@ -75,23 +75,6 @@ Using centralised system means, that the measurement devices will use one separ
Where there are at least two nodes in a system, they have to communicate together in a particular way, known to both of them. The web server naturally operates over \gls{tcpip}. Therefore, same networking stack (the way of comunication), that is used for communication between the server node and user can be used to communicate to client nodes as well. \Gls{tcpip} hardware is ready to be used and is supporting a full-blown networking \gls{stack}, powering communication over today's networks.
The measurement devices, from now on called \textbf{client nodes} will consist of blocks of the remaining hardware requirements. The resulting block diagram can be seen in the figure \ref{f:client_node})
%The centralised system proposal appears to be more economical, than a decentralised system, which would require a separate copy of hardware for doing all the things for every client node, plus some clever way for communication between them.
%\item Split the device to the server (separate GL-inet router running a web-server, data processing and data storage) and to measurement nodes (electronics powered by an ESP8266 Wi-Fi module) to create a unique, replicable and efficient solution
%\item If reasonably accurate, use the inbuilt \gls{adc} of the ESP8266 for the voltage measurement in combination with a linear transformer (the transformer also powers the entire node)
%\item Use hall-effect sensor for a current measurement
%\item If possible, prevent the use of the external \gls{adc} as well as the use of the additional microcontroller to keep the cost down (if needed, use the microcontroller of the 8-bit AVR family produced by Atmel)
%\item Include advanced configuration options (\gls{pwm} for lighting appliances or or periodic turn on/off function)
%\item Make the web-server accessible remotely via \gls{ddsn} service
%\item Make the server automatically discover all nodes and configure them
\subsection{The TCP/IP networking protocol}
\Gls{tcpip} consists of two layers. The higher layer, \gls{tcp}, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a \gls{tcp} layer that reassembles the packets into the original message. The lower layer, \gls{ip}, handles the address part of each packet so that it gets to the right destination. Each gateway computer / device on the network checks this address to see where to forward the message. Even though some packets from the same message are routed differently than others, they'll be reassembled at the destination.
\Gls{tcpip} uses the client/server model of communication in which a computer user (a client) requests and is provided a service (such as sending a Web page) by another computer (a server) in the network. TCP/IP communication is primarily point-to-point, meaning each communication is from one point (or host computer) in the network to another point or host computer. TCP/IP and the higher-level applications that use it are collectively said to be \textit{stateless} because each client request is considered a new request unrelated to any previous one (unlike ordinary phone conversations that require a dedicated connection for the call duration). Being stateless frees network paths so that everyone can use them continuously.
Peter Babič
8 years ago