Apart from glass, the windows of the trains have a steel mesh to protect the travellers. For even more protection, there is a steel wall that can be pulled down. These are remains of the war, where it was quite usual that people threw molotov cocktails and even grenades at passing trains. Our tickets from Hue to Hanoi were booked at Danang station by our hotel receptionist. While some meals are provided it's not very clear what is included and what you have to pay for.
Service seems a little erratic and meals turn up at strange times.
Hence its wise to stock up beforehand. There's not the selling frenzy associated with station stops in countries such as India or Thailand. This is because they don't go very fast and because there's only one track in the country. Thus, trains have to wait at designated passing places for others to go by. Generally, a 400km trip takes between 9 and 13 hours depending on whether your train is an express or not.