The CCS 7 is a Common Channel signalling system. That is, instead of signalling being associated with each traffic channel, a common signalling channel is used for all circuits. This signalling in telecommunication network establishes and realizes temporary connections, in accordance with the instructions and information received from subscriber lines and inter-exchange trunks, in the form of various signals. Therefore, it is necessary to interchange information between subscriber lines and between different exchanges. Though these signals may differ widely in their implementation they are collectively known as telephone signals. In this paper, the authors discuss about CCS7 system architecture, protocol stack, link congestion and performance.