Cisco 3000 Series, Hardware Installation And Maintenance

Page: 27 / 102

Preparing
to
Make
Connections
Table 2-1 RS-232
Speed
and Distance
Limitations
Data Rate
Baud
Distance Feet Distance Meters
2400 200 60
4800 100 30
9600 50
15
19200 25
7.6
38400 12
3.7
Note RS-232
is
often used in violation of these specifications
if you
understand the
electrical
problems
that can arise
and can
compensate for
them
you might be
able
to get
good
results at
distances greater than those
shown
in
Table
2-1 however
do
so
at
your
own
risk
We
recommend
that you
stay within
the
standard-defined
distance
Interference Considerations
When
you
run cables
for
any
significant
distance in an electromagnetic
field interference can occur
between
the field
and the
signals
on
the
cables This
fact
has
two
implications
for the construction
of terminal plant cabling
Plant cabling can emanate
radio interference
if it is
unshielded for too long distance
Strong electromagnetic interference
especially as
caused
by
lightning or radio transmitters can
destroy the
RS-232
drivers
and
receivers
in
the server
if you
use twisted-pair cables
in
your plant cabling with
good distribution
of grounding
conductors
the plant cabling
is
unlikely to
emit radio interference
When
exceeding
the distances
listed in
Table 2-1 ground the conductor for each data signal
If you have
cables
exceeding the
distances
in
Table 2-1
or if you have
cables
that
pass
between
bl4ildings then give special consideration to
the
effect
of lightning
strikes or ground loops The
electromagnetic pulse caused by
lightning or other high-energy
phenomena can
easily
couple
enough
energy
into
unshielded conductors
to
destroy electronic
devices
If
your
site
has experienced
problems of
this sort consult
experts
in
lightning suppression
and
shielding
Most
data centers cannot resolve the infrequent but potentially catastrophic
problems
just
described
without
pulse meters
and
other special
equipment
Take
precautions to
avoid these problems by
providing properly
grounded and shielded
environment with
special
attention
to
issues of
electrical
surge suppression
To
predict
and remedy
strong electromagnetic interference
consult experts in
RFI
2-10
Cisco 3000 Hardware
Installation
and Maintenance