POL or Passive Optical LANs for Healthcare Networks
By Alan Bertsch, Association for Passive Optical LAN
POL Deployed in Healthcare Facilities Support Mission and Life-Critical Networks
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. In a number of settings, from data centers to campus environments and into the telecom room, a passive optical LAN employs a configuration far different from that of a copper-based LAN.
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 1×16 and 1×32 are the most common, but other ratios such as 1×2, 1×4, and 1×8 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.