I am reminded of the Wang Labs 2100's of the early 1980's that connected to a
host minicomputer via RS-232 (and IIRC used a system printer). Of course the
cables didn't leave the building where installed but the host really WAS a
communications hub. I do not recall ever having to meet VDE 0871 with it.
Cortland
KA5S
----- Original Message -----
From: Monrad Monsen <mailto:monrad.mon...@oracle.com>
To: Steve O'Steen <mailto:steve.ost...@acstestlab.com>
Cc: emc-p...@ieee.org
Sent: 6/11/2010 4:19:15 PM
Subject: Re: Is Infiniband a Telecommunications/Network Port?
You have an interesting situation with your use of the RS-232 port for
this
use. Both CISPR22:2005 (adopted by most countries today) and CISPR22:2008
(the latest revision) gives the same note in the definition of
telecommunications/network port saying: "A port generally intended for
interconnection of components of an ITE system under test (e.g., RS-232 ...)
and used in accordance with its functional specifications (e.g. for the
maximum length of cable connected to it), is not considered to be a
telecommunications/network port under this definition."
The RS-232 does not define a maximum cable length but instead defines
the
maximum capacitance that a compliant drive circuit must tolerate. A
widely-used rule-of-thumb indicates that cables more than 50 feet (15 metres)
long will have too much capacitance, unless special cables are used. I see in
Wikipedia that "using low-capacitance cables, full speed communication can! be
maintained over larger distances up to about 1,000 feet.
<http://en.wikipedia.org/wiki/RS-232#cite_note-9> " (Cites a paper by Tony
Lawrence.) However, the CISPR22 note indicates that the intention was to not
define cabling for interconnection of components of a single ITE system as a
telecommunications/network port that would require conducted emissions
testing.
In contrast, your application of RS-232 does not appear to fit this
description. You describe your device as one that "employs multiple RS-232
ports to transfer data to peripheral devices that are dispersed throughout a
building which will be accessed by multiple users." This device appears to be
fulfilling the role of an Ethernet hub/switch allowing intercommunications and
can also allow sharing of printers on the network. The refere! nce is not to
the Ethernet protocol but to the purpose & use. ; As such, your application
device seems to fall into the definition "point of connection for voice, data
and signalling transfers intended to interconnect widely dispersed systems via
such means as direct connection to ... local area networks (e.g. Ethernet,
Token Ring, etc.) and similar networks." I did not find any separate
definition for "widely dispersed networks" within the CISPR22 standard.
You could probably argue the other way by emphasizing the mention of
RS-232
in the note, but you will find others that will disagree.
Personally, I am not a fan of the telecommunications/network port
testing ...
especially for products that will not be directly connected to cables leaving
the building. If there is a noise issue with a product, it would be picked up
by the other traditional tests (power line conducted emissions and radiated
emissions). For cables leaving the building, then the risk would merely be to
the switch or router! that is directly connected to that external cable. I
believe it would be extremely rare for an Ethernet line from outside to be
connected directly to a server, printer, or other device. Actually, for ports
connected to cables leaving the building, I would be more concerned about
performing surge testing rather than conducted emissions testing. To best
perform this telecommunications/network port conducted emissions testing, test
labs are forced to search for custom impedance stabilization networks (ISNs)
to support the interface. Otherwise, the alternative test method requires
messing up a cable as the the cable insulation is pulled off to get access to
individual wires during the test. This does not make anyone happy.
Unfortunately, the telecommunications/network port test requirement has
been
placed in the CISPR22 standard and is being adopted around the world.
Monrad Monsen
Worldwide Compliance Officer
Oracle
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