
Configuring ATM Services
1-8
308612-14.00 Rev 00
Depending on the ATM router type, you can connect directly to an ATM network
over any of the following physical interfaces:
• Optical carrier level 3 (OC-3)
• Digital service level 3 (DS-3)
• E-3 (the European equivalent of the North American DS-3)
Although Nortel Networks uses raw bandwidth to describe line rates, inherent
overhead within the media limits maximum bandwidth for the line. Use Table 1-1
to determine the maximum bandwidth for the media you are using.
ATM Layer
The ATM layer defines how two nodes transmit information between them. It is
concerned with the format and size of the cells and the contents of the headers.
The addresses of the cells are meaningful only to the two adjacent local nodes
(that is, usually not to the end nodes).
ATM Adaptation Layer
The ATM adaptation layer (AAL) converts upper-layer protocol data into formats
that are compatible with the requirements of the ATM layer, enabling ATM to
handle different types of information within the same format.
The AAL is divided into two sublayers: the convergence sublayer (CS) and the
segmentation and reassembly (SAR) sublayer. These two sublayers convert
variable-length messages into 48-byte segments, while ensuring the integrity of
the data.
Table 1-1. Maximum Bandwidth by Media Type
Media
Raw
Bandwidth (Mb/s)
Maximum
Bandwidth (Mb/s) Maximum Cells/s
OC-3 SONET/SDH 155 149.76 353207
DS-3 (Cbit and M23
framing)
44.736 40.704 96000
E-3 (G.832 framing) 34.368 33.920 80000
E-3 (G.751 framing) 34.368 30.528 72000
Comentarios a estos manuales