# Summary

This TIP describes the global protocol parameters for the IOTA protocol.

# Motivation

Various other protocol TIPs rely on certain constants that need to be defined for an actual implementations of nodes or other applications using the protocol. This TIP serves as a single document to provide these parameters. It also serves as a historical record of protocol parameter changes.

# Detailed design

NameValueDescription
Network Name"iota-mainnet"Identifier string of the network. Its hash it used for the Network ID field in transactions.
Protocol Version2Protocol version currently used by the network
Max Block Length32768Maximum length of a block in bytes. Limits Tangle storage size and communication costs.
Max Parents Count8Maximum number of parents of a block.
Min PoW Score4000.0Minimum PoW score for blocks to pass syntactic validation.
First Milestone Index1First valid milestone index.
Max IOTA Supply2779530283277761Total amount of IOTA coins in circulation.
Max Inputs Count128Maximum number of inputs in a transaction payload.
Max Outputs Count128Maximum number of outputs in a transaction payload.
Max Native Token Count64Maximum number of different native tokens that can be referenced in one transaction.
Max Tag Length64Maximum length of a Tag field in bytes.
Max Metadata Length8192Maximum length of a Metadata field in bytes.
VByte Cost500Minimum amount of IOTA that need to be deposited per vbyte of an output.
SLIP-44 Coin Type (decimal)4218Registered coin type (decimal) for usage in level 2 of BIP44 described in chapter "Coin type".
SLIP-44 Path Component (coin_type')0x8000107aRegistered path component for usage in level 2 of BIP44 described in chapter "Coin type".
Bech32 Human-Readable PartiotaHRP prefix to use for Bech32 encoded IOTA addresses. (e.g. iota1zzy3drvj6zugek60srqwhqctkjldx3qle5yuvapj)
Bech32 Human-Readable Part (Test)atoiHRP prefix to use for Bech32 encoded IOTA addresses on test- or development networks. (e.g. atoi1zzy3drvj6zugek60srqwhqctkjldx3qle5fhvhm6)

# Rationale for parameter choices

## Proof-of-work​

The Min PoW Score has been chosen to roughly match the difficulty of a data transaction in the legacy IOTA protocol:

• The payload length (signatureMessageFragment) of a legacy transaction is 2187 trytes or 1100 - 1300 bytes depending on the encoding.
• With a minimum weight magnitude (trailing zero trits) of 14, this corresponds to a PoW score of about 4000.

## Transaction and block limits​

The block parameter Max Block Length and Max Parent Count, as well as the transaction parameters Max Inputs Count, Max Outputs Count, Max Native Token Count, Max Tag Length and Max Metadata Length govern the block and transaction validity. Their values have been chosen to ensure functionality of the protocol within constrained resource restrictions. Furthermore, choosing more conservatives values here is preferable as increasing such limits can always been done preserving backward compatibility.

## Dust protection​

The VByte Cost is the core parameter of the dust protection. The reasoning behind its value is explained in TIP-19 Dust Protection.