Because Packet-Switched data networks don't deliver a dedicated circuit, they can't promise consistent throughputs either. This is the new services' most significant caveat. With traditional modems, users have a dedicated circuit and can expect a consistent performance level. This is also true with circuit-switched data for cellular. In the case of the new packet networks, the medium is shared, just like Ethernet, but the total available bandwidth per cell site is much lower than Ethernet's. Although CDMA2000 carriers quote their networks as having peak speeds of 144 Kbps, and say users can expect 40 Kbps to 60 Kbps, they fail to mention that at peak times under heavy voice loading, data throughput may drop to 10 Kbps. GPRS can suffer from this effect too. Also, once the number of data users increases, the available data channels will be shared, and average throughput will go down. How much? It depends to what extent the operators manage QoS (quality of service) for data. As with voice capacity, they can increase data capacity by allocating more radio channels (assuming they have spectrum available) or by adding base stations (a costly endeavor). So take the figures quoted by operators as a starting point, but do your own testing to determine how well your applications operate. Furthermore, keep in mind that any testing you do today may not capture how the networks will perform once popularity increases. Given the historical low data usage on cellular networks, this is a problem operators would love to have. Furthermore, operators have had similar voice-capacity challenges in some markets, but have managed to keep up with demand. In the case of Web access, most operators provide optional Web acceleration servers that work quite well. The accelerators increase Web throughput significantly by reducing the file size of images, compressing text and reducing the number of TCP connections used to download pages. Some operators include specialized e-mail gateways that let smart phones access conventional e-mail services.
Latency--the amount of time it takes packets to traverse the network--is as important as throughput. Wireless networks have higher latency than wireline networks. In CDMA2000 1XRTT networks, round-trip times for small packets can be 500 milliseconds to 600 ms, and with GPRS can be closer to 800 ms. High latency will take a toll on applications that require many small data transactions. Keep in mind, however, that operators are still tuning their networks for optimal performance. Do the available data rates and latencies support existing enterprise applications, such as VPNs, Microsoft Outlook, Lotus Notes, Web-based applications and database access? Yes, but you still will want to be careful how much data you download, for performance and cost reasons.
Pricing It Out
AlThough Verizon Wireless offers a flat-rate business plan at $99 per month, most plans are usage-based, and charge between $1 and $10 per megabyte, depending on the size of the monthly commitment, with $4 per megabyte being typical. It is quite easy in an interactive data session over an hour to transfer more than a megabyte of data. So costs can add up quickly. Moreover, most users, including experienced ones, have no idea what volume of data different transactions consume. You will want to characterize your applications for data volume before you commit to a pricing plan. Pricing may also influence the application architecture you choose--a thin-client approach transmits less data than a fat-client setup. See "Wireless Data Service Pricing" chart for costs for different data plans. Note that these are changing on a regular basis, and the trend will be downward as competition increases.
Platforms raise another interesting question. In the past, laptop users would attach a data-capable cell phone or plug in a PC Card modem, but the number of options is increasing quickly. First are phones with ever-increasing data capability. Although for some time phones have had microbrowsers for viewing specially formatted Web content, the newest ones can actually execute programs, enabled by both Sun Microsystems' Java 2 Micro Edition and Qualcomm's Binary Runtime Environment for Wireless. New smart phones also incorporate PDA capabilities, using either proprietary platforms or platforms supplied by Microsoft, Palm or Symbian. These slightly heavier and larger phones make sense for users who want voice and data on one device, but who favor voice.
For those who favor data, the platform of interest may be the phone-enabled PDA, which looks like a PDA rather than a phone. Palm OS, Pocket PC and RIM Blackberry represent the leading platforms, and devices are available for both GPRS and 1XRTT networks (see our recent review of Sprint's CDMA2000 service on a Handspring Treo PDA/phone). Wireless-enabled PDAs might just become the platform of choice for GPRS and 1XRTT, while notebooks may gravitate to wireless hotspots based on 802.11 technology that have the higher bandwidth preferred by communications-intensive applications.
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