From the July, 2015 Issue of Cabling Installation & Maintenance Magazine
POLs are deployed in several healthcare facilities, including hospitals and continuing-care communities, where they support mission- and life-critical networks.
By Alan Bertsch, Association for Passive Optical LAN
Passive optical LAN (POL) is the application of passive optical network (PON) technology in a local area network (LAN) environment. While PONs were originally created to provide fiber-to-the-home or fiber-to-the-premises, their advantages soon became apparent in end-user access applications and they evolved into the fiber-to-the-desktop solutions in use today. There are many benefits derived from POL's advantages, and they have different significance in several different vertical applications. The purpose of this article is to outline the application of POL in healthcare environments.
POL characteristics
To understand the benefits of POL it is helpful to recognize its basic design and characteristics. The topology is point-to-multipoint using singlemode fiber (SMF) as the cabling infrastructure, thus delivering the advantages of distance and density. The central component is an optical line terminal (OLT) that functions as a fiber aggregation switch and provides full Layer 2 functionality. The optical network terminals (ONTs) are the edge devices that convert the SMF handoff to the copper-based connectivity required by the end-user devices. Different models of ONTs are available with a multitude of connection options. Gigabit Ethernet (RJ-45), with or without Power over Ethernet (PoE); POTS (RJ-11), and RF video (F-type-connector) are the most common interfaces. The OLT and ONTs make up all of the active components.
POL provides flexible mounting, powering, and PoE options for healthcare environments. The ONT mounting can be accomplished with freestanding, above- or below-desk and wall-mounted positioning. The ONT powering can be served with both local and remote powering options that can include battery backup for critical services. As stated in the preceding paragraph, these ONTs can deliver PoE (15W) and PoE+ (30W) power down to the sub-tended powered devices.
The passive infrastructure comprises SMF, passive optical splitters, and the cable management accessories used to house the splitters and distribute the fiber. The splitters are the centerpiece of the passive portion of a POL, and are manufactured with many different split and housing options. Split configurations of 1x16 and 1x32 are the most common, but other ratios such as 1x2, 1x4, and 1x8 can be used to cascade splits and create a zoned approach to the fiber infrastructure. Additionally, 2xN splitters are available to take advantage of PON redundancy, known as Type-B PON protection, wherein two separate PON ports on an OLT feed a 2xN splitter, to guard against optics, card, or fiber failure.
The convergence of the passive and active components into a turnkey solution differentiates POL from legacy point-to-point copper-based LAN in a number of ways. Fundamentally, POL moves the Ethernet edge out of a closet and closer to the end-user devices. This topology creates a large LAN footprint, reduces telecom closet expenses such as power and cooling, reduces space requirements, reduces overall cable load, and simplifies operation by centralizing LAN management. Comparing the configurations of a legacy copper-based LAN and a POL (previous page) helps to illustrate more clearly the similarities and differences.
The power of fiber optics
While you will find all of your typical network protocol support in a POL (e.g. multiple VLAN support, 802.1x port security, access control list support, RSTP loopback detection and prevention, Link Aggregation Control Protocol/Link Aggregation Group support), a great deal of the benefit of a POL network is derived from the use of fiber-optic cable.
Traditional copper-based LANs have a distance limitation of 100 meters because of the performance characteristics of copper category cabling (Cat x) being used today. This limitation restricts deployment options as end-user devices must be placed within 100 meters of the nearest network switches/telecom closet. The use of SMF in a POL creates a LAN footprint of 20 kilometers and allows multi-story buildings, multiple buildings, or even an entire campus to function as a LAN on just one OLT. This approach eliminates the need for the aggregated network switches and their pricy environmental support.
Evolutions in the design and manufacturing of SMF have given rise to innovations such as bend-insensitive fiber, multi-strand fiber assemblies, armored cable assemblies, preterminated assemblies, and quick mechanical and fusion splice options. SMF cabling is thinner, lighter, more flexible, more crush-resistant, and has a greater tensile strength than copper category cabling. Resistance to corrosion and to electromagnetic interference have made fiber optics the preferred cabling infrastructure in modern networks. There has been a clear progression in the use of SMF as a backhaul infrastructure, to a metro area infrastructure, to premises connectivity, to vertical cabling applications, and now to the horizontal cabling solution.
With all of these benefits, the single greatest attribute is its bandwidth capability, which has been described as limitless. Indeed, this was a primary factor in the development of PONs for telecommunications providers. There is enough potential bandwidth available in the SMF cabling used in POLs today to support the next five generations of LAN speeds. As we look forward and progress through 10 Gbits/sec, 40 Gbits/sec, 100 Gbits/sec, 1 Tbit/sec, or even 10 Tbits/sec, there is enough capacity available in the SMF infrastructure being installed today to support those speeds by simply changing network hardware.
Healthcare-network challenges
There are a great many challenges in healthcare in general, and most seem to have a direct impact on network resources. Electronic medical records (EMR), computerized physician order entries (CPOE), and mobile electronic health records (mEHR) are all point-of-care practices driving the need for more robust and secure networks. The Healthcare Insurance Portability and Accountability Act (HIPAA) is a vital piece of legislation that protects healthcare coverage for workers and their families, and also led to the establishment of national standards for EMR. Interactive patient care (IPC) is another healthcare development that is driving the convergence of bedside care, patient entertainment, patient education, and patient portal applications. Each of these initiatives is driving sub-industries where companies are lining up to create the best solution, typically without regard for the impacts on adjacent technologies.
The culmination of these industry concerns is placing a heavier burden on a LAN already constrained by the impacts of Voice over IP, high data needs, imaging, picture archiving and communication system (PACS), ubiquitous 802.11-based wireless, and patient triple-play needs (TV, phone, Internet). With all these disparate services come disparate networks, and a massive infrastructure needed to interconnect, provide pathways, power, condition, and maintain these networks. Add to this mixture the hindrances of aging facilities, packed telecom rooms, and restrictions on above-ceiling work, and you can see why it is critically important to design, build, and maintain a healthcare LAN that is designed for the needs of today with the ability to adjust for the future with minimal impact to the facilities.
POL in healthcare
When telecommunications providers started deploying PONs in the mid-1990s, they did so because they were faced with the impending problems associated with the integration of cable television programming, the evolution of voice networks to native IP, and Internet access speeds growing at an exponential rate. The simple answer was to add more copper. That is what they had done for decades when faced with a new service challenge. Unfortunately, these copper networks have limitations on speed, distance, and reliability. Carrier networks had evolved into hybrid fiber/copper networks by expanding their fiber to regional locations; but multiple points of signal regeneration, management, and failure still existed. Expensive maintenance operations were required to address corroding, degrading copper plants and update/upgrade electronics and signal-booster equipment at multiple points from the central office to the end-user locations. PONs let carriers place aggregation switches in their central offices and network terminals at end-user locations with nothing but fiber, splitters, and enclosures in between. The technology allowed them to leverage the fiber cabling to provide all services (TV, phone, Internet) across a single fiber.
The use of POL brings the same advantages to a healthcare facility, and subsequently creates very industry-specific benefits.
The distance advantage of POL will reduce or eliminate most of the telecom closets including racks, grounding, cable trays, sleeves, firestopping and others. Doing away with the closets and local switches frees up valuable space and creates a reduction in power consumption, natively and through the elimination of HVAC or chillers.
The density advantage of a POL will provide multiple horizontal fibers from a single switch port, multiple ports from a single fiber-cable connection, and a 50- to 70-percent reduction in structured cabling. This translates to less stress load on the building and less footprint in plenum ceiling space.
The security advantage of POL comes from SMF being a more-secure medium than copper cabling, and ONTs being inherently secure because they are designed with no local management access.
The future-readiness advantage of using SMF as the structured cabling will provide a greater ROI on the initial capital investment as it extends the lifespan of the cable plant, from 5-7 years to 25-plus years. Additionally, facilitating network upgrades by swapping edge electronics instead of ripping/replacing the cable plant eliminates the requirement for above-ceiling work.
The operational advantage is that large networks are centrally provisioned and managed with all ports across all ONTs appearing as sub-interfaces on a single switch. A lack of susceptibility to electromagnetic interference eliminates the need to shield the infrastructure from imaging systems, and POL operates at 99.999-percent uptime (compared to 99.9 percent for legacy copper-based LAN)--which provides the reliability necessary for protecting critical-care services.
Passive optical LAN started making its mark in enterprise and government applications around 2008. While it is a relatively new application, it is standards-based technology with a solid history of evolution and an equally strong roadmap for future development. To date, it has been deployed in several healthcare facilities, including hospitals and continuing-care retirement communities, where it has been the foundation for mission- and life-critical networks. Passive optical LAN's topology and scalability make it uniquely suited to form the foundation for healthcare's large, converged networks today and into the future.
Alan Bertsch is a director with the Association for Passive Optical LAN (www.apolanglobal.org).