Power over Ethernet -- Ready to Power On? - Page 3

By Debbie Deutsch | Posted May 19, 2003
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Getting Started

At this point, you might be saying to yourself, "All this sounds fantastic! How can I start using this technology?" Introducing Power over Ethernet to your network is trivial. All of the equipment goes into your wiring closet, where the edge switches connect to networked devices. If you are expanding or upgrading your network equipment, you can purchase Ethernet switches or modules that integrate PoE into their 10/100 or 10/100/1000 ports. These ports are said to have "inline power."

Alternatively, you can add power to existing ports using a mid-span insertion device, sometimes alternatively called a mid-span insertion panel or a "power hub." When using a power hub, a patch cable connects the switch port to an input port on the power hub. The matching output port on the power hub is connected to the Powered Device. A Power over Ethernet adaptor is similar to a power hub. It adds PoE capability to a single existing Ethernet port or networked appliance.

When do you use switch ports with inline power, and when do you use a mid-span insertion device? The correct choice depends on how many powered ports you will be deploying and how much flexibility you need or want to locate or move the powered devices. You will also need to work within the space, power, and cooling constraints in your wiring closet. Of course, the biggest factor, as always, will be what your budget can support.

If you will only need to administer a handful of PoE ports in an existing or new wiring closet, a power hub may be the simplest and most cost-effective approach. You pay for PoE only where you need it, and you maintain your investment in your current switches. You have the flexibility to connect one mid-span device to ports on multiple switches. However, using mid-span insertion devices results in having three ports for every one that you would need if you used a switch that integrates PoE on its ports. This means more rack space and higher power requirements. You should take care, for example, by tagging or using color-coded cables when making the connections from switch port to the mid-span insertion device to ensure that the correct connections are made between switch ports and networked devices, and to speed and simplify the process the next time the configuration is changed.

On the other hand, if you plan to support many PoE ports -- or if space, power, or cooling in the wiring closet is at a premium -- purchasing new switch ports with inline PoE may be preferable. Note that due to the limitations of the available power and cooling, not all existing chassis-based switches can support modules with inline power. Similarly, some systems may limit the number of powered ports for the same reasons. Be sure to check the product specifications before purchasing any additional devices.

Your UPS configuration may need to be updated to support Power over Ethernet. You might discover the need to expand your existing UPS capacity or to add UPS capability to wiring closets where it is not currently present. You will want to coordinate UPS configuration with PoE configuration to ensure that power is available to the switches and power hubs where it is most needed. Likewise, you must take care to match configurations of switches and mid-span devices if you are managing power on a port-by-port basis during a power outage.

Vendors are releasing management tools to complement their hardware devices and enterprise solutions. For small PoE deployments, device-level management may be adequate. However, for large installations of Power over Ethernet, such as IP telephony, network managers may prefer a management solution that integrates PoE with the management of the application itself. This approach reduces the total configuration required and eliminates configuration errors due to inconsistency between the application and the network ports. Enterprise solution vendors have a natural advantage over device vendors in this area because they are able to fully integrate the hardware and software.

Page 4: What Is the Catch?

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