Avaya 3641 Manuale di installazione - Pagina 3

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Installation Guide

Introduction

Wi-Fi telephony enables the convergence of wireless voice and data applications using a common

wireless local area network (WLAN). Wi-Fi telephony bridges traditional telecommunications, data

communications and mobile technologies, resulting in ease-of-use and cost savings. A Wi-Fi–

enabled telephone is a WLAN client device, using the same network technology as wireless

laptops and PDAs. A Wi-Fi-enabled telephone can be functionally equivalent to a wired

telephone, and allowing for configuration and management from the local enterprise telephone

system. These benefits can result in substantial cost savings over other similar wireless

technologies by leveraging the Wi-Fi infrastructure and by eliminating recurring charges or

redundant costs.

However, a Wi-Fi telephone does impose different requirements on the network that result in

deployment considerations that differ from networks which are optimized for wireless data. Voice

and data applications have different attributes and therefore, different network requirements.

Because a Wi-Fi telephone is a mobile communication device, it requires special considerations

for continuous high-quality connections as a user moves throughout the coverage area. Another

significant difference is the tolerance for network errors and delays. Whereas data applications are

designed to accept frequent packet delays and retransmissions, voice quality will suffer with just a

few hundred milliseconds of delay or a very small percentage of lost packets. In addition, data

applications are typically bursty in terms of bandwidth utilization, while a telephone conversation

utilizes a consistent and relatively small amount of network bandwidth.

Using a WLAN for voice is not complex, but there are some aspects that must be considered,

particularly for enterprise applications. A critical objective in deploying enterprise Wi-Fi telephony

is to maintain similar voice quality, reliability and functionality as is expected in a wired telephone

environment. The key issues in deploying Wi-Fi telephony are coverage, capacity, quality of

service (QoS), telephone switch integration and wireless security.

2.0 Wireless LAN Layout Considerations

Avaya model 3616, 3620, 3626, 3641, and 3645 wireless telephones utilize a Wi-Fi network consisting

of WLAN Access Points (APs) distributed throughout an enterprise environment. The required number

and placement of APs in a given environment is driven by several factors, including intended coverage

area, system capacity, access point type, power output, physical environment, and radio type.

2.1 Coverage

One of the most critical considerations in deployment of Avaya wireless telephones is to ensure

sufficient wireless coverage. Enterprise Wi-Fi networks are often initially laid out for data applications

and may not provide adequate coverage for Wi-Fi telephony. Such networks may be designed to only

cover areas where data terminals are used and may not include coverage in other areas such as

stairwells, break rooms or building entrances – all places where telephone conversations are likely to

occur.

The overall quality of coverage is more important with telephony applications. Coverage that may be

suitable for data applications may not be seamless enough to support the requirements of 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 be received correctly within tens of milliseconds of their transmission. There is little time

for retransmission, and lost or corrupted packets must be discarded. In areas of poor wireless

coverage, the performance of data applications may be acceptable due to retransmission of data

packets, but for real-time voice, audio quality will likely suffer.

Another factor to consider when determining the coverage area is the device usage. Wireless

telephone devices are used differently than wireless data terminals. Wireless telephone users tend to

Octiober 2008