Computer Networks - 5

In software architecture, layers are created to separate concerns and provide different levels of abstraction.

In the OSI model, each layer is designed to perform a specific, well-defined function.

OSI stands for Open Systems Interconnection, which is the standard reference model for network communication.

The OSI reference model is defined by seven distinct layers.

Systems that are designed to communicate with other systems based on standard protocols are known as open systems.

The OSI model was developed by the International Organization for Standardization (ISO).

Data transfer services in networking can be either confirmed (requiring acknowledgment) or unconfirmed.

ISO stands for the International Organization for Standardization. It is an independent, non-governmental international organization that develops standards to ensure the quality, safety, and efficiency of products, services, and systems.

In the OSI service model, a CONNECT primitive is used to establish a connection, which requires a handshake between the two entities. This process is confirmed, meaning the initiator receives a response from the peer entity.

The confirm primitive is used by the service provider to inform the service user that a previously requested action has been completed or acknowledged by the peer entity.

The request primitive is used by a service user to ask the service provider to perform a specific action or service.

The response primitive is used by a service user to reply to an indication primitive that was previously received from the service provider.

The indication primitive is used by the service provider to notify a service user that an event has occurred, such as the arrival of data or a connection request from a peer.

Service primitives are categorized into four standard classes: request, indication, response, and confirm.

Primitives are the formal commands or messages exchanged between the service user and the service provider to initiate or manage actions.

Primitives are used to both request actions and report on the status or results of those actions back to the user.

A service definition is formally described by the set of primitives that the service provider makes available to the service user.

The OSI model consists of seven layers. The first layer, at the bottom, is the Physical layer, which deals with the transmission of raw bit streams over a physical medium.

The third layer of the OSI model is the Network layer, which is responsible for routing data packets between different networks.

The fifth layer of the OSI model is the Session layer, which manages and terminates connections between applications.

The fourth layer of the OSI model is the Transport layer, which ensures reliable data transfer and error recovery between end systems.

TPDU stands for Transport Protocol Data Unit, which is the unit of data exchanged between transport layer entities.

The second layer of the OSI model is the Data Link layer, which provides node-to-node data transfer and error detection for the physical layer.

The seventh and top layer of the OSI model is the Application layer, which provides network services directly to user applications.

The sixth layer of the OSI model is the Presentation layer, which handles data formatting, encryption, and compression.