3-1261200290L1-1GSection 3, ConfigurationMX2800 M13 Multiplexer User ManualFigure 3-8. T1/E1 Line Length MenuT1/E1 Loopback DetectionThe T1/E1 Loopback Detection option is used to set how the T1/E1 lines respond to loopback requestscoming from the network. SeeFigure 3-9on page 3-13.