In a mortar and pestle add the salt, peppercorns, garlic, and cilantro, then work into a rough paste.
Mix the fish sauce and soy sauce into the paste. Stir in the brown sugar and green onions.
Thai Rib Serving Sauce
In a small bowl combine the lime juice, fish sauce, sugar, chili flakes, green onions, and cilantro. Leave to rest and for the flavors to meld.
Rub the marinade into the ribs then place the ribs and leftover marinade into a large ziplock bag. Seal the bag after removing as much air as possible. Leave to marinade in a cooler for 1 hour.
Preheat the smoker to 275 degrees F (135 degrees C). When at temperature add a large chunk of hickory.
Set up the smoker for hanging, then hook your ribs under the first bone and place them in the smoker. Cook the ribs hanging for 2 1/2 hours, spinning the rack every 30 minutes. After 2 hours increase the temperature to 300 degrees F (150 degrees C).
Once the ribs are cooked remove them from the smoker and rest for 15 minutes then serve sliced with the Thai rib serving sauce, if desired garnish with additional thinly sliced green onions.