@ -998,16 +998,16 @@ Technical debt:: Because soft forks are more technically complex than a hard for
Validation relaxation:: Unmodified clients see transactions as valid, without evaluating the modified consensus rules. In effect, the unmodified clients are not validating using the full range of consensus rules, as they are blind to the new rules. This applies to NOP-based upgrades, as well as other soft fork upgrades.
Irreversible upgrades:: Because soft forks create transactions with additional consensus constraints, they become irreversible upgrades in practice. If a soft fork upgrade were to be reversed after being activated, any transactions created under the new rules could result in a loss of funds under the old rules. For example, if a CLTV transaction is evaluated under the old rules, there is no timelock constraint and it can be spent whenever. Therefore, critics contend that a failed soft fork that had to be reversed because of a bug would almost certainly lead to loss of funds.((("", startref="forks10a")))((("", startref="Crule10")))
Irreversible upgrades:: Because soft forks create transactions with additional consensus constraints, they become irreversible upgrades in practice. If a soft fork upgrade were to be reversed after being activated, any transactions created under the new rules could result in a loss of funds under the old rules. For example, if a CLTV transaction is evaluated under the old rules, there is no timelock constraint and it can be spent whenever. Therefore, critics contend that a failed soft fork that had to be reversed because of a bug would almost certainly lead to loss of funds.((("", startref="Crule10")))
[[softforksignaling]]
=== Soft Fork Signaling with Block Version
Since soft forks allow unmodified clients to continue to operate within consensus, the mechanism for "activating" a soft fork is through miners signaling readiness: A majority of miners must agree that they are ready and willing to enforce the new consensus rules. To coordinate their actions, there is a signaling mechanism that allows them to show their support for a consensus rule change. This mechanism was introduced with the activation of BIP-34 in March 2013 and replaced by the activation of BIP-9 in July 2016.
((("mining and consensus", "changing consensus rules", "signaling and activation")))((("forks", "changing consensus rules", "soft fork activation")))Since soft forks allow unmodified clients to continue to operate within consensus, the mechanism for "activating" a soft fork is through miners signaling readiness: A majority of miners must agree that they are ready and willing to enforce the new consensus rules. To coordinate their actions, there is a signaling mechanism that allows them to show their support for a consensus rule change. This mechanism was introduced with the activation of BIP-34 in March 2013 and replaced by the activation of BIP-9 in July 2016.
==== BIP-34 Signaling and Activation
The first implementation, in BIP-34, used the block version field to allow miners to signal readiness for a specific consensus rule change. Prior to BIP-34, block version was set to "1" by _convention_ not enforced by _consensus_.
((("bitcoin improvement proposals", "Block v2, Height in Coinbase (BIP-34)")))The first implementation, in BIP-34, used the block version field to allow miners to signal readiness for a specific consensus rule change. Prior to BIP-34, block version was set to "1" by _convention_ not enforced by _consensus_.
BIP-34 defined a consensus rule change that required the coinbase field (input) of the coinbase transaction to contain the block height. Prior to BIP-34, the coinbase could contain any arbitrary data the miners chose to include. After activation of BIP-34, valid blocks would have to contain a specific block-height at the beginning of the coinbase and be identified with a version number greater than or equal to "2".
@ -1031,7 +1031,7 @@ The standard is defined in https://github.com/bitcoin/bips/blob/master/bip-0034.
==== BIP-9 Signaling and Activation
The mechanism used by BIP-34, BIP-66, and BIP-65 was successful in activating three soft forks. However, it was replaced because it had several limitations:
((("bitcoin improvement proposals", "Version bits with timeout and delay (BIP-9)")))The mechanism used by BIP-34, BIP-66, and BIP-65 was successful in activating three soft forks. However, it was replaced because it had several limitations:
* By using the integer value of the block version, only one soft fork could be activated at a time, so it required coordination between soft fork proposals and agreement on their prioritization and sequencing.
@ -1072,7 +1072,7 @@ image::images/mbc2_1010.png[BIP-9 Proposal State Transition Diagram]
Proposals start in the +DEFINED+ state, once their parameters are known (defined) in the bitcoin software. For blocks with MTP after the start time, the proposal state transitions to +STARTED+. If the voting threshold is exceeded within a retarget period and the timeout has not been exceeded, the proposal state transitions to +LOCKED_IN+. One retarget period later, the proposal becomes +ACTIVE+. Proposals remain in the +ACTIVE+ state perpetually once they reach that state. If the timeout is elapsed before the voting threshold has been reached, the proposal state changes to +FAILED+, indicating a rejected proposal. +REJECTED+ proposals remain in that state perpetually.
BIP-9 was first implemented for the activation of +CHECKSEQUENCEVERIFY+ and associated BIPs (68, 112, 113). The proposal named "csv" was activated successfully in July of 2016.((("", startref="MACrule10")))
BIP-9 was first implemented for the activation of +CHECKSEQUENCEVERIFY+ and associated BIPs (68, 112, 113). The proposal named "csv" was activated successfully in July of 2016.((("", startref="MACrule10")))((("", startref="forks10a")))
The standard is defined in https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki[BIP-9 (Version bits with timeout and delay)]
judymcconville@roadrunner.com
7 years ago