Issue link: https://www.e-digitaleditions.com/i/1066130
January/February 2019 I 27 Decentralized - Fixture Centric Pros Cons TABLE 4: Pros and cons of the decentralized-fixture centric architecture. • Reduced Day 1 cabling CAPEX • Minimal connections • Limited to 10/100 Mb/s • Requires AC power at remote switches • Difficult to administer • Limited support of MAC activity • Limited support of future IB applications • Limited use of structured cabling • Network security access is compromised • Additional connection point FIGURE 11: Decentralized-fixture centric architecture. model, a digital building switch is placed between the TR and the nodes and devices to provide the processing power closer to the end device. This works well for LED lighting, but it is limited in bandwidth so may not be suitable for WAPs or high-resolution security cameras. In addition, these digital building switches require an AC outlet. A zone cabling topology can be utilized with either a centralized or decentralized set up and offers the greatest flexibility for adding more devices later, which becomes key when installing cabling infrastructures to last into the future. There are pros and cons to each scenario (see Tables 2-4), and the system designer needs to weigh each to select the layout that best suits the environment and growing needs of the end user. "One of the biggest challenges is for the low-voltage installer to understand these different architectures because it varies between device manufacturers, as there are no device standards like there are for the network infrastructure," states Luis Suau. "For example, looking at LED lighting, one manufacturer might use category cabling directly to the fixture with an RJ45 connection or plug, whereas others have their own unique layouts to a node, or a driver," Suau further explains. "In these layouts, they are using structured cabling to the node or driver and then delivering power and serial data through an 18/2 cable [18 AWG, two-conductor cable] that can be daisy chained to control devices, such as the lights and sensors and other fixtures," he adds. "And, most importantly, the installers will need to understand how to set up the power source equipment, the switch." "The number of total devices powered by the node is determined by the amount of power from the port. With 60 W at the PSE we could power up to 9 devices. The node has 2 outputs for lighting and each can power three lights daisy chained via RJ45 connection for a total of six fixtures. The third output for controls can power up to three different control devices," states Wendell Strong, GENISYS PoE lighting manager. "Since 'node centric' is different from fixture centric designs, it's very important that the installer rely on the device manufacturer for help in the design and installation," he adds. WHERE'S THE BEEF? "When we are talking lighting, HVAC and other building applications that were previously installed by electricians, who makes the decision for the installation when PoE is involved?" asks Alan Hill, president of Tera Bridge, who has been involved in many intelligent building designs and installations. "Since we are basically a design/build integration company, we are involved up front to show end users and architects the value of integrating power and data. Showing real OPEX and CAPEX savings and