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2020-01-02 12:17:48 -05:00
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 # Network-Level Validation Rules

-In some cases, transactions may be rejected by the network despite the fact that they successfully unlock their inputs, spend valid UTXOs, and do not conflict with other transactions.  That is, a node may receive the transaction and consider it valid, but it may choose not to relay it to its peers or reject it outright.  In particular, custom, or non-standard, transactions are often treated this way by the Bitcoin Cash network at large.  Custom transactions are defined as those which are not considered standard.
+In some cases, transactions may be rejected by the network despite the fact that they successfully unlock their inputs, spend valid UTXOs, and do not conflict with other transactions.
+That is, a node may receive the transaction and consider it valid, but it may choose not to relay it to its peers or reject it outright.
+In particular, custom, or non-standard, transactions are often treated this way by the Bitcoin Cash network at large.
+Custom transactions are defined as those which are not considered standard.

 ## Standard Transactions

@@ -15,7 +18,54 @@ Standard transactions are those that:
 - For [multisig](/protocol/blockchain/transaction/locking-script#Multisig) outputs, must have at most 3 parties and at least 1 required party (i.e. 1-of-1 through 3-of-3).
 - Have non-data outputs with amount above the [dust](#dust) threshold

-Be aware, however, that these rules may vary from node-to-node as they are often configurable.  Some nodes may also accept and relay non-standard transactions.  For this reason, among others, it is always wise to send transactions to multiple nodes.
+Be aware, however, that these rules may vary from node-to-node as they are often configurable.
+Some nodes may also accept and relay non-standard transactions.
+For this reason, among others, it is always wise to send transactions to multiple nodes.

 ### Dust

+In order to limit the propagation of transactions with limited utility, outputs that would be cost-prohibitive to spend are rejected as "dust."
+Dust is defined differently for different node implementations but in the simplest cases a threshold of 546 satoshis is used.
+Outputs with fewer satoshis than the dust threshold are rejected, along with the transaction they are a part of.
+The exception to this is provably unspendable outputs (e.g. data outputs), which always have a dust threshold of zero satoshis.
+
+## Node-Specific Behavior
+
+### bchd
+
+bchd provides the following comment regarding its dust calculation:
+
+    The output is considered dust if the cost to the network to spend the
+    coins is more than 1/3 of the minimum free transaction relay fee.
+    minFreeTxRelayFee is in Satoshi/KB, so multiply by 1000 to
+    convert to bytes.
+    
+    Using the typical values for a pay-to-pubkey-hash transaction from
+    the breakdown above and the default minimum free transaction relay
+    fee of 1000, this equates to values less than 546 satoshi being
+    considered dust.
+
+### Bitcoin ABC
+
+Bitcoin ABC provides the following description of its dust threshold calculation:
+
+    "Dust" is defined in terms of dustRelayFee, which has units
+    satoshis-per-kilobyte. If you'd pay more than 1/3 in fees to spend
+    something, then we consider it dust.  A typical spendable txout is 34
+    bytes big, and will need a CTxIn of at least 148 bytes to spend: so dust
+    is a spendable txout less than 546*dustRelayFee/1000 (in satoshis).
+
+### Bitcoin Unlimited
+
+Bitcoin Unlimited uses a static threshold of 546 satoshis (except provably non-spendable outputs which are zero).
+
+### Bitcoin Verde
+
+Bitcoin Verde performs a similar calculation to Bitcoin ABC but with two differences:
+
+ 1. If the address used is uncompressed, the input size is increase to 180 bytes.
+ 2. The output length used is always 34 bytes, instead of serializing the output.
+
+This is accompanied by the comment:
+
+> For the common default _satoshisPerByteFee (1), the dust threshold is 546 satoshis.