Today, we’re going to look at OSI (Open System Interconnect). It is a network interconnection model published by ISO in 1985, which defines a seven-layer framework for network interconnection. Its contents are briefly described as follows:
| The hierarchy | The name of the | explain |
|---|---|---|
| 1 | The physical layer | Transmission of bitstreams through physical media. Define pins, voltages, and network card, cable, hub, etc. |
| 2 | Data link layer | Responsible for network addressing, error detection and correction. Such as Ethernet, wireless local area network and other levels. |
| 3 | The transport layer | Provide reliable and transparent data exchange for upper level, including error handling and flow control, etc. Such as TCP, UDP protocol. |
| 4 | The network layer | The connection between two nodes is established through IP addressing, and routing occurs at this layer. Such as IP protocol. |
| 5 | The session layer | Set up and manage communication conversations between applications. |
| 6 | The presentation layer | Handling the representations of the information exchanged, such as format, encryption, and compression. |
| 7 | The application layer | Complete the external service of the application. Such as the HTTP protocol to browse the website, send mail SMTP protocol and so on. |
When we buy network equipment for a company or home, we usually search the Internet for three types: hubs, switches, and routers. Here is how network layering relates to hardware devices.
Hubs work at OSI Layer 1 (Physical Layer) and do nothing but transmit electrical signals to devices connected to them.
A switch is a layer 2 (link layer) device that is addressed by broadcasting on the same network segment and communicates with hosts on the same network segment using the MAC address of the target host. There are also switches on the market that have added routing capabilities, which we call 3-tier switches.
Routers are Layer 4 (network layer) devices that learn from each other to maintain a routing table that is responsible for addressing and forwarding across network segments.
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