Topic : Nodes Intro : I've written a summary about many types of Bitcoin nodes, including their pro's and con's, as well as their role in the Bitcoin Network

Full nodes continuously attest incoming candidate block submitted by different mining nodes. A candidate block shouldn't contain fraudulent tx that double-spend coins that are already been spent.

A candidate block could be considered invalid if :

The first miner that submit a valid candidate block along with it's nonce will be rewarded with new supply of Bitcoin. Nonce is a unique secret number tied to a Bitcoin block that is easy to verify but hard to guess.

Then, a full node will download and propagate the latest valid candidate block as a "continuation" to the previous block. Other full node that receives information about this new block will do the same cycle of attestation & propagation process.

In a nutshell, pruned nodes are full nodes budget edition. Instead of storing a complete copy of the Bitcoin timechain (from the Genesis Block until the latest block), pruned nodes only store some of the very recent blocks.

Simplified Payment Verification nodes (aka Lightweight nodes) are a much more simplified version of Bitcoin full nodes that does not enforce attestation process of blocks & txs. Instead of independently attest incoming blocks & txs, these nodes fully rely on a remote nodes as a source of information. Any mobile Bitcoin wallet that trust remote node is also an SPV node.

Neutrino nodes are the latest improvement over SPV nodes in which instead of having user fully dependent on a remote node, now most of the work is done on the client side. Neutrino nodes received a highly compressed data of blocks in which later client-side will do the transaction filtering process. In that sense, neutrino nodes are still dependent on remote node but with better privacy than usual SPV node.

Mining nodes continuously process pending transactions into a candidate block which later will be attested by full nodes. In most scenario, miners are incentive-driven which mean transactions with higher feerate will be processed first due to limited blockspace of 1 million vbytes|

Transaction that is rejected by miner (mostly due low feerate) will stays on the mempool until it get confirmed. If a mempool is full or even overloaded with pending txs, miner can "purge" certain txs (mostly those with the lowest feerate) from their own individual mempool. Mempool, mining process & candidate block submitting process are totally independent action and each miner could have different mempool, candidate block & transaction processed.

Routing nodes are the payment processor on Lightning Network. While both ruting node and mining node are tasked to process pending txs, routing nodes have some notable differences to mining node such as :

Private nodes or mobile nodes are the mobile-focused variant of Lightning node that does not require the user to having it online 24/7 because it can not route txs. Private nodes are aimed just to make regular payment (spend & receive) thus does not require much capital to start.

Technically, watchtower is not much different than just regular routing node apart from it works as a "security guard" that constantly watching other people's node from cheating it's channel counterparty by publishing malicious static channel backup.

State channel backup is kind of like a secret files used to retrieve the underlying funds that was used as a collateral for a particular Lightning channel.

In the least optimistic scenario, a malicious actor can drain his own Bitcoin (on the LN side) but then also try to recover their "mutual collateral" (aka funding tx) by providing malicious SCB with incorrect amount (on his favor).

The protocol will then send the underlying funding tx to attacker's controlled address, but since this forfeiture was not done in a collaborative-manner, the protocol locks any Bitcoin collateral (that was used for Lightning channel) for some period of time.

If a victim did not come online to do a chain sync in time, they would not know that their channel was closed and including their part of "funding tx" was fraudulently taken by attacker. Moral of the story : user must always open their Lightning wallet (to do a chain sync) at least once a day. It takes few minutes but crucial just in case SHTF.

Ark Service Provider facilitates payment on Ark network collaboratively with users (unlike on Lightning which only requires spender's signature to spend). In detail, what ASP does are :

In a very high level, Statechain Entity is kind of doing the same thing as ASP as it collaboratively helps user access to Mercury statechain. In detail, what SE does are :