ipLDK-60 SERVICE MANUAL
DIGITAL KEY TELEPHONE SYSTEM
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2.4.3 Conferencing
Conferencing is accomplished on the ipLDK-60 system by using switching block of a special custom integrated circuit
called the ACT2. This device uses a technique that involves the real time digital summation of two ports (conferee’s)
PCM data. That is, the digitized voice is added together in a digital format, and then placed on the appropriate “B”
channel. For a 3-party conference (ports A, B & C), port A will require that ports B & C be summed and placed on the
receive time slot for port A. Port B will require that ports A and C be summed and placed on the receive time slot for port
B. Port C will require that ports A and B be summed and placed on the receive time slot for port C. This provides a
feature of 3-party conference on the system.
Since the system is designed to provide up to 3 parties in a conference, the switching block on the ACT2 was
incorporated to provide this function. The digital summation process can store its output into this function. The digital
summation process can store its output into this conference memory of switching block. The memory is large enough to
support many digitally stored summations. The summed conference memories can then be used as one or both inputs
for additional summations and its output stored in memory again or placed on a “B” channel. Conference memory is
large enough to allow unlimited 3-party conference at the same time. Gain modification is performed by the switching
block. A look up table stored in ACT2 permits PCM words to be adjusted for the circuits receive volume level. The gain
word (volume level) is used as the Gain ROM index with the PCM word as the address. The output from the Look-Up
Table is the gain modified PCM signal which is placed on the appropriate receive “B” channel.
