www.tripplite.com
Practical Power Guidelines for VoIP and Internet Telephony Applications
by David Slotten
WHITE
PAPER
Cisco, Cisco Systems, the Cisco Systems logo, and the Cisco Square Bridge logo
are registered trademarks or trademarks of Cisco Systems, Inc. and/or its affiliates 95-2914 in the U.S. and certain other countries.
Integrate Backup Power into VoIP Networks
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 circuitswitched 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.”
Source: Cisco Systems white paper “The Transition to IP Telephony at Cisco Systems”.
http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800cb7fd.shtml
© 2008 TRIPP LITE. ALL RIGHTS RESERVED. THE POLICY OF TRIPP LITE IS ONE OF CONTINUOUS IMPROVEMENT. |
2 |
SPECIFICATIONS ARE SUBJECT TO CHANGE WITHOUT NOTICE.
ALL TRADEMARKS ARE THE PROPERTY OF THEIR RESPECTIVE OWNERS.
Consider the Diverse Needs of VoIP Network Equipment
Typical VoIP
Network Design
Source: Cisco Systems white paper “Power and Cooling for VoIP and IP Telephony Applications”.
http://www.cisco.com/application/pdf/en/ us/guest/netsol/ns412/c654/cdccont_ 0900aecd801a2c5f.pdf
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.
If they plug into a local AC source, they must be protected by a UPS System. Often a desktop UPS not only safeguards phone service, but also guarantees file integrity for associated PC users.
Networking Devices (switches, routers, etc.)
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.
Generally, an existing UPS will be inadequate to (a) power the increased load [watts] and (b) power the load for an acceptable length of time. Five to fifteen minutes of runtime provided to gracefully shut down the typical data network is inadequate for IP telephony users who expect phone service to continue for HOURS, not minutes.
Call Processing Devices (servers and related storage systems)
During the transition to IP telephony, dedicated servers are typically added to drive voice and messaging applications, while storage systems are required for voicemail and other messaging applications. Similar to the increased burden placed on networking devices, call processing devices will experience increased loads and will require increased runtime.
© 2008 TRIPP LITE. ALL RIGHTS RESERVED. THE POLICY OF TRIPP LITE IS ONE OF CONTINUOUS IMPROVEMENT. |
3 |
SPECIFICATIONS ARE SUBJECT TO CHANGE WITHOUT NOTICE.
ALL TRADEMARKS ARE THE PROPERTY OF THEIR RESPECTIVE OWNERS.
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 use the term “wall” to describe this source), from a single UPS System or from multiple UPS Systems.
The following tables detail a switch's operational status, from a power perspective, in both redundant and combined (non-redundant) modes. The tables detail switch status under a variety of operational scenarios, including power supply failure, utility failure and UPS System failure.
Note: Larger switches often have the capability to be alternatively configured to operate in a combined (non-redundant) configuration. In combined mode, two power supplies' capacities will be summed. A true doubling is not generally achieved. A factor of 1.67x is typical. In combined mode, there is no redundancy. Should a power supply fail, the available power is generally reduced to the capacity of a single power supply.
© 2008 TRIPP LITE. ALL RIGHTS RESERVED. THE POLICY OF TRIPP LITE IS ONE OF CONTINUOUS IMPROVEMENT. |
4 |
SPECIFICATIONS ARE SUBJECT TO CHANGE WITHOUT NOTICE.
ALL TRADEMARKS ARE THE PROPERTY OF THEIR RESPECTIVE OWNERS.
Single Power Supply, or Multiple Power Supplies Operating in Redundant Mode
STEP 1: Determine Configuration |
|
|
|
|
|
|
|
|
|||
|
|
Configuration |
|
1 |
|
2 |
|
3 |
4 |
|
5 |
|
|
Power Supply |
|
PS1 |
PS1 |
PS2 |
PS1 |
PS2 |
PS1 & PS2 |
PS1 |
PS2 |
|
|
Power Source |
|
Wall |
Wall |
Wall |
UPS1 |
Wall |
UPS1 |
UPS1 |
UPS2 |
|
|
|
|
|
|
|
|
|
|
|
|
STEP 2: Consider Failure Scenarios |
|
STEP 3: Consider System Status |
|
|
|
|
|||||
PS1 Status |
Utility Status |
UPS Status |
|
System Status |
System Status |
System Status |
System Status |
System Status |
|||
OK |
OK |
OK |
|
OK |
|
OK |
|
OK |
OK |
|
OK |
Failure |
OK |
OK |
|
Crash |
|
OK |
|
OK |
Crash |
|
OK |
OK |
Blackout |
OK |
|
Crash |
Crash |
|
OK |
OK |
|
OK |
|
OK |
Blackout |
UPS1 Battery |
|
Crash |
Crash |
|
Crash |
Crash |
|
OK |
|
|
|
Fails |
|
|
|
|
|
|
|
|
|
OK |
Blackout |
UPS1 Internal |
|
Crash |
Crash |
|
Crash |
Crash |
|
OK |
|
|
|
Fault |
|
|
|
|
|
|
|
|
|
OK |
OK |
UPS1 Battery |
|
— |
|
— |
|
OK |
OK |
|
OK |
|
|
Fails |
|
|
|
|
Hot swap battery |
Hot swap battery |
Hot swap battery |
||
OK |
OK |
UPS1 Internal |
|
— |
|
— |
Line-Interactive UPS Systems |
|
|
||
|
|
|
OK |
Crash |
|
OK |
|||||
|
|
Fault |
|
|
|
|
Replace UPS. |
Replace UPS. |
Replace UPS. |
||
|
|
|
|
|
|
|
System on PS2/Wall. |
|
System on PS2/UPS2. |
||
|
|
|
|
|
|
|
Vulnerable to outage |
|
Services OK during |
||
|
|
|
|
|
|
|
during UPS |
|
UPS replacement |
||
|
|
|
|
|
|
|
replacement |
|
|
|
|
|
|
|
|
|
|
|
On-Line UPS Systems |
|
|
||
|
|
|
|
|
|
|
|
OK |
OK |
|
OK |
|
|
|
|
|
|
|
UPS on bypass, |
UPS on bypass. |
UPS on bypass, |
||
|
|
|
|
|
|
|
System on PS2/Wall. |
System on Wall. |
System on PS2/UPS2. |
||
|
|
|
|
|
|
|
Replace UPS1. |
Services down* |
Replace UPS1. |
||
|
|
|
|
|
|
|
Vulnerable to |
while replacing |
Services OK during |
||
|
|
|
|
|
|
|
outage during UPS |
UPS1 |
UPS replacement |
||
|
|
|
|
|
|
|
replacement |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
*SmartOnline Hot-Swappable Modular 5-16KVA UPS system hardware can be hot swapped without service outage.
Multiple Power Supplies Operating in Dual (Combined, Non-Redundant) Mode
STEP 1: Determine Configuration |
|
|
|
|
|
|
||
|
|
Configuration |
|
1 |
2 |
|
|
3 |
|
|
Power Supply |
PS1 |
PS2 |
PS1 |
PS2 |
PS1 |
PS2 |
|
|
Power Source |
Wall |
Wall |
UPS1 |
|
UPS1 |
UPS2 |
|
|
|
|
|
|
|
|
|
STEP 2: Consider Failure Scenarios |
STEP 3: Consider System Status |
|
|
|
||||
PS1 Status |
Utility Status |
UPS Status |
System Status |
System Status |
|
|
System Status |
|
OK |
OK |
OK |
|
OK |
OK |
|
|
OK |
Failure |
OK |
OK |
Reduced Output |
OK |
|
|
OK |
|
OK |
Blackout |
OK |
|
Crash |
OK |
|
|
OK |
OK |
Blackout |
UPS1 Battery |
|
Crash |
Crash |
|
|
Reduced Output |
|
|
Fails |
|
|
Replace UPS1. |
|
|
Replace UPS1. |
|
|
|
|
|
Output reduced during UPS |
Output reduced during UPS |
||
|
|
|
|
|
replacement |
|
|
replacement |
OK |
Blackout |
UPS1 Internal |
|
— |
Crash |
|
|
Reduced Output |
|
|
Fault |
|
|
Replace UPS1 |
|
Replace UPS1. Output reduced |
|
|
|
|
|
|
|
|
until UPS1 replacement |
|
OK |
OK |
UPS1 Battery |
|
— |
OK |
|
|
OK |
|
|
Fails |
|
|
Hot swap battery |
|
|
Hot swap battery |
OK |
OK |
UPS1 Internal |
|
— |
Line-Interactive UPS Systems |
|
|
|
|
Crash |
|
|
Reduced Output |
||||
|
|
Fault |
|
|
Replace UPS. Plug into wall until |
Replace UPS1. Plug PS1 into wall |
||
|
|
|
|
|
UPS replacement |
|
to restore full power until UPS1 |
|
|
|
|
|
|
|
|
replacement. Output reduced |
|
|
|
|
|
|
|
|
until UPS1 replacement |
|
|
|
|
|
|
On-Line UPS Systems |
|
|
|
|
|
|
|
|
OK |
|
|
OK |
|
|
|
|
|
Replace UPS1. |
|
|
Replace UPS1. |
|
|
|
|
|
Both PS on UPS Bypass. |
PS1 on UPS1 Bypass circuit, |
||
|
|
|
|
|
Services down* while replacing |
vulnerable to outage. Reduced |
||
|
|
|
|
|
UPS1 |
|
power during UPS1 replacement |
|
|
|
|
|
|
|
|
|
|
*SmartOnline Hot-Swappable Modular 5-16KVA UPS system hardware can be hot swapped without service outage.
© 2008 TRIPP LITE. ALL RIGHTS RESERVED. THE POLICY OF TRIPP LITE IS ONE OF CONTINUOUS IMPROVEMENT. |
5 |
SPECIFICATIONS ARE SUBJECT TO CHANGE WITHOUT NOTICE.
ALL TRADEMARKS ARE THE PROPERTY OF THEIR RESPECTIVE OWNERS.