In a large pot, add the ribs and fill about 2/3 to 3/4 full with water. Bring to a boil and reduce to a high simmer. Cook until the ribs are just tender, about 45 minutes to an hour. Skim off and discard any foam that forms on the surface.
While the ribs are cooking, prepare the daikon, bok choi, celery. To prepare the mushrooms, remove the stems but leave the caps whole and for a nice touch, cut an X, very gently onto the top of the caps, not very deep, when they cook, the X will show for a nice presentation.
To prepare the coriander roots, garlic, and pepper corns, place them in a mortar and pound with a pestle for a minute or two. You are not look for a paste, just crushed up. This is optional but makes the soup more traditional. (Coriander root is a different taste than the green leafy part, there is no green leafy coriander in this soup,)
When the ribs are tender, add the bok choi, daikon, Chinese celery, mushrooms, pork broth powder, and contents from the mortar if using those. Season with a dash of soy sauce, oyster sauce, and just a pinch of salt.
Let this simmer for 30-40 minutes. Add more water as needed. Taste and adjust seasonings to your liking.
Serve with rice on the side. This is a common lunch and dinner soup.