Definitions for "Layer 1"
In OSI Model terms, the conceptual networking layer that defines electrical signaling on a wire.
the physical layer, governs hardware connections and byte-stream encoding for transmission. It is the only layer that involves a physical transfer of information between network nodes.
See Physical layer.
Keywords:  dual, deeper, disc, seamless, scanning
The upper fully reflective layer of a dual layer ( DVD-9) disc. Layer 1 can be Parallel Track Path (which starts at the ID) or Opposite Track Path (which starts above where the Layer 0 program area ends) to allow seamless playing from Layer 0 to Layer 1.
In a dual-layer disc, this is the deeper of the two layers, and the second one to be read when scanning from the beginning of the disc's data.
In a dual-layer disc, Layer 1 is the deeper of the two layers.