Avaya 3645 Посібник з монтажу - Сторінка 4

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Installation Guide

walk as they talk, while data users are usually stationary or periodically nomadic. Wireless voice

requires full mobility while data generally requires simple portability. Wireless telephones are typically

held close to the user's body, thus introducing additional radio signal attenuation. Data terminals are

usually set on a surface or held away from the body. This factor may result in reduced range for a

wireless telephone as compared with a data device, therefore the WLAN layout should account for

some reduction of radio signal propagation.

2.1.1 Overlapping Coverage

To provide comprehensive coverage for Wi-Fi telephony applications, APs must be positioned with

sufficient overlapping coverage to ensure there are no coverage gaps, or dead spots, between them.

As wireless telephones move about the workplace, they seek out other APs to handoff to and re-

associate with, in order to maintain the most reliable network connection. A properly designed Wi-Fi

network will provide for a seamless handoff between APs, ensuring excellent voice quality throughout

the facility.

The WLAN layout must factor in the transmission settings that are configured within the APs. The

transmission of voice requires relatively low data rates and a small amount of bandwidth compared to

other applications. The IEEE 802.11 standard includes automatic rate switching capabilities so that as

a user moves away from the AP, the radio adapts and uses a less complex and slower transmission

scheme to send the data. The result is increased range (coverage) when operating at reduced

transmission rates. When voice is an application on the WLAN, APs should be configured to allow

lower transmission rates in order to maximize coverage area. If a site requires configuring the APs to

only negotiate at the higher rates, the layout of the WLAN must account for the reduced coverage and

additional APs that will be required to ensure seamless overlapping coverage.

2.1.2 Signal Strength

To provide reliable service, wireless networks should be engineered to deliver adequate signal

strength in all areas where the wireless telephones will be used. The required minimum signal

strength for all Avaya wireless telephones depend on the 802.11 frequency band and modulation

used, and the data rates enabled on the AP. Recommended signal strength characteristics are

summarized in the following table.

Rate

(Mb/s)

Best

Prac-

tices

(dBm)

Octiober 2008

2.4GHz DSSS/CCK

5.5

-70

-65

-64

-60

802.11

Radio Mode

11, 5.5, 2, 1

802.11b

11 only

54, 48, 36, 24, 18, 12, 11, 9, 6, 5.5, 2, 1

802.11g

54 only

54, 48, 36, 24, 18, 12, 9, 6

802.11a

54 only

2.4GHz OFDM

Enabled Data Rates (Mb/s)

5GHz OFDM

Required Minimum

Signal Strength (RSSI)

-70dBm

-60dBm

-45dBm

-60dBm

-45dBm