Parboil pork ribs in plenty of boiling water for a minute. Remove the ribs and rinse under water. Discard the liquid.
To a clean pot, add 6 cups of water, ginger, 1½ teaspoon salt and the pork ribs. Bring to a boil then lower the heat to a simmer. Skim off any foam.
Cut half of the carrots and half of the daikon radish into large chunks (about 3-inch long) and add them to the broth. Adjust the heat to maintain a gentle simmer and skim off foam if needed. Then cover the pot with the lid slightly askew and simmer for 60-75 minutes or until the ribs are almost tender to your liking.
Cut the remaining carrot and daikon radish on a bias (roll-cut) or just cut them into thin slices or small pieces. Add them to the soup after ribs are almost tender to your liking. Cover the pot with the lid slightly askew and continue to simmer for another 10 minutes or so until the vegetables pieces you just add are cooked through and tender.
While waiting for the vegetables pieces you just add in Step 4 to cook, boil the pasta in plenty of salted water according to package instructions but undercook by 1-2 minutes.
When the pasta is ready, drain and set it aside for a minute. Open the soup pot and discard the large chunks of carrots and radish you added at the beginning in Step 3. Taste the broth and season with a bit more salt if needed, then add pasta and bring the soup to a rolling simmer.
Divide the soup with pork ribs, noodles, carrot and radish pieces among serving bowls. Sprinkle with scallion, cilantro and black pepper, then serve immediately with fish sauce, lime wedges and chilis on the side.