Defining a Wireless Solution, Page 7
5.3.4 Wireless Network
Answers to the Where category of questions are the predominate driver of network selection, however, the other categories help set other important network requirements. There are seven major criteria for defining network requirements as shown in Figure 5.9: coverage, bandwidth, latency, reliability, security, interoperability, and cost. Refer to Chapter 11 for more detailed descriptions of each criteria.
The Network Selection Cheat Sheet
- Coverage The level of coverage required to support your desired solution is the major determinant of your network options. Since your final wireless solution may involve more than one network type to gain the desired coverage, be sure to indicate all applicable requirements on the checklist. Where people will use the application in the field and how far they may roam are the determining factors for coverage. For example, if the users are waiters at a restaurant, the coverage area is obviously circumscribed. Sometimes there will be multiple locations of intended use. For salespeople using a wireless application designed to answer customer queries, coverage will be needed wherever customers are located. If salespeople also want to use their devices for e-mail, coverage may be needed at their homes or remote offices as well. If users are repair technicians servicing gas lines or power stations, coverage will be needed wherever these physical assets are located. If a "user" is a piece of equipment, coverage will be needed wherever the equipment may be located or moved. One approach to determining coverage is to create a map of the locations where the application is expected to be used, and compare this map to a potential carrier's coverage map. The more overlap, the better the coverage. The physical environment where the solution will be used also affects coverage. Environmental conditions influence the working as opposed to theoretical range of the wireless network and pose possible reception problems. For example, the range of an infrared network goes to zero if there are obstructions between communicating devices. The signals transmitted over a short-range network become progressively weaker as the distance between transmitting and receiving devices grows. In-building reception may also be poor with some WANs. Information about the environment can also help uncover interference concerns, and characteristics of the physical environment may also help narrow device choices.
- Bandwidth While short- and medium-range wireless networks can approach wired throughput, bandwidth is currently a limiting factor for wireless WANs. Although bandwidth limitations can be overcome to a degree by application design, transfers of large quantities of data over a wide coverage area remains slow and costly, and downloading of some applications, such as video, are not presently feasible over wireless WANs. Consider bandwidth requirements by the primary types of data transfers your solution will need and the user's tolerance for waiting. Users may be willing to tolerate a longer transfer time for occasional activities, such as downloading a system upgrade, if their routine activities occur at a reasonable speed.
- Latency Latency, the timeliness of information exchange, is not really an issue for local, in-building wireless networks, like WLANs or Bluetooth. Their performance depends in large part on the performance of the wired network to which they connect. Latency becomes an issue when wireless WANs are used, and organizations want the ability to push information to users wherever they are, and want mobile users to be able to transmit information back to headquarters from any locale. Data that must be accurate to the second, such as stock price quotes, requires an always on, "zero" latency approach. Less time-sensitive data, such as filing service reports, can be transmitted by storing and forwarding the information when convenient, perhaps through synching. Even when real-time information is desired, remember that coverage and data volume/network bandwidth can impede or prohibit immediate access.
- Reliability Reliability assesses the tolerance that a wireless application has for network-related problems. Applications aimed at ensuring personal safety are useless if the networks they run on are available only sporadically. Likewise, wireless applications that depend upon the integrity of transmitted data, such as processing a credit card transaction at a point-of-sale terminal, cannot afford a network that regularly drops data.
- Security Although security is ultimately an "end-to-end" issue that includes devices, servers, applications, and other solution components as well as networks, wireless networks differ in their inherent levels of security. WLANs have experienced some well-publicized security flaws, while WANs are generally highly secure.
- Interoperability This factor is more of a design "flag" than a network selection criterion. The preponderance of wireless components and platforms, from devices to modems to network equipment to cards, makes interoperability essential. As interoperability declines, costs and support overhead mount, and redundant, overlapping, and conflicting solutions emerge. Interoperability within a class of wireless network solutions, such as Wi-Fi WLANs, may be high, but interoperability between different network types is iffy at best. Interoperability is not an issue for standalone solutions that rely on a single network and limited device types, but can be a significant issue when designing a solution for rollout to a diverse and dispersed audience.
- Cost Networks and network services vary by cost of implementation and cost of usage. There may be a range of suitable wireless network options, with a range of features, available at different cost points. Knowing the correct one to choose may hinge on the amount of money budgeted for the solution.