Key considerations in vendor selection should include:
- Support for IEEE standard 802.11e or equivalent Quality of Service (QoS) technique.
- Call admission control at access points.
- Security features.
Meeting latency and jitter requirements involves prioritizing voice traffic above data. IEEE standard 802.11e, finalized in late 2005, adds QoS features to the previous 802.11 standard. Some vendors have now implemented the standard, but others continue to use nonstandard methods that may be equally effective. If possible, test your vendor's performance under realistic conditions. If running your own tests isn't possible, review tests done by a third party.
Access points (APs) can maintain acceptable call quality only by limiting the number of simultaneous calls. From your vendor, find out the following and compare with your expected usage:
- How many calls each AP can handle; compare.
- Whether an AP will continue to accept calls even though the quality is dropping, or whether it will reject calls beyond what it can handle with high quality.
Some vendors have added security features intended to address vulnerabilities that come into play with voice. For example, some wireless controllers contain a firewall that identifies a voice call and protects against any attempt to access resources that are not appropriate for a phone call. Find out how your vendor approaches this problem.
Some architectures require re-authentication every time a caller roams from AP to AP, which may result in an unacceptably long gap in the conversation. Other products perform a single authentication in a central controller and exhibit no delay when roaming. Test your vendor's product to determine how it handles roaming.
Adding voice to an existing wireless network may seem easy, but without a careful analysis of your RF environment, network security and your vendor's product capabilities, the result may be unhappy users and possibly a network break-in.
VoWLAN: Preparing your network for a voice over wireless LAN deployment
Analysis of the radio frequency environment
Review of network security
Investigation of the wireless vendor's voice experience and product features
About the author
David B. Jacobs has more than 20 years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies as well as software startups.