Each node is server and client itself. Client is used to connect to other nodes and Server is for receiving connection from other nodes. For example, Node A want to connect to Node B. In this case A's client will be connection to B's server.
Also, Client node is NEXT node and Server node is PREVIOUS node.
When two nodes are connected, it means that, 6666's client connected to 7777's server. For 6666, node 7777 is NEXT node, but for 7777, node 6666 is PREVIOUS node.
The topology of network is RING.