Hello, I was wondering if I can book a train to either Lhasa or Xining at the beginning of August. I would like to travel on the 6th of August. Preferable I would like to go to Lhasa. Do I need proof of a TTB before I buy the ticket? If so do you know of a company I could use to obtain one? If I cannot get to Lhasa I would like to go to Xining.

Thank you for your time
Kristin