Notes
OSI Model
The OSI model is composed of seven ordered layers: physical (layer 1), data link (layer 2), network (layer 3), transport (layer 4), session (layer 5), presentation (layer 6), and application (layer 7).
- Open system interconnection model
- 7 Layers
- Developed by ISO
OSI Model Diagram
| Layer number | Name |
|---|---|
| 7 | Application layer |
| 6 | Presentation layer |
| 5 | Session layer |
| 4 | Transport layer |
| 3 | Network layer |
| 2 | Data link layer |
| 1 | Physical layer |
## Basic working
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Application Layer : Layer consists many protocols such as file transfer protocol FTP , web service HTTP & HTTPS and for emails SMTP.
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Presentation Layer : Presentation layer handles translation to binary , compresion & encryption/decryption.
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Session Layer : Creates , manages & ends session. Authentication is also done here. Tracks received and sent data packerts.
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Transport Layer : DIvided data into segments and keeps track where to send data . Also do flow control means speed at data travels to application. Also handles error controls. Have protocols like TCP & UDP.
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Network Layer : Handles transmission. Handles logical addressing , path determination and routing. Data handles in terms of packets. Protocols like IPv4 , IPv6 , ICMPv4 & ICMPv6.
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Data Link Layer : physical addressing like MAC done here. Also does framing i.e. creating frames.
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Physical Layer : Handles data conversion such as signal to bits . Determines types of media like light i.e. optical fiber, voltage like cable or signal like wifi.
Function
Application Layer
- Network Virtual Terminal : To allow remote user to get software version of physical terminal
- File transfer , access and management : To access files in a remote host , change or update file on system
- Email : Email forwarding and storage
- Directory services : Distributed database sources and access gloabal information
Presentation Layer
- Translation : Converts information so system can understand it.
- Encryption : Encryptes outgoing traffic and decryptes incoming data
- Compression : Compression and decompression of data for efficient data transfer.
Session Layer
- Dialog control : Allows two processes to take place either in half duplex or full duplex mode.
- Synchronization : Adds checkpoints into stream of data for control flow.
Transport Layer
- Service-point addressing : Identifies and differentiate services using Ports .
- Segmentation and reassembly : Messages are divided into segments for transmission and reassembled upon arriving.
- Connection control : Connectionless or connection-oriented services for better transmission policy.
- Flow control : To control flow of data for end to end transmission.
- Error control : To avoid errors and cover up errors if it happens.
Network Layer
- Logical Addressing : Logical addressing using IP to distinguish multiple devices on internet.
- Routing : Transfer of packets from one device to other.
Data link Layer
- Framing : Divide packets into frames for manageable data units.
- Physical addressing : Physical addressing using MAC address.
- Flow control : Control flow of data transfer
- Access control : Determine access to link for two or more devices.
- Error control : Add trailer to achieve error control.
Physical Layer
- Physical characteristics : Defines transmission media
- Representation of bits : Bit length and encoding
- Data rate and synchronization : Synchronize data transfer and manage data rate
- Physical topology : Topology
- Transmission mode : Either simplex , half duplex or duplex
