With Ethernet systems providing flexible ways of transmitting voice, data and multimedia over integrated networks, Ethernet patch cords are becoming a familiar part of the network. They can be seen in the work areas of office buildings and trail away from the backs of computers to wall plates and other computers. If you follow the trail, you can see them snake along the paths leading from wall plates to patch panels, and then sprout up again from patch panels to meet the nearby hubs or switches. The cable wiring may look simple, but actually how much do you know about the wiring configurations like cable conductors, connector pins and wire patterns, etc. This is what will be discussed in this article.
Ethernet patch cords are flexible leads fitted at each end with an 8P8C connector plug for joining two corresponding 8P8C jacks together. 8P8C refers to 8 positions and 8 conductors. In Ethernet systems, 8P8C plugs and their corresponding jacks are commonly referred to as RJ-45 modular connectors. The RJ-45 plug shows the numbering convention for the pins and pin pairs, with the locking tab facing downward.
The male plugs and female jacks are held together by a spring-loaded tab, called a hook that keeps them securely in place while in use, but allows them to be easily unplugged when changes are made to a network system or work area. This modularization is accomplished through the eight conducting pins located on the top of RJ-45 plugs, and just inside the tops of RJ-45 jacks, as shown in the above picture. By connecting the ends of the conducting wires in a patch cable to individual pins in its two RJ-45 end-plugs, electronic data can be transferred via an 8-conductor Ethernet cable from one jack to another through its 8 connector pins.
The patch cords used in most Ethernet systems are constructed using UTP (unshielded twisted pair) cable. UTP cable consists of 8 insulated copper-core conductors grouped into 4 pairs, with each pair twisted together along the cable’s length. The conductor pairs and individual conductors in UTP cable are represented by a color code that assigns a primary color—blue, orange, green or brown—to each of the 4 twisted pairs. The insulation of a conductor within a pair is either a solid primary color, or white striped with that primary color. In this way, all conductors are identified as members of a specific twisted pair, and as individual members within that pair. The conductor pairs are numbered 1 to 4, with Pair 1 corresponding to the blue pair, Pair 2 to the orange pair, Pair 3 to the green pair, and Pair 4 to the brown pair.
Three different cable wiring patterns are described below. Actually, each cable wiring pattern means the pin on one end is connected to which pin on the other end.
T568A and T568B are EIA/TIA wiring standards specifying two different RJ-45 pin assignments for the orange and green conductor pairs in twisted pair cables. From the picture below, it can be seen that the differences between the T568A and T568B specifications lie in the swapping of the green and orange wire pairs. The striped green and solid conductors assigned to pin pair (1, 2) in the T568A standard are assigned to pair (3, 6) in a plug or jack wired according to the T568B standard. And the striped orange and solid orange conductors assigned to pin pair (3, 6) in T568A are assigned to pair (1, 2) in T568B. This is a symmetric swapping of stripe-for-stripe and solid-for-solid within the two conductor pairs, and a symmetric swapping of their corresponding pin positions on the RJ-45 connector plug or jack. T568A and T568B are straight-through wiring schemes. Each conductor inside the patch cable connects to the same pin on both modular plug ends.
With regard to these two standards, it is important that both ends of the patch cords should be wired according to the same standard. If they aren’t, the cable is a crossover cable, and will not function correctly with most devices. The wiring standard used for the connector ends of a patch cable can be determined by holding the cable with the gold contact pins of the conductor plug up, and the locking tab down as the picture above. Then the wire colors will be visible and the pins will be numbered 1-8 from left to right.
Crossover patch cords, also called flipped patch cords, are used to connect a PC directly to another PC, a hub to hub, or switch to switch. The term crossover is used because the send and receive pairs are crossed from one modular plug (end 1) to the other (end 2). From the picture below, you will see that Pin 1 on end 1 goes to Pin 3 on end 2. Pin 2 on end 1 goes to Pin 6 on end 2, ect. Crossover cables are most commonly used to connect two hosts directly.
A roll-over patch cord completely reverses the pin configurations between the two modular plugs. Pin 1 on modular plug end 1 connects to pin 8 on modular plug end 2. Pin 2 on modular plug end 1 connects to pin 7 on modular plug end 2, and so on. This kind of patch cords are not used for network connectivity, but used to serve a unique purpose.
This article has introduced the RJ-45 connectors, UTP cabling and the wire patterns in Ethernet systems. When you plan to build your own Ethernet network, you shall to make clear all these configurations. Hope the information mentioned in this article can be a guide when needed.
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