OSI Model
OSI Model
OSI Model stands for the Open System Interconnection Model. This model is the model that was published by the ISO "International organization for Standardization" in the 1984. This Model is published just for communication purposes of the different vendors. There were the different devices that manufacturing were different and their pattern of the commination mismatch to each other. So OSI model published for the communication of the different vendors because it is open source so that is the reason this model called the
Open System Interconnection Model.
This Model is known as the theoretical model. This model is classify into the seven layers just for the easy understanding of the networking how the data propagate from sender to the receiver. So following are the seven layers of Open System Interconnection Model:
Fig: OSI Model
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical layer
Application Layer
Application layer is the 7th layer of the OSI Model and if we start the top to bottom then then it will make the 1st layer. So the mainly sequence that mostly common is bottom to top. Application layer is the layer that provide the user interface for user to interact. There are many applications in the computer field and if we see applications are divided into the two types: 1)Computer Application 2)Network Application. We need the network application for the communication and communication is necessary for the resources sharing. There are the multiple protocols that operate on this layer that are the following:
Http that use the port number 80.
Https that use the port number 443.
FTP that use the port number 20-21.
SSH that use the port number 22.
Telnet that use the port number 23.
SMTP that use the port number 25.
TFTP that use the port number 69.
Presentation Layer
Presentation layer is the layer that is the 6th layer of the OSI model and this layer concerns with the presentation of the data. presentation layer is the layer at which encoding of the data and decoding of the data occur and that layers also concerns with the encryption and decryption of the data. Compression and decompression of the data also a part of the presentation layer .
Session Layer
Session layer is the 5th layer of the OSI model and that layer is play an important role for the checking the availability of the destination. That layer is very important layer which is use to establish the session, maintain the session, and the terminating of session. The other main role of this layer is data synchronization of the session streams that are the multiple. This layer work as the dialog controller. This layer is the layer that can directly communicate with presentation layer and the transport layer.
Transport Layer
Transport layer is the layer that is known as the 4th layer of the Open Systems Interconnection Model. This is the layer that concern with the identifying of the service. The main functionality of this layer is Multiplexing and Demultiplexing. The process of segmentation of data also concerns with that layer. Sequencing and reassembling of the data happen on that layer. Flow Control and error correction are also occurring on that layer. TCP transmission control protocol and UDP user datagram protocol work on this layer.
TCP {Reliable, Connection Oriented, Slower than UDP}
UDP{Unreliable, Connectionless, Faster}
Network Layer
Network layer is the 3rd layer of the OSI model and that layer is most common and important layer of the OSI model. That layer is the layer on which our most important and effective device router works. Network layer is the layer that concern with the following :
Logical Addressing
Path Determination
Routing Protocols{RIP, RIPv2, OSPF, BGP, EIGRP}
Routed Protocols {IP, IPX, AppleTalk}
Datalink link Layer
Datalink link layer is the 2nd layer of the OSI model and here switch that is the networking device operate on this layer. Data link layer is the layer that concerns with the local delivery of the frames in between the devices. Here we see the most important protocols that are the following :
HDLC
HDLC stands for the Higher Level Datalink Control Protocol.
Cisco Proprietary.
No support Authentication, compression, and error correction.
PPP
PPP stands for the point to point protocol.
Standard Protocol.
Support Authentication, compression, and error correction.
Physical layer
This layer is the first layer of the OSI model. Physical layer is the layer that concern with the bits transfer of the from one medium to other medium. Hybrid Universal Broadcast device is the device that work on that layer. This layer concerning with how the bit converted into the signals.