This page is about the Open Systems Interconnection (OSI) model that describes layers for data transmission.
The elements of each layer are:
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, …) |