Hi Steve,

"Steve Lusardi" wrote in message
...
Meindert,
Very nice to hear from you again. You have been away quite some time.

I'm lurking here every day... so not really away :-)

I can't believe I am hearing this from you. You are the perfect person for
this thread. I think you need to think a bit outside of the box. As you
know, each NMEA manufacturer today is addressing the inadequacies of NMEA
with their own propriety solutions and selling them as the next best thing
in boat electronics, like SeaTalk. Yet we have a huge, inexpensive
commercial infrastructure all around TCP/IP and yet the marine industry is
trying to reinvent the wheel.

Well, I think it is not that simple. Off course we have thousands of cheap
products for ethernet networking. Most of which are not suitable nor allowed
in marine environments. Take the average UTP CAT5 cable: not permitted on
board of SOLAS vessels. The average hub is not IEC945 compliant: not
permitted on SOLAS vessels. Not to mention the average RJ45 connector...

Furthermore, while everyone is hammering on using TCP/IP to replace NMEA:
TCP/IP is the least suitable protocol for this. In a marine network, one has
several devices all sending information to whoever it concerns. TCP/IP on
the other hand, is a point to point protocol. UDP broadcasts would be much
better since they reach every device on the network. Look at the average
Serial-Ethernet bridge: they all to TCP/IP to replace ONE serial link. Not
suitable. Look at the price of these little boxes compared to bog standard
ethernet cards and you see how in a relatively small marine market prices
would increase when you equip devices with an ethernet interface.

You should revel in this foolishness and
consider this as a golden opportunity to develop a transport network like
the CAN bus SAE J1939 standard,

NMEA2000 is based on CAN

but using TCP/IP as the flexible transport
medium.

Do you realise that basic CAN only transports 8 bytes per packet at a time?
To put TCP/IP on top of that causes a huge overhead on the network, not to
mention the burden on the processor that drives the CAN controller. CAN was
never invented for this. CAN was invented to broadcast data on a network to
every one who needs it. No point to point connections. CAN is perfect for
distributing navigation info.


Where the entry and exit ports are box standard NMEA, but are in
fact intelligent gateways to the Ethernet transport. You can buy off the
shelf single chip TCP/IP support

At a price....

and inexpensive switches. I see these
gateways programmable as talkers or listeners with a central
router/controller accepting the NMEA inputs and buffering them as well as
distributing them by IP address at any rate the listener required.

The speed of NMEA is so low that you can simply dump it on an ethernet
network as it comes, without any intelligent distributing or rate control.
Do some math: 100Mbit/s vs 38400 b/s: That is the equivalent of 2600 AIS
receivers spitting out data continuously one one UTP cable.

Meindert