Date   : Tue, 01 Aug 2006 13:20:52 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: The Beeb BBs Project

>Message-ID: <Pine.LNX.4.58.0607130952220.15101@...>
 
Chris Johns <chris@...> wrote:
> On Wed, 12 Jul 2006, Ian Wolstenholme wrote:
> > Econet uses ports.  There are certain ports reserved for communicating
> 
> If you're going to do econet over IP, you may as well use the AUN system
> tho (which I think does it all over one UDP port).
 
A NetFS file server command is as follows:
+-------+----------+--------+--------+--------+----- - - - - -+
| Reply | Function |  URD   |  CSD   |  LIB   | Parameters    |
| Port  |   Code   | Handle | Handle | Handle |               |
+-------+----------+--------+--------+--------+----- - - - - -+
 
The program API encapulates this as follows for OSWORD &14,0:
+-----+------------+-----------------------------+
| &00 |   Length   | +-------------------------+ |
|     | of command | |File Server Command Block| |
|     |    block   | +-------------------------+ |
+-----+------------+-----------------------------+
 
This is passed to the network transmission system to send to the
file server as follows, equivalent to OSWORD &10:
+-------+------+------+-----+-----+---------------+---------------+
| RxNum | Flag | Port | FS  | FS  | Command Block | Command Block |
|  &00  | &7F  | &99  | Stn | Net | Start Address | End Address+1 |
+-------+------+------+-----+-----+---------------+---------------+
 
This gets encapsulated as an Econet packet as follows:
+------+------+-----+-----+-------+-----------------------------+
| Dest | Dest | Src | Src |       | +-------------------------+ |
| Stn  | Net  | Stn | Net | Port  | |File Server Command Block| |
| (FS) | (FS) |     |     | (&99) | +-------------------------+ |
+------+------+-----+-----+-------+-----------------------------+
  <---- -  Packet Header  - ---->   <---- - Packet Data - ---->
 
The 6854 ADLC puts this on the wire as follows:
+--------------+---------------+-----+-----+--------------+
| Opening Flag | Econet packet | CRC | CRC | Closing Flag |
+--------------+---------------+-----+-----+--------------+
 
Acorn Universal Networking encapsulates an Econet packet as
a User Datagram Protocol packet as follows:
 
IP packet
+-------------------+
| IP Header:        |
|  Version          |
|  Header Length    |
|  Type             |
|  Total Length     |
|  ID               |
|  Fragment         |
|  Protocol         |
|  Header CRC       |
|  Source Address   | - Client site.network.net.stn
|  Dest Address     | - File Server site.network.net.stn
|  Options          |
| ----------------- |
| IP Data:          |
|  UDP packet       |
|  +--------------+ |
|  | UDP Header:  | |
|  |  Source Port | |
|  |  Dest Port   | |
|  |  Length      | |
|  |  Checksum    | |
|  | ------------ | |
|  | UDP Data:    | |
|  | +--------+   | |
|  | | Econet |   | |
|  | | Packet |   | |
|  | |  Data  |   | |
|  | +--------+   | |
|  +--------------+ |
+-------------------+
 
OK, I may have got some of the IP/UDP details wrong ;)
 
You can map a single AUN net in a Class C Internet network, eg eg
192.26.30.*  So, for example, my MDFS may eventually be accessible
via the Internet as, for example, 192.26.30.254
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
BBC BASIC for Windows and Internationalisation
  See http://mdfs.net/Software/BBCBasic/Windows/ProgTips