Drive Goblins out of Your Converged Network

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Trick or Treat: What's in QoS for Whom?

There are multiple benefits to implementing QoS. The quality of voice and video transmissions improves and, on the back end, QoS allows administrators to control network resources and monitor traffic to ensure critical applications receive appropriate service.

All of that, of course, makes it less daunting to adopt convergence technologies which can deliver ghoulish savings:

-- Users at different sites can make extension-to-extension calls over the existing data network rather than requiring additional land lines.

-- Businesses can implement 64-party audioconferencing bridges that save hundreds of dollars a month on conference-call services.

-- Session Initiation Protocol trunks can cut phone bills by as much as half by connecting the phone system to traditional telephone lines via the Internet over a data T1 line, reducing the use of voice T1 lines and associated costs.

What's more, with QoS, teleworkers can use a IP phone from their home office over a VPN link, making it possible for them to handle calls as if they were in the corporate office, increasing their accessibility. "Softphones" -- software on laptops -- with QoS also are an excellent option for employees who travel frequently, because they allow remote users to call extensions at the main office for free via their computer.

That's not to say that QoS is without challenges. QoS tools can relieve network congestion, but sometimes there is just too much traffic for the given bandwidth. To ensure quality, bandwidth must be high enough to support latency of 150 milliseconds or less.

Switch failure is also a concern for businesses that use IP phones with dual-port switches to connect the phone and a computer through a single drop, applying QoS to route voice traffic ahead of data traffic. If the two-port switch fails, the phone and the computer both lose connectivity. Likewise, users will lose connectivity if the LAN switch fails. Recovery systems must be in place to get the network back up and running as quickly as possible. Many businesses operate a POTS (plain old telephone service) line to maintain some access during these times, and some businesses avoid the potential challenge altogether by implementing a LAN for each type of device, though this option is more costly.

Queue overflow -- when the number of incoming packets exceeds the rate at which the network can process them -- can also be a challenge because a full queue cannot receive any additional packets and will drop those that arrive last, regardless of their priority level. This condition usually happens when voice packets are not prioritized ahead of data packets or QoS is not implemented correctly, causing jitter and echo. Network administrators should implement congestion avoidance tools, such as virtual LANs, so voice packets receive greater priority and the queue does not fill up. They also should establish mechanisms that drop low-priority packets first.

Finally, here are a few suggestions about getting the most out of your network with QoS:

-- Determine if QoS is right for you by weighing the benefits to the network applications against the cost of implementing QoS.

-- Assess network traffic to determine which applications are most critical to the business and which require the most bandwidth and availability. Failure to conduct a network assessment is the most common mistake and can lead to significant expenditures to correct configurations.

-- Select a vendor that provides training and guidance for the implementation process, as well as a reputable managed-services provider if the business does not have an in-house IT professional.

-- Establish minimum requirements for: bandwidth among multiple office sites; availability of service for priority applications; traffic-management performance -- typically a latency of 150 milliseconds or less; and the user experience and satisfaction with the performance of the phone system -- there should be crystal-clear sound without jitters, drops or echo.

-- Assess the results to verify that the service is performing at the desired level.

QoS is at the leading edge of network management, and is necessary for the optimum performance of networked applications. Remember, however, that managing QoS is an ongoing process because application and network demands change constantly. If you install QoS tools to optimize network infrastructure and improve the performance of bandwidth- and data-intensive applications, you'll have to actively manage the complete system; but the network and those it supports will be the better for it.

This story, "Drive Goblins out of Your Converged Network" was originally published by Network World.

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