From: danh@quantum.on.ca (Dan Hildebrand)
Subject: Re: Embedded Systems Networking Systems
Date: Thu, 27 Aug 92 12:23:56 GMT
Organization: Quantum Software Systems
Keywords: Echelon, LonWorks, Networks, X.25

In article <gregh.714841186@cserver> gregh@cserver.plexus.com (Greg Hawley) writes:

Why not drop an Arcnet chip onto your embedded system ? The component cost 
is very low, and it seems to meet your criteria:

>CRITERIA
>
>In choosing a networking product we have the following 
>criteria. 
>
>    1. Reliability is a larger concern than speed.
>       A system with sustained throughput of 10 kbps would
>       be adequate.

The Arcnet chips take care of all the crc checking and transmission 
retries, and they also provide about 200 Kbytes / second transfer rates ( 
2.5 Mbits / second ). The newer Arcnet chips integrate the bus interface 
and a dual port RAM packet buffer, for a very low parts count ( small board 
space requirements ) and minimal design effort.

>    2. An open protocol is desired.  

An IEEE standard is pending for Arcnet and the components are widely 
available.

>    3. Support less than 100 nodes (but more than *2*).  
>       No internetworking capability is necessary.

Supports up to 254 nodes. Being a token passing network, determinism and
consistent throughput under load is also good.

>    4. Distributed control of network is preferable.
>       No single node should control the network's
>       operation.

Arcnet provides a very robust protocol ( handled transparently inside the 
chip ) for reconfiguration of the network if a node goes down, or a new 
node is added, or if the token is lost. There is no single point of 
failure, nor is any node more "special" to the operation of the network 
than any other. Network hubs, packet sniffers and other accessories are 
available from a wide variety of sources.

>    5. Must have industrial environment capability.
>       This includes wide temperature range, high
>       electrical noise resistance, etc.

Arcnet is widely used in industrial settings and is available off-the-shelf 
with twisted pair, coax and fiber media interfaces. We've provided it as an 
option for QNX for some time now, and seen many successful industrial 
applications use Arcnet.

>    6. Wire or fiber media are acceptable.

See above. If the high-end is interesting as well, Thomas-Conrad now makes 
a product called TCNS, which is basically a 100 Mbit Arcnet for about $700 
per node. Works very well.

>QUESTIONS
>---------
>
>3.  Are there open standards (IEEE, etc.) that exist for protocols
>    like what we am looking for.  Have third party's developed
>    implementations of these protocols?  All of the standards we
>    have seen are for high capacity systems.  What about lower
>    speed stuff.  What we are really looking for is a multi-drop
>    X.25/HDLC protocol.  We think.  

Arcnet has an IEEE standard pending. One of the advantages to Arcnet is 
that writing the driver is not difficult, with most of the protocol work 
all done in the chip. All you need to do is interface the chip and write 
some basic send/receive packet code -- the chip takes care of all the 
protocol issues.

>4.  Are there are other questions we should be asking?  Are there
>    any general comments we should hear?  Are we on the right track?

Another point that may or may not matter for your application is that you 
can get Arcnet cards for almost any cardcage ( PC bus, STD bus, etc ), 
allowing you to add standard hardware to your network of embedded systems 
if you later choose to. If you use standard packet formats, you would also 
be able to talk to those nodes with another operating system ( your 
development system, maybe ). In our customer base we see a number of 
systems built where small embedded systems share the LAN with PC's, VME and 
STD bus chassis.

Dan Hildebrand                     email: danh@qnx.com
Quantum Software Systems, Ltd.     QUICS: danh     (613) 591-0934 (data)
(613) 591-0931 (voice)             mail:  175 Terrence Matthews          
(613) 591-3579 (fax)                      Kanata, Ontario, Canada K2M 1W8