ECN Forum Forums General Topics of the Trade Voice - Data - Video Discussion Cat5 2-jacks from one cable

POTS ringers will spike ethernet, mechanical bells worse than electronic noisemakers. In a home with few incoming calls and good tolerance for retransmitted packets it is not a big deal but in an office where the phone rings a lot and traffic is high on the LAN it will make a huge difference in throughput.
Of course a small wiring error will probably let the smoke out of your LAN card

The IEEE 803.2 specs specifically say that mixing POTS and 100baseT4/100baseT2 in the same cable is disallowed.

"100BASE-T2 supports three types of service in adjacent pairs of the same cable: 100BASE-T2, 10BASE-T
and digital phone service compliant with the ISDN-BR U and S/T interfaces. Analog phone service is no
supported since the noise generated during off-hook transitions and ringing source from older PBX equip
ment can cause bit errors to occur."

They make no such notation for either 100baseTX or 10baseT. For 10baseT the following is stated:

"14.4.4 Noise environment
The noise level on the link segments shall be such that the objective error ratio is met. The noise environ-
ment consists generally of two primary contributors: crosstalk from other 10BASE-T circuits; and externally
induced impulse noise, typically from telephone ringing and dialing signals, and other office and building
equipment."


As far as miswiring goes, the following is stated. This was copied form the 100base2 section, but similar text is found for other specs (10baseT, 100baseTX, etc).

"32.10.2.4 Telephony voltages
The use of building wiring brings with it the possibility of wiring errors that may connect telephony voltages
to 100BASE-T2 equipment. Other than voice signals (which are low voltage), the primary voltages that may
be encountered are the battery and ringing voltages. Although there is no universal standard, the following
maximums generally apply.
Battery voltage to a telephone line is generally 56 Vdc applied to the line through a balanced 400 source
impedance.
Ringing voltage is a composite signal consisting of an AC component and a DC component. The ac component
is up to 175 V peak at 20 Hz to 60 Hz with a 100 source resistance. The DC component is 56 Vdc with 300
to 600 source resistance. Large reactive transients can occur at the start and end of each ring interval.
Although 100BASE-T2 equipment is not required to survive such wiring hazards without damage, applica-
tion of any of the above voltages shall not result in any safety hazard.
NOTEWiring errors may impose telephony voltages differentially across 100BASE-T2 transmitters or receivers.
Because the termination resistance likely to be present across a receiver™s input is of substantially lower impedance than
an off-hook telephone instrument, receivers will generally appear to the telephone system as off-hook telephones. There-
fore, full-ring voltages will be applied for only short periods. Transmitters that are coupled using transformers will simi-
larly appear like off-hook telephones (though perhaps a bit more slowly) due to the low resistance of the transformer coil."

It has been my experience that connecting an Ethernet card to a Merlin phone system won't damage either. (Merlins use RJ45 plugs and people do get confused...)

Back in the '90s through early 2000's, we would connect Voicelines from one CAT 3 UTP 4 Pair cable across two jacks at certain stations, as follows:

1. The Blue + Orange + Green pairs to one jack,
2. The Brown pair to another jack.

The Brown Pair was for a Fax Machine option, whereas the B-O-G were for the Voiceline (Telephone Set).

This was the only "Sharing" of stuff we ever did.

Just wanted to throw this in!

Scott