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+ <head>
+ <title>new protocol</title>
+ </head>
+
+ <body bgcolor="#FFFFFF">
+ <h2>new protocol</h2>
+
+ <hr>
+ <address><a href="mailto:djk@tobit.co.uk"></a>Dirk Koopman G1TLH</address><br>
+<!-- Created: Sat Sep 4 21:11:44 BST 1999 -->
+<!-- hhmts start -->
+Last modified: Sat Sep 4 22:49:36 BST 1999
+<!-- hhmts end -->
+ <hr>
+ <h4>Some thoughts</h4>
+
+ <ol>
+ <li>The protocol must be capable of being multi/broadcast.
+ <li>The format must regular.
+ <li>All packets will have a to, from and date field and a checksum of
+ some kind.
+ <li>space is a premium, therefore I am prepared to break layering rules
+ in specific cases to avoid duplicating fields. E.g. in AX25 using
+ callsign fields as part of the data (which means reconstructing the
+ packets from ax25 to be like you expect)
+ <li>the protocol will continue to be ascii for simplicity of use.
+ </ol>
+
+ <h4>packet format</h4>
+
+ The overall format of a packet shall look like this:-
+
+ <p>
+ <table border=3>
+ <tr>
+ <td width="20%"><b>Field</b></td>
+ <td width="80%"><b>Description</b></td>
+ </tr>
+ <tr>
+ <td width="20%"><b>OP Code</b></td>
+ <td width="80%">
+ This will be 'B' for now, but will be extended when multicasting
+ comes into being
+ </td>
+ </tr>
+ <tr>
+ <td width="20%"><b>From Address</b></td>
+ <td width="80%">
+ This will always be the originating cluster callsign and shall
+ <emph>never</emph> be changed
+ </td>
+ </tr>
+ <tr>
+ <td width="20%"><b>To Address</b></td>
+ <td width="80%">
+ The <i>To</i> address can be anything at all that is likely
+ to be meaningful to a cluster program, it could be a callsign, a 'group' name of
+ some sort (eg <tt>6MUK</tt>) or it could be empty, indicating a broadcast
+ </td>
+ </tr>
+ <tr>
+ <td width="20%"><b>Date/Time/Count</b></td>
+ <td width="80%">
+ This is a unix time_t, in hex (ie 8 characters) with an optional
+ 2 byte hex count on the end which can allow up to 256 protocol messages to be originated
+ a second. Programs must allow for both 8 or 10 digit hex numbers
+ </td>
+ </tr>
+ <tr>
+ <td width="20%"><b>Data</b></td>
+ <td width="80%">
+ The actual cluster data. The data in this field can contain only
+ ascii data. Any non ascii data shall be converted to <tt>%XX</tt> format, where
+ <tt>XX</tt> is the hex equivalent of the character represented, certain special
+ characters in the data such as '%', '|' and '^' shall also be converted. Although
+ it is envisaged that most data will be ascii, things like mail files can and
+ will contain newline characters and these will be converted.
+ <br><br>It is suggested that the raw version of the data in this packet be no
+ more than 128 characters, if it any packets are likely to be routed over
+ ax25 bearers. However, programs should be prepared to accept 1024 characters (after
+ decoding) for point to point wire links and routed data.
+ </td>
+ </tr>
+ <tr>
+ <td width="20%"><b>Checksum</b></td>
+ <td width="80%">
+ This is calculated as the simple arithmetic checksum, modulo 256,
+ of the whole packet excluding
+ this field and any preceeding field separator, as two hex digits
+ this checksum is designed solely to pick up errors in any connections between
+ this protocol and lower layers - where hopefully real CRC checking is done
+ </td>
+ </tr>
+ </table>
+ </P>
+
+ <p>
+ Each field in the above packet shall be separated by the '|' character <b>EXCEPT</b> the
+ <tt>op code</tt> which is concatenated onto the <tt>from</tt> field. The '|' character
+ must not appear in any field in the overall packet, it is the data providers responsibility
+ make sure this happens. If it is necessary for operations there can be a locally generated
+ newline sequence added on the end of the packet for sending or delimiting purposes
+ which is stripped off before presenting the packet for decoding.
+ </p>
+
+ <p>
+ A typical packet might look like:- <br><br>
+ <quote>
+ BGB7DJK||8BCF65DE|DX^G1TLH^M0BAA^144123^Humungous Signal!|A8<BR>
+ BGB7DJK|SYSOP|8BCF65FC|AN^G1TLH^What @$%7C%5E!** condxs?|5C<BR>
+ BGB7DJK|GB7BAA|8BCF670102|TA^G1TLH^G8TIC^Baaaaaaaaaaa|FD<BR>
+ </quote>
+ <p>
+
+ <p>
+ As mentioned earlier, astute readers will see that there is a mix up of lower
+ layer data with higher. This is deliberate (as well as potentially messy), but it saves
+ characters and promotes regularity on format. Apart from anything else, most directed
+ data actually needs to pass from cluster to cluster and it is important for the higher
+ layers to know where a packet originated. Also higher layers need to address packets to
+ other clusters or groups and there would otherwise be considerable duplication.
+ </P>
+
+ <p>
+ If a packet fails a checksum, then it is silently dropped - for now. When reliable
+ multicast comes in, other actions will occur at this level. In any event, higher level
+ functions that require some state to be maintained between packets (eg mail transfer)
+ should make their own arrangements in case reliable multicast isn't available between
+ two cluster nodes.
+ </p>
+ <br>
+ <hr>
+ Document Id: $Id$
+ </body>
+</html>
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