You should send all candidates, it's normal behaviour.
Also this method can be called during active connection and you also should send new value to opponent. ICE engine works all the time and searches the shortest path for communication between you and opponent.
and can i connect only using SDP (Session Description Protocol ) only ?
not sure what you mean exactly, but answer is No. You need a communication protocol for signalling. It could be Websockets, XMPP or others.