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STRUCTURED CABLING: Plan a Mesh, sans Mess

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VoicenData Bureau
New Update

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.

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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.

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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.

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Planning

and Strategizing

Each customer

must consider and prioritize the following:

  • The

    sophistication of their network applications

  • The kind of

    traffic expected on the various portions of the network based on

    number of users, data transfer requirements of each user, LAN

    architecture, etc.

  • The life

    expectancy of the network and cabling infrastructure

  • The frequency

    of moves and changes

  • The growth

    potential of their network over its expected life

  • Any adverse physical conditions

    in the customer's LAN

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).

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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.

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Design Considerations

The design, architecture and specification of the system should include the following:

  • Outlet density and presentation required 
  • Resilience 
  • Patch/jumper density 
  • Wiring closet/space requirements 
  • Media selection - UTP and /or fiber 
  • Media considerations - performance, physical hazards 
  • Manufacturers support and warranty 
  • Cable containment including containment types (trunking, ducts, cable tray), and containment design (size, safety, segregation) 
  • Installation techniques and quality 
  • Adherence to standards 
  • Labeling, records, and documentation 
  • Testing and certification 
  • Maintenance and services

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.

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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.

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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.

Balancing Costs and Benefits

When evaluating cost effectiveness, the customer should always think in terms of cost over the life of the cabling, rather than only the initial installation cost and also compare the cost to electronic hardware, which will be replaced several times over the lifetime of the cabling. The lowest initial cost is not always the cheapest in the long run, however once the contract is placed it is difficult to change. Choose the right system first time. Considering cost effectiveness should include the following:

  • Initial installation cost, ensuring it covers adequately the specification to avoid unwanted extras and performance restrictions 
  • Administration, the networks ability to be easily and inexpensively reconfigured 
  • Futureproofing, the ability to support ever increasing bandwidth and data rates in the future 
  • Maintenance, the effort required to keep the system operating 
  • Life cycle value, the assurance of a warranty covering the applications and hardware

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

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