What is the Open Systems Interconnection model (OSI model)?
About
This page is about the Open Systems Interconnection (OSI) model that describes layers for data transmission.
Element
The elements of each layer are:
Layers
The level 5 (session) and 6 (presentation) are nowadays implemented in the level 7 (application) and above
| Level | Name | Data unit name | Data Unit example | Description | Protocol |
|---|---|---|---|---|---|
| 7 | Application layer | Message | Message | Higher level (Resource Sharing, Remote file access, …) | HTTP, SMTP, FTP, DHCP, DNS, Telnet, SNMP, … |
| 6 | Presentation layer | Message | Message | Data Translation (Character encoding, data compression and encryption/decryption) | MIME, XDR, ASN.1, ASCII, PGP |
| 5 | Session layer | Message | Message | Session functionality | Named pipe, NetBIOS, SAP, PPTP, RTP, SOCKS, SPDY, X.225 |
| 4 | Transport layer | Packet | Segment Packet Datagram Packet | Data transmission between network points | TCP, UDP, SCTP, DCCP, SPX |
| 3 | Network layer | Packet | IP Packet | Addressing, routing and traffic control | IP Protocol, ICMP, IPsec, IGMP, IPX, IS-IS, Apple Talk, X.25, PLP |
| 2 | Data link layer | Packet | Frame | Frames transmission between two physical nodes connected | ATM, ARP, … |
| 1 | Physical layer | Bit | Bit, Symbol | Raw bit transmission over a physical medium | IEEE 802.3 (Ethernet cable), IEEE 802.11 (Wifi), USB, Bluetooth, Rs232 (modem, printer, …) |