The Layer 1 diagram for OSS4ITS integrated architecture shows the functional objects inside each physical element, and uses the same physical interconnects as on Layer 0.
...
Legend for physical architecture:
...
The Layer 1 diagram helps the project team and stakeholders reviewing the system documentation to see just what all of the systems are doing across all of the services or applications and the interactions (physical interconnects), and shows the mid-level perspective of the project.