Cable Definitions

DEFINITIONS:

Unshielded Twisted Pair
Printer Cable
Category 5 Cable
Category 6 Cable
Category 7 Cable
Serial Cable
Plenum Cable

Unshielded Twisted Pair

Unshielded twisted pair (UTP) cabling is the most common cable used in computer networking. It is a variant of twisted pair cabling. UTP cables are often called Ethernet cables after Ethernet, the most common data networking standard that utilizes UTP cables, although not the most reliable.

In contrast to FTP and STP cabling, UTP cable is not surrounded by any shielding. It is the primary wire type for telephone usage and is very common for computer networking, especially as patch cables or temporary network connections due to the high flexibility of the cables.

Advantages

It is a thin, flexible cable that is easy to string between walls.
Most modern buildings come with CAT 5 UTP already wired into the wall outlets or at least run between the floors.
Because UTP is small, it does not quickly fill up wiring ducts.
UTP costs less per foot than any other type of LAN cable.

Disadvantages

It is more susceptible to interference than most other types of cabling. The pair twisting does help, but it doesn't make the cable impervious to electrical noise.

Its unrepeated length limit is 100 meters.

Unshielded Twisted Pair Cabling Standards

Cat 1: Currently unrecognized by TIA/EIA. Previously used for POTS telephone communications, ISDN and doorbell wiring.

Cat 2: Currently unrecognized by TIA/EIA. Previously was frequently used on 4 Mbit/s token ring networks.

Cat 3: Currently defined in TIA/EIA-568-B, used for data networks utilizing frequencies up to 16 MHz. Historically popular for 10 Mbit/s Ethernet networks.

Cat 4: Currently unrecognized by TIA/EIA. Provided performance of up to 20 MHz, and was frequently used on 16 Mbit/s token ring networks.

Cat 5: Currently unrecognized by TIA/EIA. Provided performance of up to 100 MHz, and was frequently used on 100 Mbit/s Ethernet networks. May be unsuitable for 1000BASE-T gigabit Ethernet.

Cat 5e: Currently defined in TIA/EIA-568-B. Provides performance of up to 100 MHz, and is frequently used for both 100 Mbit/s and gigabit Ethernet networks.

Cat 6: Currently defined in TIA/EIA-568-B. It provides performance of up to 250 MHz, more than double category 5 and 5e.

Cat 6a: Future specification for 10 Gbit/s applications.

Cat 7: An informal name applied to ISO/IEC 11801 Class F cabling. This standard specifies four individually-shielded pairs (STP) inside an overall shield. Designed for transmission at frequencies up to 600 MHz.

Printer Cable

Printer cable refers to the cable that carries data between a computer and a printer.

There are many different types of cables, for example:

Serial: RS-232, EIA-422

Parallel

FireWire

USB

Parallel port printers have been slowly fazed out, and are now difficult to find for the most part, being considered as an obsolete legacy port on most new computers. Those who have printers and scanners with only parallel port may still be able to connect the devices via the used of USB adapters a.k.a. Parallel-to-USB cable. Generally, FireWire's very high speeds of up to 800Mb/s are excessive for printers.

Due to request from retailers, printer manufacturers have gradually stopped including the necessary printer cable to connect the printer to a computer. Retailers usually make a huge profit on selling cables, as much as 3000% (a cable cost about $1 to produce and package, then sold at retail stores for as much as $30).

Category 5 Cable

Category 5 cable, commonly known as Cat 5, is a twisted pair cable type designed for high signal integrity, usually it is unshielded but shielded cables can also be purchased. Category 5 has been superseded by the Category 5e specification. This type of cable is often used in structured cabling for computer networks such as Ethernet, although it is also used to carry many other signals such as basic voice services, token ring, and ATM (at up to 155 Mbit/s, over short distances).

The original specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These documents specified performance characteristics and test requirements for frequencies of up to 100 MHz.

Category 5 cable includes four twisted pairs in a single cable jacket. This use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and other pairs (this latter form of interference is called crosstalk). It is most commonly used for 100 Mbps networks, such as 100BASE-TX Ethernet, although IEEE 802.3ab defines standards for 1000BASE-T - Gigabit Ethernet over category 5 cable. Cat 5 cable typically has three twists per inch of each twisted pair of 24 gauge copper wires within the cable.

Category 5e

Cat 5e cable is an enhanced version of Cat 5 that adds specifications for far end crosstalk. It was formally defined in 2001 in the TIA/EIA-568-B standard, which no longer recognizes the original Cat 5 specification. Although 1000BASE-T was designed for use with Cat 5 cable, the tighter specifications associated with Cat 5e cable and connectors make it an excellent choice for use with 1000BASE-T. Despite the stricter performance specifications, Cat 5e cable does not enable longer cable distances for Ethernet networks: cables are still limited to a maximum of 100m (328ft) in length (normal practice is to limit fixed ("horizontal") cables to 90m to allow for up to 5m of patch cable at each end). Cat 5e cable performance characteristics and test methods are defined in TIA/EIA-568-B.2-2001. (Shown on the right is PC-PC cable pin schedule).

Connectors and other information

Usually, solid core cable is used for connecting the wall socket to the socket in the patch panel, and stranded cable is used for the patch leads between hub/switch and patch panel socket and between wall port and computer. Cable types, connector types and cabling topologies are defined by TIA/EIA-568-B. Nearly always, 8P8C modular connectors are used for connecting category 5 cable.

Unshielded Twisted Pair Cabling Standards

Cat 1: Currently unrecognized by TIA/EIA. Previously used for POTS telephone communications, ISDN and doorbell wiring.

Cat 2: Currently unrecognized by TIA/EIA. Previously was frequently used on 4 Mbit/s token ring networks.

Cat 3: Currently defined in TIA/EIA-568-B, used for data networks utilizing frequencies up to 16 MHz. Historically popular for 10 Mbit/s Ethernet networks.

Cat 4: Currently unrecognized by TIA/EIA. Provided performance of up to 20 MHz, and was frequently used on 16 Mbit/s token ring networks.

Cat 5: Currently unrecognized by TIA/EIA. Provided performance of up to 100 MHz, and was frequently used on 100 Mbit/s Ethernet networks. May be unsuitable for 1000BASE-T gigabit ethernet.

Cat 5e: Currently defined in TIA/EIA-568-B. Provides performance of up to 100 MHz, and is frequently used for both 100 Mbit/s and gigabit Ethernet networks.

Cat 6: Currently defined in TIA/EIA-568-B. It provides performance of up to 250 MHz, more than double category 5 and 5e.

Cat 6a: Future specification for 10 Gbit/s applications.

Category 6 Cable

Cat 6- Category - 6, (ANSI/TIA/EIA-568-B.2-1) is a cable standard for Gigabit Ethernet and other network protocols that is backward compatible with the Category 5/5e and Category 3 cable standards. Cat-6 features more stringent specifications for crosstalk and system noise. The cable standard is suitable for 10BASE-T / 100BASE-TX and 1000BASE-T (Gigabit Ethernet) connections. It provides performance of up to 250 MHz.

The cable contains four twisted copper wire pairs, just like earlier copper cable standards. Although Cat-6 is sometimes made with 23 gauge wire, this is not a requirement; the ANSI/TIA-568-B.2-1 specification states the cable may be made with 22 to 24 gauge wire, so long as the cable meets the specified testing standards. When used as a patch cable, Cat-6 is normally terminated in RJ-45 electrical connectors, although some Cat-6 cable may be difficult to attach RJ-45 connectors without a special modular piece and is technically not standards compliant. If components of the various cable standards are intermixed, the performance of the signal path will be limited to that of the lowest category. As with all cables defined by TIA/EIA-568-B, the maximum allowed length of a Cat-6 horizontal cable is 90 meters (295 feet). A complete channel (horizontal cable plus cords on either end) is allowed to be up to 100 meters in length, depending upon the ratio of cord length:horizontal cable length.

Augmented Category 6 (Category 6a)

The TIA is working to complete a new specification that will define enhanced performance standards for unshielded twisted pair cable systems. Draft specification ANSI/TIA/EIA-568-B.2-10 specifies cable systems, called "Augmented Category 6" or more frequently as "Category 6a", that operate at frequencies up to 500 MHz and will provide up to 10 Gbit/s throughput. The new specification has limits on alien cross talk in cabling systems.

Augmented Category 6 specifies cable operating at minimum frequency of 500 MHz, for both shielded and unshielded. It can support future 10Gb/s applications up to the maximum distance of 100 meters on a 4-connector channel.

Unshielded Twisted Pair Cabling Standards

Cat 1: Currently unrecognized by TIA/EIA. Previously used for POTS telephone communications, ISDN and doorbell wiring.

Cat 2: Currently unrecognized by TIA/EIA. Previously was frequently used on 4 Mbit/s token ring networks.

Cat 3: Currently defined in TIA/EIA-568-B, used for data networks utilizing frequencies up to 16 MHz. Historically popular for 10 Mbit/s Ethernet networks.

Cat 4: Currently unrecognized by TIA/EIA. Provided performance of up to 20 MHz, and was frequently used on 16 Mbit/s token ring networks.

Cat 5: Currently unrecognized by TIA/EIA. Provided performance of up to 100 MHz, and was frequently used on 100 Mbit/s Ethernet networks. May be unsuitable for 1000BASE-T gigabit Ethernet.

Cat 5e: Currently defined in TIA/EIA-568-B. Provides performance of up to 100 MHz, and is frequently used for both 100 Mbit/s and gigabit Ethernet networks.

Cat 6: Currently defined in TIA/EIA-568-B. It provides performance of up to 250 MHz, more than double category 5 and 5e.

Cat 6a: Future specification for 10 Gbit/s applications.

Category 7 Cable

Category 7 cable (CAT7), (ISO/IEC 11801:2002 category 7/class F), is a cable standard for Ethernet and other interconnect technologies that can be made to be backwards compatible with traditional CAT5 and CAT6 Ethernet cable. CAT7 features even more stringent specifications for cross talk and system noise than CAT6. To achieve this, shielding has been added for individual wire pairs and the cable as a whole.

The CAT7 cable standard has been created to allow 10 gigabit Ethernet over 100 meters of copper cabling. The cable contains four twisted copper wire pairs, just like the earlier standards. CAT7 can be terminated either with RJ-45 compatible GG45 electrical connectors which incorporate the RJ-45 standard or with TERA connectors. When combined with GG-45 or TERA connectors, CAT7 cable is rated for transmission frequencies of up to 600 MHz.

Unshielded Twisted Pair Cabling Standards

Cat 1: Currently unrecognized by TIA/EIA. Previously used for POTS telephone communications, ISDN and doorbell wiring.

Cat 2: Currently unrecognized by TIA/EIA. Previously was frequently used on 4 Mbit/s token ring networks.

Cat 3: Currently defined in TIA/EIA-568-B, used for data networks utilizing frequencies up to 16 MHz. Historically popular for 10 Mbit/s Ethernet networks.

Cat 4: Currently unrecognized by TIA/EIA. Provided performance of up to 20 MHz, and was frequently used on 16 Mbit/s token ring networks.

Cat 5: Currently unrecognized by TIA/EIA. Provided performance of up to 100 MHz, and was frequently used on 100 Mbit/s Ethernet networks. May be unsuitable for 1000BASE-T gigabit Ethernet.

Cat 5e: Currently defined in TIA/EIA-568-B. Provides performance of up to 100 MHz, and is frequently used for both 100 Mbit/s and gigabit Ethernet networks.

Cat 6: Currently defined in TIA/EIA-568-B. It provides performance of up to 250 MHz, more than double category 5 and 5e.

Cat 6a: Future specification for 10 Gbit/s applications.

Serial Cable

A serial cable is a cable that can be used to transfer information between two devices. Serial cables use the RS-232 standards for their connectors. The serial cable can be any combination of male or female in a DE9 or DB25 connector type. The original RS-232 connector was intended to be a 25-pin connector (DB25). In the realm of computer peripherals, the serial cable has been deprecated by the Universal Serial Bus (USB) standard.

The serial cable was often used when communicating with a computer and a peripheral (such as a modem). The term null modem is used to describe serial cables used without a modem to allow two computers to communicate directly.

Originally the serial cable was designed for a speed of 300 baud (baud rate is synonymous with bits per second), with 1200 bit/s considered to be high speed. This is in stark contrast to early-21 century bandwidth needs in which a common household internet connection can exceed 512,000 bit/s on the downstream. Later versions of the cable with supporting software and hardware could handle speeds of up to 115,200 bit/s.

Used as null modems, types:

No hardware handshaking

The most simplistic type of serial cable. This cable has only the data and signal ground wires connected. All of the other pins have no connection. With this type of cable flow control has to be implemented in the software. The use of this cable is restricted to data-traffic only on its cross connected Rx and Tx lines. This cable can also be used in devices that do not need or make use of modem control signals.

Loop back handshaking

Because of the compatibility issues and potential problems with a simple null modem cable, a solution was developed to trick the software into thinking there was handshaking available. However, the cable pin out merely loops back and does not physically support the hardware flow control.

This cable could be used with more software but it had no actual enhancements over its predecessor. The software would work thinking it had hardware flow control but could suddenly stop when higher speeds were reached and with no identifiable reason.

Partial handshaking

In this cable the flow control lines are still looped back to the device. However, they are done so in a way that still permits Request To Send (RTS) and Clear To Send (CTS) flow control but has no actual functionality. The only way the flow control signal would reach the other device is if the opposite device checked for a Carrier Detect (CD) signal at pin 1. As a result only specially designed software could make use of this partial handshaking. Software flow control still worked with this cable.

Full handshaking

This cable is the most expensive of the serial cables because it has full wiring and pin-outs. This cable is incompatible with the previous types of cables hardware flow control, due to a crossing of its RTS/CTS pins. With this cable and the suitable software to take advantage of it, the cable is capable of much higher speeds than its predecessors. It also supports software flow control.

Uses

The serial cable is still in use in a few (some old or obsolete) peripheral devices. Growing use of USB technology, since the 1990s, has greatly declined the serial cable's application.

These devices (and others) have been known to communicate via serial cable:

Scientific instruments

Medical devices

Field equipment

Military equipment

Personal digital assistant (PDA)

Printers

Uninterrupted power supply (UPS)

Maximum cable lengths

Cable length is one of the most discussed items in RS232 world. The standard has a clear answer, the maximum cable length is 50 feet, or the cable length equal to a capacitance of 2500 pF. The latter rule is often forgotten. This means that using a cable with low capacitance allows you to span longer distances without going beyond the limitations of the standard. If for example UTP CAT-5 cable is used with a typical capacitance of 17 pF/ft, the maximum allowed cable length is 147 feet.

The cable length mentioned in the standard allows maximum communication speed to occur. If speed is reduced by a factor 2 or 4, the maximum length increases dramatically. Texas Instruments has done some practical experiments years ago at different baud rates to test the maximum allowed cable lengths. Keep in mind, that the RS232 standard was originally developed for 20 kbps. By halving the maximum communication speed, the allowed cable length increases a factor ten!

Plenum Cable

Plenum cable is cable that is laid in the plenum spaces of buildings. The plenum (pronounced PLEH-nuhm) is the space that is used for air circulation in heating and air conditioning systems, typically between the structural ceiling and the dropped ceiling or under a raised floor. The plenum space is typically used to house the communication cables for the buildings computer and telephone network. However, it has been proposed that the growing abandonment of cable in plenum spaces may pose a serious hazard in the event of a fire as once the fire reaches the plenum space there are few barriers to contain the smoke and flames. As plenum spaces are restricted from use as areas for storage, the principle behind removal of abandoned cable is that regulated removal prevents the use of plenum spaces as a storage area for abandoned cable.

In the United States, plastics used in the construction of plenum cable are regulated under the National Fire Protection Association standard NFPA 90A: Standard for the Installation of Air Conditioning and Ventilating Systems. Plenum cable is jacketed with a fire retardant plastic jacket of either a low-smoke polyvinyl chloride (PVC) {patented 1987} or a fluorinated ethylene polymer (FEP). Polyolefin formulations had been developed by at least two companies in the early to mid-1990's; however, these were never commercialized. All materials intended for use on wire and cables to be placed in plenum spaces are designed to meet rigorous fire safety test standards in accordance with NFPA 262 and outlined in NFPA 90A.

Cable which is to be run between floors in non-plenum areas is rated as riser cable. The fire requirements on riser cable are not as strict. Thus, plenum cable can always replace riser cable, but riser cable cannot replace plenum cable in plenum spaces. Twisted-pair and coaxial versions of cable are made in plenum and riser versions.

In 2006, significant concern developed over the potential toxicity of FEP and related fluorochemicals including the process aid perfluorooctanoic acid (PFOA) or C8 such that California has proposed some of these materials as potential human carcinogens. The NFPA Technical Committee on Air Conditioning, in response to public comment, has referred the issue of toxicity of cabling materials to the NFPA Committee on Toxicity for review before 2008.

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