Why Is The Rmb-Us Dollar Exchange Rate Regulated By China? Will the Renminbi appreciate substantially in the near future?

[eInfiniti 0]

The Chinese currency, Renminbi or RMB, is not freely exchangeable. I know that. But, I simply don't understand why its exchange rate with the world's major currencies, including the US dollar, is set/regulated by China. The US has wanted China to allow the RMB to appreciate in value more quickly but has failed so far. Any foreign exchange transaction involves two currencies. I just don't understand why the rate is set/regulated by one side, not negociated.Would you think that the RMB will appreciated substantially in the near future? Why?