Avaya 9101 - Manual (Page 12)

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The BOTTOM VIEW includes the following:
7) Tone/Pulse switch
This switch us used to select the dialing mode, either TONE (DTMF)
or PULSE (Decadic). The correct mode depends on the telephone
network.
8) Ringer volume switch
The settings on this switch affects the ringer volume during an
incoming call. There are three available ringer volume positions: Low,
Medium, and High.
9) Ringer pitch control
The pitch of the ringing sound can be changed by rotating this control
on the bottom of the telephone.