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This time I will discuss the Understanding and Function of the 7 layers of Open Systems Interconnect (7 OSI layer).

In the past when OSI has not been used, communication devices from different vendors can not communicate with each other. Communication tools created by IBM can not communicate with other vendors. Thus established OSI standards.

Understanding OSI Layer

OSI is a communication standard that is implemented within a computer network. Standards that cause all communication tools can communicate with each other through the network. The OSI reference model (Open System Interconnection) illustrates how information from an application software on a computer moves across a network medium to an application software on another computer. The OSI reference model is conceptually divided into 7 layers where each layer has a specific network function. The Open Systems Interconnection (OSI) model is created by the International Organization for Standardization (ISO) which provides a structured logic framework for how data communication processes interact through the network. This standard is developed for the computer industry for computers to communicate on different networks efficiently.
Terdapat 7 layer pada model OSI. Sеtіар layer bertanggungjawab secara khusus pada proses komunikasi data. Misalnya, satu layer bertanggungjawab untuk membentuk koneksi antar perangkat, ѕеmеntаrа layer lainnya bertanggungjawab untuk mengoreksi terjadinya “error” selama proses transfer data berlangsung.

The OSI Layer Model is divided into two groups: "upper layer" and "lower layer". "Upper layer" focuses on user applications and how files are represented on the computer. For Network Engineer, the main part of concern is the "lower layer". Lower layer is the essence of real-time data communication over a network.

The main purpose of using the OSI model is to help network designers understand the function of each layer associated with the data communication flow. Includes the types of network protocols and transmission methods.

OSI Layer 7 Functions, here are the names of the layers:

7 Application Layer:

This 7th layer describes the specification for the scope where the network application communicates with the network service. Provide services for user applications. This layer is responsible for exchanging information between computer programs, such as e-mail programs, and other services running on the network, such as printer servers or other computer applications. It functions as an interface with applications with network functionality, controls how applications can access the network, and then creates error messages.

The protocols that are in this layer:

1. HTTP (Hyper Text Transfer Protocol)

The protocol used to transfer documents and web in a web browser, via www. HTTP is also a protocol that asks and responds between clients and servers.

2. FTP (File Transfer Protocol)

Internet protocols that overnight in the application layer which is a standard for transferring computer files between machines in an internet network.

3. NFS (Network File system)
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A network protocol that enables users on a computer client to access files over the network in a manner similar to how local storage is accessed.

4. DNS (Domain Name System)

The protocol used to assign a domain name to an IP address is easier to remember.

5. POP3 (Post Office Protocol)

The protocol used to retrieve mail from a mail transfer agent that eventually mail will be dowbload into the local network.

6. MIME (Multipurpose Internet Mail Exension)

Protokol уаng digunakan untuk mengirim file binary dalam bentuk teks.

7. SMB (Server Messange Block)

The protocol used to transfer server files to DOS and Windows.

8. NNTP (Network News Transfer Protocol)

The protocol used to receive and send newsgroups.

9. DHCP (Dynamic Configuration Protocol)

The service that assigns no IP to the computer that requests it automatically.
  • Presentation Layer :
This 6th layer serves to translate data that the application wants to transmit into a format that can be transmitted over the network.

Protocols within these levels:


The protocol used for remote access goes to a host, the data runs in another text.

2. SMTP (Simple Mail Transfer Protocol)

One of the protocols commonly used in sending e-mail on the internet or to send data from the computer sending e-mail to the recipient's e-mail server.

3. SNMP (Simple Network Management Protocol)

The protocol used in a network management.

Session layer:

This 5th layer serves to define how connections can be created, maintained, or destroyed. In addition, at this level also carried the name resolution.

The protocols that are in this layer:


Serves as a message broadcasting its intent allows the user to send a single message simultaneously to another connected computer.

2. NETBEUI (NETBIOS Extended User Interface)

Served equally with NETBIOS only slightly expanded by adding functionality that enables working with a variety of hardware and software.
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3. ADSP (AppleTalk Data Stream Protocol)

his protocol functions to monitor the flow between two computers and to check the data flow is not interrupted.

4. PAP (Printer Access Protocol)

Serves the Postscript printer for access on the AppleTalk network and for controlling how the communication patterns are between nodes.

5. SPDU (Session Protocol Data unit)

Functioning supports the relationship between two user service sessions.

6. RCP

Transport layer

This 4th layer serves to break the data into data packets and provide the serial number to the packets so that it can be rearranged on the side of destination once received. In addition, at this level it also creates a sign that the packet is received successfully (acknowledgment), and retransmits the missing packets in the middle of the path.

The protocols that are in this layer:

1. TCP (Trasmission Control Protocol)

A protocol that provides a full service transport layer for the application.

2. UDP (User Datagram Protocol)

Connectionless protocol and process-to-procces that only add port address, cheksum error control and length of data information on the layer above it.

Network layer

This 3rd layer serves to define IP addresses, create headers for packets, and then routing through internetworking using routers and layer-3 switches.
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The protocols that are in this layer:

1. IP (Internetworking Protocol)

The transmission mechanism used to transport data in packets called datagrams.

2. ARP (Address Resulotion Protocol)

The protocol used to find the IP address based on the physical address of a computer.

3. RARP (Reverse Address Resulotion Protocol)

The protocol used to know the physical address through the computer IP.

4. ICMP (Internet Control Message Protocol)

The mechanism used by some hosts to send datagram notifications that are having problems with their hosts.

5. IGMP (Internet Group Message Protocol)

The protocol used to provide simultaneous message facilities to the receiving group.

 Data-link layer:

This 2nd layer serves to determine how data bits are grouped into a format called a frame. In addition, at this level there is error correction, flow control, hardware addressing (such as Media Access Control Address (MAC Address)), and determines how network devices such as hubs, bridges, repeaters, and layer 2 switches operate. The IEEE 802 specification divides this level into two child levels, the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer.

The protocols that are in this layer:

1. PPP (Point to Point Protocol)

The protocol used for point to point on a network.

2. SLIP (Serial Line Internet Protocol)

The protocol used to connect serial.

Physical layer:

This 1st layer serves to define network transmission media, signaling methods, bit synchronization, network architecture (such as Ethernet or Token Ring), network topology and cabling. In addition, this level also defines how the Network Interface Card (NIC) can interact with cable or radio media.

The protocols that are in this layer:

It does not have any specific protocols in this layer, is responsible for processing data into bits and transferring them through media, such as cables, and maintaining physical connections between systems, in this layer only sending bit bits of data.

  • TCP / IP Layer

The TCP / IP architecture is not based on the OSI seven-layer reference model, but uses the DARPA reference model. As shown in the diagram above, TCP / IP implements a layered architecture consisting of four layers.

These four layers, can be mapped (though not directly) to the OSI reference model. These four layers, sometimes referred to as DARPA Models, Internet Models, or DoD Models, remember TCP / IP is a protocol originally developed from the ARPANET project initiated by the US Department of Defense.

Here are all kinds of TCP / IP Layer, namely:
  • Application
Serves to provide services to software that runs on the computer. The protocols that operate on the Application Layer: HTTP, FTP, POP3, SMTP, etc.
  • Transport

Transport Layer serves to provide services that will be used by Application Layer. It has 2 main protocols TCP and UDP.

  • Internet

Internet Layer has a function as a provider of IP Addressing function, routing, and determine the best path. Internet Layer has 1 protocol that is TCP / IP.

  • Network Access

It functions to define the protocols and hardware-hardware used in data transmission. In this layer there are protocols like ethernet on LAN, PPP on WAN, and also Frame Relay.


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