Understanding Network Layers & Transparency in ISO/OSI Model, Study notes of Computer Science

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Mar 28, 2005 -- Lecture 25

22C:

Computer Security

Douglas W. Jones Department of Computer Science

Networks

Network Layers The ISO/OSI model Application layer Presentation layer Session layer Transport layer Network layer Data Link layer Physical layer Frequently simplified in practice But even archaic network protocols can be examined in these terms.

The Presentation Layer Network API application programmer view of network Isolate program from implementation Package network services sensibly useful abstractions related to need

The Session Layer Organize communication into: reliable streams of text from end to end Telnet protocol is example remote procedure calls Users are isolated from underlying message structure physical network topology

The Network Layer Move data between machines isolate users from actual topology Once the data reaches the destination kick it upstairs to the transport layer Responsible for routing this is a hard enough problem, even without security issues.

Data Link Layer Move data over one link between machines not concerned with global topology deals with details of the link itself interrupt handlers timeouts collision resolution