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 2 3 4 5 6
white and orange orange white and green NC NC green
TX+ TXRX+ * * RX-
7 8
NC 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 2 3 4* 5* 6 7* 8* NOTES:
3 6 1 5* 4* 2 8* 7*
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 2 3 4 5 6 7 8
white and orange orange white and green blue white and blue green white and brown brown
TX_D1+ TX_D1RX_D2+ BI_D3+ ** BI_D3- ** RX_D2BI_D4+ ** 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-overEthernet 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 hints that may help. Remember its more difficult that you think. 1. Make and test practice cables until you get it right every time - especially before you destroy a cable you just spend 2 hours fitting. 2. 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. 3. Expose a maximum of 1 inch of individual conductors when preparing the cable for connection. 4. Line up all the conductors according to the wiring standard you are using. 5. 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. 6. Carefully slide the prepared cable into the RJ45 connector making sure the end of the conductors reaches the end of the RJ45 connector. 7. Using the crimp tool make the connection using one firm squeeze operation. 8. Test the cable before fitting if possible. 9. 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.