There are huge problems for wireless VoIP coverage. The most popular wireless solution, WiFi, is also the least able to support a wide-ranging, broad-coverage network that spans large geographical areas. WiFi access points - even the most advanced versions - have ranges measured in feet or at best yards. Real wireless and mobile coverage, especially across more rural areas, is going to require miles or tens of miles. The most prevalent and successful wireless technologies are all cellular. Cellular carriers are scrambling to provide fast, efficient IP transport mechanisms across the various cellular networks. But therein lies a lot of the problem. There are multiple cellular networks globally with multiple connectivity and transmission protocols. To successfully provide global wireless VoIP coverage requires recognizing and understanding tens of protocols - all at the same time if you want proper roaming and seamless handoff from network to network.
WiMax, a microwave-based WLAN technology holds promise - it can be made to operate as simply as WiFi and has a range of a few miles. But it isn't fully ready for nationwide/global rollout. There is ClearWire with its wireless broadband access technologies that are being rolled out in Stockton that are fast enough to handle VoIP readily. There are other still faster technologies that are a few years further away that could solve wireless bandwidth issues and handle converged multimedia wireless communications.
But for now, wireless VoIP is at best a matter of switching frequently from WiFi to cellular and back again. Worth it perhaps if you spend most of your time in a convenient WiFi zone.
Wireless VoIP typically relies on more active communications mechanisms than say, cellular, for example. Client units (handsets or PCs) are constantly pinging nodes and checking signal strength and because communication is asynchronous and untimed, both the receiver and transmitter must leave a dedicated communication channel open. That leads to a lot of open channels and a very large load on the access points. WiFi in particular is able to handle on the order of tens of communicating clients simultaneously per access point even though the theoretical maximum is much larger. But common use of VoIP will take the number of real connections to hundreds and VoIP has high level peak communication demands. The result is that it will be very easy for any given access point to get overloaded. The system needs an automatic means of load balancing that hands signals off to less busy access points when they are available.
VoIP signals are unpredictable in nature because of the asynchronous untimed flow of data. In a busy municipal WiFi network it is clear that downtown access points could become overloaded as they try to handle the peak data flows, even if they could handle the data volume readily if it was evened out. One of the key issues that arises are collisions when too many signals arrive at the access point at once, some get delayed and the delay is long enough to compromise the 30ms response time needed for true voice quality. A good wireless VoIP system will have to be able to handle collisions very quickly.
Battery life is another significant factor for VoIP devices. Most forms of IP-based communication are asynchronous and unpredictable which means that a wireless VoIP device has to remain far more active both in a call and out of a call in order to properly handle the signal than, say, a cellular device. Cellular devices predictably communicate on regular intervals of slightly more frequently than every 30 ms. That almost-30ms gap gives the device time to power down briefly between receiving and transmitting information. As a result battery life is extended and preserved. VoIP handsets cannot do this and thus eat up power by comparison. Several manufacturers are working on technologies to preserve power during VoIP communication in order to bring battery life up to acceptable levels.
Three-Way Battle Royale
Finally, the wireless market is already crowded, even before VoIP gets in there. Cellular companies are proving to be more agile than telcos were at co-opting or facing down hungry VoIP competitors headed into the market. Telcos see the space as an opportunity to get back strongly into a market they have only stayed in by acquiring cellular companies. And VoIP companies see lots of gaps and opportunities in the market to exploit. While this level of competition can only be good for consumers in the long run, in the short run it means that getting ahead of the curve and putting down cash for a wireless technology could leave you holding the wireless phone equivalent of a Betamax.
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