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1 Description

The bundling process is used to group child chain transactions from a child chain into a transaction on the Ardor chain. Bundlers accept the fees from those child chain transactions, in the corresponding child chain coin, and pay fees in ARDR to the parent chain forgers.

Bundlers can be started from the cogwheel/bundlers menu, defining the coin to ARDR exchange rate they accept, a limit on the total fees in ARDR a bundler will pay, and an optional overpay amount representing an additional factor of the Ardor fee to pay in case of competing bundlers. This is a multiplier of what you will pay in terms of Ardor fee so if the fee is 100 ARDR and overpay is set to 0.1 you will pay 100 + 100 * 0.1 = 110 as bundling fee.

When a bundler is running, it checks the unconfirmed transactions pool every time a new transaction from the child chain being bundled arrives. If the transaction fee included by the transaction sender, in child chain coins, when converted to Ardor using the exchange rate accepted by the bundler is at least equal to the minimum Ardor fee required for this transaction, the bundler will generate a ChildBlock transaction, including in it this and all other currently unconfirmed child chain transactions satisfying this requirement. The Ardor fee the bundler will include for the ChildBlock transaction is equal to the sum of the minimum required Ardor fees for each, multiplied by the overpay amount, if any. Such overpay amount is optional, and may be used by bundlers willing to pay more in order to have their transactions included in a block instead of those of competing bundlers.

The new ChildBlock transaction will displace from the unconfirmed pool any ChildBlock transactions of the same child chain that include only a subset of the same child transactions. When propagating through the network, ChildBlock transactions will only be accepted by peers if they either include child transactions not already included in other ChildBlock transactions the peer already has in its pool, or offer to pay a higher fee for the same transactions. This ensures the network is not flooded with ChildBlock transactions even if every node is running a bundler, and allows bundlers to compete for propagating their transactions through the network by offering to pay higher fees.

It is now possible for child transactions to be submitted with zero fees, in child chain coins. If a bundler is willing to pay the Ardor fees for those, they will be included in the blockchain in the ChildBlock created by such bundler.

To prevent the unconfirmed pool from being overfilled with such zero-fees child chain transactions, once the maxUnconfirmedTransactions limit (configured in nxt.properties, default 2000) has been exceeded, child chain transactions will be dropped unless a bundler has already submitted a ChildBlock transaction which includes them.

Bundlers advertise their accepted bundling rates to other peers, signing such rates announcements with the private key of the bundler's account. To prevent fake rates announcements, they can be filtered based on this account effective balance (default set in nxt.minBundlerBalanceFXT is 1000 ARDR).

The GetBundlerRates API can be used to retrieve known bundlers rates, again with optional filtering by minimum bundler effective balance.

2 Bundler Setup

Bundling like Forging requires sending the passphrase to the remote node. Therefore only run a bundler on a node under your control. To view the running bundler on a node, the wallet has to include the remote node admin password in its account settings.

Existing bundlers known to the remote node

figure 1

Start a new bundler

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