North Korea's latest so-called Earth observation satellite launch raises a lot of questions about just how far its ballistic missile technology has come. With each test of its Unha, Taepodong and Nodong ballistic missiles, North Korea acquires important scientific knowledge that could potentially hasten its path to developing a successful inter-continental ballistic missile (ICBM). Sunday's test, which successfully resulted in the Kwangmyongsong-4 satellite entering polar orbit, probably iterated on the December 2012 Kwangmyongsong-3 Unit 2 test, which used an Unha-3 launch device.
While there's a lot we don't know yet about just how evolutionary Sunday's launch was over its predecessor in 2012, Melissa Hanham of the Center for Nonproliferation Studies at the Middlebury Institute of International Studies has a useful round-up of just what we do know. In particular, I'd highlight the preliminary image assessment of the outside appearance of the rocket, which is confusingly called the Kwangmyongsong (not to be confused with its satellite payload, which is the Kwangmyongsong-4 satellite). Hanham notes a "perfect fit" between the chassis of the 2012 launch device and the Kwangmyongsong rocket.
Similarly, the first and second stages of the Kwangmyongsong launch device have very similar splash zones to the 2012 Unha-3 rocket. Hanham notes that this suggests that the internals of the rockets might not have been too different. The payload and third stage of the rocket remain in orbit. As of this writing, it's not known if North Korea has been able to successfully transmit information to or establish communications with the Kwangmyongsong-4 satellite. In 2012, the Kwangmyongsong-3 was able to transmit data at a downlink frequency of 470 MHz.