



Network Working Group                                             K. Yao
Internet-Draft                                              China Mobile
Intended status: Informational                          15 February 2026
Expires: 19 August 2026


          Problem Space Analysis of AI Agent Protocols in IETF
              draft-yao-catalist-problem-space-analysis-00

Abstract

   This document aims to align with CATALIST BoF's goal for identifying
   IETF-relevant problem space and potential areas and working groups,
   exploring internal and external coordination for AI Agent protocols
   by analyzing open source efforts.  It may serve as a target for
   CATALIST BoF discussions.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Space Issue 1: Inter-domain Discovery . . . . . . . .   3
     3.1.  A2A Coverage  . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  MCP Coverage  . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Gaps and Potential Work Space in Open Internet  . . . . .   4
   4.  Problem Space Issue 2: End-to-End Session State Management  .   4
     4.1.  A2A Coverage  . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Gaps and Potential Work Space in Open Internet  . . . . .   5
   5.  Problem Space Issue 3: Fine-Grained Authorization . . . . . .   6
     5.1.  A2A Coverage  . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  MCP Coverage  . . . . . . . . . . . . . . . . . . . . . .   6
     5.3.  Gaps and Potential Work Space in Open Internet  . . . . .   6
   6.  Problem Space Issue 4: Multi-Modal Transport  . . . . . . . .   7
     6.1.  A2A Coverage  . . . . . . . . . . . . . . . . . . . . . .   7
     6.2.  Gaps and Potential Work Space in Open Internet  . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10. Informative References  . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   With the rapid development of AI technology, AI Agents have become
   key Internet interaction entities, driving growing demand for Agent-
   to-Agent (A2A) and Agent-to-Tool (A2T) interworking.  Open source
   communities like A2A, Model Context Protocol (MCP) are actively
   advancing related protocols.  While these efforts lay a preliminary
   foundation, there are still some missing pieces and potential
   protocol design space that could be handled by standardization body
   like IETF.

   IETF has held multiple side meetings on AI agent protocol during IETF
   123 and 124, bringing discussions over AI agent identity and
   identifier, discovery, interaction, authorization, and multi-modal
   transport.  These meetings clarified key directions and highlighted
   standardization urgency.

   Coordinating A2A list of efforts (CATALIST) BoF meeting is approved
   to facilitate consensus on the actual scope that IETF should work on,
   figure out potential area(s) and working group(s) to proceed the
   work, and explore coordination activities in and out IETF.






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   This document does not propose any detailed solution or protocol, but
   tries to propose the problem space that IETF may care about by
   analyzing open source projects efforts.  This document may serve as a
   target document for CATALIST BoF meeting discussion.

2.  Definition of Terms

   ** AI Agent: An autonomous, adaptive intelligent entity that
   perceives the environment, makes decisions, executes actions, and
   interacts with other Agents, tools, or humans to complete tasks.

   ** A2A: Agent-to-Agent, Interconnection and interaction between AI
   Agents (data transmission, context sharing, collaboration)
   standardized by dedicated protocols for cross-vendor
   interoperability.

   ** A2T: Agent-to-Tool, Interaction between AI Agents and external
   tools (APIs, databases, etc.), focusing on standardizing tool
   invocation to leverage external resources efficiently.

3.  Problem Space Issue 1: Inter-domain Discovery

3.1.  A2A Coverage

   Existing A2A protocol (as analyzed from available open source schema
   definitions [A2A-spec]) provides a foundational discovery mechanism
   centered on the "Agent Card" construct, which encapsulates critical
   metadata foragent identification and interaction:

   ** Core Metadata: Agents advertise identity (name, version,
   provider), capabilities, skills, authentication requirements, input/
   output modes, and communication interfaces (URLs, protocol bindings)
   via the Agent Card.

   ** Static Retrieval: Protocols support direct retrieval of Agent Card
   metadata via dedicated requests (e.g., Get Agent Card Request),
   enabling clients to obtain necessary information to initiate
   communication.

   ** Tenant Differentiation: A "tenant" field supports basic multi-
   tenancy, allowing agents to serve multiple isolated groups within a
   single administrative domain.

   ** Extension Points: Agent Extension allows agents to declare custom
   protocol extensions, enabling domain-specific discovery metadata.






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3.2.  MCP Coverage

   MCP is a typical A2T protocol.  Existing MCP protocol (as analyzed
   from available open source schema definitions [MCP-spec]).

   TBD.

3.3.  Gaps and Potential Work Space in Open Internet

   The current discovery mechanisms are insufficient for open Internet
   deployments, where agents and clients operate across administrative
   domains, lack pre-configured knowledge of each other, and require
   dynamic, secure discovery.  Current A2A protocol allow three types of
   extension on discovery mechanisms.  A Well-known URI labelled by
   server domain, registry or catalog based approach, and direct
   configuration.  Based on this, in open Internet, the following should
   be considered:

   ** Dynamic Directory Services: Open Internet scenarios require agents
   to be discoverable via standardized directory services or registries.
   The current model relies on clients having prior knowledge of an
   agent's URL to retrieve its Agent Card, preventing "directory-based
   discovery" of unknown agents.

   ** Cross-Domain Addressing: There is no standardized mechanism for
   resolving agent identifiers to network locations across domains.

   ** Domain Identification and Trust: Protocols lack standardized
   "domain" identifiers (e.g., Fully Qualified Domain Name (FQDN) of the
   network domain) and mechanisms to express cross-domain trust
   relationships.  Clients cannot easily determine an agent's domain or
   whether their local domain trusts it.

   ** Dynamic Metadata Synchronization: Agent Card updates
   (e.g.,capability changes, endpoint updates) are not propagated across
   domains.  Cross-domain clients may rely on stale metadata, leading to
   failed interactions.

4.  Problem Space Issue 2: End-to-End Session State Management

4.1.  A2A Coverage

   Existing A2A protocol creates a "TASK" object struct, which serves as
   the core unit of session management, providing a robust foundation
   for tracking interaction lifecycles between AI agents:






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   ** Task Object: A Task aggregates all session-related state,
   including a unique id (task_ID), status (the current status of a
   Task, including state and a message), history (message log),
   artifacts (task outputs),and contextId (Unique identifier for the
   contextual collection of interactions).

   ** Interaction State Machine: A comprehensive state
   machine(SUBMITTED, WORKING, COMPLETED, FAILED,
   CANCELED,INPUT_REQUIRED, AUTH_REQUIRED, REJECTED) covers key
   interaction scenarios, including user input prompts and
   authentication interruptions.

   ** Synchronous/Asynchronous/Streaming Modes: Protocol supports
   synchronous requests, asynchronous requests (via
   "pushNotifications"), and streaming responses for incremental
   results.

4.2.  Gaps and Potential Work Space in Open Internet

   While the core session model is relatively robust, open Internet
   deployments impose additional requirements for reliability, and
   interoperability across heterogeneous implementations:

   ** Session Timeout and Expiration: A2A Protocol lacks standardized
   session timeout, idle timeout, and expiration mechanisms.  Servers
   cannot automatically clean up stale sessions, leading to resource
   leaks, and clients cannot reliably determine if a session is still
   valid.

   ** Context Propagation Rules: While contextId supports cross-task
   context, A2A protocol does not standardize how context is inherited
   (e.g., which fields are carried over to new tasks), truncated (e.g.,
   handling long message histories), or merged (e.g., combining contexts
   from multiple agents).  This leads to inconsistent behavior across
   implementations.

   ** Session Recovery and Reconnection: The protocol lacks detailed
   mechanisms to recover sessions after network disconnections.  Clients
   cannot resume streaming responses, confirm the last received message,
   or continue partial task execution.

   ** User-Session Binding: Protocols only support tenant isolation but
   lack standardized user identity fields.  This prevents user-level
   session isolation, cross-device session synchronization, and user-
   specific session management.






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   ** Extended State Semantics: The state machine lacks semantics for
   long-running interactions, such as SUSPENDED (temporarily paused), or
   PENDING_EXTERNAL (e.g., waiting for a response from an external
   system).  This forces long-running tasks to remain in WORKING state,
   leading to ambiguous semantics.

5.  Problem Space Issue 3: Fine-Grained Authorization

5.1.  A2A Coverage

   Existing A2A protocol provides a foundational authorization framework
   covering high-level access control requirements:

   ** OAuth Scope Support: OAuth 2.0 flows support coarse-grained
   permission grants.

5.2.  MCP Coverage

   TBD.

5.3.  Gaps and Potential Work Space in Open Internet

   The current authorization framework is insufficient for open Internet
   deployments, where cross-domain access, fine-grained resource
   control,and dynamic trust relationships are required:

   ** Resource-Level Authorization: Protocols only support agent-level
   authorization.  There is no mechanism to enforce permissions at the
   resource level (e.g., Task, Artifact, or Message), preventing use
   cases such as "allow read access to this task but not that one".

   ** Delegation Authorization: Cross-domain and multi-agent scenarios
   require delegation (e.g., Agent A acting on behalf of a user to
   access Agent B).  Protocols lack standardized delegation mechanisms,
   including delegation scope, time limits,and revocation.

   ** Cross-Domain Permission Propagation: When an agent delegates a
   task to a cross-domain agent, there is no mechanism to propagate
   permissions in a controlled manner (e.g., "Agent A can access Agent
   B's read skill on behalf of the user, but not write").  This leads to
   either over-privileged delegation or failed cross-domain
   interactions.

   ** Authorization Auditing: There is no standardized mechanism to log
   authorization events (e.g., who accessed what resource, when, with
   what permission).  This hinders compliance with regulatory
   requirements and security incident investigation.




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6.  Problem Space Issue 4: Multi-Modal Transport

6.1.  A2A Coverage

   Existing A2A protocols provide a foundational multi-modal
   transmission framework centered on the "part" construct, enabling
   exchange of diverse data types:

   ** Unified Multi-Modal Carrier: The "part" construct supports
   multiple data types, including text, binary data, etc., with
   "mediaType" to indicate the data format(e.g., text/plain,
   application/json, image/png).

   ** Streaming Multi-Modal Transmission: The protocol supports
   incremental transmission of multi-modal data, including
   (e.g.,streaming video frames, incremental text + images).

6.2.  Gaps and Potential Work Space in Open Internet

   While the core multi-modal framework is functional, open Internet
   deployments require additional support for large data, dynamic
   adaptation, and interactive use cases:

   ** Large File and Chunked Transmission: There is no support for
   chunked upload/download of large multi-modal data (e.g., videos,
   high-resolution images).  The raw field uses base64 encoding for
   binary data, which is inefficient for large files, and there is no
   mechanism for hash verification.

7.  Security Considerations

   Beyond identity authentication and authorization, Agent
   interconnection faces additional security challenges that require
   IETF attention to ensure ecosystem security and trustworthiness.

   ** Data Encryption: All Agents interaction data (context, task
   requests, results) must be encrypted in transit and at rest to
   prevent tampering.  The IETF should enforce encryption requirements
   for multi-modal data and ensure compatibility with existing TLS
   standards.

   ** Anonymity and Privacy: Agent interactions may involve sensitive
   user/Agent data.  The IETF should investigate privacy-preserving
   mechanisms to protect data while enabling effective interconnection.

   ** Malicious Agent Mitigation: Malicious Agents may launch prompt
   injection, or spoofing attacks.  The IETF should investigate attack
   detection and mitigation mechanisms.



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8.  IANA Considerations

   TBD.

9.  Acknowledgements

10.  Informative References

   [A2A-spec] "A2A Specification", n.d.,
              <https://a2a-protocol.org/latest/definitions/>.

   [MCP-spec] "MCP Specification", n.d.,
              <https://modelcontextprotocol.io/specification/2025-11-
              25/basic/authorization>.

Author's Address

   Kehan Yao
   China Mobile
   Email: yaokehan@chinamobile.com































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