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Overview

Secure Low-Latency Interactive Messaging (SLIM) is a secure, scalable, and developer-friendly messaging framework that provides the transport layer for agent communication protocols like A2A. While A2A defines what agents say (message formats, task semantics, coordination patterns), SLIM defines how these messages are securely delivered across distributed networks.

At its core, SLIM combines:

  • gRPC's performance and reliability — Built on HTTP/2 for efficient, multiplexed transport
  • Messaging capabilities — Native support for channels and group communication
  • End-to-end encryption — Using Message Layer Security (MLS) protocol
  • Native RPC support — SRPC (SLIM RPC) for request-response patterns alongside messaging
  • Distributed architecture — Separate control and data planes for scalability and management
  • Protocol flexibility — Transport layer for A2A, MCP, and custom agent protocols

SLIM enables AI agents to communicate securely whether they're running in a data center, in a browser, on mobile devices, or across organizational boundaries — all while maintaining low latencies and strong security guarantees.

SLIM Components

SLIM is composed of two main components that work together to provide secure, scalable messaging infrastructure:

  • SLIM Messaging Layer: The data plane component that handles message routing, delivery, and secure communication between applications. It consists of two layers: the session layer that provides end-to-end encryption (using the MLS protocol) and reliable message delivery, and the data plane that enables efficient message distribution across the network.

  • SLIM Controller: The control plane component that manages SLIM node configurations, monitors the network, and provides a unified interface for administering the messaging infrastructure. It enables centralized management of routes, connections, and node deployments.

Architecture Overview

The following diagram illustrates how SLIM components are distributed across applications and intermediate routing nodes:

graph TB
    subgraph "Application Node (Agent A)"
        A1[Session Layer 1]
        A2[Session Layer 2]
        A3[Data Plane Client]
        A1 --> A3
        A2 --> A3
    end

    subgraph "Intermediate SLIM Node 1"
        I1[Data Plane]
    end

    subgraph "Intermediate SLIM Node 2"
        I2[Data Plane]
    end

    subgraph "Application Node (Agent B)"
        B1[Session Layer 1]
        B2[Session Layer 2]
        B3[Data Plane Client]
        B1 --> B3
        B2 --> B3
    end

    subgraph "Control Plane"
        CP[Configuration & Monitoring]
    end

    A3 -.->|encrypted messages| I1
    I1 -.->|route| I2
    I2 -.->|encrypted messages| B3

    CP -.->|manages| I1
    CP -.->|manages| I2

    style A1 fill:#4a90e2,stroke:#2e5c8a,stroke-width:2px,color:#fff
    style A2 fill:#4a90e2,stroke:#2e5c8a,stroke-width:2px,color:#fff
    style A3 fill:#f39c12,stroke:#d68910,stroke-width:2px,color:#fff
    style B1 fill:#4a90e2,stroke:#2e5c8a,stroke-width:2px,color:#fff
    style B2 fill:#4a90e2,stroke:#2e5c8a,stroke-width:2px,color:#fff
    style B3 fill:#f39c12,stroke:#d68910,stroke-width:2px,color:#fff
    style I1 fill:#f39c12,stroke:#d68910,stroke-width:2px,color:#fff
    style I2 fill:#f39c12,stroke:#d68910,stroke-width:2px,color:#fff
    style CP fill:#7f8c8d,stroke:#5a6970,stroke-width:2px,color:#fff

Component Distribution

SLIM's architecture enables efficient distribution of components:

Pure Data Plane

The slim binary and Docker images are distributed as pure data-plane artifacts. Since SLIM routing nodes only forward messages and don't participate in application sessions, they don't need the session layer. This keeps the infrastructure lightweight, fast, and simple to deploy.

Language Bindings

Libraries (Python, Go, etc.) include both the data plane client and the session layer on top. Applications use these bindings to get the full stack: secure, reliable, encrypted communication with automatic session management.

Separation of Concerns

You can run a global network of SLIM routing nodes without any application logic, while your agents use the rich, full-featured language bindings for their communication needs. The control plane manages the routing infrastructure independently, ensuring the network operates efficiently.

To get started with SLIM, see the Getting Started with SLIM guide.