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Tech Note #22: Asynchronous Transfer Mode (ATM)  Addresses
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1998 Bionic Buffalo Corporation; All Rights Reserved.
       14 September 1998
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adaptation
layer
user plane
connection points
adaptation
layer
physical layer
ATM layer
ATM layer
The ATM layer of these protocol stacks translates the VPI and VCI numbers, as the cell moves
through the network. Other functions of the ATM layer include cell header process, cell
multiplexing and demultiplexing, and some flow control. If a cell passes through a single
intermediate node while going from one connection point to another, the associated protocol
stack might have the following configuration:
adaptation
layer
user plane
connection points
ATM
layer
adaptation
layer
physical layer (1st link)
ATM
layer
ATM layer (does VPI/
VCI translation)
physical layer (2nd link)
sending node
receiving node
intermediate node
In the most complex and interesting cases, however, the VPI and VCI numbers are assigned
dynamically as part of the routing and switching process, as connections are established and
broken down. Adding these functions requires increasing the complexity of the architecture, as
explained in the next section.