In computer networking, the layered concept of networking was developed to accommodate changes in technology. Each layer of a specific network model may be responsible for a different function of the network. Each layer will pass information up and down to the next subsequent layer as data is processed.
The OSI (Open System Interconnection) Network Model Standard
The OSI network model layers are arranged here from the lower levels starting with the physical (hardware) to the higher levels.
The 7 layers of OSI
Figure from webopedia
- Physical Layer
An application that communicates with other computers that corresponds to the application's communication service.
- Data Link Layer
It defines how to transfer data on a single link
- Network Layer
This layer defines the end-to-end packet transport, which defines the logical addresses that identify all nodes and also defines how the routes are implemented and how they are learned.
- Transport Layer
The functions of this layer include whether to choose the error recovery protocol or the error-free recovery protocol, and multiplex the input of different application data streams on the same host, and also include the function of reordering received packets that are not in the correct sequence.
- Session Layer
It defines how to start, control and end a session, including the control and management of multiple bidirectional messages so that applications can be notified when only a portion of a continuous message has been completed, so that the data seen by the presentation layer is contiguous, In some cases, if the presentation layer has received all of the data, the data represents the presentation layer.
- Presentation Layer
The main function of this layer is to define the data format and encryption.
- Application Layer
An application that communicates with other computers that corresponds to the application's communication service.
What is presentation layer?
The presentation layer is located at the sixth level of the OSI model, it is responsible for the delivery and formatting of information to the application layer for further processing or display. This type of service is needed because different computer architectures use different data representations. In contrast to providing transparent data transport at the fifth level, the presentation layer handles all issues related to data presentation and transport, including translation, encryption, and compression.
Figure from https://www.xmind.net/m/WV6b
Presentation layer functions
The actual functions of the presentation layer include the following aspects:
- Network security and confidentiality management, text compression and packaging, virtual terminal protocol (VTP).
- Syntax conversion - The abstract syntax is converted to the transfer syntax, and the other side to achieve the opposite conversion (transfer syntax will be converted to abstract syntax). Involved in the contents of the code conversion, character conversion, data format modification, as well as data structure operation adaptation, data compression, encryption and so on.
- Grammar negotiation - According to the requirements of the application layer to negotiate the appropriate choice of context, that is, to determine the transmission syntax and transmission.
- Connection management - Including the use of the session layer service to establish a connection, manage data transport and synchronization control over this connection (using the corresponding services at the session level), and terminate the connection either normally or absently.
Presentation layer of OSI model
It has developed a series of standards such as DP8822, DP8823, DIS6937 / 2 for service, agreement, text communication symbol. The presentation layer acts as a translator between the application and the network, mainly addressing the syntax representation of user information, ie, providing formatted representations and translation data services. Data compression, decompression, encryption, decryption are completed in this layer.
Presentation layer protocols
Other protocols sometimes considered at this level (though perhaps not strictly adhering to the OSI model) include:
- Apple Filing Protocol (AFP)
- Independent Computing Architecture (ICA), the Citrix system core protocol
- Lightweight Presentation Protocol (LPP)
- NetWare Core Protocol (NCP)
- Network Data Representation (NDR)
- Telnet (a remote terminal access protocol)
- Tox, The Tox protocol is sometimes regarded as part of both the presentation and application layer
- eXternal Data Representation (XDR)
- 25 Packet Assembler/Disassembler Protocol (PAD)