# 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         |