I am making a tracking system and i would like to know, if i have 1000 cars (clients) transmitting via sockets(tcp) at an interval of 5 seconds. Should the client open ,send then close the socket. Or should client keep the socket open though out as it transmits.
Depends on many things. For example, if there is a maximum number a server can handle sockets at same time, then you better close them in case you are going to have lots of requests. At the same time, if a live and fast connection really matters to you (1 request per 5 sec is normal, not too high not too low in my opinion) then live socket connections are better for you. Note that they also give you power in server side to broadcast messages to clients at any times, while with none persistent connections you have to broadcast messages as response to each 5 second request.
The tags you used suggests me you are trying to choose between websocket or HTTP. Finally, I should clarify that it really depends on your needs. With HTTP you can serve your logic to more clients, while with websocket you have to deal with server loads a little harder while you have advantage of sending messages to clients and faster tracking, and handshake just happens once.