OSI model

OSI (Open Systems Interconnection) model was created by the international organization for Standardization (ISO), an international standard-setting body. it had been designed to be a reference model for describing the functions of a communication system. it’s seven layers, with every layer describing a different perform of data traveling through a network.

Here is that the graphical illustration of those layers:

The layers are usually numbered from the last one, that means that the Physical layer is consider to be the primary layer. it’s sensible to be told these layers, since there’ll definitely be a few of queries on the CCNA examination relating to them. most of the people learn the mnemonic „Please do not Throw sausage pizza Away“:

So, what’s the aim of those layers?
They are most typically used by vendors. they permit them to implement some functionality into a networking device, that then permits easier ability with devices from alternative vendors.

Here may be a brief description of every of those layers.

Physicaldefines the way to move bits from one device to a different. It details how cables, connectors and network interface cards are attending to work and the way to send and receive bits.

Data Link – encapsulates a packet in a frame. A frame contains a header and a trailer that enable devices to communicate. A header, most typically, contains a supply and a destination mac address. A trailer contains the Frame Check Sequence field, that is used to find transmission errors.
The data link layer has two sublayers:

1.    Logical Link control – used for flow management and error detection
2.    Media Access control – used for hardware addressing and controlling the access technique

Network – defines device addressing, routing, and path determination. Device (logical) addressing is used to identify a host on a network (e.g. by its ip address).

Transport – segments nice chunks of data received from the higher layer protocols. Establishes and terminates connections between 2 computers. Used for flow control and data recovery.

Session – defines the way to establish and terminate a session between the 2 systems.

Presentation – defines data formats. Compression and encryption are defined at this layer.

Application – this layer is that the nearest to the user. It permits network applications to communicate with alternative network applications.
The following table shows that protocols reside on which layer:

TCP/IP model
The TCP/IP model was created within the Nineteen Seventies by the Defense Advance research Agency (DARPA). just like the OSI model, it describes general guidelines for designing and implementing pc protocols.
It consists of 4 layers: Network Access, Internet, Transport, and Application.

The following show the comparison between the TCP/IP model and OSI model:

As you can see, the TCP/IP model has fewer layers than the OSI model. the applying, Presentation, and Session layers of the OSI model are integrated in just one layer, Application layer, within the TCP/IP model. Also, Physical and data link layers ar known as Network Access layer in the TCP/IP model.

Differences between OSI and TCP/IP model

There are another variations between these 2 models, besides the plain difference within the range of layers. OSI model prescribes the steps required to transfer data over a network and it’s very specific in it, defining that protocol is used at every layer and how. The TCP/IP model isn’t that specific. It can be said that the OSI model prescribes and TCP/IP model describes.


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