ilable technologies can then be directly assessed against these attributes. A simple table, similar to the example shown Chapter Seven in Table 7-3, can be used to display the assessment, resulting in a transparent and objective comparison of the available solutions. More sophisticated evaluation methods can also be applied, for example, by assigning a weighting factor to each requirement and a score to each technical solution depending on the extent to which it meets the requirements. Network Capacity The total required network capacity will be determined by the sum of the bandwidth requirements of the maximum number of concurrent users expected on the network, with some allowance being made for the fact that this maximum will occur infrequently and some limited degradation of performance may be acceptable during brief periods of high usage. If this requirement exceeds the capacity of a single access point then multiple access points will be required, up to the limit imposed by the number of available non-overlapping channels. The total achievable network capacity for 802.11 networks defined by that limit is shown in Table 7-4. As described in the Section "Spectrum Management at 5 GHz (802.11h), p. 160", the 802.11h enhancements open up an additional 12 OFDM channels in the 5 GHz band, doubling the achievable network capacity for 802.11a networks. Operating Range The operating range of a wireless network link is influenced by a wide range of factors, from the modulation and coding scheme being used to the nature of the materials used in the construction of the building in which the network operates. The key factors are summarised in Table 7-5. The operating range for 802.11a/b/g networks for varying PHY layer data rates in a typical office environment is shown in Table 7-6, based on transmitted power levels of 100 mW for 802.11a/b, 30 mW for 802.11g and antenna gains of 2 dBi. Implementing Wireless LANs Table 7-3: WLAN Technologies; Technical Attribute Comparison Requirement type 802.11b 802.11g 802.11a 802.11n 