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Tech Note #22: Asynchronous Transfer Mode (ATM)  Addresses
1998 Bionic Buffalo Corporation; All Rights Reserved.
       14 September 1998
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The Control Plane
To allow applications and system software to control the behaviour of the connections and
protocol stacks, ATM adds several more planes to the model. After the user plane, the next
plane is the control plane.
The control plane is a parallel entity to the user plane. Control messages use the same
underlying transport structure as the user connections. Viewed from the user’s perspective, the
two planes together exist side-by-side. The difference is that, while the user plane connects one
user to another, the control plane connects users to the switch or local exchange.
User Plane
connection points
Control Plane
User 1
User 2
or Switch
Signalling System 7, or SS7, also calls the user plane, the information plane. Because of the
close relationship between the architectures of ISDN, B-ISDN, ATM, and SDH, the
terminology often is interchanged.
Overall, the ATM network with the user and control planes can be viewed this way: