Beyond the Basics: The Unanticipated Advantages of ePBS

Summary

We explore a range of lesser-known benefits associated with ePBS, shedding light on the unexpected positive side effects that extend beyond its primary objectives.

Improved Pipelining

The original ePBS strategy increased slot time by using a two-slot approach, which separated the roles of proposer and builder into two distinct phases, each followed by a round of aggregated voting. In contrast, recent ePBS enhancements have streamlined this process. Now, a smaller committee votes on the payload reveal, bypassing the need for broad aggregation and maintaining the slot time at 12 seconds:

• Proposers can submit their consensus block without waiting for a payload, mirroring the efficiency seen in pre-merge operations. This adjustment allows for faster block preparation, propagation, and validation, and the attestation deadline can be reduced to 3 seconds.
• This allows for more efficient resource management by distributing the tasks of consensus block validation and execution payload validation over the entire slot duration. This distribution ensures a more balanced utilization of CPU and disk resources, preventing bottlenecks and enhancing the system's overall performance. By spreading these validations, ePBS optimizes hardware resource usage, leading to improved throughput and system responsiveness.

Enhanced Incentives for Blob Inclusion

The existing PBS framework incentivizes proposers to delay their block submissions to capture the maximum MEV, leading to efficiency losses. Blob transaction inclusion slows down block propagation by approximately 200 milliseconds, directly impacting monetary gains. Consequently, rational builders would demand higher tips for including these transactions, costs that ultimately burden rollup users who pay for transaction inclusion.

ePBS introduces a significant improvement by allowing builders to broadcast blob sidecars immediately after identifying the consensus block, a full 3 seconds before their payload reveal. This enhancement provides multiple benefits:

• Improved utilization of bandwidth throughout the slot, as blob transmission occurs immediately following the consensus layer (CL) block and precedes the execution payload, exemplifying more effective pipelining.
• Elimination of disincentives for including blob transactions in ePBS: builders face no penalties for incorporating blobs, as validators have ample time to process these sidecars before payload reception.

Market and Mechanism Flexibility

ePBS introduces a more versatile set of interactions for proposers and builders, extending beyond the current capabilities seen in Mev-Boost-type PBS systems. As outlined in the ePBS Design Constraints, the goal is to mitigate trust issues, providing a framework where proposers can engage with builders without mandatory trust, yet not limiting their interaction options. This flexibility addresses concerns that enshrining PBS might confine payload delivery to specific market types.

A novel concept under ePBS is the potential for slot auctions, a significant shift from the conventional payload auctions. In this model, the proposer endorses a builder without committing to a particular payload, giving the builder autonomy over block composition until the payload reveal:

• This system allows builders to leverage newly available information post-CL block propagation to extract maximum MEV and enhance block efficiency, a strategy not viable under fixed payload commitments.
• Given the predictability of slot proposers' identities within (and with almost certainty across) epochs, proposers could feasibly pre-sell their building rights, a move that would necessitate some technical adjustments but offer new strategic possibilities.
• Builders acquiring slot rights gain the freedom to explore various market mechanisms for selling block space, potentially adopting innovative models like execution tickets or PEPC, thereby fostering a diverse and dynamic market environment.

By removing the trust prerequisite and broadening the scope of market interactions, ePBS sets the stage for a more adaptable and capital-efficient block construction ecosystem, contrary to the common belief that it constrains these markets.

On the other hand, by not committing to a specific payload in the block, we need to deal with payload equivocations by the builder. To maintain the safety and cryptoeconomic properties of Ethereum we would be forced to have new slashing conditions for payload equivocations.

Inclusion list flexibility

ePBS, and specially the option of selling the slot instead of commiting to a specific payload, enable a wider range of inclusion list designs. Same slot inclusion lists become possible as the payload is not yet committed, and the proposer may force some transactions to be included, if not in his own payload, in any subsequent one. This avoids the drawback of next slot inclusion in which a proposer can shape a future builder, creating separate off-protocol markets and incentive-alignment issues.