# Protocols

The gateway implements these open standard protocols across its surface types, federation transport, and payment layer. Not all are surface protocols. DIDComm is the encrypted transport used for gateway-to-gateway (G2G) federation. The x402 protocol is used for agent payment paywalls.

| Concept | Used in | What it explains |
| [A2A](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/a2a.md) | Surfaces | Google Agent-to-Agent protocol: structured task execution between agents. |
| [MCP](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/mcp.md) | Surfaces | Model Context Protocol: tool, resource, and prompt serving for AI models. |
| [DIDComm](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/didcomm.md) | Gateway federation (G2G) | End-to-end encrypted messaging transport used for gateway-to-gateway federation. |
| [x402](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/x402.md) | Surface policy | HTTP-native payment protocol enabling on-chain micropayments between agents. |
| [MPP](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/mpp.md) | Surface policy | Machine Payments Protocol: an HTTP-native payment challenge and settlement protocol supporting both card and on-chain crypto payment methods. |

## Pages in this section
- [A2A protocol](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/a2a.md): How the Agent Gateway handles Google Agent-to-Agent protocol traffic, including extensions, identity, and trust verification.
- [MCP protocol](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/mcp.md): How the Agent Gateway handles Model Context Protocol traffic across the 2024-11-05 and 2026-07-28 revisions, including transport, methods, agent identity, OpenAPI proxying, and tool-level access control.
- [DIDComm messaging](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/didcomm.md): How the Agent Gateway uses DIDComm v2.1 for end-to-end encrypted gateway-to-gateway messaging and federation.
- [x402 payment protocol](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/x402.md): How the HTTP 402 Payment Required status code enables on-chain micropayments between agents via the Agent Gateway.
- [MPP (Machine Payments Protocol)](/products/affinidi-trust-fabric/agent-gateway/concepts/protocols/mpp.md): How the Machine Payments Protocol enables agents to pay for HTTP-gated services using standard authentication headers, and how the Agent Gateway handles MPP challenges on behalf of calling agents.