The OSI and TCP/IP are two models used to explain how networking protocols work together. Note that the TCP/IP model is older than the OSI model and does not follow it exactly. This chart compares the two.
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OSI Model page 2

TCP/IP
Model

Examples that overlap layers

Examples by layer

OSI
Model

Application

HTTP, FTP, DHCP, NFS, Telnet, SNMP (Simple Network Management Protocol), SMTP (Simple Mail Transfer Protocol)

7. Application

Compression, Encryption, SSL (Secure Socket layer)

6. Presentation

TCP/IP sockets
RPC (Remote Procedure Calls)

5. Session

TCP, UDP
Flow Control
multiplexing

4. Transport

Transport

IP, IPv6
Routing

3. Network

Internet

Overlapping: ARP, RARP
(maps between Layer 2 physical addresses and Layer 3 IP addresses)

Low level data transfer across the physical link including detecting and possibly correcting errors.
Interface with network adaptor
MAC (Media Access Control)
LLC (Logical Link Control)
Ethernet, Token Ring, FDDI, Wi-Fi (802.11 wireless ethernet

2. Data Link

Network
Access

Defines encoding and signaling, data transmission and reception, topology and  hardware specifications.  Note that hardware can also be functions of layer 2.

1. Physical

Peter V. Tamas is the author of UNIX for Application Support Staff