Organizations are becoming increasingly mobile, but many business people remain chained to their desks. That’s because one very important communication device — the desktop phone — remains firmly tethered, and a personal cell phone isn’t always a good alternative.

Luckily that’s changing thanks to voice over wireless LAN (VoWLAN), which combines voice over IP (VoIP) and wireless networking technology to free the desktop phone from its cord. When an organization adds VoIP to an exiting wireless network, every employee can carry their extensions with them everywhere they go without the need to buy cell phone contracts for everyone.

In addition to wireless VoIP phones, smartphones can be used to make calls over the WLAN. Dual mode handsets allow users to switch seamlessly between WLAN and cellular, even in the middle of a call.

End-users can be reached via a single phone number wherever they are, and can take advantage of PBX features even when they’re on the mobile carrier’s network. VoWLAN also offers a means to reduce cell phone charges, address the problem of spotty cell phone coverage inside many buildings, and bring mobile users back into the corporate voice network.

VoWLAN Challenges

In a wireless VoIP implementation, mobile handsets connect to the network over wireless access points (APs) that route the voice traffic to the telephony server. It’s similar to the way handsets connect to the network over Ethernet cables in a wired LAN. However, implementing VoWLAN isn’t simply a matter of adding another application to the wireless data network. Just as wired LANs must be upgraded for VoIP to account for QoS, reliability and security concerns, chances are that an existing WLAN will also need upgrading.

Part of the problem is that wireless is a contention medium — users must share the available bandwidth, so wireless will always have overhead issues and more complex management requirements. While data traffic tends to be sporadic and bursty, voice can’t tolerate delays, so throughput is a key consideration. The WLAN must be engineered with consideration for those factors.

Coverage is another key issue. Unlike data-only WLANs, a VoWLAN infrastructure must be designed for mobile use, with blanket coverage of places such as hallways, stairwells and elevators where people will often need to use their phones. This means more APs must be positioned throughout the facility with sufficient overlapping coverage to eliminate dead spots.

Making the Switch

In recent years the WLAN market has shifted away from so-called “fat” APs toward a more centralized management approach — primarily to support VoWLAN roaming. As users move across multiple APs in the network, handoffs must take less than 50 milliseconds in order to maintain voice quality. However, distributed architectures severely hamper handoffs as all the intelligence resides in the AP itself.

Centralized WLAN switching solutions borrow from the best practices of cellular networks to actively improve call quality. If the switch sees that a client is getting a weaker signal, it can pre-authenticate the handoff to reduce latency. Stateful flow classification gives voice traffic top priority to further improve QoS, and load balancing distributes users across multiple APs.

VoWLAN is not meant to replace cellular phones. However, it helps organizations gain maximum advantage of their VoIP systems by giving every user one phone for both desktop and mobile use. And with evolving WLAN technology and sophisticated handset functionality, VoWLAN solutions can help organizations minimize cell phone costs while improving communications.

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