By Peter Rysavy  Wide-Area Wireless Computing Planning You must consider a number of issues before you use wireless data. In this section we evaluate your requirements step by step and help you identify areas to focus on. You will then be in a better position to evaluate the various wireless networks that are available for your application. General Issues Protocols and interfaces, hardware and wireless middleware will be discussed in subsequent sections, but let's introduce these subjects now. One of the most important considerations in choosing a wireless network is selecting the protocols and interaces to use. They determine to a great extent how your wireless application accesses the services of the wireless network and what types of applications are feasible. See Protocols and Interfaces for more detail. With har dware, the issues of form factor, power consumption and cost come into play. See Hardware for more detail. Wireless middleware can insulate your application from problems like intermittent connections and specialized protocols. Some applications will work well over wireless connections as is, but some will work only with the assistance of middleware. Others must be rewritten completely. See Wireless Middleware for more detail. Suitability of Your Application The first order of business is to look closely at the kind of information you will be communicating. Wireless data communications makes most sense when: Data needs to be communicated in real-time The amount of data communicated is relatively small (tens of kilobytes rather than hundreds of kilobytes or megabytes) Your users are mobile and do not have convenient access to wireline connections In evaluating which software programs make most sense for wireless connections, consider those that can limit the amount of information that is downloaded. Look for features such as progress indicators and the ability to cancel lengthy operations. Operating Costs Wireless communications can be highly cost effective, but its costs generally are higher than wireline communications. We have become spoiled by our use of modems over local dial-up connections that are charged a flat rate, so that first cellular telephone bill may have been a shock. But you quickly learned how to use cellphones judiciously. Similarly, wireless data services can be expensive if used indiscriminately, but reasonable if used carefully. Surfing the Web with no particular destination in mind is not a good use of many wireless networks; downloading text based e-mail is. Examples of usage charges are as follows: Network Usage Costs Data over analog cellular (such as cellular service from AirTouch, AT&T Wireless Services , Bell Atlantic) Pay for duration of call. Same cost as for voice, about 30 cents per minute in home area, $1 per minute when roaming. Packet data networks (ARDIS, CDPD, RAM Mobile Data) Usually pay for amount of traffic. Rates vary between about 3 cents and 30 cents per kilobyte. Some networks charge on a flat-rate basis. Two-way paging networks (Skytel) About 25 cents per 80 character message. Satellite (Iridium, Globalstar) $1 to $3 per minute (these services are not yet available). Analyze your application for the amount of time or the amount of data you expect to communicate. For instance, with a TCP/IP application you might run it over a Windows 95 Dial-Up Networking connection, and look at the status screen for a count of bytes sent and received. Other TCP/IP stacks, e.g. from WRQ can provide even more detailed statistics. Coverage Most wireless networks provide broad coverage areas, but no service extends everywhere yet. You need to evaluate where you need coverage and choose a wireless network accordingly. Packet networks, such as ARDIS, CDPD and RAM Mobile Data, offer coverage in most major metropolitan areas (though for only the dense population areas and not outlying areas). Some networks are available only in certain cities. Metricom's Ricochet network is available in less than half a dozen cities in the United States. Our profiles of wireless networks below provides coverage information, but for complete detail you will need to consult with the specific networks. Many provide coverage maps on their Web sites. For example, you can view ARDIS coverage maps at http://www.ardis.com/ardis_hp/mapintro.htm Circuit Switched versus Packet Switched With circuit-switched connections, you have a dedicated connection for your entire session, reg ardless of whether you are communicating data. Voice or modem connections over the telephone network are circuit-switched connections. In the wireless world, the most common type of circuit-switched data connection is through a cellular telephone. Such connections are best-suited for batch operations, file transfers, faxing, database replications and other transactions where the connection is infrequent, but the amount of information transferred can be large. One reason for this is that the minimum billing unit is often one minute and almost half of the first minute is consumed by the modems training to establish a connection. Usually the application or actively involved user has tight control over connection setup and teardown. With packet-switched connections, as used by wireless WANs, the wireless modem registers with the network, but then occupies a radio channel only while sending or receiving packets of data. Data can be transmitted almost immediately because no call setup is involved. But because of current pricing plans, most wireless WANs are best-suited for short and bursty communications. Examples include short personal messages, stock information, updates from vending machine, taxi dispatch and credit card transactions. A major advantage of packet-switched communications is that client software on the mobile computer can maintain a "logical" connection with a server for extended period of time. Packet-switched connections tend to be more robust because a communications problem may require that a packet be resent, whereas with a circuit-switched connection the entire connection may have to be reestablished if a call is dropped. Performance Although wireless data offers many benefits, it also poses some challenges relative to wireline connections: wireless connections can be slower, data rates can vary depending on the RF environment and connections can be lost. Wireless WANs have quoted data rates ranging from 4 Kbps to 28.8 Kbps, but actual throughput is often half this rate beca use of overhead in the communications protocols. In addition, wireless WANs have latencies (end-to-end delays) that can range from less than a second to several seconds. For applications that involve a large amount of back-and-forth traffic, such as SQL transactions, the time to complete transactions can prove unacceptable. You must examine the nature of your application and do some actual testing to determine how well your application will function. End-to-end communications When we think about wireless communications, we think of data traversing a radio link. But we don't consider the entire end-to-end connection, which might involve a number of networks. Wireless networks are complex networks involving wire-line infrastructure, and they connect to other complex networks -- value-added networks, corporate intranets and the Internet. As you can see, the wireless link is only one element of the network. In deploying your application, you'll have to consider how the mobile user will access the fixed-end services on the back end. With circuit-switched data, the fixed-end connection will be a straightforward modem link through the public switched telephone network (PSTN). But with a wireless WAN, the connection between the end service and the wireless data network could include any of the following: a wireless connection, a dedicated circuit, a connection via the Internet, X.25 or a frame relay PVC. Of these, usually a wire-line circuit is used. You will need to consider the options available for the network of interest and analyze the additional costs associated with the fixed-end connection. Re-engineering work patterns Human and job-related considerations are often overlooked by companies planning wireless applications. However, wireless represents a huge opportunity for companies to increase the effectiveness of their people. Because wireless communications provides a fundamental new capability, how a person does his job can change pro foundly. For example, an insurance agent that used to call a client back or make another visit to present a quote can now present that quote at the first meeting. A real estate agent can obtain listings of new properties the moment the listings become available. Police officers can instantly determine whether a particular vehicle has been stolen. Managers can stay current with their e-mail while waiting for flights. In many cases, workers not only become more productive but can do their jobs in entirely new ways. It takes time, however, for companies to fully understand and define new job structures, especially because such changes can ripple throughout an organization. You should think how wireless data might impact your company operations. Don't just consider automating existing methods, also examine how the technology can enhance the services you offer your customers. Introduction Planning Protocols and Interfaces Hardware Wireless Middleware Profile of Wireless Networks Integration Print This Page E-mail this URL