Thursday, February 21, 2008

Hacking phone wiring for FastEthernet AND phone

In most recently-built homes the phone wiring is run using CAT5e or Cat6e cable. These cables have 4 pairs of twisted wire for a total of 8 wires. A POTS (plain Old Telephone System) phone requires just 2 wires (tip and ring). Therefore we usually have 3 pair running through the walls completely unused.

Most phone wires are also run in a star topology, which is an easy conversion to "poor-man's" structured wiring.

FastE requires two pair (4 wires) to work:

Ethernet 10BaseT (Twisted Pair)
Pin # Signal Name Function
1 TD+ Transmit Data
2 TD- Transmit Data
3 RD+ Receive Data
4 NC No Connection
5 NC No Connection
6 RD- Receive Data
7 NC No Connection
8 NC No Connection

Only 1 pair is used for phone, so its easy to convert the whole house to use Fast Ethernet without running any additional wiring.

It should be noted that Gigabit Ethernet in this fashion would not be possible, because GigE uses all 4 available pairs in a cat5e or 6 cable. See below:

Ethernet 1000BaseT (Twisted Pair Pinout)
Pin # Signal Name Function
1 BI_DA+ Bi-directional pair +A
2 BI_DA- Bi-directional pair -A
3 BI_DB+ Bi-directional pair +B
4 BI_DC+ Bi-directional pair +C
5 BI_DC- Bi-directional pair -C
6 BI_DB- Bi-directional pair -B
7 BI_DD+ Bi-directional pair +D
8 BI_DD- Bi-directional pair -D

So how does one go about doing this? Well, its simple, really. Buy RJ11/RJ45 wall plates like, and wire the pins according to the T568A standard below:

Standard, Straight-Through Wiring (both ends are the same):

RJ45 Pin # Wire Color
Wire Diagram
10Base-T Signal
100Base-TX Signal
1000Base-T Signal
1 White/Green white/green Transmit+ BI_DA+
2 Green green Transmit- BI_DA-
3 White/Orange white/orange Receive+ BI_DB+
4 Blue blue Unused BI_DC+
5 White/Blue white/blue Unused BI_DC-
6 Orange orange Receive- BI_DB-
7 White/Brown white/brown Unused BI_DD+
8 Brown brown Unused BI_DD-

Pins 4/5 or 7/8 can be used for your phone jack. It really doesn't matter.

On the other side of the cable, the same thing will need to be done.

1 comment:

benthomasson said...

or you can get a skype phone.