You may have heard an industry buzz in recent years over the expanding market in voice and data cables. For many installers, terms such as category cables, IBM token ring, star topology, etc. are either unfamiliar or misunderstood. A general understanding of these concepts is helpful to fully comprehend and compete in today’s exciting voice and data market.


History And Background


Original Standards
The telecommunication industry originally responded to the needs of the LAN (local area network) cable and data communications industry by supplying separate standards to reflect implementation of industry applications. These included:
  1. Token Ring - 150 ohm shielded twisted pair (STP)
  2. 3270 - RG62 coax
  3. Ethernet - RG58 coax
  4. Phones - Quad or 100 ohm unshielded twisted pair (UTP)


Changes For Local Area Network And Category Cabling

As the number of LAN installations grew, additional standards were needed to address compatibility and performance between suppliers of different equipment. The existing standards were not adequate, making installation and maintenance of multiple and incompatible wiring systems difficult for installers and engineers. These serious limitations regarding system operation, adaptability and maintenance brought about a need for common cabling system requirements. International Business Machines (IBM) technical interface specification GA27-3773-1 (standard spec) was the first hierarchy of data communication cabling. This pioneered the EIA/TIA-568A standard for category cabling as we know it today.


Basic Standards

EIA/TIA-568A & 570 Wiring - Star Wiring Topology
EIA/TIA standards are designed with flexibility in mind. Their “generic” quality not only supports future equipment and service changes, but also allows successful use of multiple vendor equipment. “Topology” refers to the architecture, of the way the network is designed. EIA/TIA-568A and 570 wiring systems are based on a “star” topology. A star topology is a system in which all workstations or devices are connected to a central location. A star topology may also support several different variations of direct connections such as ring, bus, loop, etc.


Simple Star Topology


Simple Ring Topology


Simple Bus Toplogy


Special Note:
Some applications require “baluns” to convert coax applications (unbalanced) to UTP applications (balanced).


The Category Rating System

The category rating system was developed by TIA as a response to the industry’s request for higher data rate specifications on applications over unshielded (UTP) and shielded (STP) twisted pair. This rating system has been integrated into the body of the EIA/TIA-568A standard document. The category rating system only applies to 100 ohm UTP and STP wiring systems. EIA/TIA-568A also allows 150 ohm STP (also called type 1) and 62.5/125 um multi-mode optical fiber.


An Overview Of Category Cables

4 pair 100 ohm UTP Category 3 cabling is the recommended minimum requirement for residential and light commercial installations. This standard provides excellent flexibility. Category 2 and 4 cables have been replaced in the mind of the industry by Category 3 and 5 cables respectively. Pair counts have also been consolidated with 4 pair for “desktop” and 25 pair for “backbone” cabling leading the way.

Category 1 - meets the minimum requirements for analog voice or Plain Old Telephone Service (POTS).
Category 2 - defined as the IBM Type 3 cabling system. IBM Type 3 components were designed as a higher grade 100 ohm UTP system capable of operating 1 Mbps Token Ring, 5250 and 3270 applications over shortened distances.
Category 3 - characterized to 16 MHz and supports applications up to 10 Mbps. Applications may range from voice to 10BASE-T.
Category 4 - characterized to 20 MHz and supports applications up to 16 Mbps. Applications may range from voice to 16 Mbps Token Ring.
Category 5 - characterized to 100 MHz and supports applications up to 100 Mbps. Applications may range from voice to 100BASET.
Category 5e - characterized to 100 MHz and supports Gigabit applications up to 100 Mbps. Applications may range from voice to 1000BASET.
Category 6 - characterized to 200/250 MHz (still under discussion) and supports future applications (no LAN applications have yet emerged which require cabling performance beyond Category 5e) and is backward compatible with Category 5 cabling systems.
Proposed Category 7 - Possible shield system still under discussion. Application have yet to emerge which require cabling performance beyond Category 5e.
UTP Category Cabling Evolution
With the publication of EIA/TIA 568 standards in 1991 the term "Category" made its way into the vocabulary of LAN managers and cable installers to describe the performance of UTP cabling systems. Category 3 was initially the biggest seller for use in cabling systems running voice traffic and 10BaseT LAN traffic. Shortly after Category 4 was introduced to provide a higher grade of cable capable of running 16 Mbps Token Ring networks. When 100BaseTX (100 Mbps) was introduced, Category 4 soon gave way to Category 5, which now constitutes the majority of data cable runs.
Similar to 100BaseTX the recent introduction of Gigabit Ethernet (1000BaseT) has forced some changes in UTP cabling standards. Even though existing category 4 cabling systems may support the robust Gigabit ethernet channels they will definitely be stretched to their limits. Due to these concerns, a new cabling Category (5e) has been defined to ensure Gigabit performance.
What is Category 5e?
A new specification (Category 5e) has been developed to handle the challenges of Gigabit traffic (1000BaseT). The category 5e specification for cabling and testing procedures are covered under TIA documents SP4194 and SP4196. The category 5e specification addresses the minimum equal level far end crosstalk (ELFEXT) and return loss requirements necessary to support 1000CBAseT.
Tips For Installing Category Cables


Most high speed data application failure is due to improper installation techniques. To insure proper performance of category cable products, always follow these guidelines:
  • When pulling cable, avoid kinking and tugging. Constant tension should be used when pulling cable into place. EIA/TIA-568A specifies a 25 pound maximum pulling tension for category cable installations.
  • Do not crush or pinch the cable.
  • Avoid sharp turns over 90°. This may cause disruption in conductor and cable integrity.
  • Home run cable wherever possible to maximize data transmission.
  • Avoid running cable close to external power sources. EMI (electromagnetic interference) and RFI (radio frequency interference) may cause data transmission problems.
  • Avoid heat and moisture. High temperature and moist locations may cause attenuation problems.
  • Select only the highest grade category cables available. Overall performance is a key ingredient for system success.
  • Standard cable ties may pinch category cables. Specially designed fasteners are available to avoid placing pressure and stress on the cable.
  • Special termination procedures must be followed. Remove only as much jacket and insulation as is recommended. Do not untwist conductors more than necessary. For details consult your equipment manufacturer or EIA/TIA guidelines.
  • Always use proper tools and equipment.


Definitions of Electrical Properties

Commercial Building Telecommunication Standard


Asynchronous Transfer Mode
Attenuation is the loss of signal strength during transmission. Due to losses in the transmission medium, (such as resistance in a cable), the received signal may be lower in strength than the transmitted signal.  Attenuation of a digital signal reduces the height of the square wave, which may be received incorrectly by less sensitive equipment.
Attenuation-to-Crosstalk Ratio (ACR):
ACR is a ratio not a measurement. The ratio of attenuation (strength of signal over the length of a cable link) to crosstalk (undesirable signal transmission from one pair to another pair) at a specific frequency. The larger the ACR the better the link performance.
Building Industry Consulting Services International
Capacitance refers to a cable’s unique ability to store an electric charge and to resist sudden changes in the magnitude of that charge (voltage). It is found not only between the two wires of a twisted pair, but also between two adjacent conductors in the same cable. The capacitance between two adjacent conductors is called the mutual capacitance. In a shielded cable, the capacitance between conductors in contact with the shield is called electrostatic.With high frequency digital transmissions, mutual capacitance distorts the square wave shape of the signal, causing errors in data transmission. The larger the capacitance, the higher the distortion and error rate.
Crosstalk is an interference caused when signal frequencies from one line are coupled onto an adjacent line. Crosstalk may cause distortion of data in the system.
Measurement of a signals strength based on a ratio of 2 signals.
Equal Level Far End Crosstalk (ELFEXT):
A method of subtracting out the cables attenuation in order to accurately compare FEXT values from one cable to another.
Far End Crosstalk (EFEXT)
Crosstalk that is measured at the receiver end or opposite end from signal source.
Institute of Electrical and Electronic Engineers
Impedance is the total opposition a circuit, cable or component offers to alternating current (AC). It contains both resistance and reactance and is expressed in ohms.
Local Area Network (LAN):
Local Area Network is a private communications network for transferring data among computers and peripheral devices.
Megabits Per Second (Mbps):
Megabits per second corresponds to one million units (bits) of information transference per second between two pieces of digital equipment.
Megahertz (MHz):
Megahertz is a bandwidth-length product rating. MHz usually refers to the upper frequency band on a cabling system.
Near-End Crosstalk (NEXT):
Near-End Crosstalk is a measurement for crosstalk in multi-pair category cables. In a two-way circuit, crosstalk problems are most noticeable when the signal leaves the transmitter. At this point the detector for the adjacent pair is closest and the energy level is highest. This area is called the “near end” point.
National Electric Code
Pair to Pair Testing:
The effects that one energized pair of cable has on one other pair within the same jacket.
Power Sum Testing:
The effect that all energized pairs of cable have on one unenergized pair within the same jacket.
The resistance to the flow of current is expressed in ohms. Every material offers some resistance or opposition to the flow of electric current. The size and type of material in a circuit is chosen to provide the lowest resistance possible. Copper is an excellent conductor for the price. The larger the gauge (AWG) size, the lower the resistance.
Return Loss:
Return loss is the measurement in decibels (db) of noise or interference caused by dissimilarities in impedance along a transmission line at various frequencies.
Structural Return Loss (SRL):
A measurement of reflected energy of a transmitted signal due to impedance variations along the length of the cable.
Gigabit Ethernet over twisted pair cable.