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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
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
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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