White Paper

2.1Coverage

2.1.1Overlapping Coverage

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One of the most critical issues in deploying NetLink Wireless Telephones is ensuring sufficient wireless coverage. Often enterprise Wi-Fi networks are designed only for data applications and may not provide adequate coverage for wireless telephone users. Quite often these networks are designed to cover only areas where data terminals will be used, and do not include coverage in other areas such as stairwells, bathrooms, building entrances, or lobby areas where NetLink handsets may be used.

The overall quality of coverage is also more important with telephony applications. Coverage that is suitable for data applications may not be adequate for Wi-Fi telephony. Most data communication protocols provide a mechanism for retransmission of lost or corrupted packets. Delays caused by retransmissions are not harmful, or even discernable, for most data applications. However, the real-time nature of a full-duplex telephone conversation requires that voice packets need to be received correctly within tens of milliseconds of their transmission. There is little time for retransmission; lost or corrupted packets must be discarded. In areas of poor coverage, data application performance may be acceptable due to retransmission protocols, but real-time voice quality may not be acceptable.

Another factor to consider in determining the coverage area is the device usage. Wireless telephone devices are used differently than wireless data terminals. Telephone users tend to walk as they talk, while data users are most often stationary. NetLink Wireless Telephones are usually held next to the user’s head, introducing additional radio signal attenuation. Data terminals are usually set on a surface or held out at arms length so the user’s body has little affect. Because of these factors, a wireless telephone may have less range than a data terminal and the wireless LAN layout should account for a general reduction in radio signal propagation.

To provide comprehensive coverage for Wi-Fi telephony applications, APs need to be positioned with sufficient overlapping coverage to ensure that there are no coverage gaps, or dead spots, between them. As NetLink Wireless Telephones move out of range of a particular AP, they seek out another AP to hand-off to, or re-associate with, in order to maintain their network connection. A properly designed Wi-Fi network will provide seamless hand-offs between APs, ensuring excellent voice quality throughout the facility.

The wireless LAN layout must factor in the transmission settings that will be configured within the APs. The transmission of voice requires relatively low data rates and a small amount of bandwidth compared to other applications. The 802.11 standard includes data rate reduction specifications so that as a user moves away from the access point, the radio adapts and uses a less complex and slower mechanism to send the data. The result is increased range (coverage) when operating at reduced transmission rates. Access points should generally not be configured to limit the transmission to only the higher rates if wireless