Client

var socket = io.connect('/global');

socket.on('server-news', function(data) {

  console.log(data.i);
  socket.emit('client-news', { i: data.i + 1 });

});

Server

io.of('/global').on('connection', function(socket) {

  socket.emit('server-news', { i: i });
  
  socket.on('client-news', function(data) {
    i = data.i;
    console.log(i);
  });

});