The present application relates to a variant Fc region comprising at least one modification relative to a wild-type human Fc region, where the modification selected from the group consisting of 434S, 252Y428L, 252Y434S, and 428L434S, and the numbering is according to the EU index. The station-side line terminal apparatus switches a physical line from a working physical line to a backup physical line of the physical lines. The apparatus includes an electromagnetic radiation source for directing electromagnetic radiation rays toward the interior of the enclosed housing and an electromagnetic radiation detector for receiving and measuring reflected electromagnetic radiation rays.