The open Systems Interconnection (OSI) Reference design is a conceptual framework that defines functions that the networking or telecommunication system individually from the underlying technology infrastructure. That divides data communication into 7 abstraction layers and standardizes protocols into proper groups the networking usability to ensure interoperability within the interaction system regardless of the technology type, vendor, and model.

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The OSI design was originally occurred to facilitate interoperability in between vendors and to specify clear criter for network communication. However, the enlarge TCP/IP model remains the ubiquitous reference framework for Internet interactions today.

The 7 class of the OSI model

This image illustrates the 7 layers that the OSI model. Below, we’ll briefly define each layer, native bottom come top.


1. Physical

The lowest layer the the OSI design is came to with data communication in the form of electrical, optic, or electromagnetic signal physically transmitting information between networking devices and also infrastructure. The physics layer is responsible because that the communication of unstructured life data streams end a physics medium. It specifies a range of aspects, including:

Electrical, mechanical, and also physical systems and networking gadgets that encompass specifications such as cable size, signal frequency, voltages, etc.Modulation, switching, and interfacing through the physical transmission mediumHardware including networking devices, antennas, cables, modem, and intermediate gadgets such as repeaters and also hubs

2. Data Link

The 2nd layer the the OSI model concerns data transmission in between the nodes within a network and manages the connections between physically connected devices such as switches. The raw data got from the physics layer is synchronized and also packaged right into data frames the contain the vital protocols to route information between ideal nodes. The data connect layer is further split into two sublayers:

The Media accessibility Control (MAC) sublayer is responsible for managing accessibility and permissions to transmit data between the network nodes. The data is sent sequentially and also the class expects acknowledgement for the encapsulated life data sent between the nodes.

3. Network

The 3rd layer of the OSI version organizes and transmits data between multiple networks.

The network great is responsible for routing the data via the finest physical path based on a variety of factors including network characteristics, best easily accessible path, web traffic controls, congestion of data packets, and priority that service, amongst others. The network great implements reasonable addressing because that data packets to distinguish in between the resource and location networks.

Other functions incorporate encapsulation and also fragmentation, congestion controls, and error handling. The outgoing data is split into packets and incoming data is reassembled into info that is consumable in ~ a higher application level. Network layer hardware includes routes, bridge routers, 3-layer switches, and also protocols together as web (IPv4) Protocol version 4 and Internet Protocol version 6 (IPv6).

4. Transport

The fourth layer that the OSI version ensures complete and reliable distribution of data packets.

Common protocols incorporate the Transmission control Protocol (TCP) because that connection-oriented data transmission and also User Datagram Protocol (UDP) for connectionless data transmission.

5. Session

As the first of 3 layers that deal with the software level, the conference layer manages sessions between servers to coordinate communication. Conference refers to any type of interactive data exchange between two entities in ~ a network. Common examples encompass HTTPS sessions that enable Internet individuals to visit and browse websites for a specific time period. The conference Layer is responsible because that a selection of attributes including opening, closing, and also re-establishing conference activities, authentication and authorization of communication between specific apps and also servers, identify full-duplex or half-duplex operations, and also synchronizing data streams.

Common session Layer protocols include:

Remote procedure call protocol (RPC)Point-to-Point Tunneling Protocol (PPTP)Session regulate Protocol (SCP)

6. Presentation

The sixth layer that the OSI design converts data formats between applications and also the networks. Responsibilities of the presentation great include:

The presentation layer, likewise called the syntax layer, maps the semantics and also syntax of the data such that the received info is consumable for every unique network entity. For example, the data we deliver from our encryption-based communication application is formatted and also encrypted at this layer before it is sent throughout the network.

At the receiving end, the data is decrypted and also formatted into text or media information as originally intended. The presentation layer additionally serializes facility information into transportable formats. The data streams room then deserialized and reassembled into original object layout at the destination.

7. Application

The application layer involves the networking processes at the application level. This layer interacts straight with end-users to carry out support because that email, network data sharing, paper transfers, and also directory services, amongst other dispersed information services. The upper most layer that the OSI design identifies networking entities to facilitate networking inquiry by end-user requests, determines resource availability, synchronizes communication, and also manages application-specific networking requirements. The applications layer also identifies constraints in ~ the applications level such together those associated with authentication, privacy, quality of service, networking devices, and also data syntax.

Common applications layer protocols include:

File transfer Protocol (FTP)Simple Mail transport Protocol (SMTP)Domain Name mechanism (DNS)

The web doesn’t welcome OSI

The OSI version is commonly criticized because that an natural implementation complexity that makes networking operations inefficient and also slow. The scholastic approach to arising the OSI protocol suite relied on instead of existing protocols across all interaction layers with far better alternatives.

This technique failed to get traction in the industry; sellers had currently invested significant resources in TCP/IP products and had to control interoperability v the substantial choices the protocols and specifications available by the OSI model. Additionally, academia itself taken into consideration the OSI model as an invention politically influenced by the europe telecommunication and also U.S. Government authorities.

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The larger TCP/IP architecture model had already itself in real-world network environments. It offered as a solid foundation for the Internet–including every one of the security, privacy, and performance-related challenges. Ongoing research and development, investments, and industry-wide fostering of the OSI model can have make today’s cyber people a various (and perhaps better) place, but the pragmatism that the TCP/IP model gave us the internet that prevails today.