TCP/IP and OSI Comparisons

Internet Protocol (IP) version 4 (IPv4) is the current standard “IP” protocol used with TCP/IP — Transmission Control Protocol/Internet Protocol — which is the protocol for Internet addressing. Like the Open System Interconnection (OSI) model, TCP/IP has its own model.

The OSI model and the TCP/IP models were both created independently. The TCP/IP network model represents reality in the world, whereas the OSI mode represents an ideal. With that said, the TCP/IP network model matches the standard layered network model as it should.

The following figure shows the relationship between the OSI model and the TCP/IP model.

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The TCP/IP network model has four basic layers:

  • Network interface (layer 1): Deals with all physical components of network connectivity between the network and the IP protocol

  • Internet (layer 2): Contains all functionality that manages the movement of data between two network devices over a routed network

  • Host-to-host (layer 3): Manages the flow of traffic between two hosts or devices, ensuring that data arrives at the application on the host for which it is targeted

  • Application (layer 4): Acts as final endpoints at either end of a communication session between two network hosts

 

• Layer 7 – application: This layer works with the application software to provide communications functions as required. It verifies the availability of a communications partner and the resources to support any data transfer. It also works with end applications such as domain name service (DNS), file transfer protocol (FTP), hypertext transfer protocol (HTTP), Internet message access protocol (IMAP), post office protocol (POP), simple mail transfer protocol (SMTP), Telenet, and terminal emulation.

• Layer 6 – presentation: This layer checks the data to ensure that it is compatible with the communications resources. It ensures compatibility between the data formats at the applications level and the lower levels. It also handles any needed data formatting or code conversion, as well as data compression and encryption.

• Layer 5 – session: Layer 5 software handles authentication and authorization functions. It also manages the connection between the two communicating devices, establishing a connection, maintaining the connection, and ultimately terminating it. This layer verifies that the data is delivered as well.

• Layer 4 – transport: This layer provides quality of service (QoS) functions and ensures the complete delivery of the data. The integrity of the data is guaranteed at this layer via error correction and similar functions.

• Layer 3 – network: The network layer handles packet routing via logical addressing and switching functions.

• Layer 2 – data link: Layer 2 operations package and unpack the data in frames.

• Layer 1 – physical: This layer defines the logic levels, data rate, physical media, and data conversion functions that make up the bit stream of packets from one device to another.