ISO-OSI 7-Layer Network Architecture

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ISO-OSI 7-Layer Network Architecture

This lecture introduces the ISO-OSI layered architecture of Networks. According to the ISO standards, networks have been divided into 7 layers depending on the complexity of the fucntionality each of these layers provide. The detailed description of each of these layers is given in the notes below. We will first list the layers as defined by the standard in the increasing order of function complexity:

1. Physical Layer
2. Data Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer

Physical Layer

This layer is the lowest layer in the OSI model. It helps in the transmission of data between two machines that are communicating through a physical medium, which can be optical fibres,copper wire or wireless etc. The following are the main functions of the physical layer:

RF based electronics notice board,sms tranmission

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 RF based notice board

Introduction

Single or Multi electronic notice boards with operating distance up to 1000meters using RS485 protocol

Notice boards play a vital role mostly in educational institutions. The events, occasions or any news, which has to be passed to the students, will be written on the notice boards present in every floor in the colleges or schools. The present system is like, a person will be told the news and he has to update this news on all the notice boards present in the college or school. This will be seen mostly during the examination seasons.

The time table or the schedule of the exams has to be given to the students. This will be done by writing the details on the notice boards. But this process consumes a lot time to update the news on all the notice boards and there may be chances that the person responsible may commit some mistakes or he may be absent sometimes. So, this may create disturbances and the entire schedule may be disturbed. To avoid all these, electronic Notice Board have been designed which completely eliminates the manual work.
   Here we are using RS48.  It is an  alternative for RS-232 for long distance. RS-232 only up  to 15m. but in MAX 485 up to 1500m limit. in addition we connect up to 32 devices.                           If your control system needs to receiving and sending data in the same time you must use full duplex transmission mode. It is possible (and in real world this is the most popular case) that control system first sends request message to ROV (e.g. get temperature) and than waits for the response. In this scenario, there is no possibility that control system and ROV sends data in the same time, so half duplex communication is sufficient.  For full duplex communication you need 4 wires, for half duplex only 2 wires. MAX485 is providing half duplex mode. If you need to use full duplex you must use 2 units (or full duplex chip).