ATM Configuration and Management Manual

Overview of the ATM Subsystem
ATM Configuration and Management Manual—522307-003
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The Asynchronous Transfer Mode (ATM) Protocol
The layers are:
The plane specifies domains of activity in the protocol. The planes in the ATM protocol
are:
•
Control plane. Calls and connection are established and maintained on the control
plane.
•
User plane. Users exchange data on the user plane.
•
Management plane. Network and layer management occurs on the management
plane. The management plane also coordinates the planes and manages
resources for the layers.
The ATM protocol also has two interfaces: the UNI and the network-node interface
(NNI).
Physical Layer Corresponds to layer 1 of the seven layer OSI reference
model. This layer handles bit-timing and checks the validity of
cells created and transmitted.
ATM Layer Creates cell headers and trailers, defines virtual channels and
paths – and gives them unique identifiers, and multiplexes or
demultiplexes cells. This layer is service-independent.
ATM Adaptation
Layer (AAL)
Provides translation between ATM and other services (voice,
video, or data) involved in transmission. AAL has four
classes, which use five protocols, and two sublayers.
The classes are:
•
Class A used for constant bit-rate data and appropriate
for the transmission of voice data. Class A uses the AAL
1 protocol.
•
Class B used for variable bit-rate data and appropriate for
the transmission of video data. Class B uses the AAL 2
protocol.
•
Class C used for connection-oriented data transmissions.
Class C uses the AAL 3 or AAL 5 protocol.
•
Class D used for the connectionless data transmission.
Class D uses the AAL 4 or AAL 5 protocol.
The two sublayers are:
•
Convergence sublayer provides the interface for the
various services.
•
Segmentation and reassembly (SAR) sublayer, packages
variable-sized packets into fixed-size cells at transmission
and repackages them at reception.