ISO/OSI Model

1
ISO/OSI Model

• Open Systems Interconnection
• Developed by the International Organization for
  Standardization (ISO)
• Seven layers
• A theoretical system delivered too late!
• TCP/IP is the de facto standard

2
OSI Layers All People Seem To Need Data
ProcessingPlease Do Not Throw Sausage Pizza
Away.

• Application
• Presentation
• Session
• Transport
• Network
• Data Link
• Physical

3
Communications Across Layers

• Peer to peer processes
• Each layer only sees its peer layer
• Virtual communication between layers

4
Communication Between Layers

• Envelopes
• Each layer wraps the information passed to it in
  an appropriate header and trailer if required.
• Headers are added to layers 2-6
• Trailers added to layer 2

5
OSI Layers
Figure 3-2
6
Organization of Model

• Network Support Layers
• Deal with the physical aspects of moving data
  from one device to another
• Layer 1 Bits
• Layer 2 Packets and Addressing/Flow control
• Layer 3 Logical Addressing/Routing

7
Organization of Model

• Layer 4 Transport
• Reliable delivery of messages
• Service point addressing port address
• Segmentation and re-assembly
• Connection control
• Flow Control
• Error Control

8
Organization of Model

• Layer 5 Session
• Dialog Controller
• Synchronization
• Layer 6 - Presentation
• Translation
• Encryption
• Compression

9
Organization of Model

• Layer 7 Application
• User Access to Network Services
• X.400 Message handling email
• X.500 Directory Services
• FTAM

10
An Exchange Using the OSI Model
Figure 3-3
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Figure 3-4
Physical Layer
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Figure 3-5
Data Link Layer
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Figure 3-6
Data Link Layer Example
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Figure 3-7
Network Layer
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Network Layer Example
Figure 3-8
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Figure 3-8-continued
Network Layer Example
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Transport Layer
Figure 3-9
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Figure 3-10
Transport Layer Example
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Figure 3-10-continued
Transport Layer Example
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Figure 3-11
Session Layer
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Figure 3-12
Presentation Layer
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Figure 3-13
Application Layer
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Figure 3-14
Summary of Layer Functions
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
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OSI v TCP/IP