We are usually using copper ethernet cable for transporting Ethernet signal today. At our homes or work places the Ethernet cable is used between computer and switch or two devices which have need Ethernet connection.
The two main factors for using Ethernet cable is price and distance. The distance for transporting Ethernet signal from source to destination safely is 100 meters long. The distances above 100m, we usually use fiber optic cables for Ethernet communications.
Although using 1 pair (2) copper cable for phone communication is enough, for transporting Ethernet signal we need 2 pair (4) copper cables. One pair of these cables are used for sending signal (transmit) and the other pair of cable is used for getting signal (receive).
Why 4 Pair (8) Cable?
Copper Ethernet cable is including 4 pair (8) cables. Why the cable including 8 copper cable if we need only 4 of them? You thing that other 4 cable will be wasted, but engineers think that other 4 cable will be able to use later on, so they designed not 2 pair, but 4 pair cable.
So, these days some applications (some sort of PoE applications) are using other pairs for energy transmission. But usually we use only 2 pair of cable and put other 2 ones are spare.
So, if you ask which cables do we use, the answer is number 1,2,3 and 6 are using. 1 and 2 are using for transmit signal, 3 and 6 are using for receive signal. 4-5 and 7-8 pairs are not used by standard Ethernet applications today.
Why Twisted Pair?
We mentioned before, data is transferring over physical layer at BIT level, so the information is converted to the 0 and 1 electronic pulses. If you transfer an electrical current from copper cable, there is an electromagnetic shield occur through line. If the wires get close each other, the occurring magnetic shield on one cable will be effective for another copper cable. So, the magnetic shield will be started to disrupt the electronic signal on other copper cable.
We called this effect as cross-talk. According to minimize this cross-talk effect, engineers were discovered twisted pair architecture. They realized that, if we carry signal with twisted pair form, the cross-talk effect will minimize.
Why 100 Meters?
In addition to cross-talk effect we mentioned, when the electric current passed through the copper line, the resistance effect is occurred on it. This mean, the signal will be weaker directly proportional with cable length. So, the engineers make calculations and they find the best length of carrying signal from one point to another safely is above 100 meter. According to minimize tolerances the standards was determined this length has to be maximum 100-meter long.
Today we can carry Ethernet signal over 100 meter if the medium is suitable but none of cable producers don’t give any guarantee over 100 meter.
How Cable Order Has to Be?
The cable order is most important part of preparing Ethernet cable. We have to order cables for minimizing cross-talk effect and get best performance from this cable.
Cables are pre-painted different colours, this colours are;
There are two standards for making cable, one of them is T568A and other is T568B. The main difference from two standards is settlement of transmit and receive pairs.
As you see, Orange and Green pairs are switch over between two standards. Usually the T568B standard is used. If you will see a connector or patch panel somewhere you realised that you prefer B standard.
If you ask, what is the cable order number? How can we determine numbers? The answer is easy, when you get an RJ-45 Ethernet connector to your hand, take it as copper pins are up and cable hole is towards to you, the left pin represents number 1 and the right end represents number 8.
This is the picture of RJ-45 cable;
You can see the picture below that made according to standards. Don’t forget, left hand represents number 1 and right end represents number 8.
As you see, the Orange Peers are located on 1-2 pins, so it is prepared by T568B standard.
Let’s look at a cable that both ends are finished;
The cable order for standard is
Do you see the green pair’s location? The all other colour pairs are next-to each other but green pair is located on 3-6 pins. Also, there is a difference with blue pair. At the other pairs the white coloured cable comes first but for blue pair the solid coloured cable comes first.
Straight Through and Cross Cable
New generation may not be able to know what the cross cable is. Because the devices produced these days are created with capable of auto straight or cross detection ability (it known as auto MDI/MDI-X ability). So, we can make our all cable connections with using straight-through cable.
Actually, the working mentality can be explained as below;
The Ethernet ports of user devices (computers, routers, servers etc.) are created to suitable for T568B standard. This means, I send the transmit signal from my 1-2 pins and receive from my 3-6 pins. The opposite device has to be receive my transmit signal from its receive pairs and send its transmit signal to my receive pairs.
If opposite devices Ethernet port is also created with T568B standard, I sent to my transmit signal from my 1-2 pins and the opposite device also sent its transmit signal from 1-2 pins. Our transmit signals are crashed and the communication will not occurred.
Actually, my transmitted signal from 1-2 pairs has to be reach to other devices 3-6 receive pairs and at the same way, other devices transmit signal from 1-2 pairs has to be send my 3-6 receive pairs.
So, the cable which connects my 1-2 transmit pairs to other side’s 3-6 receive pair and other side’s 1-2 pairs to my 3-6 receive pairs represents as Cross-Cable.
Let’s look at cross cable;
As you see, 1-2 pins at the left connector is go through 3-6 pairs at the right side and 3-6 pairs at the left connector is go through 1-2 pairs at the left side.
I want to show another picture;
The ports on switch devices are designed according to T568A standard so, we can use straight-through cable with switch devices naturally. Normally you have to use cross cable, if you connect two same type of devices together but, as I mentioned before nowadays almost all device’s Ethernet ports are designed with auto mdi/mdi-x capable. It means the device ports are arrange their transmit and receive pairs according to device they connected.
Let’ look at straight-through and cross cables togetler;
Copper Ethernet cables are separated to different categories according to data they can transmit and also technological improvements. The copper quality, wire diameter and used technology defines this category.
Category 1: Mostly used for phone lines.
Category 2: Old technology, maximum data transfer rate is 4Mbps.
Category 3: It was used for old 10BaseT networks and it was support 10Mbps rate.
Category 4: It was used for old token-ring networks. It supports 16Mbps data rate.
Category 5: It supports 100Mbps data rate, also formerly used. It usually using for phone cabling now.
Category 5e: It supports to 1Gbps line rate. It is using now but the usage is decreasing after Cat6.
Category 6: The most common cable type using today. It supports 1Gbps line rate.
Shielded Twisted Pair – STP
I mentioned UTP (Unshielded twisted pair) cables above. Addition to UTP cables, there are shielded twisted pair (STP) cables also used specially data centres.
The main difference of STP cable from UTP is shielding as it called. At the shielded cable, all cable pairs are covered also aluminium foil. This technology makes the cable more magnetic resistant for exterior factors. So, you can transfer more data without corruption with this cable.
Nowadays, STP cables can transfer up to 10Gbps data.
The STP cable seems below;
The RJ-45 connector that suitable for STP cable is also special for shielding.
STP connector is below;
STP cable is more expensive than UTP cable and also making STP cable is harder than STP. Making STP cable needs special equipment and special knowledge.
UTP cable is cheaper than STP cable and the cable can be prepared easily. So, STP cables are usually using in data centres which are require more speed and high availability.
The cabling standards for STP are named Cat6A or Cat7 today.