by Brad Amano, Business Development Manager, Eaton Corporation
With the adoption of Power over Ethernet (PoE) there is a change in the way we think about powering network components. At the same time, new network applications and devices are adapting to and greatly benefiting from the latest technology advancements.
For example, an IP telephone can be powered by a PoE midspan, PoE endspan or an AC adapter. In environments where an existing Ethernet switch has been previously installed and is providing VolP Quality of Service (QoS) capabilities, there is no need to purchase and install a new switch to provide PoE functionality. ln this case, the simplest means to power the IP phones over the LAN infrastructure is to add an external PoE midspan. By doing so, the user can realize savings on installation costs and preservation of existing infrastructure while supporting pre-standard and IEEE 802.3af standard terminals.
PoE endspan products are readily available; however, some are not IEEE 802.3af compliant which may cause it to be incompatible with certain types of equipment. Powering IP phones through an AC adapter has significant drawbacks as it is more cumbersome with two cables – data and power – needed on each user’s desk. Additionally, any utility outage, unless the user is equipped with a local UPS, will result in the unavailability of the phone.
The level of power typically consumed in a communication room with PoE capabilities is approximately 400 percent of that consumed by networks without it. For example, a typical 24-port Ethernet switch consumes an average of 100 watts whereas a simple installation of a switch providing a power solution to 24 IP phones requires powering backup in the range of 400 watts.
More specifically, the PoE standard specifies up to 15 watts per attached device, while the typical PoE-compatible terminals consume in the range of three to five watts for IP phones, six to 10 for wireless access points, and nine to 12 for IP cameras.
In a typical communication room, eight stackable Ethernet switches are installed, providing service to 192 users. The power backup requirements can be fulfilled with a UPS of 1.5k watts. However, to achieve the same level of reliability in a converged voice environment with PoE, the UPS backup systems should be in the range of 6 kilowatts.
To calculate the exact amount of power being used in a PoE environment with a view to reducing costs by right-sizing the appropriate UPS, it is important to figure the exact amount of power consumed by the IP phones. This can be done using an SNMP midspan product which provides telemetry of the device’s power consumption. With this information a user can calculate the exact amount of power consumed by the network in case of power failure and adapt the UPS size accordingly.
Contact the author at bradamano@eaton.com.
© 2008 Telecom Reseller. All Rights Reserved.