In some 4-wire systems, expanding a matrix to the next bigger block yields more fixed assets. Expansion above a standard size is achieved with more matrix frames and controllers. Expanded versions of matrix intercoms also may require additional ancillary equipment. This table reflects the number of fixed assets for a 50 x 50 system. Some fixed assets are crosspoint related.
Direct access occurs when a caller depresses a talk key.
At the destination panel, a tally indicator displays the origin of the call, and the caller is heard in the destination speaker or headset. The destination hears the call hands free. No one else on the matrix hears the conversation. The PL connection is the hallmark of 2-wire systems. Four-wire systems can create multiple PL's dynamically through the central matrix.