Overview
Transport bindings for the Agent Session Protocol
ASP is transport-agnostic. The protocol defines session lifecycle, performatives, and trust scoring independently of how messages are delivered. Transport bindings map these protocol concepts to concrete delivery mechanisms.
Available Bindings
| Binding | Type | Delivery Guarantee | Encryption | Cross-Region | Best For |
|---|---|---|---|---|---|
| npayload | Primary | At-least-once with DLQ | Standard, E2E, Hybrid | Yes | Production agent-to-agent communication |
| HTTP/SSE | Secondary | Best-effort | TLS | No | Browser clients, REST integrations, gateways |
| WebSocket | Secondary | Best-effort | TLS | No | Real-time dashboards, IDE plugins, low-latency agents |
The HTTP/SSE and WebSocket bindings route through npayload internally. Regardless of which binding your client uses, messages benefit from the same core infrastructure.
Serialization
ASP supports two serialization formats:
| Format | Content Type | Required | Description |
|---|---|---|---|
| JSON | application/asp+json | Yes | Human-readable. All implementations MUST support this format. |
| MessagePack | application/asp+msgpack | No | Binary format for high-throughput scenarios. Reduces message size by 30-50%. |
The serialization format is negotiated during the INVITE phase and remains fixed for the lifetime of the session. Both participants MUST agree on the format before the session transitions to INTRODUCED.
Selecting a Binding
| Requirement | Recommended Binding |
|---|---|
| DLQ, delivery receipts, cross-region | npayload |
| Browser client or REST API | HTTP/SSE |
| Real-time bidirectional with sub-100ms latency | WebSocket |
| E2E or Hybrid encryption | npayload |
| All of the above | npayload (HTTP/SSE and WebSocket route through it) |
If you are unsure which binding to use, start with npayload. It supports every feature of the protocol and the SDKs default to it.
Bindings
npayload Binding
Primary transport with at-least-once delivery, DLQ, three encryption modes, delivery receipts, and cross-region routing.
HTTP/SSE Binding
RESTful access with server-sent events for real-time updates. Designed for browser clients and REST integrations.
WebSocket Binding
Full-duplex real-time communication. Designed for IDE plugins, dashboards, and sub-second message delivery.
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