Network Cabling

Introduction

Today's networks mostly use twisted pair cables or fibre optic cable.

In this article I concentrate only on twisted pair cable for Ethernet networks.

Twisted pair cable was invented and patented by Graham Bell in 1881.

It is a type of cable that consists of two independently insulated wires twisted around one another. The use of two wires twisted together helps to reduce crosstalk, sometimes referred to as NEXT ( Near End X Talk) and/or FEXT (Far end X Talk) and electromagnetic induction.

In the context of the 100-ohm UTP (Unshielded Twisted Pair) type of cable used for Ethernet wiring the only categories of interest are CAT3, CAT4, CAT5, CAT5e, CAT6, and CAT7. CATx is an abbreviation for the category number that defines the performance of building telecommunications cabling as outlined by the Electronic Industries Association (EIA) standards. Some specifications for these categories are shown in the table below.

Up until the late 1980s thick or thin coaxial cable was typically used for 10-Mbps Ethernet networks, but around that time, UTP cabling became more commonly used because it was easier to install and less expensive. UTP CAT3 and CAT4 were used for a quite limited time since the emergence of 100Base-TX networks meant a quick shift to CAT5. By the year 2000, moves to gigabit (1000Base-TX) Ethernet LANs created a need for another specification.

Specifications for CAT3, CAT4, CAT5, CAT5e, CAT6, and CAT7 Cables

Category	Type	Speed Up to	Spectral B/W	Length	LAN Applications	Notes
CAT3	UTP	10 MBs	16 MHz	100m	10Base-T, 4Mbps	Now mainly for telephone cables
CAT4	UTP	16 MBs	20 MHz	100m	16Mbps	Rarely seen
CAT5	UTP	100 MBs	100MHz	100m	100Base-Tx,ATM,CDDI	Common for current LANs
CAT5e	UTP	1 GBS	100MHz	100m	1000Base-T	Common for current LANs
CAT6	UTP	1 GBs 10 GBS	250MHz	100m 50M	1000Base-T
CAT7	ScTP	10 GBs	600MHz	100m	1000Base-T

CAT7 is seldom used today, since fibre is often less expensive and is more powerful.

Comparison UTP versus STP and FTP

Ethernet cable comes in different versions, UTP, STP and FTP, as well as Stranded and Solid.

Solid cable is used for long runs and mainly in trunking. It consists of 1 solid copper conductor, making it easily breakable, but less expensive and with better transmission capabilities than stranded cable.  Stranded cable is used for fly leads and short runs, where it is handled a lot, since it does not break as easily as solid UTP.

The following abbreviations are often used in the industry to identify different shielding for ethernet cable. (With thanks to Wikipedia)

Industry abbreviations	ISO/IEC 11801 designation	Cable shielding	Pair shielding
UTP, TP	U/UTP	None	None
STP, ScTP, PiMF	U/FTP	None	Foil
FTP, STP, ScTP	F/UTP	Foil	None
STP, ScTP	S/UTP	Braiding	None
SFTP, S-FTP, STP	SF/UTP	Braiding and Foil	None
FFTP, STP	F/FTP	Foil	Foil
SSTP, SFTP, STP, STP PiMF	S/FTP	Braiding	Foil
SSTP, SFTP, STP	SF/FTP	Braiding and Foil	Foil

The code before the slash designates the shielding for the cable itself, while the code after the slash determines the shielding for the individual pairs:

U = unshielded

F = foil shielding

S = braided shielding (outer layer only)

TP = twisted pair

TQ = twisted pair, individual shielding in quads.

Below are images of the different cables:

UTP Cable

STP Cable

FTP Cable

Wiring

See modular connector for numbering of the pins.^[8]

Pin	T568A pair	T568B pair	10BASE-T 100BASE-TX	1000BASE-T signal ID	Wire	T568A color	T568B color	Pins on plug face (socket is reversed)
1	3	2	TX+	DA+	tip	white/green stripe	white/orange stripe
2	3	2	TX−	DA−	ring	green solid	orange solid
3	2	3	RX+	DB+	tip	white/orange stripe	white/green stripe
4	1	1	—	DC+	ring	blue solid	blue solid
5	1	1	—	DC−	tip	white/blue stripe	white/blue stripe
6	2	3	RX−	DB−	ring	orange solid	green solid
7	4	4	—	DD+	tip	white/brown stripe	white/brown stripe
8	4	4	—	DD−	ring	brown solid	brown solid

Some RJ45 wall sockets indicate T568A and T568B termination schemes internally.

Note that the only difference between T568A and T568B is that pairs 2 and 3 (orange and green) are swapped. Both configurations wire the pins "straight through", i.e., pins 1 through 8 on one end are connected to pins 1 through 8 on the other end. Also, the same sets of pins connect to the opposite ends that are paired in both configurations: pins 1 and 2 form a pair, as do 3 and 6, 4 and 5, and 7 and 8. One can use cables wired according to either configuration in the same installation without significant problem, as long as the connections are the same on both ends.

Avoid swapping two lines between different pairs. This creates crosstalk. This is rectified by correctly pairing the pins. Crosstalk creates errors in Ethernet and is more significant with 1GB Ethernet and up, as these standards use all 4 pairs. (10 Base/T and 100 Base/T Ethernet use only 2 pairs).

FTP and STP use a shielded RJ45 as shown below:

Remember for a STP/FTP lead the drain wire should be connected to the shield of the RJ45 connector on both ends.

What is a crossover cable?

Two of the most frequently asked questions on wiring are: “How do I make a crossover cable” and “when is it used”?

Computers that are equipped with 10Base-T or 100Base-TX network adapters can be connected “back-to-back”; meaning they do not require a hub to be networked together. Back-to-back connections via crossover cables are useful in a small or home office. Crossover cables are also used to link together two pieces of network equipment (e.g., hubs, switches, and routers) if the equipment does not have an uplink or crossover port built-in. A crossover cable is just a patch cord that is wired to a T568A pinout scheme on one end and a T568B pinout scheme on the other end. In other words pairs 2 and 3 are not connected straight pin to pin, but crossed over.

For an in-depth explanation of all the ins and outs of networking, I recommend the book:

Cabling: The Complete Guide to Network Wiring by David Barnett, David Groth and Jim McBee

It is available from us, free of charge.