I have few questions that I need help with...

When on an RTW ticket, it says that one must travel in one general direction; east or westward. Also that one has 12 months to complete the trip.

What I don't understand is how trips are broken up...

For example, if I want the following westward trip (DFW-LAX-HKG-DXB-LHR-MAD-ORD-DFW) how do I break it up in the middle, and finish the 2nd half a few months later? Let's say I do the first 4 flights this fall, and want to finish the remaining 3 in the spring. Am I correct to assume that I need to purchase a separate flight from LHR-back home-back to LHR to pick up where I left off?