EIP-4 is a document that outlines the different classifications that an EIP can have. These classifications include Standards Track, Informational, Meta, and Process. Standards Track EIPs are those that propose changes to the Ethereum protocol and must go through a rigorous review process before being accepted as a final standard. Informational EIPs provide information about Ethereum but do not propose any changes to the protocol. Meta EIPs are those that propose changes to the EIP process itself. Process EIPs are those that propose changes to the way that Ethereum is developed and maintained. EIP-4 also outlines the different statuses that an EIP can have, including Draft, Last Call, Final, Withdrawn, and Living. Draft EIPs are those that are still being developed and are not yet ready for review. Last Call EIPs are those that are in the final review window before being moved to Final status. Final EIPs are those that represent the final standard and should only be updated to correct errors or add clarifications. Withdrawn EIPs are those that have been withdrawn by the author and can no longer be resurrected using the same EIP number. Living EIPs are those that are designed to be continually updated and not reach a state of finality. Overall, EIP-4 provides a clear framework for classifying and managing EIPs within the Ethereum community.
This document describes a classification scheme for EIPs, adapted from BIP 123.
EIPs are classified by system layers with lower numbered layers involving more intricate interoperability requirements.
The specification defines the layers and sets forth specific criteria for deciding to which layer a particular standards EIP belongs.
Ethereum is a system involving a number of different standards. Some standards are absolute requirements for interoperability while others can be considered optional, giving implementors a choice of whether to support them.
In order to have a EIP process which more closely reflects the interoperability requirements, it is necessary to categorize EIPs accordingly. Lower layers present considerably greater challenges in getting standards accepted and deployed.
Standards EIPs are placed in one of four layers:
1. Consensus Layer
The consensus layer defines cryptographic commitment structures. Its purpose is ensuring that anyone can locally evaluate whether a particular state and history is valid, providing settlement guarantees, and assuring eventual convergence.
The consensus layer is not concerned with how messages are propagated on a network.
Disagreements over the consensus layer can result in network partitioning, or forks, where different nodes might end up accepting different incompatible histories. We further subdivide consensus layer changes into soft forks and hard forks.
In a soft fork, some structures that were valid under the old rules are no longer valid under the new rules. Structures that were invalid under the old rules continue to be invalid under the new rules.
In a hard fork, structures that were invalid under the old rules become valid under the new rules.
2. Networking Layer
The networking layer specifies the Ethereum wire protocol (eth) and the Light Ethereum Subprotocol (les). RLPx is excluded and tracked in the [https://github.com/ethereum/devp2p devp2p repository].
Only a subset of subprotocols are required for basic node interoperability. Nodes can support further optional extensions.
It is always possible to add new subprotocols without breaking compatibility with existing protocols, then gradually deprecate older protocols. In this manner, the entire network can be upgraded without serious risks of service disruption.
3. API/RPC Layer
The API/RPC layer specifies higher level calls accessible to applications. Support for these EIPs is not required for basic network interoperability but might be expected by some client applications.
There's room at this layer to allow for competing standards without breaking basic network interoperability.
4. Applications Layer
The applications layer specifies high level structures, abstractions, and conventions that allow different applications to support similar features and share data.
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