Re: FEC paper, implementation

["Fred R. Goldstein" <fgoldstein@bbn.com>]

In response to the discussion over using Ethernet instead of RS-232
to an external DSP-based box,

>   From: rob@sys3.pe1chl.ampr.org (Rob Janssen)
>
>   The only tricky problem that surfaces is "what protocol to use".  Of
>   course the natural answer would be "TCP/IP" (e.g. telnet) but it means
>   a lot of code has to be written for the modem (A TCP/IP stack for the
>   8051, Russ?).
>
>C compilers exist for the 8051, and a very early version of NET might
>be small enough, and suffice for many purposes (and is licensable for
>others).  Also, a commercial TCP/IP stack is available from US Software.

There's no need to burden the Ethernet link and DSP box with TCP/IP or
anything else like it, except for say management functions.  Let the PC talk
Ethernet.  Let the DSP-based "modem" talk Ethernet, but as a dumb "bridge"
or even "repeater".  (Bridges can be shared among multiple 10-base-2 bus
devices; repeaters are simpler but take only one client.)  Thus the PC
software talk to the Ethernet, which passes the packet to the DSP box, which
strips away the Ethernet but doesn't bother to look inside.  Thus the device
at the far end of the radio link will look like it's on the local Ethernet,
except a bit slow.

This is the approach taken by several successful ISDN devices.  The Gandalf
5510 was a dumb repeater, AUI-to-ISDN, which typically talked to a
multipoint bridge at the dial-in end.  The Gandalf 5242i is a true (limited)
bridge, suitable for a tiny LAN at its end.  The Digiboaard IMAC is a true
bridge.  The Combinet
150/160 is, I think, a very limited bridge; the full-price Combinet is a
full-scale bridge (big local-LAN learning table).  These devices are the
easiest way to get a PC onto ISDN -- especially if it's not running DOS/Windoze!

All need some kind of "management" function, especially to make the call.
Some have SNMP.  Some have serial ports.  Some use Telnet to a command
interface.  Some use modified Hayes commands over an out-of-band serial port.
(ATDTxxx-yyyy on a serial port to make the ISDN dial that data number.)
Some have push buttons (press to connect, or menu up/down/select with LCD
display).  Some have touch-tone-phone proxy dialing (*0xxxyyyy to dial
xxxyyyy on the data port).

I rather like the way the 5242i has a "connect" toggle button, and lets
everything else go via a Telnet interface.  Too bad it's an awful command
interface.  Fortunately, I rarely use that interface once it's set up.
(It also allows some functions, not all, to be set via touch-tone.)
___
Fred R. Goldstein      fgoldstein@bbn.com
Bolt Beranek & Newman Inc.  Cambridge MA  USA +1 617 873 3850