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OSI reference model of open network or OSI Reference Model for open networking is a network architectural model that was developed by the International Organization for Standardization (ISO) in Europe in 1977. OSI itself is an acronym of the Open Systems Interconnection. This model is also called the model "seven layers of OSI Model" (OSI seven layer model).

Before the emergence of the OSI reference model, a computer network system depends on the supplier (vendor). OSI tries to form a general standard computer networks to support interoperatibilitas between different suppliers. In a large network there are usually many different network protocols. The absence of a similar protocol, making many devices can not communicate with each other.
This reference model in awalnnya intended as a basis for developing network protocols, despite the fact that this initiative had failed. The failure was caused by several factors:

This standard reference model, as compared with the reference model of DARPA (the Internet model) developed by the Internet Engineering Task Force (IETF), very close together. DARPA model is the base model of TCP / IP protocol that is popular.
This reference model is considered very complex. Some functions (such as connectionless communication method) is considered not good enough, while other functions (such as flow control and error correction) are repeated in several layers.
The growth of the Internet and TCP / IP (a real-world network protocol) to make the OSI Reference Model became less attractive.
The U.S. government tried to support the OSI Reference Model protocol in the government network solutions in the 1980s, with the implementation of some standard called Open Systems Interconnection Profile Government (gossip). Nevertheless. This effort finally abandoned in 1995, and implementation of networks using the OSI Reference model is rarely found outside Europe.

OSI Reference Model was eventually seen as an ideal model of logical connections that have to happen for data communication in a network can take place. Some of the protocols used in the real world, a kind of TCP / IP, DECnet and IBM Systems Network Architecture (SNA) to map the protocol stack (protocol stack) them to the OSI Reference Model. OSI Reference Model was used as a starting point to learn how some network protocols in a set of protocols can function and interact.

OSI Reference Model has seven layers, namely the following
Layer to layer-Name Description
7 Application Layer
Functioning as an interface with applications with network functionality, govern how applications can access the network, and then make the error messages. Protocols that are in this layer is the HTTP, FTP, SMTP, and NFS.

6 Presentation Layer
Serves to translate the data to be transmitted by the application into a format that can be transmitted through the network. Protocols that are in this level is redirektor software (Redirector software), such as the Workstation service (in Windows NT) and Network shell (such as Virtual Network Computing (VNC) or Remote Desktop Protocol (RDP)).

5 Session Layer
Serves to define how connections can be created, maintained, or destroyed. In addition, at this level is also performed name resolution.
4 Transport Layer
Serves to break down data into packets of data and to provide serial numbers to the packages so it can be rearranged on the side of the goal after receipt. In addition, at this level also makes a sign that the packet is received successfully (acknowledgment), and re-transmits terhadp packages lost in the middle of the road.
3 Network Layer
Serves to define the IP addresses, create a header for the packets, and then make internetworking routing through routers and switches using Layer-3.

2 Data-link layer
Befungsi to determine how the bits are grouped into a format called a frame. In addition, at this level error correction, flow control, addressing hardware (such as Media Access Control Address (MAC Address)), and determining how network devices such as hubs, bridges, repeaters, and Layer 2 switches operate. IEEE Specification 802, divide this level into two levels, that is, layers Logical Link Control (LLC) and Media Access Control layer (MAC).

1 Physical layer
Serves to define the network transmission media, signaling method, synchronization bits, network architecture (such as Ethernet or Token Ring), network topology and pengabelan. In addition, this level also defines how the Network Interface Card (NIC) can interact with the media, cable or radio.