise, you would expect to keep your packet station available for BBS connects in order to receive your mail. If yours is a part-time packet station, perhaps you should consider leaving the messages on the BBS for manual retrieval.
You also would want to keep mail forwarding resticted to the times when your LAN frequency is least congested. Involved forwarding sessions can reduce someone else's packet throughput. Your BBS Sysop may also have forwarding to other BBS's scheduled for a particular time. Consult your BBS Sysop when deciding what time to forward.
Obviously, you need to know the call-sign of the BBS and how to get to it. If you use a node to get to the BBS, you have to know just what text to send to the node in order to get to the BBS. Most TNC's that accommodate node connections to a BBS for forwarding can only utilize one node connection. If your BBS is some distance away from you and requires multiple node connections to reach it, you might best use a BBS closer to you. If you connect to your local BBS directly or through just one node, then you are a good candidate to interact with the BBS network.
It is best to have your home BBS the same as the one you intend to forward with. Otherwise, things may get confusing for respondents of your messages. Therefore, you may get your messages out, but not back. This may also leave some poor BBS Sysop down the line wondering what to do with your mail. He may not know how to get it to you.
The last item you will need to know is the correct, complete hierarchical address of your home BBS. This is entered into your outgoing messages so that people may respond to your messages correctly. The BBS network may know very little about your mailbox-in-a-TNC, but it will know how to forward to your home BBS. It is your home BBS that knows enough to pass a message along to you.
In the next few installments, we will look at some of the most common
TNC's and how to specifically set them up for door-to-door mail service.
On to Part 28 - How to set a Tiny-2 TNC up for mailbox forwarding
Back to Part 26 - More TCP/IP and future packet - Network Needs
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