Nortel Communication Server 1000 Manual page 16

16 Overview
•
DASS2 is specified in terms of the International Standards Organization
(ISO) reference model for Open Systems Interconnection (OSI). Level
1 (Physical) of the model is a 2.048 Mbit/s digital interface and level 2
(Data Link) is the Link Access Protocol (LAP) defined for DASS2. Level 3
(Network) is the message layer unique to DASS2.
Model works" (page 16)
Figure 1
How the OSI Model works
Each layer in the model depends on the services offered by the layer
below it and, in turn, builds on those services to perform a specific set of
communication functions. Protocols are the mechanism by which each layer
accomplishes its communication functions. It then offers these functions
to the layer above it in the form of its own set of services. Note that,
Copyright © 2007, Nortel Networks
.
DPNSS1 private networking interface
Nortel Communication Server 1000
DASS2 Fundamentals
NN43001-571 02.01 Standard
Release 5.5 7 December 2007
illustrates the OSI model.
Figure 1 "How the OSI