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: – – – –

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 Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum MCS 426, Fall 1999 Instructor: Adomas Svirskas

Microcomputer Networking II

The Physical Layer • Transmission of raw bits over communication channel • Transmission media, its physical properties – – – – –

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 • • • • •

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 – – – – – – – –

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 Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum MCS 426, Fall 1999 Instructor: Adomas Svirskas

Microcomputer Networking II

The TCP/IP Reference Model

St. Cloud State University Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum MCS 426, Fall 1999 Instructor: Adomas Svirskas

Microcomputer Networking II

Initial TCP/IP protocols

St. Cloud State University Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum MCS 426, Fall 1999 Instructor: Adomas Svirskas