Keywords: ethernet, cat5, RJ45,

First article on the subject:

From DUX Computer Digest (duxcw . com) See other version of the following in separate file RJ45Jack wiring.htm.

Consider one long cable with plugs at both ends. Then imagine cutting it into two pieces.

The jack and additional plug you'd use to rejoin the cable merely splice the cable back together again.

So at a wall jack, you just want a straight-through wiring.  Note that, apparently there's some disagreement/misunderstanding as to

whether your typical plug and jack is 568A or 568B.  Inspection of some CAT5 non-patch cables I have show that they are 568B as shown below.

Patch Cable

A patch cable is the very common item you use all the time with your home network. See this WikiPedia article. The word patch is perhaps misleading. And, this kind of ethernet cable is not a crossover cable.

Connectors

The 8P8C (8 position, 8 contact) modular connector, of the RJ45 flavor is used for computers.

Some people intend for the term to encompass not just the connector shape and size, but the wiring standard for it, described by TIA/EIA-568-B , as well.

TIA/EIA-568-B specifies that horizontal cables should be terminated using the T568A pin/pair assignments, "or, optionally, per [T568B] if necessary ....."

Despite this instruction, many organizations continue to implement T568B [I don't want to use T568B !! -FNC] for various reasons, chiefly associated with tradition (T568B is equivalent to AT&T 258A). The United States National Communication Systems Federal Telecommunications Recommendations do not [even] recognize T568B.

Here is another article on the subject,

from http://www.ertyu.org/steven_nikkel/ethernetcables.html

How to wire your own ethernet cables and connectors.

What You Need:

Required:

• 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:

  • RJ45 Plugs

  • RJ45 Crimper

• For Fixed Wiring:

  • RJ45 Jacks

  • 110 Punch Down Tool

Recommended:

• 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 cable. Braided 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 RJ45 Plugs and Jacks:

The RJ45 (8P8C) 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.

RJ45 jacks come in a variety styles intended for several different mounting options. The choice is one of requirements and preference. RJ45 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:

 
RJ45 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 RJ45 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.

Notes:

Power over Ethernet (PoE):

Power over Ethernet has been implemented in many variations before IEEE standardized 802.3af. 802.3af specifies the ability to supply an endpoint with 48V DC at up 350mA or 16.8W. The endpoint must be capable of receiving power on either the data pairs [Mode A] (often called phantom power) or the unused pairs [Mode B] in 100Base-TX. PoE can be used with any ethernet configuration, including 10Base-T, 100Base-TX and 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:

*Designed to work on MOST Cat 5 ethernet cable, Cat 5e specifications ensure 1000Base-T operation
**Reduced range when used with Cat 5e and Cat 6, Cat 6a gives the full 100m range

Cable Category Details:

Increasing category levels are backward compatible.
Manufacturers will often test and certify their ethernet cable well beyond the standards.

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

• The Switch Book: The Complete Guide to LAN Switching Technology

• TCP/IP Illustrated 3 Volume Set

  • The Protocols (TCP/IP Illustrated, Volume 1)

  • The Implementation (TCP/IP Illustrated, Volume 2)

  • TCP for Transactions, HTTP, NNTP, and the UNIX(R) Domain Protocols (TCP/IP Illustrated, Volume 3)

• UNIX Network Programming

  • Unix Network Programming, Vol. 1: The Sockets Networking API, Third Edition

  • UNIX Network Programming, Volume 2: Interprocess Communications (2nd Edition)