Original soon-dae 순대 is some kind of sausage made of bean curd, mung-bean sprouts and pig’s blood stuffed in pig intestine. But normally 순대 is made of noodle, and is more cheaper.
soon-dae-guk 순대국 is pork soup mixed with sliced 순대, soon-dae-guk-bab 순대국밥 is 순대국 with bowl of rice(as you can see in the picture).
Many people thought this 순대 is from Mongol. Mongolian and Korean has many similar things. Face, food, word, game...