Anatomy of a distributed network architecture

It's possible to implement a new approach to horizontal fiber distribution and keep standards-compliant.

Jul 1st, 2000
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It's possible to implement a new approach to horizontal fiber distribution and keep standards-compliant.

Jorg Lorscheider and Court Klinck / Holocom Networks
Vic Phillips / Compass Telecommunications Consulting Corp.

Despite continued substantial expenditures on cabling, relatively little attention has been paid to developing new, higher-performance, lower-cost cabling approaches until recently. In the past, the cabling portion of a premises or campus network has often been taken for granted by network designers, information-technology (IT) managers, systems integrators, cabling installers, facilities managers, and others involved in network design, installation, and maintenance. These networking professionals have generally assumed that cabling would be done in the traditional homerun manner: connecting desktop devices to communications equipment rooms-or telecommunications closets (TCs), as they are often called-via individual horizontal copper cables. For several reasons, networking professionals can no longer make this assumption without substantially sacrificing cost and network performance.

Today, networking professionals are, for the first time, carefully examining new cabling approaches such as a fiber-based distributed network architecture.

Technological and market forces

New applications involving dramatic increases in information transfer have created an accelerating need for greater communications bandwidth. Where 10 Mbits/sec was sufficient for most applications a few years ago, today, 100 Mbits/sec or autonegotiating 10/100-Mbit/sec throughput to the desktop is common. Speeds exceeding 100 Mbits/sec have been commonplace in local-area-network (LAN) backbones for some time, and Gigabit Ethernet is currently being implemented in the backbones of many large and medium-sized networks. Currently, network-equipment manufacturers, telecommunications carriers, and large end-user organizations are seriously discussing 10-Gbit/sec service.

As the cost of fiber connectivity continues to decrease, fiber is increasingly being used not only in LAN backbones, but also as a horizontal medium. Because fiber can handle higher speeds over longer distances than twisted-pair copper alternatives, it is ideally suited for these established and developing higher-speed applications.


This work-area enclosure, which is affixed to the top of a modular-furniture system, includes fiber-optic cable and connecting hardware, a wireless LAN access point, media converters, and a network switch.
Click here to enlarge image

With the emergence of high-speed applications, the availability of cost-effective high-performance technologies (such as fiber-optic cabling), new network-switching techniques, and voice/data convergence, several new networking architectures, configurations, and services are also emerging. Among these much-talked-about and soon-to-be widely implemented approaches are Gigabit Ethernet, 11-Mbit/sec wireless LANs, and storage area networks. New equipment types such as voice-over-Internet protocol (IP) gateways, IP telephones, wireless access points and hubs, high-capacity storage devices, and zone-cabling communications products require cost-effective and functionally efficient integration into the network infrastructure.

The open-office-space design, which incorporates the use of modular furniture, is widely deployed within commercial buildings. Modular furniture is created for flexibility and rearrangement. Furniture panels come in all shapes and sizes, are easily configured into work areas, and are grouped into work-area clusters, typically including six to 12 desktops per cluster. When traditional wiring methods are employed in this type of environment, flexibility is inhibited because of the costs associated with rearrangement and reinstallation of homerun cabling from the TC to the work area.

In a traditional homerun cabling environment, when furniture is rearranged, the cabling crew must remove the cabling. After the appropriate crew reconfigures the furniture, the cabling crew then tries to reinstall the existing cabling into the furniture. More often than not, the cabling is not long enough for reinstallation, so the crew installs new cabling from the TC to the work area. This method is an expensive proposition and brings to light the inflexibility of this type of installation strategy. The rate at which the furniture configuration churns varies from one organization to another, but one figure often used estimates a 44% annual churn rate.

Because of the overall increase in workplace technology, employers now expect employees to be more productive. New-technology implementations at the work area in particular allow these employees to meet their employers' productivity expectations. This new technology creates demand for additional bandwidth and throughput to the work area, and the integration of technologies, including voice, data, video, and low-voltage control, further heightens this bandwidth demand.

Fiber-based distributed cabling

The first step in pursuing a high-performing, cost-effective distributed cabling approach is to upgrade from copper to fiber media and extend the fiber backbone wherever practical through efficient work-area enclosures as well as associated switches and other network devices. In an ideal situation, virtually all copper cabling used for data transmission can be replaced with a minimum number of fiber-optic cables. Copper horizontal cabling for voice will still be necessary until some type of voice/data convergence, such as VoIP (voice over IP), is implemented. Once that happens (and VoIP products are rapidily being introduced), fiber cabling will handle both voice and data.

The second step in creating a distributed infrastructure involves moving network devices such as LAN switches and hubs from the TC to enclosures placed directly in or next to work areas. Using this approach to a distributed infrastructure design provides a means to economically route high-bandwidth information to the desktop and facilitate equipment additions and network/workspace reconfigurations.

To provide a standardized approach to distributed network cabling, the work-area enclosure must have sufficient capacity to house a wide variety of network devices, including switches, hubs, wireless access points, and media converters. Holocom, adopting the trade name Virtual Wiring Closet to describe this type of device, is calling its own product the Communications Gateway. Efficient housing of network devices is necessary to optimize the distributed network infrastructure from a price/performance standpoint and provide for a secure and reliable overall network design.

Bandwidth and reliability benefits

Everyone benefits from a fiber-based distributed network architecture. Network designers now have a new approach for bringing bandwidth to the desktop cost-effectively. Facilities managers can realize time and economic savings as they deal with new office installations and reconfigurations. Network engineers and administrators can count on more reliable networks and maintain their networks more easily. Cabling installers can install and reconfigure work areas more efficiently than with the homerun design cited earlier.

By extending the backbone closer to the user, the fiber-based architecture delivers higher bandwidth. Fully redundant high-speed transport implementations like Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH) are possible, potentially providing 2,488 Mbits/sec or more to each workgroup. In addition, extending the backbone to the workgroup and using a workgroup enclosure like the Virtual Wiring Closet significantly reduces the length of the copper cable required to service individual desktop users. This shorter overall length, using stranded patch cords, benefits cabling-system performance.

The distributed architecture also offers increased reliability over traditional homerun cabling. This advantage is further enhanced with the implementation of optical fiber to the work area. As with other architectures in the outside-plant environment, the closer fiber is brought to the user, the more reliable the bandwidth-distribution method. This setup involves fewer connection points than a homerun style and alleviates concerns about electromagnetic or radio-frequency interference. It can also be argued that fiber is less susceptible to poor installation practices than high-performance copper cabling.


Despite the fact that it can hold several pieces of networking equipment, the work-area enclosure does not occupy a large footprint in an open-office cabling environment.
Click here to enlarge image

In a typical open-office setup, there are two patch panels in the TC and multiuser telecommunications outlet assemblies (MUTOAs) or consolidation points (CPs) between the user devices and the network equipment in the TC. The total number of connection points in this arrangement can be as high as six. But in the distributed approach, the backbone is extended to the work area, and there is only one connection between the network equipment-housed in the work-area enclosure-and the user. Even more reliability is possible by distributing the backbone throughout the work areas, building, and campus, then creating fault-tolerant loops or other similar redundant network configurations.

You can easily and reliably relocate network devices from the TC to the work area and house them in work-area enclosures. Today's network switches and hubs are as reliable as or more reliable than other office electronic devices such as personal computers (PCs), fax machines, and printers. Network devices are resistant to power fluctuations and operate at room temperature. Similar to the way you approach PCs, you can employ surge-protection devices and power-supply systems with these network devices if you so choose.

The TIA/EIA-568A Commercial Building Telecommuni-cations Cabling Standard requires the use of stranded patch cords in the work area. Stranded patch cords provide better mechanical performance than solid cable; they are flexible and allow a smaller bend radius than solid cable, which is particularly important in the modular-furniture environment.

Future considerations

The fiber-based distributed architecture is a forward-thinking approach that creates an application-independent infrastructure. By building your premises or campus network-infrastructure solution around work-area enclosures, you can cost-effectively bring fiber to the work area. This approach to network design allows for a future increase in capacity-in terms of more connections and higher speeds to the desktop-without significant recabling or increased cost.

The extended-backbone concept, which uses fiber in conjunction with a work-area enclosure, can support Gigabit backbone speeds. Gigabit-to-the-desk is also possible through proper switch selection and the use of appropriate work-area cables and network interface cards. You can achieve expansion by installing larger work-area enclosures that support more cubicle clusters and desktop devices or by adding work-area data cables from switches in the work-area enclosure. Either way, the distributed approach provides an efficient initial solution and offers flexibility and expandability down the road.

Users can implement this approach regardless of network size. Switches are available in a variety of port sizes and configurations that you can match to your workgroup setup. While the system is going in, you can choose to run spare fiber cables to different areas of the building, anticipating future needs based on usable floor space. Subsequently, it will be easier to add new work areas or expand existing areas. This capability, combined with the extended distances that fiber offers, makes the distributed approach a flexible option.

Economic impact

Because this design concept reduces the number of horizontal cables required by extending the backbone, the result is labor savings related to installation, termination, and testing of horizontal cables. Lifecycle cost savings are dramatic, since having fewer cables to redistribute can achieve desktop changes from an adjacent workgroup switch rather than from a TC, major reconfigurations are easier and less expensive than what you have probably experienced in the past. With the homerun approach, most open-office cabling is thrown away during each reconfiguration. With the distributed approach, virtually nothing is ever thrown away. Technicians can remove fiber-optic and copper cables and coil them in the ceiling during office reconfiguration. Once the clusters are in place, the technicians can bring the fiber down for reuse in the new setup.

The backbone-extension approach, in conjunction with work-area enclosures, either altogether eliminates or at least reduces in size the traditional TC, providing more usable building space. In the case of premises that were built with TCs, when network electronics are moved out, some of the floor space previously dedicated to the network can be reclaimed for general office use. And because the backbone can extend as far as 500 meters, one communications room can serve a larger area than it could if a homerun architecture was in place.

Standards compliance

The proposed distributed network architecture complies with standards covering pathways, spaces, cabling, and termination hardware. Some of the key standards and other documents that relate to premises cabling include:

  • TIA/EIA-568A, which specifies the manufacture, design, and installation of both copper and optical-fiber cabling networks.
  • TIA/EIA-569A, which specifies the design and installation of horizontal and backbone pathways and telecommunications spaces in commercial buildings.
  • TIA/EIA telecommunications systems bulletin TSB-75, which covers the modularization of horizontal cabling that accentuates the flexibility associated with modular-furniture installations and implements MUTOAs and CPs to achieve that purpose.
  • BICSI's (Tampa, FL) Telecommunications Distribution Methods Manual, which explains methodology for designers, architects, and engineers for telecommunications infrastructure inside and outside buildings.
  • The BICS/NECA (Bethesda, MD) Telecommunications Cabling Installation Standard, which covers practices for the installation of wiring, cabling, and termination hardware in commercial buildings.

These documents are widely recognized within the industry as the necessary rules for design and installation to ensure safety, performance, and usability of cabling systems and associated electronics in TCs and work areas. They collectively provide the necessary manufacturing, design, and installation guidelines to ensure customer satisfaction with cabling products and services. When you adhere to these important documents, you will provide a quality installation.

As new technologies emerge and cabling architectures evolve to meet customer needs, changes to existing standards and the creation of new standards will undoubtedly be necessary. However, some truisms will remain constant: Where standards are ignored or violated, performance degrades and the customer suffers. Where standards are adhered to, reliable performance is ensured, and initial and lifecycle costs are significantly reduced.

Jorg Lorscheider is vice president of product development and Court Klinck is director of product marketing at Holocom Networks (Carlsbad, CA). Vic Phillips, RCDD, RTEC, is principal of Compass Telecommunications Consulting Corp. (Florence, SC).

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