The Open Systems Interconnection (OSI) Reference
Model, also called OSI Reference Model or just OSI Model, roughly translated, is
the reference model of Open Systems Connectivity; it is a design based on the
principles of an abstract digital communications connection between computers
and the network protocol design to implement the connection. This model was
developed as part of plans for open systems connectivity (Open Systems
Interconnection) by ISO; IUT-T initiated. It is also known as the seven layers
of the OSI model. (According to the Wikipedia).
- Function OSI model:
The OSI model divides the functions of a protocol
into a series of layers. Each level has a characteristic story that it uses,
each level interacts only with lower levels, while only higher levels can use
its functions. An installed system includes a protocol layer above the chain
called the "stack" (protocol stack). Protocol stacks can be installed on the
hardware, or software, or a combination of both. Typically, only the
lower level are installed in the hardware, while the other floors are installed
in the software.
- The advantage of the OSI model
- Split complexity of network operation into the
simple task.
- Allow designers to develop the ability to
function in each module.
- Provide the ability to define interfaces with
high compatibility, the ability to "plug and play" and integrate multi-vendor
products.
- OSI model structure
The OSI model consists of seven layers, each
layer performing separate functions in networking activities. Among them: the
fourth (Transport) layer defines the settings on the device end hardware to
connect and exchange data; the third (Network) layer is for application
development, user interface.
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- Physical layer
The Physical layer defines all the electrical
specifications and physical devices. This includes the layout of pins (pin), the
voltage, and the specification of cables (cable). The Physical layer devices
including Hub, repeater (repeater), network adapters (network adapter) and set
host channel adapter (Host Bus Adapter (HBA)). (The HBA is used in storage area
networks (Storage Area Networks).)
The functions and basic services performed by the Physical layer include:
- Set the circuit breaker or electrical connections
(electrical connection) to a [[transmission medium [[File: | media]]
communications (transmission medium).
- Participation in the process whereby the
communication resources are effectively shared among multiple users. Such
dispute resolution resources (contention) and flow control.
- Modulation (modulation), or change between
performance data (digital data) of the user equipment and the corresponding
signals are transmitted through communication channels (communication channel).
Cable (bus) SCSI Parallel operation of this floor. Many different standards for
Ethernet Physical layer is also in this layer; Active Ethernet Physical layer to
the Data Link layer into one. The same thing happens to the internal network
such as Token Ring, FDDI and IEEE 802.11.
- Data Link layer
Data Link layer provides the functional means and processes to transfer data
between network entities, can detect and fix errors in the Physical layer, if
any. The addressing physical nature, in other words address (MAC address) is
hard-coded into the network card (network card) when they are produced. The
system does not identify the address class (flat scheme). Note: The most typical
example is Ethernet. Other examples of data link protocols (data link protocol)
is the protocol HDLC; ADCCP for point-to-point network or a packet-switched
network (packet-switched networks) and Aloha protocol for local network. In the
local area network standard IEEE 802, and a network of other standards, such as
FDDI, Data Link layer can be divided into the 2 levels: the MAC (Media Access
Control - Access Control line) level and the LLC (Logical Link Control - Logical
Link Control) IEEE 802.2 standard layer.
The Data Link layer is for the bridge (bridge) and switches (switches)
activities. The connectivity provided between the network nodes are connected
together within the network. However, it is reasonable to argue that this device
actually belongs to the layer more appropraitely under 2.5 but not the second
layer.
- Network layer
The Network layer provides the function and process for transferring the data
series varied in length, from a source to a destination via one or more networks
while maintaining the quality of service (quality of service) that requires the
Transport layer. The Network layer performs the routing function. The Routing
device (router) operates in this layer, sending data throughout the extended
network, making the network link becomes feasible (there are switches (switch)
third layer, also called IP switches). This is a positioning system logical
address (logical addressing scheme), the value chosen by the network engineer.
This system is the structured pedigree. Typical examples of a 3-layer protocol
is the IP protocol.
- Transport layer
The Transport layer provides transparent transfer of data between end-users, so
that the upper floors are not interested in the provision of data transmission
services reliably and efficiently. The Transport layer controls the reliability
of a given connection. A number of protocol-oriented and connection status
(state and connection orientated). This means that the Transport layer can
monitor packets and retransmit those that fail. A typical example of the 4-layer
protocol is TCP. This layer is where the messages are converted into TCP or UDP
packets. On the fourth layer is the address; an address is considered to include
the port, ports distinguish address swap applications.
- Session layer
The session layer controls conversations between computers. This layer's setup
manages and ends the connection between local applications and remote
applications. This layer also supports full duplex operation (two-way) or half
duplex (one-way) or simplex (only one way) and sets the marking process
completed (checkpointing). It helps to achieve faster communication when an
error occurs, because the point was marked complete - delayed (adjournment), end
(termination) and reboot (restart). The OSI model made this layer responsible
for the "light switches" (graceful close) sessions (a characteristic of the
transport control protocol TCP) and responsible for checking and recovery
sessions, this is the generally not used in the TCP/IP protocol.
- Presentation layer
The Presentation layer acts as the data on the Network layer. This transfers
duty service data sent from the Application layer into a common formate. And at
the receiving computer, this class is moved from formate general format of the
Application layer. The class can implement the following functions: Translation
of characters from the ASCII code to/from EBCDIC; Data Conversion, for example
from integer to floating point numbers; Data compression to reduce the amount of
data transmitted over the network and encryption & decryption of data to ensure
network security.
- Application layer
The Application layer is the layer closest to most users. It provides a means
for users to access information and data on the network through the application
program. This layer is the main interface for users to interact with
applications, and through it to the network. Some examples of applications in
this layer include Telnet, File Transfer Protocol (FTP) and the email
communications protocols SMTP, HTTP, Mail remote X.400.