[c-nsp] Max length of 9600 serial over CAT5e

[Bill Wichers]

RS-232 has more limitations than just cable capacitance. RS-232 is a
single-ended communication protocol (on the physical level), so it's
noise immunity is not very good. This is especially a problem if you're
running the cable in an electrically noisy environment (like a cable
tray or wiring closet(s), etc.).

If you need to run a long distance, why not just convert your RS-232
signal to RS-422 where you can safely run a 9600bps signal out to over a
kilometer? All you need is a 2 pair cable, ideally with a shield,
provided you don't need hardware flow control. The converters are
usually cheap, maybe $50 or so per end unless you need electrical
isolation.

   -Bill

> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> bounces at puck.nether.net] On Behalf Of Richard Halfpenny
> Sent: Wednesday, April 08, 2009 7:32 AM
> To: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] Max length of 9600 serial over CAT5e
> 
> Sam Stickland wrote:
> >  Hi,
> >
> >  What's the maximum length of you can run async-serial (9600 baud)
> >  over CAT5e (from a terminal server to console port).
> >
> >  My google-fu has failed me.
> 
> If I remember correctly, the spec for RS-232 says the maximum
> capacitance of a cable can be 2500pF at 20kbps.  A Cat5e of approx
46pF
> / metre would give you a maximum length of 54 metres.  At 9600bps you
> could probably drive slightly longer.
> 
> Rich
> 
> --
> Network Operations
> Exa Networks Ltd :: AS30740
> richard.halfpenny at exa-networks.co.uk
> 
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