Communication Technologies
OSI / TCP/IP mODELS
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OSI Model
OSI stands for Open Systems Interconnection. The OSI Model has seven layers. These are the application layer, presentation layer, session layer, transport layer, network layer, data link layer and the physical layer.
The application layer of the OSI Model helps programs to communicate with other programs.
“The application layer provides services for an application program to ensure that effective communication with another application program in a network is possible.”
Presentation layers are used to format data before it is presented to the application layer. It acts like a translator, converting data into suitable formats for each layer to understand.
The session layer controls communication between two layers using the communication system set up by the transport layer.
“The session layer allows session establishment between processes running on different stations.”
The transport layer helps to make sure that nothing goes wrong when sending or receiving messages, so that there is no errors when they are delivered
“The network layer controls the operation of the subnet, deciding which physical path the data should take based on network conditions, priority of service, and other factors.”
The data link layer is there to make sure the transfer of data between nodes are error-free. The transmission is done over the physical layer.
“The physical layer, the lowest layer of the OSI model, is concerned with the transmission and reception of the unstructured raw bit stream over a physical medium. It describes the electrical/optical, mechanical, and functional interfaces to the physical medium, and carries the signals for all of the higher layers.”
TCP/IP Model
TCP/IP stands for Transmission Control Protocol/Internet Protocol. This model has only four layers; the application layer, the transport layer, the internet layer and the subnet layer.
The application layer....
“Defines TCP/IP application protocols and how host programs interface with transport layer services to use the network.”
This is the main interface layer which provides network services to different applications. Examples of protocols that use this layer are HTTP, SMTP and FTP.
The transport layer....
“Provides communication session management between host computers. Defines the level of service and status of the connection used when transporting data.”
This layer is designed to help the transmission of information between layers. Examples of two protocols that operate at this layer are TCP and UDP.
The internet layer....
“Packages data into IP datagrams, which contain source and destination address information that is used to forward the datagrams between hosts and across networks. Performs routing of IP datagrams.”
This layer uses a 'packet' which has a source IP address, destination IP address and the data that needs to be transmitted.
Network Access Layer....
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Network Access Layer defines details of how data is physically sent through the network, including how bits are electrically or optically signaled by hardware devices that interface directly with a network medium, such as coaxial cable, optical fiber, or twisted pair copper wire."