A twisted-pair cable contains two individually insulated wires that are twisted together in pairs. Each pair consists of two insulated copper wires twisted together.
The wires use copper as a conductor. The wire pairs are twisted to reduce crosstalk and noise susceptibility. In a wire pair, one wire carries the signal to the receiver while the other acts as a ground reference. At the receiving end, the receiver examines the difference in the values of the signal between the two wires. Twisted-pair cables are used for voice and data communication. Also, high quality twisted-pair cables have about 1 to 3 twists per inch.
Twisted-pair cables are further categorized into three types, which are as follows:
- Shielded Twisted-Pair (STP) Cable
- Unshielded Twisted-Pair (UTP) Cable
- Screened Twisted-Pair (ScTP) Cable
Shielded Twisted-Pair Cable
STP is a version of the 150 ohm twisted cable defined by International Business Machines (IBM) Cabling System specifications for use with Token Ring networks. This cable has a metal shield that covers each pair of insulated cable wires.
The twisted pairs are individually wrapped in a foil shield and then are enclosed in an overall outer braided wire shield. This type of shielding protects the cables from external electromagnetic interferences and crosstalk.
STP cable is available in various versions, which are identified by a Type number. Common Type numbers such as Type 1, 2, 6, 8, and 9 are described by IBM Cabling System specification. These Type numbers supports a frequency of 16 MHz. However, with the advancement in technology, IBM Cabling System defines the Type numbers for enhanced STP cable (STP-A). Common Type numbers defined are Type 1 A, 2A, 6A, and 9A which supports Fiber Distributed Data Interface (FDDI) as well as enhanced frequency of 300 MHz.
Unshielded Twisted-Pair Cable
UTP is a 100 ohm twisted pair cable. It is the most commonly used cable in data communication. It is used in Ethernet networks and telephone systems. This cable is easy to install, and its installation charges are cheap.
UTP cable only has an outer covering (jacket) and no shielding. The outer covering contains a type of non-conducting material and covers pairs of wire that are twisted together. Usually, a UTP cable contains four twisted pairs.
The American National Standards Institute/Telecommunications Industry Association/Electrical Industries Association-568-A (ANSI/TIA/EIA-568-A) standard defines various categories of UTP cable, such as Category 3, 4, and 5, to help customers in selecting the right cable for the right application. In addition to these categories, some other categories of UTP cable such as Category 5e, 6, and 7 have been defined by ANSI/TIA/EIA-568-A for offering high-speed data transmission. Various categories of UTP cable are as follows:
Category 1: Supports frequencies less than 1 MHz. Category 1 cables are commonly used in analog voice telephone systems. These cables are not defined by ANSI/TIA/EIA-568-A standard.
Category 2: Supports frequencies up to 1 MHz. This type of cable offers data and voice transmission speed of 4Mbps. Category 2 cables are used only in twisted-pair ARCnet and Apple LocalTalk networks. These cables are not defined by ANSI/TIA/EIA-568-A standard.
Category 3: Supports frequencies up to 16 MHz. Category 3 cables are used in UTP Token Ring, 10Base-T Ethernet, 100Base-T4 Ethernet, and telephone systems. These cables are defined by ANSI/TIA/EIA-568-A standard for voice applications.
Category 4: Support frequencies up to 20 MHz. Category 4 cables are especially designed for Token Ring LANs of 16 Mbps.
Category- 5: Supports frequencies up to 100 MHz. Category 5 cables are used in applications that use FDDI and 100BaseTX over copper and 155 Mbps Asynchronous Transfer Mode (ATM) over UTP.
Category 5e (Enhanced Category 5): Supports frequencies up to 100 MHz. In addition, Category 5e cable-, provide enhanced performance and a tighter transmission test requirement. These cables are used in applications that run on high speed, such as Gigabit Ethernet.
Category 6: Supports frequencies up to 250 MHz. These cables are used for high-speed applications. These cables are used with 10BASE-T, 100BASE-TX, and Gigabit Ethernet. Category 6 cables are defined by ANSI/TIA/EIA-568-A standard.
Category 6A (Augmented Category 6): Supports frequencies up to 500 MHz. These cables are used in the area of unknown crosstalk. It provides better performance in comparison to category 6 cables.
Category 7: Supports frequencies up to 600 MHz. This category is defined by International Organization for Standardization/International Electro-technical Commission (ISO/IEC) standard. These cables are used for Gigabit Ethernet.
UTP Categories and Corresponding Data Transfer Rate:
|UTP Category||Purpose||Data Transfer Rate|
|Category 1||Voice Only||1 Mbps|
|Category 2||Data||4 Mbps|
|Category 3||Data||10 Mbps|
|Category 4||Data||16 Mbps|
|Category 5||Data||100 Mbps|
|Category 5e||Data||1 Gbps|
|Category 6||Data||1 Gbps|
|Category 6A||Data||10 Gbps|
|Category 7||Data||40 Gbps|
Screened Twisted-Pair Cable
The ScTP cable refers to UTP cable which has a resistivity of 100 ohm and contains four pair of wires. These wire pairs are covered by a single foil or braided screen for derogating the electromagnetic interference as well as outside noise. This cable is also called Foil Twisted-Pair cable or Screened UTP cable. ScTP cables are used with Ethernet.