I don't think you've actually answered my question directly (or explained why it might be irrelevant): what incentive will these 'servers' have to participate in the system?
Obviously, senders of transactions must generate a POW in order to participate, so their incentive is clear, but the servers are not users so must have different incentives.
Okay agreed I didn't yet explain all the economics of the mining. The servers involved in the ephemeral intra-block partitions (which are merged into each PoW block) charge transaction fees, but the key point is that they are just dumb signatories that don't have any power except to refuse to sign, and the payer's can choose any server (and I expect the community to maintain a list of servers that are well behaving), thus the transaction fees will trend to the actual cost of the service (which should be microscopically low) since these servers do not have any power (unless they collude in a 50% attack but then the payers can minority fork).
The payers have the incentive to compute the PoW because the protocol requires it to be attached to each transaction. Note
the payer has to sign the PoW (which
CfB explained upthread can not be the case for Iota![1]), so the server can't be outsourced to do this PoW for the payer without a roundtrip network communication and since it is faster to compute the PoW locally than wait for this latency (and since the inefficiency of computing the PoW locally versus as ASIC is irrelevant in this context because the payer is only computing this when he pays not continuously), so payers will not outsource their PoW computations to ASICs.
You are probably wondering how payers can sign full blocks without being full nodes. Well that is one the things I am not going to reveal now for competitive reasons. But it shouldn't be too difficult for you to contemplate a way to do this. I'd prefer you not post your ideas about this and give me a chance to implement first. If I fail to implement timely, then I will open source my entire design so others can implement it.
There is an additional wrinkle to this that you would not have likely contemplated. The servers have to broadcast transactions to each other which thus creates DDoS (amplification) and Tragedy of the Commons economic issues. The DDoS issues I addressed already in a white paper
DDoS Defense Employing Public Key Cryptography which was also discussed in the Bitcoin Technical Discussion forum in a thread I started there.
The Tragedy of the Commons issue is that if one server is a signatory for more transactions then it gains a larger percentage of the transaction fees but all servers have to process/verify all transactions in order to keep their local copy of the block chain up-to-date. So a server that gains more payers than the rest of the network thus has lower relative costs and thus can charge lower transaction fees. This would seem to be a centralization issue (and was one of the first flaws that initially caused me to think the design was going to fail to sustain decentralized, permissionless attributes). However, note that the cost per transaction is so insignificant (unlike in Bitcoin where the electricity cost is ~$9 per transaction!), that payers don't really have a cost incentive to favor one server over another and the community is very likely to maintain a list of the concentration of network activity per server so that payers can make sure they decentralize where they send their transactions (in order words using human social intelligence to thwart centralization, which will develop the correct non-apathetic attitudes in users). So this means that the economics encourages a proliferation of servers since everyone who makes a server can make a reliable and fast server will get some network share of the profit, for as long their fees are insignificant. Likely servers will compete on being as transparent and high availability as possible. This is a much different
insoluble economic situation than we have with profitable PoW mining which
mathematically forces the use of pools with signifiant network share (to maximize profitability since mining is barely profitable at the margins).
This is really a paradigm shift as compared to Satoshi's design and a very important breakthrough for crypto currency.
[1] | Make sure you understand the implications of this. Iota (any DAG) can't sign the PoW because it creates an attack vector. Thus it seems that Iota's mining can be outsourced to ASICS, thus Iota's mining will economically centralize same as for Bitcoin! |