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VoIP over WAN: Basic network considerations

Lisa Sampson

Voice over IP (VoIP) performs extremely well over a wide area network (WAN), as long as your network

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infrastructure is properly provisioned and managed.

Enterprises should expect no difference in performance between a VoIP system and a traditional TDM PBX, according to Mark Arman, vice president of marketing at ShoreTel, provided that two essential requirements are met for VoIP over WAN:

  • The enterprise network must be configured for quality of service (QoS).
  • Every enterprise installation should be staffed with a qualified system manager who assures that the network is maintained and monitored.

Once an enterprise puts VoIP over WAN into production, the network and infrastructure will change over time, according to Zeus Kerravala, Principal Analyst at ZK Research. The network manager must be able to correlate system performance with configuration changes and monitor the network.

“If you’re monitoring regularly you know who made what changes when and why,” Kerravala said, “and you can go back and undo a change if necessary.”

Assess your infrastructure for VoIP over WAN

An enterprise should start with the basics when preparing to implement VoIP over WAN. First of all, it will be “only as good as its electrical system. If power is an issue for the enterprise, that’s a hurdle it must clear long before IP telephony procurement starts,” Arman said.

When utilities and power specifications conform to technology requirements, then the telephony vendor will assess the enterprise network to determine its suitability for VoIP over WAN, Arman said. In addition, he said the vendor may suggest some software and network equipment upgrades.

After preparing the infrastructure, engineers can use both wideband VoIP and the vendor-recommended codec to obtain the best voice quality, according to Kerravala.

When using wideband VoIP, also known as HD voice, Kerravala said engineers should create rules for allocating bandwidth. That will ensure wideband availability for important communications. Although wideband soaks up bandwidth, “the quality is outstanding,” he said.

A checklist for running VoIP over WAN

To achieve the best QoS with three nines of reliability -- meaning freedom from latency and jitter -- Kerravala recommends that network engineers adhere to the following checklist:

  • Attain the necessary electrical VoIP power requirements. An old, poorly maintained electrical system with power surges and intermittent outages will not deliver good quality VoIP.
  • Work with a consultant, a system integrator, or a value-added reseller (VAR) that has extensive experience implementing VoIP over WAN.
  • Do your pre-work: For reliability, know your network and make sure facilities, computers, telephones, and the network are properly prepared before cutover. Centralize call control and use the WAN to distribute voice by letting it deliver voice the way the WAN delivers other applications.
  • Use redundant WAN links to ensure high availability (HA) and reliability. Most vendors have failover switching as insurance against system failures, so there will be no downtime after installation.
  • Maintain Multiprotocol Label Switching (MPLS) as a separate class of service (CoS) to eliminate contention with other applications.
  • Dedicate bandwidth to VoIP: For best QoS, find a way to have reserved, dedicated bandwidth for voice.
  • Know your maximum call traffic volume to be sure there’s enough bandwidth to support business requirements.

Let us know what you think about the story; email: Lisa Sampson, Feature Writer


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