TCP/IP over RS232 (Adam Dunkel's TCP/IP)
Bahri Okuroglu
it adds nearly zero hw cost to a project.
By the way if I have board which runs Adam Dunkel's TCP/IP over
SLIP over RS232 code, how can I connect this device to the
network? Samples include a code for mounting a device and assigning
IP addresses and defining route for a Linux machine but what if I have,
say, 10 of these embedded devices?
If these had ethernet interfaces it would be easy to connect them to the
network using a HUB. Is there a similar and cheap device to connect
"N" SLIP devices to the network?
Maybe I'm missing something which makes all these worthless.
Tauno Voipio
"Bahri Okuroglu" <bah...@netas.com.tr> wrote in message
news:3C0DF1B7...@netas.com.tr...
A SLIP or PPP connection is - by definition - point-to-point. They cannot be
networked directly. To connect 10 SLIP devices together, you need a router
with 10 serial ports - 1 for each device. The network is then created inside
the router by the IP assignments and routing tables.
Tauno Voipio
tauno voipio @ iki fi
Tsvetan Usunov
there are RS232 hubs also, do you think your ISP have 200 computers to
allow 200 modem entry points for dialup ;)
Best regards
Tsvetan
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Spehro Pefhany
> there are RS232 hubs also, do you think your ISP have 200 computers to
> allow 200 modem entry points for dialup ;)
What is "dialup" ? ;-)
Any idea what these things cost, Tsventan?
Best regards,
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Jeremy Bentham
> it adds nearly zero hw cost to a project.
I disagree.
1. Any microcontroller running serial TCP/IP must allocate significant
amounts of RAM for packet processing (to accomodate the 576-byte minimum
datagram size). If an external Ethernet controller is available, its RAM can
be used as the primary buffer, so reducing the RAM requirement on the
microcontroller, eliminating any time-critical serial interrupts, and
massively increasing throughput.
2. RS232 uses single-ended (signal & ground) electrical signalling, and has
rudimentary error detection, so is unsuitable as a network medium. SLIP just
adds framing; it has no error detection, so you are dependant on the 16-bit
IP checksum (not 32-bit CRC) for your data integrity. If you want to use
asynchronous protocols over any distance, you'd have to switch to, say, a
balanced-pair system such as opto-isolated RS422, which adds to your
hardware cost, or just run your RS232 at a low baud rate, and hope the
electrical noise isn't too bad!
3. SLIP hubs (routers) with large numbers of RS232 ports are relatively
unusual, so will be expensive. Ethernet hubs are cheap, due to massive sales
volumes.
4. An RS232 solution is a lot harder to debug, as there are relatively few
TCP/IP serial diagnostic tools available (e.g. SerialTest Async), and these
have to be physically inserted into the circuit under test. There are
excellent Ethernet diagnostic tools available for free (e.g. Ethereal),
which operate non-invasively.
<snip>
> Maybe I'm missing something which makes all these worthless.
You can buy the Realtek Ethernet controller chip for around 3 dollars in
moderate volumes, and soon we'll have microcontrollers with on-chip
Ethernet. The RS232 SLIP 'nonstandard' was intended for short ad-hoc
point-to-point links; can't we keep it that way?
Jeremy Bentham
Iosoft Ltd.
Pete Zaitcev
> TCP/IP serial diagnostic tools available (e.g. SerialTest Async), and these
> have to be physically inserted into the circuit under test. There are
> excellent Ethernet diagnostic tools available for free (e.g. Ethereal),
> which operate non-invasively.
You can do tcpdump -i sl0 on the host - worked well for ages.
-- Pete
Robert Reimiller
<j...@iosoft.nospam.uk> wrote:
>3. SLIP hubs (routers) with large numbers of RS232 ports are relatively
>unusual, so will be expensive. Ethernet hubs are cheap, due to massive sales
>volumes.
>
communications over spread-spectrum radio modems. Cisco makes routers
with like 8 or 16 serial ports that go into ethernet to merge all those
data streams into one connection to the data collection computer.
Sometimes ethernet just isn't available economically or at a low enough
power consumption. So, I'm not as pessimistic as Jeremy about SLIP.
Jeremy Bentham
> I know that there are a lot of seismic stations that use SLIP
> communications over spread-spectrum radio modems. Cisco makes routers
> with like 8 or 16 serial ports that go into ethernet to merge all those
> data streams into one connection to the data collection computer.
Fine, but not low-cost.
> Sometimes ethernet just isn't available economically or at a low enough
> power consumption. So, I'm not as pessimistic as Jeremy about SLIP.
I agree that SLIP is useful for simple point-to-point links, but felt that
the suggestion "it adds nearly zero hw cost to a project" is potentially
misleading, and tried to redress the balance.
Choosing the right networking system for a given application is difficult,
and it's important to view the system as a whole - in a past life I chose
MIL 1553B networking for use on a tube train, so know how costly a wrong
decision can be!
Jeremy Bentham
Iosoft Ltd.
Tsvetan Usunov
> > allow 200 modem entry points for dialup ;)
>
> What is "dialup" ? ;-)
something still pretty popular overhere ;)
> Any idea what these things cost, Tsventan?
$$$
check on www.pricewatch.com or on www.cisco.com
these things are named serial port routers IIRC
Peter Desnoyers
>> > there are RS232 hubs also, do you think your ISP have 200 computers to
>> > allow 200 modem entry points for dialup ;)
>>
>> What is "dialup" ? ;-)
>
>something still pretty popular overhere ;)
>
>> Any idea what these things cost, Tsventan?
New or used? They're called 'terminal servers' or 'remote access
servers', and you can find a bunch of them on EBay if you search
for terminal servers. I bought an old 16-port Xyplex for $50 a
while back, and the guy tossed in two more at $10 apiece. That was
a steal, however, and in addition the Xyplexes are enough of a pain
to justify paying a fair bit more - I would guess you could get a
decent 16-port Xylogics micro-annex or something like that for maybe
$100-$200 on Ebay.
These things are obsolete nowadays, as you can't provide 56k dialup
access using external analog modems - you need a digital T1 into the
modem, at which point you might as well integrate the whole shebang.
Black Box, of course, still makes them anyway, for a large premium.
--
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Chinook Communications (617) 661-1979 p...@fred.cambridge.ma.us
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