Cisco 7925G Administration Guide - Page 36

Understanding WLAN Standards and Technologies Chapter 2 Overview of the VoIP Wireless Network • Orthogonal Frequency Division Multiplexing (OFDM)-Transmits signals by using RF. OFDM is a physical-layer encoding technology that breaks one high-speed data carrier into several lower-speed carriers to transmit in parallel across the RF spectrum. OFDM, when used with 802.11g and 802.11a, can support data rates as high as 54 Mbps. Table 2-3 provides a comparison of data rates, number of channels, and modulation technologies by standard. Table 2-3 Data Rates, Number of Channels, and Modulation Technologies by IEEE Standard Item Data Rates 802.11b 1, 2, 5.5, 11 Mbps Non-overlapping Channels Wireless Modulation 3 (Japan uses 4) DSSS 802.11g 6, 9, 12, 18, 24, 36, 48, 54 Mbps 3 (Japan uses 4) 802.11a 6, 9, 12, 18, 24, 36, 48, 54 Mbps Up to 23 DSSS, ODFM ODFM AP, Channel, and Domain Relationships APs transmit and receive RF signals over channels within the 2.4 GHz or 5.1 to 5.8 GHz frequency band. To provide a stable wireless environment and reduce channel interference, you must specify non-overlapping channels for each AP. The recommended channels for 802.11b and 802.11g in North America are 1, 6, and 11. Regulatory domains determine the number of channels that wireless communications can use within the frequency band. Table 2-1 lists the frequency ranges, operating channels, and product numbers for four regulatory domains. The Cisco Unified Wireless IP Phone 7925G uses the fourth domain for all other regions in the world. Wireless LANs in the rest of the world use 802.11d to identify band ranges and channels. Note In a non controller-based wireless network, it is recommended that you statically configure channels for each AP. If your wireless network uses a controller, use the Auto-RF feature with minimal voice disruption. The AP coverage area depends on its type of antenna and transmission power. The AP coverage range is from 500 to 1000 feet with effective isotropic radiated power (EIRP) output that scales at 1, 5, 20, and 50 mW. To provide effective coverage, APs need a range overlap of approximately 20 percent to allow uninterrupted connections as phone users roam from one AP to another. Wireless networks use a service set identifier (SSID). The SSID differentiates one WLAN from another, so all APs and all devices attempting to connect to a specific WLAN must use the same SSID. The SSID groups user devices and associates the group with the APs. For more information about wireless network components and design, refer to the Overview: Cisco Unified Wireless Network at http://www.cisco.com/en/US/solutions/ns175/networking_solutions_products_genericcontent0900aecd 80529a5f.html. For more information about APs, see the "VoIP WLAN Configuration" section on page 2-21. Cisco Unified Wireless IP Phone 7925G Administration Guide for Cisco Unified Communications Manager 7.0(1) 2-6 OL-15984-01