1 introduction, 1 atm protocol stack, 1 introduction -2 – Nortel Networks 8000 User Manual
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Nortel Secure Router 8000 Series
Configuration -WAN Access
10 Low-speed ATM configuration
10.1 Introduction
This section covers the following topics that you need to know before you configure ATM:
10.1.1 ATM protocol stack
Asynchronous Transfer Mode (ATM) is the transmission and switching mode for broadband
ISDN services by the International Telecommunication Union - Telecommunication
Standardization Sector (ITU-T) in June, 1992. Because of its high flexibility and its capability
for supporting the multi-media service, ATM is considered as the key to realize broadband
communications.
As defined by ITU-T, ATM implements transmission and switching of data based on cells. An
ATM cell has a fixed length of 53 bytes. The first 5 bytes make up the cell header that
contains the cell routing and priority information. The remaining 48 bytes are used for
payloads.
ATM is connection-oriented. Each virtual circuit (V C) is identified by a Virtual Path Identifier
(VPI) and a Virtual Channel Identifier (VCI) together. One VPI/VCI value has local
significance on a segment of the link between ATM nodes. When you release a connection,
the relevant VPI/VCI values are also released.
The ATM protocol architecture has the following three planes:
•
User Plane
•
Control Plane
•
Management Plane
User Plane and Control Plane are divided into four layers respectively:
•
Physical Layer
•
ATM Layer
•
ATM Adaptation Layer (AAL)
•
Upper Layer
Each layer is further divided into several sub-layers.
The Control Plane uses signaling protocols to establish and release connections.
Management Plane is divided into Layer Management and Plane Management.
•
Layer Management: manages all the layers in each plane. It has a layered structure
corresponding to other planes.
•
Plane Management: performs system management and communication between different
planes.
The relationships among layers and planes are shown in Figure 10-1.
Issue 5.3 (30 March 2009)
Nortel Networks Inc.
10-3