Laying the Groundwork for IP Telephony

You've studied the promising return on investment for IP telephony and researched vendor solutions that appear to fit your company's needs. If you've done your homework, you also know that merging voice and data networks into one integrated network is a complex undertaking that requires careful analysis of existing infrastructure. An objective evaluation of network capabilities is essential to any IP telephony implementation for several reasons:

  • Knowing the existing traffic demands on your data and voice networks will help you determine quality-of-service (QoS) requirements and potential increased bandwidth needs for your new IP telephony network.
  • Detecting and resolving underlying network issues, such as bottlenecks or frequent retransmissions of data packets, will clear the path for a smoother implementation.
  • Having an accurate picture of your current network topology points to areas that require improvement prior to implementation, such as rerouting multisite paths to more efficient configurations.
  • Establishing a baseline of existing network performance offers a solid basis of comparison against future expected levels so you know how well you're meeting your technology goals.

Areas Assessed

The success of a new IP telephony implementation depends on the capability of its existing network components. From the data network side, every device that is expected to carry application traffic should be tested and benchmarked, from the WAN to the LAN. These devices include routers, switches, servers, gateways and the virtual private network.

More often than not, these devices are not IP telephony-ready and will require upgrading, modifying or replacing. Testing confirms and validates this need.

This critical first step is to determine what kind of traffic patterns occur throughout the day, as peak utilization times might warrant increased amounts of bandwidth to support IP telephony. Other factors to study are the type of users and traffic, their priority, packet types, application usage and transmission problems. IP telephony is sensitive to time and delay, so the existing network design should also be assessed for ways to make routing more efficient.

Maintaining good voice quality is a key consideration in IP telephony, so it's important to know whether your current communications system and voice gateways can adequately handle the converged network's traffic. To assess this, a voice quality-testing device measures the network's current voice quality. Voice-over-IP (VoIP) traffic is then injected, and measurements are taken again to determine any improvements that must be made to ensure good voice quality in the new converged environment.

Voice Quality

Most users will expect excellent "toll-call" voice quality, even if it occurs through a time-insensitive packet network. Since this is the standard by which IP telephony will be measured, appraising voice parameters such as clarity, delay and echo becomes paramount to maintaining good voice quality in a newly converged network.

Clarity refers to the clearness of a voice signal and how intelligible it sounds to the ear. Many voice quality testers use two algorithms, Perceptual Speech Quality Measurement and Perceptual Analysis Measurement System, to measure clarity of a voice signal after it has been transmitted from a phone.

Delay is the time it takes for a voice signal to travel from the caller to the person called. The concern over time lag is a particular issue for IP telephony, because packet networks introduce additional transactions into a call, including packetization of the voice signal. Routers or switches may also add small amounts of time as well. A properly calibrated network, however, will experience little discernable delay.

Echo refers to the sound of the speaker's voice returning to his ear via the same telephone. In many cases, echo is caused by an electrical mismatch between the trunk line and the phone line. A voice quality tester can measure echo produced through natural or simulated voice signals. Additional testing and analysis will help to isolate the cause.

An IP telephony assessment should also examine the QoS delivered by a network, specifically jitter and packet loss. Jitter, which renders conversations choppy through uneven delays, can become noticeable in an IP telephony network if not detected and controlled before implementation. Likewise, the additional traffic that IP telephony brings may cause routers and switches to drop packets and calls, if not properly addressed beforehand.

The Assessment Process

Some IP telephony assessments focus solely on answering the question: "How well will IP telephony run on my existing network?"

In this scenario, VoIP traffic is injected into the network flow and voice quality is analyzed to see how much improvement needs to be made for the network to run successfully.

While it's beneficial to know what voice quality issues exist with IP telephony prior to implementation, it is equally important to analyze the health of the data network -- since this is the platform on which VoIP will run, and ultimately depend on. Conducting voice quality tests will tell you how much delay you have, but not where network congestion -- a major culprit behind packet loss -- is occurring. Knowing what issues are occurring on the data side is as important as understanding those on the voice side, because each affects the other.

This data network assessment process begins with gathering detailed information about your network infrastructure; such as LAN/WAN protocols in use, IT policies and procedures, targeted service levels and an inventory of affected network devices. Business expectations are also important to note and figure prominently in the subsequent recommendations.

After gathering the information, the network engineer will conduct and document a physical survey of the site(s) to determine whether the physical environment -- cabling, circuits and security -- is helping or hindering the current network in its journey to IP telephony.

Using a protocol analyzer, testing of various network segments for variables such as peak usage, dropped packets and retransmissions provide additional details of the network. Statistical reports are then generated and analyzed for causes of network issues such as congestion or packet retransmissions.

At this point, voice quality tests of the existing voice infrastructure are conducted to establish a baseline against which to measure IP telephony performance. VoIP traffic is then injected in the network flow for measurement and detailed statistical reports are generated for analysis.

Using the combined information collected from interviews, site surveys and test reports, a final assessment report is issued, containing analysis, findings and recommendations, outlining any necessary improvements in network infrastructure that should be made prior to implementation.

An Outsider's Perspective?

The decision to outsource the critical services of a network and IP telephony assessment is an important one. There are many factors to consider, including: Does my staff have the tools and expertise required to perform the assessments? Does my staff understand voice technology? If I want to build the expertise in-house, have I budgeted for the expenses associated with building the expertise?

When making this decision, consider your business requirements, time frame to deploy and internal core competencies. Deploying a successful IP telephony solution for your organization will depend as much on the planning and services you select prior to the implementation as the IP telephony products you choose.

IP telephony offers many benefits because of its ability to consolidate separate voice and data networks. However, before purchasing any hardware, companies should first have an objective evaluation conducted of their existing infrastructure and network performance. The IP telephony assessment provides an effective way to address any underlying network performance or topology issues that could hinder an IP telephony implementation.

John Borusheski is vice president of emerging technologies at NEC Unified Solutions Inc. in Irving, Texas.

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Copyright © 2005 IDG Communications, Inc.

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