Analog telephones connected through VoIP adapters can support call transfer functionality using the device’s “R” (hook flash) button.
This guide explains how to transfer calls between users and how to configure the correct hook flash timing for proper operation with VoIP adapters such as the Cisco SPA112.
Call Transfer Procedure
Let us assume that user A is currently in an active call with user B and wishes to transfer the call to user Γ (the number of user Γ may be an internal extension, landline, or mobile number). Follow the steps below to transfer the call:
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User A should press the “R” button on their device.
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After pressing “R”, user B will begin to hear hold music.
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User A should dial the number of user Γ.
At this point, user A has two options:
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End the call immediately so that once user Γ answers, they will be connected with user B.
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Wait for user Γ to answer and inform them about the call that is about to be transferred. Once informed, user A may end the call, allowing user B to continue the conversation with user Γ.
The “R” button on analogue phones simulates the closing and opening of the hook switch button for a few milliseconds, depending on the device timer configuration.
It is important that the device timer is configured between 200-600 milliseconds so that the SPA112 correctly interprets the signal and ensures proper operation between the two devices.