Cross Cable - Straight Cable or LAN Wiring & Pinouts

10base-T, 100base-TX/T4, 1000base-T

There is NOTHING more annoying than spending 30 minutes debugging a network problem to find it was the cable. Badly made or non-standard cabling is a foolish thing to spend time on - do it once and do it right. This guide may help you to forget cabling problems and spend time time doing really useful things - like pondering the meaning of life!

Notes:

1. LAN cables are generically called UTP (Unshielded Twisted Pair) and are identified with a category rating. When installing new cable, unless there is a very good reason not to, you should be using category 5, 5e or 6 UTP which is rated for both 10 and 100mb LAN operation.

2. UTP comes in two forms SOLID or STRANDED. SOLID refers to the fact that each internal conductor is made up of a single (solid!) wire, STRANDED means that each conductor is made up of multiple smaller wires. The only obvious benefit of using stranded cable (which is typically more expensive) is that it has a smaller 'bend- radius' (you can squeeze the cable round tighter corners with lower loss) or where you plug and unplug the cable frequently. All other things being equal the performance of both types of cable is the same. In general solid cable is used for backbone wiring and stranded for PC to wall plug cables. Beware: Each type of wire, solid or stranded, needs its own connector type.

3. There is NO excuse with all the choice of color cable and other techniques available to-day for not being able to visually spot the difference between at least a straight and a crossed cable before you spend 1 hour fitting the wrong cable into your network. For cheap-skates (which includes us) you can get heat-shrink colour tubing in a slew of colours which you fit on each end of the cable beside the connector to indicate the wiring type and standard instead of using different coloured cables. The advantage of this scheme is that when you change your wiring standard you can just change the sleeve colour - you don't have to rip out the cable. Disadvantage: You have to remember to put the tubing on BEFORE the connector!

4. You CAN use 100base-TX wiring with a 10base-T network (but not always the other way round). ALWAYS use 100baseTX/T4 wiring standards.

5. If you are using category 5, 5e or 6 wiring EVERYWHERE you can use the 100base-TX standard (this only uses 2 pairs , 4 conductors). Most of the information below assumes you are using category 5, 5e or 6 cables.

6. If you are using category 3 or 4 cables with 100M LANs ANYWHERE you MUST use the 100Base-T4 standard and this has ADDITIONAL RESTRICTIONS documented throughout (it uses all 4 pairs, 8 conductors). LAN connections/pinouts are defined by IEEE 802.3u.

7. Maximum LAN cable runs are 100 meters (~300ft).

8. We provide a Cabling FAQ which may provide additional information or background.

9. We have added an article on mixing 100 MB LAN and Telephony on a single category 5(e) or 5 cable. It can be done but you must be very cautious.

10. We have updated some of the material for 1000base-T (Gigabit Ethernet 802.3ab) which uses all 4 pairs (8 conductors) and added notes where relevant about Power-over-Ethernet (PoE 802.3af). A copper standard for 10GB Ethernet is being worked on (802.3an) but as of February 2005 the IEEE was still standardizing away.

Contents

Crossed and Straight cables - when to use them.

Category 5 (UTP) colour coding table

10base Straight Cable (PC to HUB/SWITCH)

10baseT Crossed cable (PC to PC or HUB to HUB)

100baseT Straight Cable (PC to HUB/SWITCH)

100baseT Crossed cable (PC to PC or HUB to HUB)

1000base-T Gigabit Ethernet

RJ45 Connector Pin Numbering

RJ45 Connections - some hints

Crossed and Straight cables - when to use them

The following diagram shows the Normal use of Crossed and Straight cables (see also the notes below).

Notes:

1. We show Straight cables as BLUE and Crossed as RED. That is our convention the cable color can be anything you choose or more likely the vendor decides.

2. To avoid the need for Crossed cables many vendors provide UPLINK ports on Hubs or Switches - these are specially designed to allow the use of a STRAIGHT cable when connecting back-to-back Hubs or Switches. Read the manufacturers documentation carefully.

Category 5(e) (UTP) colour coding table

The following table shows the normal colour coding for category 5 cables (4 pair) based on the two standards supported by TIA/EIA (see also our primer on this topic)

10baseT 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 the 568B category 5(e) wiring colors you could, of course, use the 568A colour scheme.

Pin No.	strand color	Name
1	white and orange	TX+
2	orange	TX-
3	white and green	RX+
4	NC	*
5	NC	*
6	green	RX-
7	NC	*
8	NC	*

NOTE: Items marked * are not necessary for 10M LANs (10base-T) but since you will be moving shortly to 100MB LANs (won't you) you will save yourself a LOT OF TIME finding crappy cable (that you made) that does not work. Instead we suggest you wire to 100Base-T4 standards. After all you gotta stick the ends somewhere man.

We use BLUE for 10base-T straight cables. NOTE: All our wiring is now done to the 100base-T4 spec which you can use with 10base-T networks - but NOT necessarily the other way around.

10baseT 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 cables 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.

One end RJ45 Male	Other end RJ45 Male
1	3
2	6
3	1
4 *	5 *
5 *	4 *
6	2
7 *	8 *
8 *	7 *

NOTES:

1. Items marked * are not necessary for 10M LANs but since you will be moving shortly to 100MB LANs (won't you) you will save yourself a LOT OF TIME finding crappy cable (that you made) that does not work. Instead we suggest you wire to 100BaseT standards.
2. We use RED for crossed cables (or more commonly now a red heat-shrink collar at each end).
3. All our crossed wiring is done to the 100baseT spec which you can use with 10baseT networks - but NOT always the other way around.

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.	strand 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 (using any combination of category 3/4/5 cables and MAY be for Power-over-Ethernet see below)) but are not required for 100Base-TX (using cat 5/5e ONLY cables) and CAN be used for other purposes e.g. telephony but, .. beware .. read this FAQ and our LAN plus Telephony article before you wire your entire neighbourhood for surround sound.
2. 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 Endpoint PSE, Alternative B and Midspan PSE, 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.
3. Gigabit Ethernet requires all 4 pairs (8 conductors).
4. All our wiring is now done to the 100baseT spec which you can use with 10baseT networks - but NOT the other way around.

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. 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 which you can use with 10base-T networks - but NOT necessarily the other way around.
2. Most commercial cables these days 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.

1000base-T Gigabit Ethernet

1000base-T is the copper base 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. 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.

RJ45 Connector Pin Numbering

RJ45 Male Connector

RJ45 Connections - some hints

We get mail saying 'Help. I've wired it correctly but it does not work'. Here are some simple notes that may help. Remember its more difficult that you think.

1. The RJ45 connector is the critical connection always use the highest quality connectors you can afford. The most common cause of connection faults is bad connectors. There are different connectors for stranded and solid cable. Sometimes you have to work quite hard to make sure you are getting the right type. 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.