Introduction 1-3
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
Figure 1-2
OSI seven-layered reference model
Protocols
Protocols
Protocols
Protocols
Layer 7
Layer 3
Layer 2
Layer 1
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Services
Services
Layer 7
Layer 3
Layer 2
Layer 1
Services
Services
to layer 3 to layer 3
to layer 2 to layer 2
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Protocols
Layer 6
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Layer 6
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Protocols
Layer 5
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Layer 5
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Protocols
Layer 4
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Layer 4
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Physical Physical
Link Link
Network Network
Transport Transport
Session Session
Presentation Presentation
Application Application
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.
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