Unorganized cabling can result in serious network disruption. Structured cabling can be your answer to maximize network performance. by Mahesh Rathod

Structured cabling system provides a flexible cabling plan and can support different computer and telephone systems from any vendor

With networks becoming more complex and their requirements changing constantly, having a good foundation for these networks is crucial. Cabling, the backbone of any data communications system is vital when it comes to determining performance and reliability of any network. Structured cabling is the first step towards achieving optimum performance from your network.

Origin of structured cabling
During the early days of networking, various vendor-dependent cabling systems existed for carrying data and voice. Troubleshooting and managing these proprietary systems was very difficult and time consuming as network managers had to maintain two distinct networks (data and voice). This lead to the evolution of structured cabling.

Structured cabling provides a flexible cabling plan and can support computers and telephone systems from any vendor. Structured cabling is a hierarchy based on backbone cables that carry signals between telecommunication closets and floors of a building, and on horizontal cables that deliver services from telecom closets to work areas.

The central standard for structured cabling system is the ANSI/TIA/EIA-568-A, "Commercial Building Telecommunications Cabling Standard". This standard specifies a generic telecommunications cabling system to support a multi-product and multi-vendor environment.

Six Elements of a Structured Cabling System

The TIA/EIA 568 cabling standard specifies the six basic elements of a structured cabling system.

Building entrance facilities: This is the service entrance into the building including the cables, surge protection equipment and connecting hardware that may be used to link the cabling inside your building with the campus data network or public telephone network.

Equipment room: This is a centralized space where telecommunications equipment is located (e.g., PBX, computing equipment, video switch, etc.)

Backbone cabling: In a Star topology backbone cabling is used to provide connections between telecom closets, equipment rooms and entrance facilities.

Telecommunications closet: The main role of the telecommunications closet is to provide a location for the termination of the horizontal cable on a given floor of a building. This closet houses the mechanical cable termination and any cross-connects for the horizontal and backbone cabling systems. It may also house interconnection equipment like switches.

Horizontal cabling: It consists of physical media used to connect each outlet to a closet. Various types of cables can be used for horizontal distribution. Each type has its own performance limitations, size, cost and ease-of-use.

Work Area: This is the area where computers and other equipment are located. The work area components include patch cables required to connect the computer and telephone to the communications outlet on the wall.

Support for Star Topology
The structured cabling standard TIA/EIA 568 is based on a Star topology. The standard specifies a backbone system with a star cabling topology that has no more than two levels of hierarchy within a building. This means that a cable should not go through more than one intermediate cross-connect device between the main cross-connect located in an equipment room and the horizontal cross-connect located in a wiring closet. There are many advantages to using star topology. The first is that central equipment switches can be easily migrated to new technologies. The second is the physical security that can be provided for critical equipment preventing widespread network failure as a result of tampering. Lastly the central cabling points make it easier to troubleshoot networking problems.

Media types for Structured Cabling

The TIA/EIA 568 recognizes three different kinds of cables.

Unshielded Twisted Pair (UTP) is one of the media types. UTP can be classified into three categories depending on their performance. Category 3 is rated to 10 MHz, suitable for Ethernet (10 Mbps). Category 4 is rated to 20 MHz, suitable for token ring (16 Mbps). Category 5 is rated to 100 MHz, suitable for Fast Ethernet (100 Mbps) and ATM (155 Mbps). Cat 5 or Category 5 is the de-facto standard now as it is easy to install and has a lower installation cost. Cat 5 also has a most commonly used variation: Cat 5e. This standard is used for Gigabit Ethernet.

The new upcoming standard is Cat 6.

Shielded Twisted Pair (STP) also known as the IBM Type 1 is the other cable type. The 568-A standard for STP is known as STP-A. This standard extends the system's rating through 300 MHz. But if installed properly STP-A structured cabling system can run a 16 Mbps token ring signal and a 550 MHz broadband video signal at the same time.

Fiber optic cable offers near infinite bandwidth and perfect immunity to noise. Fiber offers more bandwidth than copper cables. In fact, a single pair of fibers can handle the same amount of voice traffic as 1400 pairs of copper. The trade-off here is that fiber costs significantly more and installation is difficult.

Installation and design practices
It is advisable to follow installation and design principals laid down by the 568 standard to get optimal cabling performance. The 568-A standard requires a minimum of two ports (voice & data) per workstation. The first port must use 4-pair, 100 Ohm, Cat 3 or higher UTP cable. The second port can make use of UTP, STP or optical fiber cable. The maximum length for horizontal cabling between the switch and any outlet must be 90 meters.

The first installation practice is pulling cables from the telecommunications closet to each outlet location. The maximum pulling tension for Category 5 is 25 lbf. Higher tension on the cable may stretch the twists and can result in increased attenuation. As per the 568, the pairs in a Category 5 cable should never be untwisted more than half inch from the point of termination. Any further untwisting of the pairs will increase crosstalk and susceptibility to EMI/RFI (electromagnetic interference/radio frequency interference).

The next cable installation practice is to prepare the cable for termination. This involves stripping away some of the jacketing material and untwisting the conductors. After the cables have been terminated, the cable must be dressed or managed.

Final word
The initial investment for structured cabling is much more than the traditional methods of cabling, but it is very important to understand that structured cabling entails long-term investment.

Structured cabling is vendor independent. A standards-based cable plant will support your applications and hardware even after you change or mix and match any vendor. Structured cabling maintains consistency and it simplifies troubleshooting.

Mahesh Rathod can be reached at rathodmp@hotmail.com