Network Working Group K. Yao
Internet-Draft China Mobile
Intended status: Informational Z. Sarker
Expires: 3 September 2026 Nokia
2 March 2026
Problem Space Analysis of AI Agent Protocols in IETF
draft-yao-catalist-problem-space-analysis-01
Abstract
This document aims to identify 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 . 5
4.1. A2A Coverage . . . . . . . . . . . . . . . . . . . . . . 5
4.2. MCP Coverage . . . . . . . . . . . . . . . . . . . . . . 5
4.3. 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 . . . . . . . . . . . . . . . . . . . . . . 7
5.3. Gaps and Potential Work Space in Open Internet . . . . . 7
6. Problem Space Issue 4: Multi-Modal Transport . . . . . . . . 7
6.1. A2A Coverage . . . . . . . . . . . . . . . . . . . . . . 7
6.2. MCP Coverage . . . . . . . . . . . . . . . . . . . . . . 8
6.3. Gaps and Potential Work Space in Open Internet . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
With the rapid development of AI technology, AI Agents are becoming
key Internet interaction entities, driving growing demand for Agent-
to-Agent (A2A) and Agent-to-Tool (A2T) interworking. Open source
projects like A2A, Model Context Protocol (MCP) are actively
advancing related protocols with focused use cases. While these
efforts lay a preliminary foundation, there are still some missing
pieces and potential protocol design aspects that should be handled
by open standardization body like IETF to ensure global
interoperability.
IETF has held multiple side meetings on AI agent protocol during IETF
123 and IETF 124 meetings, bringing discussions over AI agent
identity and identifier, discovery, interaction, authorization, and
multi-modal transport. These meetings clarified key directions and
highlighted standardization urgency.
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Coordinating A2A list of efforts (CATALIST) BoF meeting is planned in
IETF125 meeting 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.
This document does not propose any detailed solution or protocol, but
tries to propose the problem space that IETF should care about by
analyzing existing 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 software system that
uses AI to complete a specific task. While doing so it makes
decisions, executes actions, and interacts with other Agents, tools,
or humans.
** 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.
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** 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.
3.2. MCP Coverage
MCP is a typical A2T protocol. Since MCP connects tools to the
agent, the developer will have to know beforehand the tools urls and
thus it is done in a manual local configs manner. The usual approch
is to provide resource links as a primary application entry point.
Existing MCP protocol (as analyzed from available open source schema
definitions [MCP-spec]).
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., organizational ID, 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.
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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:
** 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. MCP Coverage
MCP is stateful per connection and stateless across connections. It
does not support session resumption and native session timeouts,
applicaitons can retry and that it implementaiton specific.
4.3. 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.
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** 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. Current designs assume best-
effort reconnection semantics and do not specify maximum recovery
windows or reconnection deadlines. This gap is particularly critical
for long-running or mission-critical agent workflows that rely on
uninterrupted session continuity.
** 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.
** 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.
** Session level constrains: While A2A allows message metadata to
provid a deadline, it does not have any scheduling gurantee or
univarsal deadline. Session-level Quality-of-Service (QoS)
attributes, such as maximum task-completion deadlines, bounded
execution times, or task priority levels attached to session
operations left unclear or to the application implementaiton.
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.
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5.2. MCP Coverage
MCP incorporate transport level authorization using OAuth 2.1 and
OAuth 2.0 protocol. However, it implements a subset of protocol
features for simplicity.
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.
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).
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** Streaming Multi-Modal Transmission: The protocol supports
incremental transmission of multi-modal data, including
(e.g.,streaming video frames, incremental text + images).
6.2. MCP Coverage
MCP is desinged primarity for text based JSON-RPC communication.
6.3. 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. ** latency bounded transmission: The
protocols lack mechanism for predictable/controlled ordering and loss
handling of task for critical agent message. As a result, timing-
sensitive agent behaviors (e.g., cooperative planning loops ) cannot
rely on predictable inter-agent message timing.
** Ordering, and loss-handling of messages : MCP and A2A both lack
mechanisms for conveying message ordering requirements across multi-
modal data transmission. Similarly, no mechanisms exists to
distinguish between messages that e.g. must be reliably delivered,
those that may be dropped or superseded.
** Message importance/scheduling support : While MCP has non-
interperable way to annotate priority as a tool argument, both MCP
and A2A left prioritization and scheduling of message and task
completion to the host of the application or agent orchastrator, not
in the protocol. This would be a potential feature required in cross
domain functioning of agents.
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.
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** 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.
8. IANA Considerations
TBD.
9. Acknowledgements
10. Informative References
[A2A-spec] "A2A Specification", n.d.,
.
[MCP-spec] "MCP Specification", n.d.,
.
Authors' Addresses
Kehan Yao
China Mobile
Email: yaokehan@chinamobile.com
Zaheduzzamam Sarker
Nokia
Email: zaheduzzaman.sarker@nokia.com
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