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Layer 6 OSI Model

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High Level Explanation:

Layer 6 is responsible for filtering and processing data to be later displayed to the end user or processed by the node in which the data was planed to be send , without it things would get very complicated because everyone is using a different OS or browser meaning that if the data was processed exactly as it was sended from the server the user would probably get a syntax error, each browser and OS has a different way to handle data received for example if you are writing a paragraph and it has spaces, tabs or any kind of special characteristic that needs to be added, layer six will do it so then layer seven can easily take care of the rest. In the end we can interpret it as a translator between different data formats and computer systems.

Low Level Explanation:

Layer 6 will get the mapping (a set of instructions) distributed by the browser, OS, framework, etc that the data needs to be received and encapsulated into session protocol data units, and passed down the stack, which means that data is processed, filtered and send into stacks of data to layer 7. For example when you send a string of data like “Bye World” it will be processed by layer six as “Bye\0World” because it is adding a null-terminated string which is a standart format to handle data. It also encrypts and decrypts data, so, if you are using https instead of http it needs to decrypts all data send to you using the key that you and the server has exchanged.

Hardware:

This layer doesn’t really have any hardware, because its only purpose is mainly presenting protocols.

Protocols:

All the following protocols have one main definition which is allowing data to be transferred between different kinds of computer systems.

  • Lightweight Presentation Protocol

  • External Data Representation (XDR)

  • Network Data Representation

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Layer 5 OSI Model

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High Level Explanation:

Layer 5 is responsible for maintaining connections and for controlling ports and session during the process of messages transfer between nodes.

Low Level Explanation:

The session layer has a lot of correlation with layer four for the reason that both are responsible for the integrity of the data, while layer four verifies that data was lost or not, layer five will do the hard work by establishing, managing and terminating connections to the other node using the ISO-SP, OSI session-layer protocol (X.225, ISO 8327).

Hardware:

This layer doesn’t really have any hardware, because its only purpose is mainly managing protocols.

Protocols:

You will notice that all protocols mentioned bellow do very similar functions that may clarify a little more why we use layers for computer networking as a separation method.

  • ITU X.225 (ISO 8327) :

    • Also known as ISO 8327 is a connection-oriented session layer protocol in the Open Systems Interconnection (OSI) model. It does literally what we have just mentioned about layer 5, it establishes, manage and terminate communications between node. More about this layer…
  • AppleTalk Data Stream Protocol (ADSP)

    • ADSP is a session-level protocol that provides symmetric, connection-oriented, full-duplex communication between two sockets on the AppleTalk internet. In addition, it handles flow-control and reliability.
  • Network Basic Input/Output System (NetBIOS)

    • NetBIOS is an acronym for Network Basic Input/Output System. It provides services related to the session layer of the OSI model allowing applications on separate computers to communicate over a local area network.
  • Password Authentication Protocol (PAP)

    • Password Authentication Protocol is a password-based authentication protocol used by Point to Point Protocol to validate users.
  • Remote Procedure Call Protocol (RPC)

    • In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure (subroutine) to execute in a different address space (commonly on another computer on a shared network)

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Layer 4 OSI Model

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High Level Explanation:

Transport layer is very self explanatory by itself, it will be responsible for the for the delivery of the package. Imagine that you as a person can send the letter to a address (layer three) but who actually make sure that the latter will reach the right person ? that is right the mail person (layer four). It controls and responds if the node in which the “address” is destined to is reachable and if not how to handle it (error control). And what if you send a huge component let’s say a industrial machine, you can’t really send it using only one package or transport that is when the “mail person” will choose which boxes to use or if it will be transported via plane, ship, truck etc (Segmentation)

Low Level Explanation: reference where I have taken this paragraph

The transport layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control. Some protocols are state- and connection-oriented (TCP). This means that the transport layer can keep track of the segments and retransmit those that fail delivery. The transport layer also provides the acknowledgement of the successful data transmission and sends the next data if no errors occurred. The transport layer creates segments out of the message received from the application layer. Segmentation is the process of dividing a long message into smaller messages.

In other words the layer four is also the spokesperson between layer 3 and 5,6, and 7 . It will tell layer three if a package failed to be delivered and ask another one to substitute the one that hasn’t reached its destination, and layers 5,6, and 7 which protocol they will be using , number of packages that they are supposed to receive and so on.

Hardware:

This layer doesn’t really have any hardware, because its only purpose is mainly managing protocols.

Protocols:

The protocols used by this layer are the TCP and UDP.

TCP: is a connection-oriented protocol which will make sure that every bit send by the server is delivery to the destined node for example when you send a message or send a email to a person.

UDP: is a connection-less protocol which doesn’t care all data send will be delivery or not as long as it gets send to the destined node like all steaming platform uses when a person is live streaming something.

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