Transcript The ISO/OSI Reference Model

Microcomputer Networking II
The ISO/OSI Reference Model
• The Model
• Functionality of Layers
• Example Networks
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The OSI Model
• Basic principles of layered architecture:
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Each layer means different layer of abstraction
Each layer should perform a well defined function
The functions of layer should promote standardization
The information flow across the interfaces should be
minimized
– The number of layers should be large enough to
separate functionality and small enough to keep the
architecture under control
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The OSI Model
• Introduced in 1983
• The OSI model has seven layers
• The OSI model is not a network architecture
– It does not specify the exact services ant protocols
– It specifies what kind of functions each layer should
perform
– ISO has produced standards for each layer as separate
documents
• Good model to study networking concepts
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The OSI reference model
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Figure from book Computer Networks 3rd ed., by A.S.
Tanenbaum
Microcomputer Networking II
The Physical Layer
• Transmission of raw bits over communication
channel
• Transmission media, its physical properties
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Magnetic media
Twisted pair
Coaxial cable
Fiber optics
Wireless transmission
• Data rate of communication channel
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The Data Link Layer
• Providing error-free transmission line for upper
layers between two adjacent nodes
• Breaking information into frames and using
services of physical layer
– Error-detecting codes
– Error-correcting codes
• Ensuring uniqueness and correctness of frames
• Flow control between sender and receiver
• Access to shared communication channel
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The Network Layer
• Routing of data packets from source host to
destination host
• Controlling network congestion
• Accounting of network traffic
• Internetworking - interconnection of multiple
heterogeneous networks
– Addressing issues
– Packet sizes
– Protocol differences
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The Transport Layer
• Transmission of data between software entities on
end-point hosts
• Providing channel for each application, mapping
channels to Network Layer connection
• Ensuring uniqueness and correctness transmitted
of data units
• Quality of Service (QoS) management
• Connection management, naming
• Flow control and buffering
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The Session Layer
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Establishment of sessions between applications
Enhancing Transport Layer services
Dialogue control: directions, etc.
Token management
Synchronization: checkpoints
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The Presentation Layer
• Providing general solutions to syntax and
semantics transmitted data
• Encoding of data “on the wire” into intermediate
format
• Compression of data
• Encryption of data
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
The Application Layer
• All the network application software
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Network virtual terminals
File transmission
Electronic mail
File servers
Database servers
Application servers
Object servers
Transaction servers
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Microcomputer Networking II
Data Transmission in OSI model
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Figure from book Computer Networks 3rd ed., by A.S.
Tanenbaum
Microcomputer Networking II
The TCP/IP Reference Model
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Figure from book Computer Networks 3rd ed., by A.S.
Tanenbaum
Microcomputer Networking II
Initial TCP/IP protocols
St. Cloud State University
MCS 426, Fall 1999 Instructor: Adomas Svirskas
Figure from book Computer Networks 3rd ed., by A.S.
Tanenbaum