In the early days of computer networking (pre 1969), connections between were hardwired, and the software to implement the connection was custom tailored to the operating systems of the connected computers. As the ARPANET (predecessor of the modern Internet) was being built, it became clear that connecting a large number of computers together in one large network required a well designed network architecture.
Gradually the Open Systems Institute (OSI) Seven Layer Model was developed, starting in 1977.
| Level | Name | Description | Examples |
|---|---|---|---|
| 1 | Physical | Defines the method that the data bits are Sent over the network (electric, light, radio). | DSL, Ethernet, ISDN, RS-232 |
| 2 | Data Link | Determines the low level details of how data is moved between hosts (individual computers) and/or network equipment (routers and bridges). | Ethernet, PPP, SLIP, HDLC |
| 3 | Network | Determines route from source host to destination host. Controls congestion. | IP, IPX, DDP |
| 4 | Transport | Sends data from application to application. Responsable for error detection and retransmission. | TCP, UDP, OSPF, BGP |
| 5 | Session | Coordinates dialogs or data exchanges between applications. Allows interrupted sessions to resume without starting over. | NetBios, AppleTalk, Sockets |
| 6 | Presentation | Handles encryption, compression, or other encoding of data. | ASCII, MIME, UTF-8, XML, SOAP, XDR |
| 7 | Application | Supports end user application software such as e-mail, file transfer, or other network software. | HTTP, HTTPS, FTP, SMTP, telnet |
| DSL | Digital Describer Line |
| ISDN | Integrated Serviced Digital Network |
| PPP | Point-to-Point Protocol |
| SLIP | Serial Line Internet Protocol |
| HDLC | High-level Data Link Protocol |
| IP | Internet Protocol |
| IPX | Internetwork Packet Exchange |
| DDP | Datagram Delivery Protocol |
| TCP | Transport Control Protocol |
| UDP | User Datagram Protocol |
| OSPF | Open Shortest Path First |
| BGP | Border Gateway Protocol |
| NetBios | Network Basic Input/Output System |
| ASCII | American Standard Code for Information Interchange |
| MIME | Multipurpose Internet Mail Extensions |
| UTF-8 | 8-bit Unicode Transmission Format |
| XML | Extensible Markup Language |
| SOAP | Simple Object Access Protocol |
| XDR | External Date Representation Standard |
| HTTP | Hypertext Transfer Protocol |
| HTTPS | Hypertext Transfer Protocol Secure |
| FTP | File Transfer Protocol |
| STMP | Simple Mail Transfer Protocol |
| Telnet | Command line interface to remote host |
See this Wikepedia article for more details about the OSI Model.
