Did you ever want to have a high-level overview of how 3G/4G mobile networks work? Where GGSN and SGSN fit in? What the PDP contexts are ... and why you need two for dual-stack connectivity? All that (and a lot more) is explained in very well written IETF draft IPv6 in 3GPP Evolved Packet System. Reading highly recommended.
Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.