Description of OSI layers
The recommendation X.200 describes seven layers, labeled 1 to 7. Layer 1 is the lowest layer in this model.
| OSI Model | ||||
|---|---|---|---|---|
| Layer | Prorotocol Data Unit(PDU) | Function | Examples | |
| Host layers | 7. Application | Data | High-level APIs, including resource sharing, remote file access, directory services and virtual terminals | |
| 6. Presentation | Translation of data between a networking service and an application; including character encoding, data compression and encryption/decryption | |||
| 5. Session | Managing communication sessions, i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes | RPC, SCP, NFS, PAP, TLS, FTP, HTTP,HTTPS, SMTP, SSH, Telnet | ||
| 4. Transport | Segment (TCP) /Datagram (UDP) | Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing | NBF, TCP, UDP | |
| Media layers | 3. Network | Packet | Structuring and managing a multi-node network, including addressing, routing and traffic control | AppleTalk, ICMP, IPsec, IPv4, IPv6 |
| 2. Data link | Frame | Reliable transmission of data frames between two nodes connected by a physical layer | IEEE 802.2, L2TP, LLDP, MAC, PPP | |
| 1. Physical | Bit | Transmission and reception of raw bit streams over a physical medium | DOCSIS, DSL, Ethernet physical layer, ISDN,USB | |
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