Cat5 Cable Pin Assignment Of Rj45

Ethernet Cable – Color Coding Diagram for:

  • Category-5 cables
  • Category-5E cables
  • Category-6 cables
  • Category-6E cables

The information listed here is to assist Network Administrators in the color coding of Ethernet cables. Please be aware that modifying Ethernet cables improperly may cause loss of network connectivity. Use this information at your own risk, and insure all connectors and cables are modified in accordance with standards. The Internet Centre and its affiliates cannot be held liable for the use of this information in whole or in part.

T-568A Straight-Through Ethernet Cable

The TIA/EIA 568-A standard which was ratified in 1995, was replaced by the TIA/EIA 568-B standard in 2002 and has been updated since. Both standards define the T-568A and T-568B pin-outs for using Unshielded Twisted Pair cable and RJ-45 connectors for Ethernet connectivity. The standards and pin-out specification appear to be related and interchangeable, but are not the same and should not be used interchangeably.

T-568B Straight-Through Ethernet Cable

Both the T-568A and the T-568B standard Straight-Through cables are used most often as patch cords for your Ethernet connections. If you require a cable to connect two Ethernet devices directly together without a hub or when you connect two hubs together, you will need to use a Crossover cable instead.

RJ-45 Crossover Ethernet Cable

A good way of remembering how to wire a Crossover Ethernet cable is to wire one end using the T-568A standard and the other end using the T-568B standard. Another way of remembering the color coding is to simply switch the Green set of wires in place with the Orange set of wires. Specifically, switch the solid Green (G) with the solid Orange, and switch the green/white with the orange/white.

Ethernet Cable Instructions:

  • Pull the cable off the reel to the desired length and cut. If you are pulling cables through holes, its easier to attach the RJ-45 plugs after the cable is pulled. The total length of wire segments between a PC and a hub or between two PC’s cannot exceed 100 Meters (328 feet) for 100BASE-TX and 300 Meters for 10BASE-T.
  • Start on one end and strip the cable jacket off (about 1″) using a stripper or a knife. Be extra careful not to nick the wires, otherwise you will need to start over.
  • Spread, untwist the pairs, and arrange the wires in the order of the desired cable end. Flatten the end between your thumb and forefinger. Trim the ends of the wires so they are even with one another, leaving only 1/2″ in wire length. If it is longer than 1/2″ it will be out-of-spec and susceptible to crosstalk. Flatten and insure there are no spaces between wires.
  • Hold the RJ-45 plug with the clip facing down or away from you. Push the wires firmly into the plug. Inspect each wire is flat even at the front of the plug. Check the order of the wires. Double check again. Check that the jacket is fitted right against the stop of the plug. Carefully hold the wire and firmly crimp the RJ-45 with the crimper.
  • Check the color orientation, check that the crimped connection is not about to come apart, and check to see if the wires are flat against the front of the plug. If even one of these are incorrect, you will have to start over. Test the Ethernet cable.

Ethernet Cable Tips:

  • A straight-thru cable has identical ends.
  • A crossover cable has different ends.
  • A straight-thru is used as a patch cord in Ethernet connections.
  • A crossover is used to connect two Ethernet devices without a hub or for connecting two hubs.
  • A crossover has one end with the Orange set of wires switched with the Green set.
  • Odd numbered pins are always striped, even numbered pins are always solid colored.
  • Looking at the RJ-45 with the clip facing away from you, Brown is always on the right, and pin 1 is on the left.
  • No more than 1/2″ of the Ethernet cable should be untwisted otherwise it will be susceptible to crosstalk.
  • Do not deform, do not bend, do not stretch, do not staple, do not run parallel with power cables, and do not run Ethernet cables near noise inducing components.

Basic Theory:

By looking at a T-568A UTP Ethernet straight-thru cable and an Ethernet crossover cable with a T-568B end, we see that the TX (transmitter) pins are connected to the corresponding RX (receiver) pins, plus to plus and minus to minus. You can also see that both the blue and brown wire pairs on pins 4, 5, 7, and 8 are not used in either standard. What you may not realize is that, these same pins 4, 5, 7, and 8 are not used or required in 100BASE-TX as well. So why bother using these wires, well for one thing its simply easier to make a connection with all the wires grouped together. Otherwise you’ll be spending time trying to fit those tiny little wires into each of the corresponding holes in the RJ-45 connector.

How to wire your own ethernet cables and connectors.

What You Need:

  • Ethernet Cable - bulk Category (Cat) 5, 5e, 6, 6a or higher ethernet cable
  • Wire Cutters - to cut and strip the ethernet cable if necessary
  • For Patch Cables:
    • 8P8C Modular Connector Plugs ("RJ45")
    • Modular Connector Crimper ("RJ45")
  • For Fixed Wiring:
    • 8P8C Modular Connector Jacks ("RJ45")
    • 110 Punch Down Tool
  • Wire Stripper
  • Cable Tester

About the Cable:

You can find bulk supplies of ethernet cable at many computer stores or most electrical or home centers. You want UTP (Unshielded Twisted Pair) ethernet cable of at least Category 5 (Cat 5). Cat 5 is required for basic 10/100 functionality, you will want Cat 5e for gigabit (1000BaseT) operation and Cat 6 or higher gives you a measure of future proofing. You can also use STP (Shielded Twisted Pair) for extra resistance to external interference but I won't cover shielded connectors. Bulk ethernet cable comes in many types, there are 2 basic categories, solid and braided stranded cable. Stranded ethernet cable tends to work better in patch applications for desktop use. It is more flexible and resilient than solid ethernet cable and easier to work with, but really meant for shorter lengths. Solid ethernet cable is meant for longer runs in a fixed position. Plenum rated ethernet cable must be used whenever the cable travels through an air circulation space. For example, above a false ceiling or below a raised floor. It may be difficult or impossible to tell from the package or labelling what type of ethernet cable it is, so peal out an end and investigate.

Here is what the internals of the ethernet cable look like:

Internal Cable Structure and Color Coding

Inside the ethernet cable, there are 8 color coded wires. These wires are twisted into 4 pairs of wires, each pair has a common color theme. One wire in the pair being a solid or primarily solid colored wire and the other being a primarily white wire with a colored stripe (Sometimes ethernet cables won't have any color on the striped wire, the only way to tell which is which is to check which wire it is twisted around). Examples of the naming schemes used are: Orange (alternatively Orange/White) for the solid colored wire and White/Orange for the striped cable. The twists are extremely important. They are there to counteract noise and interference. It is important to wire according to a standard to get proper performance from the ethernet cable. The TIA/EIA-568-A specifies two wiring standards for an 8-position modular connector such as RJ45. The two wiring standards, T568A and T568B vary only in the arrangement of the colored pairs. Tom writes to say "...sources suggest using T568A cabling since T568B is the AT&T standard, but the US Government specifies T568A since it matches USOC cabling for pairs 1 & 2, which allows it to work for 1/2 line phones...". Your choice might be determined by the need to match existing wiring, jacks or personal preference, but you should maintain consistency. I've shown both below for straight through cabling and just T568B for crossover cabling.

About Modular Connector Plugs and Jacks:

The 8P8C modular connectors for Ethernet are often called RJ45 due to their physical ressemblance. The plug is an 8-position modular connector that looks like a large phone plug. There are a couple variations available. The primary variation you need to pay attention to is whether the connector is intended for braided or solid wire. For braided/stranded wires, the connector has sharp pointed contacts that actually pierce the wire. For solid wires, the connector has fingers which cut through the insulation and make contact with the wire by grasping it from both sides. The connector is the weak point in an ethernet cable, choosing the wrong one will often cause grief later. If you just walk into a computer store, it's nearly impossible to tell what type of plug it is. You may be able to determine what type it is by crimping one without a cable.

Modular connector jacks come in a variety styles intended for several different mounting options. The choice is one of requirements and preference. Jacks are designed to work only with solid ethernet cable. Most jacks come labeled with color coded wiring diagrams for either T568A, T568B or both. Make sure you end up with the correct one.

Here is a wiring diagram and pin out:

Modular Connector Plug and Jack Pin Out

Ethernet Cable Pin Outs:

There are two basic ethernet cable pin outs. A straight through ethernet cable, which is used to connect to a hub or switch, and a crossover ethernet cable used to operate in a peer-to-peer fashion without a hub/switch. Generally all fixed wiring should be run as straight through. Some ethernet interfaces can cross and un-cross a cable automatically as needed, a handy feature.

Standard, Straight-Through Wiring Diagram(both ends are the same):

Straight-Through Ethernet Cable Pin Out for T568A Straight-Through Ethernet Cable Pin Out for T568B

Crossover Cable Wiring Diagram(T568B):

Crossover Ethernet Cable Pin Outs

+Note: The crossover ethernet cable layout is suitable for 1000Base-T operation, all 4 pairs are crossed.

How to wire Ethernet Patch Cables:

  1. Strip off about 2 inches of the ethernet cable sheath.
  2. Untwist the pairs - don't untwist them beyond what you have exposed, the more untwisted cable you have the worse the problems you can run into.
  3. Align the colored wires according to the wiring diagrams above.
  4. Trim all the wires to the same length, about 1/2" to 3/4" left exposed from the sheath.
  5. Insert the wires into the RJ45 plug - make sure each wire is fully inserted to the front of the RJ45 plug and in the correct order. The sheath of the ethernet cable should extend into the plug by about 1/2" and will be held in place by the crimp.
  6. Crimp the RJ45 plug with the crimper tool.
  7. Verify the wires ended up the right order and that the wires extend to the front of the RJ45 plug and make good contact with the metal contacts in the RJ45 plug
  8. Cut the ethernet cable to length - make sure it is more than long enough for your needs.
  9. Repeat the above steps for the second RJ45 plug.

How to wire fixed Ethernet Cables:

  1. Run the full length of ethernet cable in place, from endpoint to endpoint, making sure to leave excess.
  2. At one end, cut the wire to length leaving enough length to work, but not too much excess.
  3. Strip off about 2 inches of the ethernet cable sheath.
  4. Align each of the colored wires according to the layout of the jack.
  5. Use the punch down tool to insert each wire into the jack.
  6. Repeat the above steps for the second RJ45 jack.

If an ethernet cable tester is available, use it to verify the proper connectivity of the cable. That should be it, if your ethernet cable doesn't turn out, look closely at each end and see if you can find the problem. Often a wire ended up in the wrong place or one of the wires is making no contact or poor contact. Also double check the color coding to verify it is correct. If you see a mistake or problem, cut the end off and start again. A ethernet cable tester is invaluable at identifying and highlighting these issues.

When sizing ethernet cables remember that an end to end connection should not extend more than 100m (~328ft). Try to minimize the ethernet cable length, the longer the cable becomes, the more it may affect performance. This is usually noticeable as a gradual decrease in speed and increase in latency.


Power over Ethernet (PoE):

Power over Ethernet has been implemented in many variations before IEEE standardized 802.3af. IEEE 802.3af specifies the ability to supply an endpoint device with 48V DC at up 350mA or approximatlely 16.8W. IEEE 802.3at updates the PoE standard to supply up to 600mA or approximately 28.8W, it is often known as PoE+. The device must be capable of receiving power on either the data pairs [Mode A] (often called phantom power) or the unused pairs in 100Base-TX [Mode B]. PoE can be used with any ethernet configuration, including 10Base-T, 100Base-TX or 1000Base-T. Power is only supplied when a valid PoE endpoint is detected by using a low voltage probe to look for the PoE signature on the endpoint. PoE power is typically supplied in one of two ways, either the host ethernet switch provides the power, or a "midspan" device is plugged in between the switch and endpoints and supplies the power. No special cabling is required. Power over Ethernet Power Delivery

Protocol Details:

ProtocolStandardSymbol EncodingSymbol Rate (Mbaud)Data EncodingData Bits per SymbolPairs per ChannelPairs UsedNyquist Frequency Bandwidth (MHz)Minimum Cable Category
10Base-TIEEE 802.3iManchester10None112103
100Base-TXIEEE 802.3uMLT-31254B5B4/51262.55
1000Base-TIEEE 802.3ab4D-PAM5125None24462.55e (5)1
2.5GBase-TIEEE 802.3bzDSQ128 (2D-PAM16)200LDPC(1723,2048), 64B/65B, CRC83.125441005e2
5GBase-TIEEE 802.3bzDSQ128 (2D-PAM16)400LDPC(1723,2048), 64B/65B, CRC83.125442006 (5e)2
10GBase-TIEEE 802.3anDSQ128 (2D-PAM16)800LDPC(1723,2048), 64B/65B, CRC83.125444006a (6)3
25GBase-TIEEE 802.3bqDSQ128 (2D-PAM16)2000LDPC(1723,2048), 64B/65B, CRC83.12544100084
40GBase-TIEEE 802.3bqDSQ128 (2D-PAM16)3200LDPC(1723,2048), 64B/65B, CRC83.12544160084
Data Rate = Symbol Rate x Data Bits per Symbol x Pairs per Channel
The combination of the Symbol Encoding and Data Encoding determines how many Data Bits per Symbol there are.
1. Designed to work on most Cat 5 ethernet cable, Cat 5e specifications ensure 1000Base-T operation.
2. Although designed for Cat 5e/6, not all cabling will be usable at the full range, especially for 5GBase-T on Cat 5e.
3. Reduced range when used with Cat 6 (55m), Cat 6a supports the full 100m range. Some Cat 5e may support operation at reduced distance.
4. 30m range.

Cable Category Details:

Cable CategoryRated Nyquist Frequency Bandwidth (MHz)Common Uses
1NoneTelephone Wiring
21Telephone Wiring
316Telephone Wiring, 10Base-T
420Token-Ring, 10Base-T
5100100Base-TX, 10Base-T
5e1001000Base-T, 100Base-TX
62501000Base-T, 100Base-TX
8200025GBase-T, 40GBase-T
Increasing category levels are backward compatible.
Manufacturers will often test and certify their ethernet cable well beyond the standards.
1. Category 7/7a cabling does not use RJ45 connectors.

Related Reading Material

  • Get IEEE 802 - Ethernet Standards
  • Charles Spurgeon's Ethernet Website
  • Network Connection Speeds Reference
  • Fiber Optic Connector Reference
  • Ethernet: The Definitive Guide
  • Interconnections: Bridges, Routers, Switches, and Internetworking Protocols (2nd Edition)
  • The All-New Switch Book: The Complete Guide to LAN Switching Technology
  • TCP/IP Illustrated
  • UNIX Network Programming

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