Date   : Thu, 09 Aug 2007 01:30:23 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Emulating Econet hardware?

Chris Thornley wrote:
> An Ethernet to econet device would require some sort of router (not bridge)
> software to be written. Perhaps hiding the econet datagram's in IP packets.
 
An Econet packet is encapsulated in an IP packet as follows:
 
Econet packet:
+------+------+-----+-----+---------+------+------------------------+
| Dest | Dest | Src | Src | Control |      |                        |
| Stn  | Net  | Stn | Net |  Byte   | Port |          Data          |
+------+------+-----+-----+---------+------+------------------------+
  <------ - - Packet Header - - ------>   <-- - Packet Data - -->
 
Becomes IP packet:
+-------------------+
| IP Header:        |
|  Version          |
|  Header Length    |
|  Type             |
|  Total Length     | <- header length + UDP packet length
|  ID               |
|  Fragment         |
|  Protocol         | <- UDP
|  Header CRC       |
|  Source Address   | <- source site.network.net.stn
|  Dest Address     | <- dest site.network.net.stn
|  Options          |
| ----------------- |
| IP Data:          |
|  UDP packet       |
|  +--------------+ |
|  | UDP Header:  | |
|  |  Source Port | |
|  |  Dest Port   | | <- &8000 for Econet-Over-IP
|  |  Length      | | <- Data length + UDP header length
|  |  Checksum    | |
|  | ------------ | |
|  | UDP Data:    | |
|  | +--------+   | |  Somewhere in here is:
|  | | Econet |   | |   Magic number &02
|  | | Packet |   | |   Port
|  | |  Data  |   | |   Control Byte
|  | +--------+   | |   Padding &00
|  +--------------+ |   Handle &nnnnnnnn
+-------------------+
 
(I'm sure I've posted this before...)
 
Conversely, an IP packet can be encapsulated in an Econet packet as
follows:
 
+------+------+-----+-----+---------+------+---------------+
| Dest | Dest | Src | Src | Control | Port | +-----------+ |
| Stn  | Net  | Stn | Net |  Byte   | &D2  | | IP Packet | |
|      |      |     |     |         |      | +-----------+ |
+------+------+-----+-----+---------+------+---------------+
The Flag byte determines the type of IP packet:
  &81 IP
  &A1 ARP_REQUEST
  &A2 ARP_REPLY
  &8F IPBCAST_REQUEST
  &8E IPBCAST_REPLY
 
> The first thing that need doing is for the econet protocol / datagram's /
> command, will need to be documented, in an easy to follow form. You should
 
It is documented, and I've been putting online at http://mdfs.net/Docs/Comp/Econet
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
BBC BASIC for 30+ platforms - http://mdfs.net/Software/BBCBasic