The hybrid POS implementation will be controlled by an on-chain contract. The drawback here is that messaging is expensive, but not a problem if the stake is big enough.
What is the plan for the full POS implementation, will it also be controlled by an on-chain contract?
The PREPARE and COMMIT messages seem to be replaced by a VOTE message. Will this change the messaging cost for the hybrid POS, or will it still require approximately the same number of messages?
Not sure about the plans for “full PoS implementation.” However, regarding:
The simplification from PREPARE & COMMIT to VOTE will also be accompanied by two tweaks: (1) epoch time goes from 100 blocks to 50 blocks, and (2) instead of taking one epoch of PREPAREs and COMMITs, it takes two epochs of VOTEs for checkpoint finalization.
Then, here are the two notable implications: (a) the average time to finalization goes from 150 blocks to 125 blocks (1 + 1/2 100 block epochs vs. 2 + 1/2 50 block epochs), and (b) for a given validator set, the average number of messages per 100 blocks in the network will remain the same (because we doubled the # of epochs it takes to finalize a checkpoint but halved the epoch time to 50 blocks).
Hope that answers the second part of your post. This is based on my understanding from discussion with @vbuterin a few weeks back, so feel free to correct if I’m missing anything. Thanks! cc @virgil @karl
p.s. Hi everyone! I’m new to this board and to Ethereum research. I will be working on economics of casper, sharding and gas pricing to start. Excited to work with you all 