Ethernet to Ethernet ovr slow serial link?

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Dear Community -
I'm thinking of having a Ethernet communication "bridge" over a much
slower serial line. My questions are:
- Does anybody built it already? Hopefully with schematics etc. Lniks
on the Net?
- Exists time-out values in the Ethernet spec? If I have a slow link
there maybe several hundred milliseconds before the answer comes back.
Overflow possible?
- I think of using a W3100A or Realtek Ethernet Controller along with
a AVR. Is it possible to use a generic Ethernet Controller?
- I don't know if the circuit would be a Router, Bridge, Rub, Switch,
Gateway in the Ethernet sense. What is the simplest answer?
- Would it be possible to make the circuit entirely protocol
"transparent" (other than the long delay)?
- Anyone interested to share infos/project?
BTW: I'm a electronics design engineer and don't want infos about
commercial products.
Regards -
Henry

Re: Ethernet to Ethernet ovr slow serial link?
This is not a new idea. An ethernet-to-serial port at each end.

http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=ethernet+to+serial+port&btnG=Google+Search


Henry wrote:
Quoted text here. Click to load it


Re: Ethernet to Ethernet ovr slow serial link?

Quoted text here. Click to load it
http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=ethernet+to+serial+port&btnG=Google+Search

Did you _read_ any of the hits?  I read the first 10 or so, and
none of them had anything to do with what the OP wants to do.

I even designed the software for one of the products sited on
one of the hits you posted.  My product doesn't do what the OP
wants, and I'm not aware of any competing products that do
either.

Putting any of the cited serial-to-ethernet devices at each end
of a cable will not create an Ethernet bridge.  The most you
could hope to do with the cited products is to tunnel a single
UDP or TCP port through the serial line.

Quoted text here. Click to load it

Probably -- protocols designed to run on top of Ethernet may
going to tolerate the latencies.

--
Grant Edwards                   grante             Yow!  Like I always
                                  at               say -- nothing can beat
We've slightly trimmed the long signature. Click to see the full one.
Re: Ethernet to Ethernet ovr slow serial link?
2nd:
I should clearly state that I want to make a "packet link". Each Ethernet
packet will be send across a link (serial like V24, wireless, etc) in duplex
mode. I found nothing on the Net. That's why it is impossible or to
difficult? Surely there exists applications for it. Think of having your PC
in one room with ordinary Ethernet cable to another PC and you want a little
embedded PC somewhere connected with a cheap ordinary telephone cable (That
can be your freezer :-)))
- Henry




Re: Ethernet to Ethernet ovr slow serial link?

Quoted text here. Click to load it

It's difficult.


Possibly.  More likely people will want to route IP over a
serial link.  That's what PPP is for.  

In theory, you can use PPP to encapsulate anything, but IP is
the most common.

Quoted text here. Click to load it

FWIW, "cheap ordinay telephone cable" is what most of us run
10baseT and 100baseT Ethernet on.  Cat-3 or even Cat-5 is
pretty cheap and common (at least in the US, it is what phone
wiring is done with).

Quoted text here. Click to load it

--
Grant Edwards                   grante             Yow!  World War III? No
                                  at               thanks!
We've slightly trimmed the long signature. Click to see the full one.
Re: Ethernet to Ethernet ovr slow serial link?
Quoted text here. Click to load it


Unless I'm misunderstanding your question, you just want a remote
bridge, as implemented by every (non-low-end) bridge/router vendor in
the world.  Bridges, as opposed to routers, work below the network
(eg. IP) layer and forward frames based on the MAC address.  If you
want to build such a bridge that's interoperable with other bridges
(and switches, as switches are just plain old multi-port bridges with
better marketing), see the 802.1 (spanning tree bridge) spec.  The
fact that one of the link is over a slow serial line is immaterial,
except, perhaps, to some overly timeout sensitive higher level
protocols.

If you don't care to be 802.1 interoperable - and I don't recommend
this since you'll break with even the most basic switch (as opposed to
pure hub) on either side of the bridge - the basic procedure is as
follows.  Open the network cards in promiscuous mode.  Capture all the
packets and inspect the destination MAC address.  If that address is
on the "other" side of the link, forward the packet.  The trick is
coming up with a good scheme to figure out which MAC address is on
which segment, which is exactly what 802.1 addresses.

There is bridging software available on various Linux distributions as
well, if you want access to source code.

Re: Ethernet to Ethernet ovr slow serial link?
Quoted text here. Click to load it

It sounds like what any ISP with dial-up lines does with PPP.  The
appliance-side should just need PPP code.  The other end could be a
Linux/xBSD box configured as a gateway to route to the serial link.

The "grasshopper" DNS and BIND O'Reilly book might be a good place to
start.  (Why a grasshopper when one of the authors is _Cricket_ Liu, I
dunno. :^)

--
Ron Sharp.



Re: Ethernet to Ethernet ovr slow serial link?
Quoted text here. Click to load it

On second thought, perhaps the PPP solution seems too easy.  Did I miss
something?  Is there a reason that you want to route packets at the
Ethernet level or do you just need to route IP packets from an Ethernet
LAN across a serial link?

The packet level makes a big difference.  The former seems like a lot of
work; the latter is off-the-shelf gateway and router config.  (And with
TCP/IP, you get handshake and retry for free.)

--
Ron Sharp.
"This is .. wrong tool. No. No. Not good. No. No. Never use this."



Re: Ethernet to Ethernet ovr slow serial link?
Quoted text here. Click to load it

Seems odd to route ethernet over a serial link  but anyway.

You have a couple of options.

Use it as a router, (assuming IP) and have it connect subnets, then packets
are sent to the mac of the Ethernet card at each end when they need to cross
the link.  Then you can just use something simple like slip to transport the
packet to the other end and send it out the other card.  This would be my
preference in almost every situation

Use it as a bridge, passing all packets.  You stick the Ethernet chip in
promiscuous mode (where it received all packets on the lan) and transport
them all.  I assume the serial link is many times slower than the Ethernet
link so this could be a problem.

for either of these tasks you could use a couple of ethernut boards to
experiment quite quickly and easily.

Have fun.

Ralph




Re: Ethernet to Ethernet ovr slow serial link?
Quoted text here. Click to load it

We tend to do that over many wide area network (WAN) connections with
speeds of 56K up to T3. I'd guess that what the OP is requesting is
more like what some people do with a dialup except instead of routing
using bridging. In the late '80s I had heard that refered to as half
bridges (2 makes a complete bridge). So it is possible (examine the
Open Source code for tcp/ip, bridging, & PPP). At one time I would
have guessed that it wasn't possible to it with 8/16 bit processors
but I've seen too much imaginative work to doubt it anymore.

--
Linux Home Automation         Neil Cherry         snipped-for-privacy@comcast.net
http://home.comcast.net/~ncherry/ (Text only)
We've slightly trimmed the long signature. Click to see the full one.
Re: Ethernet to Ethernet ovr slow serial link?

Quoted text here. Click to load it

Use the PPP encapsulation. If you do not need negotiated options, you can
forget about PPP link control protocols and the initial negotiation. If
needed, you can also transfer the Ethernet frame header with MAC addresses
and type/size word.

Been there - done that. (It's sloooow).

HTH

Tauno Voipio
tauno voipio @ iki fi




Re: Ethernet to Ethernet ovr slow serial link?
Quoted text here. Click to load it

Check-out the IEEE 802.1d MAC bridge specification.
No ... its *not* "free". We built one of these during
the eighties. To reduce the amount of traffic over the
slow Wide Area Network (WAN) link, you need to do some
filtering at each ethernet port.

To do this, there is an algorithm that looks at the
MAC source address of each received packet, and saves
it as a known local MAC address. Incomming destination
MAC addresses are compared to this list of local addresses,
and if the destination is not found in the local list,
then the frame is forwarded over the WAN link to the other
end of the bridge.

Yes, thats an oversimplification of the algorithm. It gets
even more ... interesting ... when there is more than a
simple point-to-point connection.

The nice thing about MAC bridges is that they are independent
of the higher level protocols (e.g. IP).


--
Michael N. Moran           (h) 770 516 7918
5009 Old Field Ct.         (c) 678 521 5460
We've slightly trimmed the long signature. Click to see the full one.
Re: Ethernet to Ethernet ovr slow serial link?
Quoted text here. Click to load it


IEEE has convinced some folks to "sponsor" free (personal use) access
to most of the current 802.x specs.

http://standards.ieee.org/

and click on "Get IEEE 802".

Re: Ethernet to Ethernet ovr slow serial link?
Thanky you all folks for the really informative answers. Maybe the project
will come true...
- Henry




Site Timeline