OSI Reference Model

What is OSI?   Sending messages from one network to another is a very complex process. OSI formation a little story, in 1977 a Subcommittee of the International Organization for Standarddization (ISO) began working to create multiple sets of standards to facilitate communication networks. This work was completed in 1984 and known as the OSI reference model - OSI Open Systems Interconnection.Model This is the method most widely used to describe the communication network. The following section covers topics:

Layer 7 of the OSI model 
OSI reference model and which is not a physical model divide tasks into 7 layer network to be described more following details:Physical layer is the first layer, but unusual in This reference model are stacked on the bottom layer to emphasize how a message is sent through the network. For more details, the following will be briefly described each layer of the OSI and I try analogy with the simple concept of our lives.

 Layer 7: Application Layer
 Layer 7 is the Application layer defines the interfaces between the software or applications that communicate out of the computer where the application is located. This layer describes the rules for the following:1. The provision of network services2. Offer - service advertising network3. Accessing network servicesThe following example is protocol-protocol implementing rules Application layer.1. Netware's services advertising protocol (SAP)2. TCP / IP Network File System (NFS)3. TCP / IP Simple Mail Transfer Protocol (SMTP); telnet; HTTP; FTP; WWW browser4. Included in this example is a file; print; database applications; message.

 Layer 6: Presentation Layer 
Layer 6 is a presentation layer whose main purpose is defining data formats such as ASCII text, EBCDIC text, binary, BCD and jpeg. Encryption is also defined in this layer 6. Presentation Layer-2 specifies rules for the following:1. Data Translations2. Encryption and compression of dataProtocol-2 The following is an example that implements rules Presentation layer:1. Netware Core Protocol (NCP)2. AppleTalk Filing Protocol (AFP)3. JPEG; ASCII; EBCDIC; TIFF; GIF; PICT; encryption; MPEG; MIDIEg mainframe has EBCDIC format; while WIndows have ASCII data format. Presentation layer task is to translate these different formats so they can connect with each other.

Layer 5: Session Layer
 Session layer defines how to start, control, and end a conversation (called a session) .This included in the control and management of a variety of bidirectional messages so that the application could include a notification signal or notification if some messages have been complete. Layer to the five-second rule specifies Sessionfollowing:1. Control of the communication session between the two devices2. Make; manage; and remove the connectionsThe following is a protocol that menimplementasikan session layer of the OSI model:1. Netware's Servise Advertising Protocol (SAP)2. TCP / IP remote procedure call (RPC)3. SQL; NFS; NetBIOS names; AppleTalk ASP; DECnet SCPA simple example is the operator telpon.Jika analogy you want to call a number while you do not know the number, then you can ask the operator.

Layer 4: Transport layer 
Layer 4 (transport layer) is more focused on the issues associated with the transmission of data to other computers such as process memperaiki a mistake or error recovery, segmentation of the blocks of data from a large application into smaller pieces-2 to be sent, and on the receiving computer pieces -2 are rearranged. OSI Layer 4-to-2 specifies rules for the following:1. Hiding the network structure of the layer above2. Notice that the message data has been received3. Ensuring reliability, error-free message deliveryExample 2 The following is a protocol-2 transport layer which implements rules1. Netware's Sequence Packet Exchange (SPX) protocol2. TCP / IP's Transmission Control Protocol (TCP)3. TCP / IP's Domain Name System (DNS)Analogies of this transport layer kayak package delivery service providers, eg TIKI, POS or Fedex. Tiki or Fedex is solely responsible for the arrival of packets to the destination address and packet intact without defects. As well as ISP, if we type WWW.dotkom.com then the ISP will translate into a destination address. 

Layer 3: Network Layer 
Network layer of the OSI model defines the package delivery of end-to-end. To complete this work, the Network layer defines the logical address so that each device communicating endpoints can be identified. This layer also defines how routing works and how to learn lines so that all packages can be sent.Network Layer-2 specifies rules for the following:1. Data routing across multiple networks2. Fragmentation and reshapes the data3. Identify the network cable segmentProtocol-2 following rules apply layer Network1. Netware's Internetwork Packet Exchange (IPX) Protocol2. TCP / IP's Internet Protocol (IP); AppleTalk DDPAnalogy of this layer duty to send a letter or package to a specific city or zip code, not directly sent to the destination address. This layer is very important in complex networks, where the network layer to send data packets to the network layer function logical.Router this. 

Layer 2: Data Link Layer 
Data link layer specifies the following rules:1. Coordination of bits into two logical groups of the information2. Detect and sometimes correct errors3. Controlling the flow of data4. Identification of network devicesProtocol-2 Data link layer implements the following:1. Ntware's Link Support Layer (LSL)2. Asynchronouse Transfer Mode (ATM)3. IEEE 802.3 / 802.2, HDLC, Frame Relay, PPP, FDDI, IEEE802.5 / 802.2The analogy of this data link as a registered letter which was sent to the home address and are guaranteed up to the receipt signed by the recipient. This layer identifies the actual address of a device. 

Layer 1: Physical Layer
 Physical Layer of the OSI model is related to the characteristics of the media transmisi.Contoh-2 specifications of connectors, pins, use of pins, electrical currents, encoding and modulation of light. Usually in completing all the details of this involves a lot of physical layer specifications. This layer-2 specifies the following rules:1. The physical structure of a network missal form and rules connector pins on the RJ-45 cable connector. And 802.3 Ethernet standard defines the use of the cable to pin 1,2,3 and 6 used in Cat 5 cable with RJ-45 connectors for Ethernet connections.2. The rules in the use of mechanical and electrical transmission medium3. Protocol Ethernet such as IBM Token Ring; AppleTalk4. Fiber Distributed Data Interface (FDDI) EIA / TIA-232; V.35, EIA / TIA-449, RJ-45, Ethernet, 802.3, 802.5, B8ZS5. Sync-2 electrical signal through the network6. Encoding data in electronic 

Implementation Protocol 
Keep in mind that the OSI model is simply a theory about how to view communication within the network. Each layer specifies standards for followed when mengimplementsikan network. But remember OSI layers that do not perform real tasks, OSI only models. The following discussion summarizes the advantages and disadvantages of the use of the OSI model in describing the communication network. 

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