OSI LAYER MODEL
The OSI model is not a protocol. The OSI model is used to explain the workings of the computer network logically. In general, the OSI model divides various network functions into 7 layers. The OSI model is a kind of reference for anyone who wants to understand how computers work. The OSI model consists of 7 layers. The seven layers are:
- Physical Layer
This layer determines electrical / wave / field problems and various procedures / functions related to physical links, such as voltage / electric current, maximum length of transmission media , phase change, cable type, and connectors.
- Data Link Layer
Determine physical addressing, error detection, frame flow control and network topology. There are two sub-layers in the data link namely Logical Link Control (LLC) and Media Access Control (MAC). LLC manages communications such as error notification and flow control. Whereas MAC regulates physical addressing that is used in the communication process between adapters.
- Network Layer
Determine the route traveled by data. This layer provides logical addressing and path determination.
- Transport Layer
Provides end-to-end communication protocol. This layer is responsible for “data safety” and “data segmentation”, such as: controlling data flow control, error detection and correction, data sequence, and packet sequence.
- Session Layer
Manage sessions that include establishing (starting a session), maintaining (maintaining a session), and terminating (ending a session) between entities owned by the presentation layer.
- Presentation Layer
Manage the conversion and translation of various data formats, such as data compression and data encryption.
- Application Layer
Provides services for various network applications.
TCP / IP MODEL
TCP / IP is a communication protocol. Communication protocol means a set of rules that govern how relationships and data transfer occur between two or more computers. TCP / IP has several characteristics that are standard, open and do not depend on specific hardware or OS; free from certain physical networks that allow integration of various types of networks; have a common addressing scheme for each device connected to the network; and provides various services for users. The following is an explanation of layers in TCP / IP:
- Network Access Layer
This layer is almost the same as the Physical layer and Data Link Layer on OSI. At this layer, it is defined how data is distributed in the form of data frames on physical media that are used reliably. This layer usually provides services for error detection and correction of data transmitted.
- Internet Layer
This layer is almost the same as the Network Layer on OSI. This layer has the duty to guarantee that a packet sent can find its destination . Some important tasks of this layer are Addressing and Routing . Addressing is to complete each data packet with an internet address or what is known as an Internet Protocol Address (IP Address). Routing is to determine the route where the data packet will be sent to reach the desired destination.
- Transport Layer
This layer is almost the same as the Transport Layer on OSI. At this layer, a method is defined for sending data between end-to-end hosts. Some functions of this layer are:
- Flow Control Sending data that has been broken down into data packages must be arranged so that the sender does not send data at a speed that exceeds the recipient’s ability to receive data.
- Error Detection. The sender and receiver also complete the data with a number of information that can be used to check whether the data sent has been error free. If an error is found in the received data packet, the recipient will not receive the data.
- Application Layer
This layer is almost the same as the Application, Presentation, and Session Layer layers in OSI. This layer defines applications that run on the network. Quite a lot of protocols have been developed in this protocol such as SMTP (Simple Mail Transfer Protocol) for sending e-mail, FTP (File Transfer Protocol) for file transfer, HTTP or WWW for Web-based applications.
OSI LAYER AND TCP / IP COMPARATIONS
Difference between OSI Layer and TCP / IP:
- OSI has 7 layers while TCP / IP has 4 layers.
- The OSI layer is an independent protocol, while TCP / IP is a suite of protocols.
- The standard OSI layer is not used for free.
- The development of the OSI layer faltered unlike TCP / IP.
- TCP / IP is becoming the world standard for computer networks.
- The OSI layer develops a model based on theory.
- TCP / IP is more credible because of the protocol.
TCP / IP PORT
Ports can be analogous to apartments, IP addresses are street numbers. all
The apartment has the same street number, but each apartment also has an apartment number such as a port number. Port numbers use 16 bits so they can be valued from 0 to 65535. Port 0-1023 – Allocated to server services from the Internet Assigned Numbers Authority . For example, port 80 for web servers and port 25 for SMTP servers. Ports 1024-49151 are also called Registered Ports . Programs created by users do not use this port. Ports 49152-65535 are used for client programs and can be used free of charge. When the web browser is connected to the web server, the browser will allocate ports within the reach of this port.
Following are the commonly used port numbers:
|Port Number||Process Name||Description|
|21||FTP||Network protocol standard used to transfer files in a computer between client and server on one network.|
|22||SSH||A cryptographic network protocol for secure data communication, remote execution commands and other network services between two computer networks.|
|23||TELNET||A network protocol used on the internet or LAN to provide text-based communication facilities in two-way interactions that use virtual terminal connections.|
|25||SMTP||Simple Mail Transfer Protocol is an internet standard for e-mail transmission.|
|53||DNS||A system that stores information about host names or domain names in the form of databases spread over a computer network.|
|80||HTTP||An application layer network protocol used for distributed, collaborative, and hypermedia information systems.|
|110||POP3||Post Office Protocol version 3 is a standard application-layer internet protocol used by e-mail clients to receive e-mail from a mail server.|
|123||NTP||A protocol used for time synchronization in a network, it can be on a LAN network or on the internet network.|
|143||IMAP||The standard protocol for access / retrieve mail from the server.|
|443||HTTPS||HTTPS is a secure version of regular HTTP.|
Sofana, Iwan. 2012. CISO CCNA & Jaringan Komputer. Bandung. Penerbit Informatika.