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Ethernet Cabling Specifications


Last Reviewed: 19-Sep-2017
Article ID: 000007187

Intel® Ethernet Adapters have a small, snap-in RJ45 connector. RJ45 cabling is also known as twisted-pair Ethernet (TPE), unshielded twisted pair (UTP), and 10BASE-T cabling. The type of cabling you must use depends on your adapter.

Topics covered below:

  • Cabling basics
  • Fast Ethernet and Gigabit adapters
  • 100BASE-T4 adapters
  • Connecting two stations without a switch
  • Link integrity
  • Common problems
Note For 10 MBPS operation, refer to the 10 MBPS cabling specifications help file.
 

Cabling basics

Cables must comply with the IEEE 802.3 10BASE-T standard for two-pair, UTP cable.

  • For Fast Ethernet and Gigabit, the cable must be category 5 or 6.
  • For 100BASE-T4, the cable must be category 3 or higher.

The cable between the computer and the switch must be less than 100 meters long.

Each signal requires a wire pair (+ and - signal polarities). Pair refers to two wires, typically of a common color base, within the larger cable.

You should maintain the polarity of the wires from end to end. For example, the wire connected to pin 1 at one end should connect to pin 1 at the other end.

Intervening cabling hardware, such as punch down blocks and wall plates, must match or exceed the category rating of the cable.

When untwisting the wire pair for crimping, don't untwist the wire more than 1/2 inch, or about 1½ turns.

 

Fast Ethernet and Gigabit adapters

  
Cable and connector pinouts

If you need to repair a cable or provide connectors for UTP cable, wire straight through (MDI cable shown):

Function Pin# Pin#
TX+ 1 1
TX- 2 2
RX+ 3 3
RX- 6 6
 

Pins 1 and 2 must be a pair. Pins 3 and 6 must be a pair. Pair refers to two wires, typically of a common color base, twisted around each other within the larger cable.

To allow for a straight-through cable, the switch provides an internal transmit/receive crossover function. The transmit circuit of the network card is connected to the receive circuit of the switch and vice versa.

Pinout for the RJ45 connector (suggested wire colors):

1 |-- | 8 |brown or brown/white---|\
2 |-- | 7 |--white/brown--------------| \
3 |-- ---- 6 |green or green/white----| \
4 |-- | 5 |blue or blue white--------| -
5 |-- | 4 |--white/blue-----------------| _CABLE
6 |-- ---- 3 |--white/green---------------| /
7 |-- | 2 |orange or orange/white-| /
8 |-- | 1 |--white/orange--------------|/
VIEWED FROM END VIEWED FROM TOP (opposite the retaining clip)
 

Pin name and function:

  1. Transmit Data Plus (TD+): The positive signal for the TD differential pair. The signal contains the serial output data stream transmitted onto the network.

  2. Transmit Data Minus (TD-): The negative signal for the TD differential pair. This contains the same output as pin 1.

  3. Receive Data Plus (RD+): The positive signal for the RD differential pair. The signal contains the serial input data stream received from the network.

  4. Not used.

  5. Not used.

  6. Receive Data Minus (RD-): The negative signal for the RD differential pair. The signal contains the same input as pin 3.

  7. Not used.

  8. Not used.

 

Cable and connector pinouts

Unlike TX cabling, T4 cabling does not use separate dedicated pairs to transmit or receive data. T4 cabling uses all four pairs of wires. Three pairs transmit data, while the fourth pair detects collisions.

Pin pairings:

Pin# Signal
1 TX_D1+
2 TX_D1-
3 RX_D2+
4 BI_D3+
5 BI_D3-
6 RX_D2-
7 BI_D4+
8 BI_D4-
 

Pins 1 and 2 must be a pair.
Pins 3 and 6 must be a pair.
Pins 4 and 5 must be a pair.
Pins 7 and 8 must be a pair.

To allow for a straight-through cable, the switch provides an internal transmit/receive crossover function. The transmit circuit of the network card is connected to the receive circuit of the switch and vice versa.

 

Connecting two workstations without a switch

Fast Ethernet and Gigabit use a star topology. A switch is in the center of a star, and each workstation or server is connected to the switch.

For test purposes, you can directly connect two workstations or a workstation and a server without using a switch. The setup requires a special cable incorporating the crossover function described earlier in this document. See the below diagram for which wires to cross over.

Ethernet Crossover (MDI-X) cable diagram:

Function Pin# Pin# Function
TX+ 1 3 RX+
TX- 2 6 RX-
RX+ 3 1 TX+
RX- 6 2 TX-
 

The receive data pair (the two wires designated RD) must be a twisted pair. The transmit data pair (designated TD) must be a twisted pair.

 

Ethernet crossover cable diagram

Pin# Signal Signal Pin#
1 TX_D1+ RX_D2+ 3
2 TX_D1- RX_D2- 6
3 RX_D2+ TX_D1+ 1
4 BI_D3+ BI_D4+ 7
5 BI_D3- BI_D4- 8
6 RX_D2- TX_D1- 2
7 BI_D4+ BI_D3+ 4
8 BI_D4- BI_D3- 5
 

The receive data pair (the two wires designated RX_D2) must be a twisted pair. The transmit data pair (designated TX_D1) must be a twisted pair. The first bidirectional pair (designated BI_D3) must be a twisted pair and the second bi-directional pair (designated BI_D4) must be a twisted pair. You may use a category 3, 4, 5, or 6 cable.

 

Link integrity

LEDs on the adapters show link integrity:

  • A LNK light for link
  • An ACT light for activity
  • A 1000 light that indicates a 1000 MBPS connection

Some models use one LED to show both link and activity.

Refer to your adapter installation guide or the Diagnostic LEDs Readme file for more information.

Note The ACT LED indicates read/write activity on the network, not necessarily activity on the adapter.
 

Common problems

If a crossed wire is in the cable or wiring closet, the switch can't detect a workstation. You should have a link light on both the switch and the adapter. Make sure the wiring is correct.

Polarity problems

A common problem in 10BASE-T wiring is crossing the positive and negative phases of the transmit or receive signals. For example, crossing pins 1 (TX+) and 2 (TX-).

Intel® Ethernet Adapters automatically detect this problem and adjust for it internally. We recommend that you check your wiring to correct the problem.

This article applies to:

Active Products

Intel® 82567 Gigabit Ethernet Controller

Discontinued Products