HUT Comms. Lab, Timo O. Korhonen
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Sends data block with synchronization, error and flow
control for end-to-end connections*. Layer of bridges.
Transforms electrical signal into bits. In local networks
standardized by 802.x standard. Layer or repeaters
Provides independence of applications from
differences in data presentations
User access to OSI environment applications
The OSI-functions
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical
Establishing, managing and termination connections
(sessions) between cooperating applications
Provides reliable, transparent data transfer for
lower level data segments or blocks
Gives routing service for transport layer.
Layer of routers.
Text Box: Gateway Layers
Gateway Layers
*For instance in a classroom of workstations
Text Box: LAN Layers
LAN Layers
ISO was founded 1947 including 90 countries. Includes 160 technical comities,
590 subcommittees and 1300 workgroups.
OSI: ISO standard describing how systems should be interconnected.
The fundamental principle is to define network functions but not the realization.
Network layers are defined by interfaces transmitting acknowledgments, requests,
and other information. Functions of a layer are called services.