OSI Model & TCP/IP Model
The OSI and TCP/IP models are communications standard over a network. The key difference is that OSI is the theoretical and conceptual model, while TCP/IP is the real-life applicable model.
❖ TCP/IP Application Layer — OSI L7, L6, L5
Application layer in TCP/IP model is responsible for user interfaces and provides lots of protocols for users. This layer corresponds to application/presentation/session layer in OSI model.
OSI Layer 7 : Application
The application layer provides interfaces and network services to users. In this layer, users make some data to be transferred and read data received from a server. According to protocols, a specific service is provided. HTTP for Internet, FTP for file transfer, Telnet for remote access. DNS, DHCP, SMTP, and SNMP are also protocols.
OSI Layer 6 : Presentation
In the presentation layer, the data users created is interpreted so that computer recognize it. It determines the way of encoding/decoding. A music file is represented in .mp3 extension. A picture file in .jepg or .png, a text file in .txt or .doc etc.
OSI Layer 5 : Session
Sessions are communication channels between applaications. So the session layer is responsible for establishing, disconnecting, maintaining connections between applications or networks.
❖ TCP/IP Transport Layer — OSI L4
Transport layer in TCP/IP model decides how to transmit data rom a host to a host. It corresponds to transport layer in OSI model.
OSI Layer 4 : Transport
The transport layer determines how the data is transmitted and can distinguish the port number of a service.
There are two types of data transmission methods, TCP and UDP, and we can distinguish them by reliability and speed.
❖ TCP/IP Network Layer — OSI L3
Network layer(or internet layer) in TCP/IP model logically transmits data packets based on IP address. It corresponds to network layer in OSI model.
OSI Layer 3 : Network
The network layer determines the optimal data path from the source to the destination based on the logical address. IP addresses are used for logical addresses.
❖ TCP/IP Access Layer — OSI L2, L1
Access layer in TCP/IP model is responsible for real transmission of data in the form of bits. It corresponds to data-link and physical layer in OSI model.
OSI Layer 2 : Data Link
The data link layer makes a connection or disconnection between two physically different nodes on a network. It also determines a transmission type on the format of data. There are two parts in this layer. LLC (logical link control) and MAC (media access control).
OSI Layer 1 : physical
The physical layer is literally real physical forms of a network like ethernet cables and NIC etc. In this layer, data frames are converted to bit signals and transmitted to other devices.
