I've had the pleasure to participate in upgrading from CAT5 to CAT5e on several offices throughout the years. The amount of employees varied from down to the twenties up to several thousands.
We ran different scenarios from a complete upgrade, where all cabling was changed, to only upgrading what was necessary. Since the last option was the most economical, that was the one management chose to run with.
It was pretty basic. We hired a professional electrician/network engineer to run certified CAT5e tests on every single CAT5 cable installation in every office (using a Fluke CableIQ). Those that were approved, were left as is and those who failed where changed to new CAT6 cabling.
For example, the test included:
- Wiremap - Checks for proper pin to pin termination, and for each of
the 8 conductors the wire map checks for: Continuity to the far end,
Shorts between any two or more conductors, Reversed Pairs, Split
Pairs, Transposed Pairs, Any other wiring faults.
- Length - The physical length of the cable is the actual length
derived by measurement of the cable(s) between the two end points.
The electrical length is the length derived from the propagation
delay of the signal and depends on the construction of the cable. The
maximum physical length of the horizontal cable (permanent link) one
end of the cable to the other is 90 meters. The maximum length of the
channel model is 100 meters.
- Insertion Loss - Insertion loss is the loss derived from inserting a
device into a transmission line. The insertion loss for both the
permanent link and the channel models are the total insertion losses
of all the components.
- Near End Cross Talk (NEXT) - Pair to pair NEXT loss is the
measurement of signal coupling from one pair to another. The result
is based on the worst pair to pair measurement.
- Power Sum Near End Cross Talk (PSNEXT) - Power sum NEXT takes into
account the statistical crosstalk between all pairs while energized.
This is a calculated amount derived by adding up the crosstalk
results between all pair combinations.
- Equal Level Far End Cross Talk (ELFEXT) - FEXT is the unwanted
coupling of a signal induced by a transmitter at the near end,
measured on the disturbed pair at the far end. ELFEXT is the same
measurement of FEXT, less the effect of attenuation.
- Power Sum Equal Level Far End Crosstalk (PSELFEXT) - As in Power Sum
NEXT, these are computed values based on the sum of all the possible
pair combinations under the respective tests.
- Return Loss - Return loss is the value of energy reflected by
impedance variations when devices are inserted into the cabling
- Propagation Delay - Is the time it takes the signal to travel from
one end of the cable/system to the other. The maximum channel
propagation delay is 555ns (nanoseconds) and for the link it is 498
ns, both measured at 10 MHz.
- Delay Skew - Delay skew is the signalling delay difference in time
(nanoseconds) between the fastest pair and the slowest pair. The
maximum channel delay skew is 50 ns, and in the permanent link it is
Ethernet cables like the CAT5 and CAT5e use twisted pair wiring to decrease electromagnetic interference and crosstalk between the wires themselves. The main difference between the CAT5 and CAT5e wiring comes down to specification. CAT5e cables have more stringent requirements than the CAT5 when it comes to the tightness of the wire twisting; more tightly twisted wiring equals less crosstalk interference.
Surprisingly over 50% of the CAT5 cabling managed to get a CAT5e approval and they could be used for Gigabit Ethernet.
In the end we saved a lot of money. I know this method might not be allowed or the way to go, where you are located, but I think it's a good way to start. It's important to have professionals run proper tests on your installations.
The testing parameters were borrowed from Ron Mauping from:
The maximum length of CAT6 for intranet network?