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Sunday, July 26, 2009

100base-T Straight Cable (PC to HUB/SWITCH)

Straight cables are used to connect PCs or other equipment to a HUB or Switch. If your connection is PC to PC or HUB to HUB you MUST use a Crossed cable.

The following cable description is for the wiring of BOTH ends (RJ45 Male connectors) with your category 5 wiring colors (TIA/EIA 568A or 568B though the example uses 568B colors).

Pin No. conductor color Name
1 white and orange TX_D1+
2 orange TX_D1-
3 white and green RX_D2+
4 blue BI_D3+ **
5 white and blue BI_D3- **
6 green RX_D2-
7 white and brown BI_D4+ **
8 brown BI_D4- **

We use BLUE for 100baseT straight cables.


  1. Wires marked ** are ABSOLUTELY NECESSARY for 100Base-T4 networks - used when any combination of category 3/4/5 cables are present, when using 1000base-T (GigE) and MAY be required for Power-over-Ethernet (PoE) - see below.

  2. Wires marked ** are not essential for 100Base-TX (using cat 5/5e ONLY cables) and CAN be used for other purposes, for example, telephony but, and our LAN plus Telephony article before you wire your entire neighbourhood for surround sound.

  3. The Power-over-Ethernet spec (802.3af) allows three schemes where power may be supplied. Two of these schemes use pairs 4,5 and 7,8 (marked ** in above table) for power (called Midspan PSE and Alternative B or Mode B), one scheme uses ONLY pairs 1,2 and 3,6 (Endpoint PSE, Alternative A or Mode A) for both signals and power. Depending on which scheme you use pairs 4,5 and 7,8 may be required.

  4. Gigabit Ethernet requires all 4 pairs (8 conductors).

  5. All our wiring is now done to the 100base-T4 spec which you can use with 10baseT networks - but NOT the other way around.

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