What is OSI model?
The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to their underlying internal structure and technology. ... The original version of the model defined seven layers.
Let's start with the first one:
1)The physical layer is the first layer of the Open System Interconnection Model (OSI Model). The physical layer deals with bit-level transmission between different devices and supports electrical or mechanical interfaces connecting to the physical medium for synchronized communication.
Physical Layer includes:
-electrical /optional protocol voltage level
-the timing of voltage change
-physical data rates -maximum transmission distance
-physical connectors
-network interface cards
2)The Data-Link layer is the protocol layer in a program that handles the moving of data in and out across a physical link in a network. The Data-Link layer is layer 2 in the Open Systems Interconnect (OSI) model for a set of telecommunication protocols.
Data Link layer includes:
-media access control (MAC)
-logical link control (LLC)
-play at this layer:-PPP (point-to-point protocol), -FR (frame relay ),-Ethernet,-Token Ring,-LAPD (Link Access Procedures, D channel ),-FDDI ,
Switches are layer 2 devices except for layer 3 ones
3)The network layer is the third level of the Open Systems Interconnection Model (OSI Model) and the layer that provides data routing paths for network communication. Data is transferred in the form of packets via logical network paths in an ordered format controlled by the network layer.
Network Layer includes:
-routing of that across a logical network path is enabled here and defines packets and addressing format.
-IP (internet protocol)
-IPX (internetwork packet exchange)
-ARP(address resolution protocol)
-ICMP(Internet Control Message Protocol)
4)Transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet Protocol Suite and the Open Systems Interconnection (OSI). The protocols of the layer provide host-to-host communication services for applications.
-TCP
-UDP
-SPX
-Flow and error control
5)The session layer provides the mechanism for opening, closing and managing a session between end-user application processes, i.e., a semi-permanent dialogue.
-RPC
-NetBios
6)The presentation layer is used to present data to the application layer (layer 7) in an accurate, well-defined and standardized format. The presentation layer is sometimes called the syntax layer.
-ASCIIm
-EBCDICm jpg
-MIDI encryption
-Compression and translation
7)Application Layer is the layer of the ISO Open Systems Interconnection (OSI) model that interacts with software applications that implement a communicating component.
-Telnet
-FTP
-WWW
-SMTP
-Interface by which user application access the network.
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