Voice Over Wireless LAN Analysis
Even though the idea of voice being carried by radio waves has been adopted for years by the cordless and cell phone industries, with the introduction of WiFi based wireless LANs, one of the uses that this technology is being applied to is voice. In analyzing this implementation of technology, it is necessary to separate the application into two distinct groups; internal LAN conversations and those that reach beyond the LAN.
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Technology
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Beginning in the late 1990s and finally making it into the public market place in the early 2000s, WiFi went from an obscure technology toy to one of the greatest successes in interoperability since the introduction of the IBM PC. It is estimated that 700 million WiFi-enabled devices will be sold in 2011 alone. The original WiFi standard, technically referred to as 802.11b, has evolved from a reasonably slow 5Mbps of real data transfer rates to the newer 802.11n which promises speeds of 600Mbps, but in the real world only delivers somewhat less than half of that speed. The future looks even brighter with the WiGig alliance pushing for gigabit and multi-gigabit speeds being delivered wirelessly at prices that rival WiFi pricing today.
Full Duplex vs Half Duplex
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To understand the dynamics of Voice over WiFi, or VoWiFi in industry terms, it is necessary to have a basic comprehension of duplexing. Voice communications, as we have grown used to in out current telephone conversations are a full duplex application, meaning that you can talk and listen at the same time. This contrasts a "push to talk" service where you can only talk or listen, but not both, during a conversation. For example, if two people choose to have a conversation using half duplex, person A will speak and then turn control of the radio over to person B. At one point in history, this handing off was identified by using the word "over," even though now that seems to have fallen out of favor. WiFi is a half duplex technology, but pretends to be a full duplex one by switching from transmit to receive extremely quickly. This issue is exacerbated when a conversation is carried out by two or more people across one access point. As more and more people place demands for the radio to switch from send to receive, the limit of this technology gets pushed to the breaking point. This scenario is significantly more taxing on the wireless hardware than when one or more people have voice conversations that are terminated outside the LAN.
Limitations
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As discussed above, the ability of WiFi to rapidly switch between send and receive allows for the perceived impression that you can interrupt someone who is speaking and that he will be able to hear you do so. However, this process does have limitations, specifically the radio can only switch a finite number of times between send and receive before it becomes overwhelmed. While WiFi can support a single conversation without issues, and can support a conversation at the same time data is being carried across the same network, at some point, this system will be overloaded. While many technologies are being employed to increase this capability, packet prioritization being foremost, there is still a point where the maximum amount of calls will be reached.
Applications
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VoWiFi is used in everything from medical applications to cell phone service. T-Mobile's Unlimited HotSpot Calling uses a dual mode cell phone with WiFi capability to allow for their customers to make calls anywhere a WiFi access point is available.
Products
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Vocera Communications manufacturers a Star Trek style communicator that can be pinned on a pocket and allow for voice commands to connect anyone on the network on demand. D-Link, to name only one manufacturer, builds WiFi phones that look and act just like a cell phone. Nokia, again only naming one manufacturer, makes a number of phones that integrate WiFi, and the list grows every day.
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