A Few Everyday Examples, cont

L1/L2 Message Mapping/Interworking
Amplification/Coupling

TDM over IP [TDMOIP]
Vertical Coupling (Synchronization)

IMS (3GPP IP Multimedia Subsystem)
Vertical Coupling 
Services to transport

IP over ATM with P-NNI
Control plane coupling

Layering Considered Harmful
What?