WiFi has gone from an accessory to a basic connectivity technology and has even become the Internet Service Provider of choice for some. You can hardly walk into a restaurant anymore without seeing a "Free WiFi Hotspot" sticker on the front door. WiFi at the present is doing exactly what the technology was designed to do. That is, transmit broadband network packets reliably throughout a room sized area. It's because WiFi has become SO prolific that it is now being asked to step into a greater role, that of telecommunications carrier.
It seems that everybody suddenly wants to be in the carrier business. The wireline telephone companies had 100 years to get it right. The cellular companies have been perfecting their act for about 30 and they're only now on the verge of offering high speed data everywhere they offer basic voice calls. The heat is on to make WiFi a third contender with WiMAX the distant up and comer.
So what new role is WiFi being asked to assume? It's the whole idea of voice, video and data convergence that is sometimes called the triple-play. If your network can deliver quality voice, video and data, then you can play in the same carrier game as the big telecom companies. Honestly, though, the real push is voice in the form of VoWi-fi or Voice over WiFi that hopes to compete with cellular for telephone service. VoWi-fi is VoIP gone wireless. There are even cell phone designs coming out that will work in a WiFi hotspot and then seamlessly switch to a cellular signal when you move out of WiFi range.
The only problem with this rosy scenario is that WiFi was never designed with differentiated levels of service in mind. Packets are packets are packets to the venerable 802.11 standard. But not for long. The IEEE will likely standardize a new set of Quality of Service extensions called 802.11e in the near future. In the meantime, the Wi-Fi Alliance, the industry certification group, has implemented its own pre-e extensions called WMM or Wi-Fi Multimedia.
The basic idea with both standards, WMM being a subset of the expected 802.11e, is that packets should get different priorities on the network depending on what they are carrying. Both voice and video are real-time data streams that turn ugly when pieces get dropped or delayed. Computer data exchanges such as email and web surfing are much less sensitive. Background activities like data backups to a central storage site are not fussy at all.
The way that QoS is implemented for WiFi is to tinker with the basic operation of collision prevention system. You can't have every device on the network talking at the same time or their packets will collide and nothing will get through. So they have to take turns. Each station listens for a quiet period and then waits a random time before trying to transmit. If it hears another station transmit, it stays silent and waits for the next opening. That's essentially how the classic Ethernet works on a wired network that uses hubs instead of switches.
Right now all WiFi devices have an equal chance at the radio channel. With QoS classes, voice and video devices get to wait a shorter time before transmitting their packets. They get to jump out sooner when the channel is clear and thus make the lower priority data-only devices wait longer. In effect, voice and video get a bigger percentage of the network time so that they have a better chance of staying intact when there isn't enough bandwidth for everybody to run at maximum speed.
With WMM and 802.11e, WiFi networks will be poised to handle VoIP and video phones, perhaps even before QoS is completely implemented on the wired corporate networks.
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