Definition
Layered Architecture ( Distributed System)
A layered architecture organises components into ordered layers
. Each layer provides services to higher layers through a defined interface and uses lower-layer services to implement them. Requests descend through the layers needed to perform an operation; responses return upwards. Each layer can process a request or response rather than merely forwarding it.
Strict Layering
A layer uses only the immediately lower layer:
may call , but does not bypass it to call deeper layers. Relaxed Layering
A layer may use any lower layer, allowing some intermediate layers to be bypassed.
Layer Boundaries
Layer interfaces hide implementation details: a lower layer can be replaced without changing its clients if its contract is preserved. Traversing layers can nevertheless add processing and communication overhead.
Layers describe logical responsibilities and dependencies, not physical placement. Several layers may run on one computer, and a layer’s components may be distributed across several computers.