Nortel DMS-250 Reference Manual page 25

Figure 1-2
OSI seven-layered reference model
Layer 7
Application
.
.
.
Layer 6
Presentation
.
.
.
Layer 5
Session
.
.
.
Layer 4
Transport
.
.
.
Layer 3
Network
Services
to layer 3
Layer 2
Link
Services
to layer 2
Layer 1
Physical
The following list describes the seven OSI layers and their associated
functions:
Layer 1, Physical—Maintains, connects, and disconnects the circuits that
form the communication facility. Layer 1 handles the electrical,
mechanical, and functional control of a data interface.
Layer 2, Link—Provides services related to the reliable interchange of
data across the data link established by the physical layer. This layer
manages the establishment, maintenance, and release of data link
connections. Layer 2 controls the flow of data while supervising error
recovery and link flow control.
Layer 3, Network—Provides services related to moving data through a
network. Layer 3 provides and manages logical channel connections
between end points of a network.
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
Protocols
Protocols
Protocols
Protocols
Protocols
Protocols
Protocols
Introduction 1-3
Layer 7
Application
.
. .
Layer 6
Presentation
.
. .
Layer 5
Session
.
. .
Layer 4
Transport
.
. .
Layer 3
Network
Services
to layer 3
Layer 2
Link
Services
to layer 2
Layer 1
Physical