Enabling this feature repurposes otherwise-unused overhead bytes in the SDH frame header to carry an auxiliary E1 wayside channel across the radio link, essentially smuggling a low-bandwidth extra circuit inside header space that would otherwise go unused. This only works if both ends of the link and any intermediate SDH equipment agree on the same overhead byte usage, so enabling it on one end without matching configuration on the far end could corrupt either the wayside channel or the SDH overhead functions relying on those bytes. A site using this to carry an auxiliary voice or telemetry circuit alongside the main SDH payload would set this to enabled(2) on both radio terminals of the hop.