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Voice over IP (VoIP) is exploding in popularity as an application for business data networks. VoIP promises to consolidate a company's data and telecommunications infrastructure as well as its support resources. As a result, a company can lower its hardware and service costs while raising productivity through the use of more elaborate and customizable telephony applications.
Unfortunately, there are serious limitations inherent to the data networks that are increasingly called upon to support VoIP. The primary limitation is power availability. Before moving voice traffic from traditional circuit-switched public phone systems to private data network connections, one must consider a public phone system's unique attribute?battery support. In order to deliver extremely high availability for such vital services as emergency 911 support in the event of extended power outages, public phone systems are connected to massive battery arrays.
While most data networks have some type of backup support during power outages (provided by UPS Systems and/or generators), the backup runtime is generally much less than the 4 to 8 hours of backup that is typically provided for public phone systems. Because of this shortcoming, VoIP applications generally require an increase in the UPS System-supported power capacity (e.g. more or larger UPS Systems). Increased UPS System capacity provides power for network-dependent phones and increases overall backup runtime to ensure that normal telephone operation (including 911 service) remains available in the event of an extended power outage.
Reflecting on important lessons learned during its own transition to IP telephony, Cisco provides several best-practice recommendations. One of the most important recommendations is installing a UPS System to guarantee availability:
?Plan Your Power: When an IP network carries voice, reliability is essential. In case of an emergency, people need to summon assistance by dialing 911. When using inline power to switches and routers, make sure they are connected to an uninterruptible power supply [UPS System] to guarantee dial tone if the power should go out.?
Consider the Diverse Needs of VoIP Network Equipment
Before selecting a UPS System to ensure 100% availability of IP telephony systems, it's important to consider the unique requirements of VoIP network equipment. Network designs hosting VoIP applications will vary widely from business to business due to a number of variables, including the scale of the network and the variety of legacy equipment involved. However, three devices are common to all networks:
Client Devices (phones, PC-based soft phones, etc.)
During the transition to IP telephony, these devices will either (a) derive their power from the network cable via a Power over Ethernet (PoE) connection scheme, or (b) plug into a local AC source.
During the transition to IP telephony, port capacity on the network and in wiring closets will increase to accommodate additional devices (phones) connected to the network. Increased port capacity will increase the power requirements placed on your UPS System, either reducing runtime or overloading the UPS. Note that if a networking device also supplies Power over Ethernet, the aggregate load of all client devices will also be borne by the networking device's UPS System.
Select a UPS System which Provides the Highest Availability, Resiliency and Manageability
When selecting a UPS System, the most obvious criterion to consider is whether a UPS System has enough capacity (VA/watts) to power equipment while having enough battery capacity to operate during a power outage for your required duration. Specific Tripp Lite UPS System recommendations are listed at the end of this document. Often overlooked during the selection process, however, are more subtle, yet critical, criteria that should be considered, including availability, resiliency to power anomalies and manageability.
1. Availability
Availability hinges on three considerations: the VoIP equipment's power supply configuration, the UPS System's battery configuration and the UPS System's power electronics topology.
A. VoIP Equipment Power Supply Configuration
Many switches and routers are equipped with redundant power supply capability. If one power supply fails, a second power supply steps in and powers the device. Redundant power supply configurations are strongly recommended to ensure continuous system availability.
Whether one or two power supplies are deployed, the equipment can draw power from one of three sources: directly from facility power alone (for simplicity's sake we will term this ?wall?), from a single UPS System or from multiple UPS Systems.
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