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Rapidly evolving applications and technologies are drastically increasing the speed and volume of traffic on LAN/WAN networks. Ensuring that your cabling solution is designed to accommodate the higher transmission rates associated with these evolving bandwidth intensive applications is critical.

Due to the versatility and wide range of applications support, UTP/fiber cabling systems have been developed to satisfy virtually all of customers' network and building infrastructure needs.

In addition to the performance of the cabling solution itself, the right cabling architecture needs to be chosen to optimize the investment and return for the particular building environment. Balancing cabling system cost versus the electronics, and also the ongoing management and flexibility of the solution is a key part of effective cabling infrastructure design.

There are three main cabling architectures that are commonly used for structured cabling systems. These are the traditional two-level hierarchical star, the centralized cross-connect, and the zone wiring.

The traditional two-level hierarchical star architecture is the normal standards recommended architecture, while the others are more oriented to particular applications and environments.

Hierarchical Star
The two-level hierarchical star configuration is the standard cabling topology followed by International and North American standards.

The concept is to limit administration points to a maximum of two so that the cabling infrastructure can be easily maintained. The two administration points are the equipment room and the telecommunications closet. Electronics can be located in both the equipment room and telecommunications closets.

Backbone cabling, whether copper or fiber depending on the application, interconnects the equipment rooms and closets (Statistics show that vast majority of building backbones are less than 300m) while horizontal cabling runs from the telecommunications closet to the work areas (maximum length 100 meters including all cords).

This architecture has been widely accepted by the building industry, the cabling industry, and applications developers. It is the benchmark to compare other architectures too.

Centralized Cross-Connect
Centralized cross-connect, also known as single-point administration, is an optional architecture that was introduced to the standards by the fiber cabling industry in an effort to make fiber to the desk a more attractive solution.

In this architecture, the telecommunications closet does not contain active electronics. This closet is only a pull-though point, a splice point, or a interconnect/cross-connect point between the horizontal and riser/backbone cabling.

The maximum length of the combined horizontal and backbone/riser cabling is 300m including all cords. Although this length is less than the total length (horizontal plus backbone/riser) supported by the hierarchical star, it is within the length requirements of most buildings and therefore not a major concern.

If we assume the average horizontal length is 50 meters, then based on several surveys, about 70% of combined horizontal plus backbone/riser lengths are 300m or less. The extended cabling lengths make this architecture a viable LAN option for fiber.

The main goal of the centralized cross-connect architecture is to facilitate collapsed backbones where the hubs/switches are all within one location (the backbone connection is actually just a backplane within the hub or a cord interconnecting stacked hubs). This facilitates fewer total administration points and the use of larger hubs.

One can conclude that centralized cross-connects provide a number of different advantages likely to be appealing to different customers. This architecture can be an effective tool for positioning Fiber to the Desk as an alternative to the hierarchical star.

Zone Cabling
Zone cabling is to a certain degree the opposite of centralized cabling. It adds an extra connection in the horizontal to allow for rearrangements of open office spaces.

The concept here is to reduce the ongoing maintenance costs when reconfiguring open office spaces. Instead of abandoning/replacing all horizontal cabling when modular furniture clusters are rearranged, only the portion in the modular furniture clusters (between the outlets and the consolidation point or 'extra connection') needs to be replaced.

Reconfiguration is much simpler, lower cost, and less disruptive. Churn rates are often stated as being up to 100 percent per year (although this applies to people moving, not offices being reconfigured) thereby justifying the additional up-front cost of extra connections. With the apparent market move towards open offices, this type of architecture will continue to grow.

Customers may demand design freedom above and beyond the standards in order to fully reap the benefits of these architectures.

Reasons for wanting this freedom may be that the customer likes to keep their electronics in secure cabinets and interconnect the ports to dedicated external patch panels.

These patch panels are in turn connected to regular cross-connect fields, which means a total of three connections in the equipment room/telecommunications closet.

Other reasons for three connections near the work area is to allow additional flexibility when disconnecting work area panels for re-arrangement. The additional connector would be located where an individual work area panel is joined to the furniture distribution pathway. The consolidation point will be at the other end of the distribution pathway for a total of three connections (consolidation point connection, furniture distribution pathway connection, and telecommunications outlet connection).

Cabling Selection
By choosing UTP and fiber optics as the media for the cabling solution, support for the widest range of architectures is possible in the most effective manner.

For many users, a combination of advanced UTP cable and multimode/singlemode fiber is the best choice. Both support a wide variety of applications, are specified as media for emerging high speed LANs, and meet the specifications for virtually all cabling standards.

In the past, copper was ideally suited to lower speed applications while fiber was best used for high speed, longer distance, and security-dependent applications. Today, high quality twisted pair copper and fiber optic cabling system infrastructures overlap in capability up to Gbps data rates.

To the Desk-Copper or Fiber?
Network providers are often faced with the question of whether to install an unshielded twisted pair (UTP) copper or multimode fiber cabling system to the desktop.

Unfortunately, there is not a clearly defined answer to this question. Most private networks require a mixture of both media to create the most cost-effective networks for voice and data across the horizontal and backbone segments of the network. High performance category 5e and 6 UTP provide the lowest initial cost for today's LANs up to rates of 1Gbps.

Fiber-based networks can reduce recurring operational charges and clearly have higher performance. However, with the introduction of newer Category 6 systems, the capabilities of UTP cabling have been substantially increased, pushing out the move to fiber to the desk top.

Time to Plan
In order to determine which combination of twisted pair and/or fiber to install and in which architecture, each customer must evaluate their application needs, considering the various advantages of each cable type and their relative importance.

Cost, ease of installation, moves and arrangements, current and anticipated applications, and the expected life of the system are typically major decision factors. Environmental considerations such as electrical noise and clean rooms may also influence the decision, as well as building type, industry sector, and cabling system ownership.

The anticipated need for low-speed applications, short system lifetimes, and low initial cost might lead to a predominantly twisted pair cabling system. High-speed application, extended distances, harsh environmental conditions, and graphics intensive multimedia applications might lead to a heavily fiber based system. Most systems will fall between these two extremes.

Given that there is some overlap in the customer base and capabilities for Category 5, 5e, and 6 cabling and multimode/singlemode fiber optic cabling system infrastructures, an understanding of the customer's specific requirements is needed to recommend the optimal cabling solution.

The decision will incorporate three phases-the definition of strategy, the design of the system, and the cost effectiveness of the choice.

Customers need to be careful that in selecting a solution today, they do not limit themselves in the future. With advanced twisted pair and multimode fiber cable, connectors, and apparatus, users can easily support all of their current applications, as well as their emerging and future applications.

Prasanna Kumar V sales director Systimax Solutions-India and Saarc