RJ45 Connections - Some Basic Hints

1. The RJ45 connector is the critical connection - always use the highest quality connectors you can afford. The most common cause of connection faults are bad connectors.

   There are different connectors for stranded and solid cable and manufacturers do not always do a good job at differentiating them. Spend the time to make sure you have the right connector type. If you use the wrong type of connector the cable may or may not work initially but it will almost certainly fail very quickly.

2. Make and test practice cables until you get it right every time - especially before you destroy a cable you just spend 2 hours fitting.
3. When cutting the exterior cover of the cable be very careful not to cut the insulation cover of the conductors since this can cause shorts - bottom line: the cable won't work.
4. Expose a maximum of 1 inch of individual conductors when preparing the cable for connection.
5. Line up all the conductors according to the wiring standard you are using.
6. Measure the cable and trim the conductor ends so they are are all the same length and no individual conductor wire is visible outside the plastic cover of the RJ45 connector.
7. Carefully slide the prepared cable into the RJ45 connector making sure the end of the conductors reaches the end of the RJ45 connector.
8. Using the crimp tool make the connection using one firm squeeze operation.
9. Test the cable before fitting if possible.

RJ45 Male Connector Pin Numbering

RJ45 Male Connector

1000base-T Gigabit Ethernet

1000base-T is the copper based version of the gigabit Ethernet standard defined by 802.3ab which, since it is over 6 months old, is available free of charge from the enlightened IEEE. Great work. In passing, if you want to see sophistry raised to an art form read the EIA's justification for charging for their specifications. (Note: The original EIA statement is unfortunately no longer avilable on-line. This is a great loss to both the development of the English language in general, and comedy writing in particular.) The following notes apply to the 1000base-T spec:

1. The standard defines auto-negotiation of speed between 10, 100 and 1000 Mbit/s so the speed will fall to the maximum supported by both ends - ensuring inter-working with existing installations.

2. The cable specification base-line is ANSI/TIA/EIA-568-A-1995 (which you have to pay for). This means that if you know your cat5 cable was manufactured to this standard (there was a lower spec 1991 version of this specification) then it will support Gigabit Ethernet. Cat5 cable manufactured to the old specification may work or it may not - you need to run some tests. Cat5e and cat6 being higher spec cables will clearly support Gigabit Ethernet.

3. Maximum runs are the standard 100m (~300ft).

4. Gigabit Ethernet uses all 4 pairs (8 conductors). The transmission scheme is radically different (PAM-5 a 5 level amplitude modulation scheme) and each conductor is used for send and receive.

5. Crossed Gigabit Ethernet cables must cross all 4 pairs.

100base-T Crossed cable (PC to PC or HUB to HUB)

Crossed cables are used to connect PCs to one other PC or to connect a HUB to a HUB. Crossed cable are sometimes called Crossover, Patch or Jumper cables. If your connection is PC to HUB you MUST use a Straight cable.

The following description shows the wiring at both ends (male RJ45 connectors) of the crossed cable. Note: The diagrams below shows crossing of all 4 pairs and allows for the use of cat3/4 cables with 100m LANs (100base-T4). Pairs 4,5 and 7,8 do not NEED to be crossed in 100base-TX wiring. See notes below.

We use RED for crossed cables (or more commonly now a red heat-shrink collar at each end).

NOTES:

1. All our crossed wiring is now done to the 100base-T4 spec (uses all 4 pairs, 8 conductors) which you can use with 10base-T networks - but NOT necessarily the other way around.
2. Many commercial 100m LAN cables seem not to cross pairs 4,5 and 7,8. If there is no cat3/4 wiring in the network this perfectly acceptable.
3. Gigabit Ethernet uses all 4 pairs so requires the full 4 pair (8 conductor) cross configuration (shown above).
4. If you are using Power-over-Ethernet (802.3af) then Mode A or Alternative A uses pairs 1,2 and 3,6 for both signals and power. Mode B or alternative B uses 4,5 and 7,8 to carry power. In all cases the spec calls for polarity insensitive implementation (using a diode bridge) and therefore crossing or not crossing pairs 4,5 and 7,8 will have no effect.

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.

NOTES:

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.