Centralized fiber-based architecture improves operations and lowers costs

Aug 1st, 1996

Centralized fiber-based architecture improves operations and lowers costs

The installation of an all-fiber-optic network in a single-tenant building contributes to the centralization of all network electronics, such as bridges, hubs, routers and switches, in one electronics closet, thereby decreasing network costs and upgrading network management

n. d?arcy roche

amp inc.

As local area networks (LANs) become larger and more complex, corporations are seeking ways to reduce the escalating costs associated with cabling, equipment, management and maintenance. An increasingly cost-efficient solution is to install an all-fiber-optic network and to put all the network electronics, such as routers, bridges, hubs and switches, into a single equipment closet within a single-tenant building.

Although there is a 90-meter limit on Category 5 copper cable runs, optical fiber can support high-speed LAN applications over cable lengths to 300 meters. Rather than having to distribute electronics in multiple communications closets close to user workstations, as is done for copper-based networks, optical fiber enables the installation of one centrally located electronics closet. This centralized approach to network design simplifies network operations cost and management--including user and workstation moves, adds and changes--and simplifies maintenance and testing.

Key factors in making a centralized network architecture feasible are new fiber-optic products specifically designed for fiber-to-the-desktop networks. These products help reduce the premium cost over copper for an initial network installation to about $16 for a typical data link, or drop, distance of 150 feet (see Table 1). They include all the necessary passive components, such as optical cables, connectors, outlets and patch panels, and required LAN electronics and patch cords.

Forrester Research, a Cambridge, MA-based technology research consultancy, concludes that the average corporation spends more on ongoing management and maintenance of a network than on the initial installation. Indeed, over the lifetime of a network, fiber-optic cables and parts provide important cost savings compared to traditional copper installations. In fact, network users can realize savings of as much as $175 per drop after the first year, based on lower network-management overhead and fewer equipment outages, and a realistic savings of more than $620 over five years (see figure).

Network challenges

Enterprise networks are undergoing radical changes and posing new business challenges as they are being expanded rapidly to support increasingly mission-critical operations. Corporate, medical, educational and government institutions are adding users to their networks at an escalating rate, while adopting new applications such as electronic messaging, work groups and intranets. The result is an unprecedented burden on the network computing infrastructure (see Table 2). At the same time, information system managers are confronted with supporting these networks, while restrained by tighter budgets and limited resources.

A novel network approach is, therefore, needed to minimize management overhead and optimize expensive equipment electronics. Reflecting this trend toward consolidating network servers into fewer, more-powerful hardware platforms, the centralized approach overcomes problems related to equipment outages and underutilization of distributed LAN electronics.

Equipment centralization is made feasible by the increasing availability of cost-effective fiber-optic cabling and components. Fiber cables permit longer passive links between the network electronics and user workstations, thereby facilitating centralized network administration. For example, 62.5-micron optical-fiber cable can support high-speed LAN applications over cable lengths to 300 meters. On the other hand, Category 5 un shielded twisted-pair (UTP) copper-wire networks are restricted to a 90-meter length limit on cable runs between the electronics and workstations. This copper constraint typically necessitates the distribution of electronics in multiple communications closets near the workstations, resulting in an expensive installation.

Traditionally, fiber has carried a cost premium compared to copper, but recent advances in fiber technology have resulted in near price parity with copper for initial installation. More important, fiber-optic cable installation can save network lifetime costs. To determine these network lifetime costs, material and labor cost factors must be included, such as:

Component costs, such as cables, wall outlets, patch panels and connectors

Labor costs for installing and testing the system

Electronics costs for routers, hubs, switches and network interface cards

Management costs associated with adds, moves and changes

Downtime costs related to lost user productivity

Scaling costs to accommodate higher-bandwidth technologies.

The important savings, however, come from the need for fewer network components. Being able to emplace all the LAN electronics in one central equipment room effectively reduces the number of ports and chassis needed throughout the network. The actual savings from equipment utilization depends mainly on the number of users per closet, number of closets and port size of the electronics. Centralized fiber-optic networks work more economically in a single building, preferably user-owned or long-term leased.

However, entrepreneur building owners or third-party network companies that provide both cabling and networking solutions may also find centralized fiber networks economical. The building should still contain telecommunications closets on each floor. These closets, however, are now passive, housing only splices and interconnects.

To illustrate the possible network cost savings, consider a building that contains six telecommunications closets and 72 users per closet for distributed electronics. Also assume a 24-port hub, such as an Ethernet stackable hub. Based strictly on mathematical probabilities, the distributed electronics would furnish a mean probability of 70% utilization.

Alternatively, assume that the same building has 432 users served by a centralized room for network electronics. This centralized architecture would provide a mean probability of 90% equipment utilization. The 20% difference in equipment utilization equates to a savings of $30 per user, based on system costs of $150 per user. Adding the converging pricing for fiber and copper electronics to the 20% savings further decreases the overall cost of electronics equipment.

The real costs, however, arise after initial equipment and installation. The initial cost of a copper-based LAN installation represents only a fraction of the overall network cost. Forrester Research states that the average corporation spends $280 per user for physical LAN support and $110 per user for bridge/router support. Losses for network outages run about $160 per user per year. The resulting annual operating cost is about $550 per user. Operating and lifetime network costs far outweigh the initial costs of installation and offer the greatest potential for savings.

To estimate the possible savings, assume that 25% efficiency can be gained in LAN support through a centralized fiber-optic network administration. Also assume that 15% of the network problems relate to copper cable and that the use of fiber solves 80% of the problems. Applying these numbers means the centralized fiber network would incur a total annual operating cost of $375 per user, versus the noncentralized copper-based network cost of $550. The difference translates to an annual savings of $175 per user, or a typical payback of the associated premium--cabling and electronics--by the end of the first year of network operation.

Network flexibility

Another benefit of centralized network administration is the simplicity, flexibility and cost-effectiveness of arranging special work group networks on short notice. New groupware applications are letting users communicate with each other as part of a work group, even when the users are at different locations throughout a building. Terminating the network`s horizontal fiber-optic cables for each work group user in one centralized communications room brings the required electronics and interconnectivity directly to the work group. Such networks are often impossible or difficult to configure with a distributed network architecture.

Centralized optical-fiber cabling can also be implemented in zone network architectures such as those used for open-plan offices, which are often structured from movable wall panels and modular furniture. When the panels are moved and the layout is changed to accommodate new employees or departmental reorganization, the cabling and outlets generally have to be moved.

These changes can be simplified through use of centralized optical-fiber cabling. In practice, the office is prewired by area and anticipated user density rather than by individual outlets. The floor plan is divided into zones by area or number of users. A concentrated bundle of fiber-optic communications cables is pulled from the closet to a single, fixed distribution point within the zone. Individual fiber-cable runs are then connected from the distribution point to each office outlet or directly to the equipment within each office. In this case, the horizontal distribution cable used would typically be 12- to 24-fiber versus the normal 2- or 4-fiber cable for single-user cabling. By using a splice or interconnect option, the backbone cable remains the same, and the installer splices the multiuser cable to the feeder or backbone cable.

Related standards

The Fiber Optic Task Group of TR 41.8.1, the working subcommittee responsible for the TIA/EIA-568A commercial building telecommunications cabling standard, has balloted Centralized Optical Fiber Cabling Guidelines for potential publication as an official document. This draft, referred to as PN-3523, provides recommendations for the proper implementation of this modified centralized cabling topology in support of optical-fiber cabling and fiber-to-the-desk networks within buildings. The draft resulted from nine months of discussions within the task group, which was represented by manufacturers, consultants and contractors. u

N. D`Arcy Roche is vice president and general manager of premises systems and services at AMP Inc., Harrisburg, PA.

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