Wow, it was so long ago, I don't remember the exact data structures, but I'm pretty sure it wasn't a skiplist.

If you've already asked, one cool part of that technology is that the order of received packets is not important to assemble the stream. Basically every 1 second of video is reassembled without importance to the order of packets received. You need N packets to assemble a "data frame", IIRC pending incomplete data frames were stored in a simple hash table, but honestly it was so long ago I don't remember.