Nonce

Transactions signed by the same private key (i.e., with the same address) are submitted and handled in an order using nonce. Usually, nonce is a non-negative integer value, starting from 0, that stands for the number of transactions accepted to blocks so far. Whenever a transaction is submitted its nonce is check in the following way:

• If the nonce value is equal to (the number of transactions with the same address in blocks) + 1, it's accepted

• Otherwise, it's kept in pending mode with a predefined timeout value until the condition met.

We call this type of nonce numbered nonce. This is enough for typical human-generated transactions. For more use cases like machine-generated transactions, we support two more types: ordered nonce and unordered nonce.

Transactions with loosely ordered nonce are ordered using timestamp:

• If the timestamp is larger than the last timestamp, it's accepted

• Otherwise, it' rejected

Transactions with unordered nonce is always accepted unless a transaction with the same transaction hash is already in blocks.

Three different types of nonce can be compared as follows:

Type	Nonce Field	When To Use	Good For	API Version
Numbered	Non-negative integer	Single client	Human-generated txs	1.0
Unordered	-1	Single or multiple clients, transactions are not aligned with each other.	Machine-generated txs with different generation time and submission time	1.0
Ordered	-2	Multiple clients, transactions are aligned with time	Machine-generated txs with multiple clients	1.0