Nortel Networks 8000 - Manual (Page 445)

11 High-speed ATM configuration
Nortel Secure Router 8000 Series
Configuration -WAN Access
11.1 Introduction
CD NOTE
• Only the Secure Router 8012 routers support the high-speed ATM interface card.
• The command lines of the high-speed ATM interface card are different from those of the low-speed
ATM interface card. Therefore, when configuring the ATM interfaces, you must identify the type of
the ATM interface.
This section covers the following topics that you need to know before you configure ATM:
• ATM protocol stack
• ATM interface
• ATM applications
• references
11.1.1 ATM protocol stack
Asynchronous Transfer Mode (ATM) is the transmission and switching mode for broadband
ISDN services by the ITU-T in June, 1992. Because of its high flexibility and the ability to
support the multi-media service, ATM is considered as the most important aspect to realize
broadband communications.
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. Virtual Path Identifier (VPI) and a Virtual Channel Identifier
(VCI) together identifies each virtual circuit (VC). 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
You divide User Plane and Control Plane into four layers respectively:
• Physical Layer
• ATM Layer
• ATM Adaptation Layer (AAL)
• Upper Layer
You further divide each layer into several sub-layers.
The Control Plane uses signaling protocols to establish and release connections.
You divide Management Plane into Layer Management and Plane Management.
• Layer Management manages all the layers in a plane. It has a layered structure
corresponding to other planes.
11-2 Nortel Networks Inc. Issue 5.3 (30 March 2009)