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Requirements and Gap Analysis of Multicast in AI Data Centers
draft-zhang-rtgwg-multicast-requirements-gaps-aidc-02

Document Type Active Internet-Draft (individual)
Authors Junye Zhang , Weiqiang Cheng , Kefei Liu
Last updated 2026-07-04
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draft-zhang-rtgwg-multicast-requirements-gaps-aidc-02
RTGWG                                                           J. Zhang
Internet-Draft                                                  W. Cheng
Intended status: Informational                                    K. Liu
Expires: 5 January 2027                                     China Mobile
                                                             4 July 2026

     Requirements and Gap Analysis of Multicast in AI Data Centers
         draft-zhang-rtgwg-multicast-requirements-gaps-aidc-02

Abstract

   Multicast has the potential to be applied in Artificial Intelligence
   Data Centers (AIDCs) to improve the efficiency of point-to-multipoint
   data transmission during large language model training and inference.
   This document identifies key requirements of multicast in AIDCs, and
   analyzes the gaps between these requirements and the capabilities of
   existing multicast technologies.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 5 January 2027.

Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Multicast Use Cases . . . . . . . . . . . . . . . . . . . . .   3
   3.  Multicast Requirements  . . . . . . . . . . . . . . . . . . .   4
     3.1.  Bidirectional Interactivity . . . . . . . . . . . . . . .   4
     3.2.  High Reliability  . . . . . . . . . . . . . . . . . . . .   6
     3.3.  High Dynamics . . . . . . . . . . . . . . . . . . . . . .   7
     3.4.  Sparseness  . . . . . . . . . . . . . . . . . . . . . . .   7
     3.5.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Gap Analysis  . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Typical Multicast Technologies  . . . . . . . . . . . . .   8
     4.2.  Gap Analysis Against Requirements . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Artificial Intelligence (AI) Data Centers (AIDCs) serve as the key
   infrastructure for AI large language model (LLM) training and
   inference, where point-to-multipoint (P2MP) communication patterns
   are common and critical to overall system efficiency.  Network
   multicast leverages in-network data replication to achieve efficient
   distribution of identical data, reducing processing overhead and
   network bandwidth consumption of the sender, thereby enhancing the
   efficiency of P2MP data transmission.  Multicast is a promising
   technology for deployment in AIDCs.

   Despite the potential opportunities, existing multicast technologies
   are not originally designed to address the specific characteristics
   of AIDC networks.  AIDC networks are defined by ultra-high bandwidth
   (often 400 Gbps or greater), microsecond-level latency, and high
   reliability that demands near-zero packet loss.  These core
   performance characteristics necessitate corresponding qualities in

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   multicast technologies, including interactivity, reliability, and
   simplicity.  Furthermore, emerging multicast use cases in AIDCs, such
   as token dispatch, also introduce specific requirements, including
   high dynamics and membership sparseness.

   This document identifies the typical multicast use cases and key
   requirements for multicast in AIDCs, and analyzes the limitations of
   existing multicast technologies in meeting these requirements.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Multicast Use Cases

   Tasks in AIDC include model loading and distribution, model training
   and inference, model saving, and other key operations.  These tasks
   generate various traffic patterns, including communication between
   computing devices (e.g., GPUs), traffic among storage nodes, and data
   transmission between computing devices and storage nodes.  Among
   these, many typical communication patterns exhibit P2MP
   characteristics, making multicast a critical enabling technology.
   The typical multicast use cases in AIDCs are as follows:

   *  Token dispatch in Mixture-of-Experts (MoE) models: MoE is a
      mainstream architecture for LLM training and inference, adopted by
      many LLMs such as Llama4, Mixtral and DeepSeekV3.  During
      execution, an input token is dispatched to multiple selected
      expert nodes based on the real-time routing decision.  With expert
      parallelism, the token dispatch process manifests as an AlltoAll
      collective communication phase, where tokens are sent from source
      devices to multiple destination devices hosting the target
      experts.  This token dispatch process naturally follows the P2MP
      traffic pattern [I-D.zzhang-bier-optimized-use-in-aidc].

   *  Broadcast phase in AllReduce operation: In distributed training of
      LLMs, AllReduce is a core collective communication operation for
      data parallelism and tensor parallelism.  Although AllReduce can
      be implemented in several ways, decomposing it into Reduce and
      Broadcast phases is a basic approach, where the Broadcast phase
      exhibits a P2MP traffic pattern, natively matching the multicast
      semantics.

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   *  Parameter Server (PS) architecture is a traditional architecture
      for parameter synchronization in LLM training, and is effective in
      recommendation systems.  Model parameters are distributed from
      parameter servers to multiple GPU workers, embodying a typical
      P2MP multicast traffic pattern.

   *  Model distribution: The initial distribution of model parameters
      or checkpoints from storage nodes to all computing nodes is a
      critical step before training iterations begin.  Given that the
      model data can reach terabytes in size, simultaneously
      transmitting this massive data from the storage node to many GPUs
      constitutes a typical P2MP traffic pattern.

   *  Key-Value (KV) Cache distribution: In LLM inference with prefill-
      decode separation, multiple decode nodes will request the KV Cache
      generated by the same prefill node within a short timeframe.  The
      KV Cache scheduler is required to transmit identical KV Cache data
      to multiple requesting nodes nearly simultaneously.  In multi-
      agent systems, multiple subordinate agents will most likely reuse
      the KV Cache produced by the master agent.  The system can
      proactively distribute KV Cache data to all subordinate agents.

   *  Multi-replica checkpoint storage: To avoid the loss of training
      progress due to failures, training programs periodically save
      model states, i.e., checkpoints, to multiple storage nodes.
      Multicast is a promising technique in this scenario, which is
      supposed to improve the efficiency of transmitting massive data to
      multiple replicas [I-D.liu-multicast-for-computing-storage].

3.  Multicast Requirements

3.1.  Bidirectional Interactivity

   AI workloads are highly sensitive to packet loss.  In LLM training,
   packet loss without a reliability acknowledgment mechanism can
   corrupt model parameters, leading to degraded model quality or even
   training failures.  Moreover, congestion control is required to
   actively avoid congestion and packet loss.  Therefore, networks in
   AIDCs are required to support closed-loop control, such
   acknowledgment and congestion control, to meet the high-performance
   and high-reliability requirements of AI workloads.

   Traditional IP multicast only supports best-effort P2MP data
   delivery, while multicast in AIDCs should support bidirectional
   interaction, including both efficient P2MP data forwarding and
   multipoint-to-point (MP2P) feedback forwarding, as shown in Figure 1.

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                    XPU1     Switch       XPU2    XPU3
                     |          |          |       |
                     |        <P2MP>       |       |
                     |    Data  |  Data    |       |
                     |--------> |--------->|       |
                     |          |  Data            |
                     |          |----------------->|
                     |          |          |       |
                     |          |          |       |
                     |        <MP2P>       |       |
                     |    ACK   |   ACK    |       |
                     |<---------|<---------|       |
                     |          |          |  ACK  |
                     |          |<-----------------|

                                  Figure 1

   The core interactivity demands are as follows:

   *  P2MP forwarding and replication: Multicast should support
      efficient P2MP forwarding and in-network data replication, which
      is the fundamental requirement of multicast.

   *  MP2P forwarding: Multicast in AIDCs should natively support
      efficient MP2P forwarding, particularly for feedback signals
      generated from receivers to senders such as acknowledgments (ACKs)
      to confirm successful data reception and negative acknowledgments
      (NACKs) to report packet loss, as well as congestion notification
      signals.

   *  MP2P packet aggregation: In large-scale AIDCs with numerous
      receivers, if each receiver sends feedback packets to the sender
      independently, it can lead to excessive reverse traffic to the
      sender, resulting in network congestion, and amplified processing
      overhead and latency.  To address this issue, multicast in AIDCs
      should support MP2P packet aggregation.  Network devices serving
      as rendezvous points should aggregate multiple feedback packets
      from different receivers into a single packet and send it to the
      sender.

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3.2.  High Reliability

   AI workloads exhibit near-zero tolerance for packet loss.  Even with
   acknowledgments and retransmissions mechanisms with the support of
   bidirectional interactivity, extremely low packet loss rates can
   trigger massive retransmissions.  In multicast scenarios, loss at any
   receiver can force the sender to retransmit data to all receivers,
   causing significant redundant traffic and efficiency degradation.
   Furthermore, maintaining uninterrupted tasks for long periods is
   crucial for LLM training.  However, hardware is prone to failures,
   and as the scale of training networks increases, the likelihood of
   network failures rises due to an increasing number of switches,
   network interface cards, and optical modules
   [I-D.cheng-rtgwg-ai-network-reliability-problem].  Therefore,
   multicast in AIDCs should provide high reliability to ensure service
   performance and continuity.  The specific requirements are as
   follows:

   *  Lossless transmission: Under normal network conditions without
      network failures, multicast in AIDCs should satisfy the lossless
      requirement with no packet loss, to ensure both high reliability
      and high performance.  To achieve lossless transmission, multicast
      should support reliability acknowledgment and effective flow/
      congestion control, which need support of interactivity
      requirement.

   *  Fast failure detection: The multicast should support fast
      detection of link failures and node failures and efficient
      detection of gray failures, which are the prerequisite for any
      subsequent recovery action.

   *  Fast failure recovery: Upon failure detection, the multicast
      should support fast recovery mechanisms to restore multicast
      traffic rapidly.  It is unacceptable to rely solely on global
      control-plane convergence and multicast tree reconstruction for
      slow recovery time.

   *  Minimized failure domain: The recovery mechanism should confine
      the impact of a failure to the smallest possible set of receivers.
      Local link or node failures should only affect the faulty segment,
      without spreading to the entire multicast tree or other service
      branches.

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3.3.  High Dynamics

   AI workloads, especially those using sparse architectures like MoE,
   have highly dynamic communication patterns.  MoE-based AI training
   and inference uses token dispatch, where gating networks select
   expert nodes per token at microsecond timescales, dynamically
   determining real-time multicast receiver sets with no fixed groups.
   This ultra-fast selection leaves no time for traditional multicast to
   establish, update, or tear down trees, leading to delays, packet
   loss, or AI task failure [I-D.zhang-rtgwg-llmmoe-multicast].
   Therefore, multicast in AIDC should meet high dynamics requirements,
   and the key points are as follows:

   *  Fast change of multicast members: Multicast should be able to
      adapt to the dynamic change of multicast members in microsecond
      timescales.

   *  Low overhead for dynamic change: The dynamic change of multicast
      members should generate minimal overhead in both the control plane
      and data plane.  Excessive signaling or processing overhead during
      dynamic change will increase transmission latency and reduce the
      efficiency of AI workloads.

3.4.  Sparseness

   Multicast in AIDCs frequently involves multicast groups where only a
   small fraction of the total nodes in the cluster are multicast
   members, a characteristic closely tied to the sparse activation
   mechanism of modern AI models such as MoE.  For example, DeepSeekV3
   uses 256 experts and activates 9 experts at a time.  Multicast
   technologies that are designed for dense groups are inefficient for
   this sparse mode.  The multicast should be efficient when the group
   size is small relative to the network size, and meet the following
   sparseness requirements:

   *  Efficient sparse member identification: Multicast technologies
      should support efficient identification of sparse multicast
      members.  The methods for identifying multicast members should
      avoid unnecessary scanning or signaling of non-member nodes, and
      be efficient for forwarding.

   *  Low overhead for sparse state maintenance: The maintenance of
      multicast member state should be lightweight and low-overhead,
      adapting to the sparse characteristics of AIDC multicast groups.
      It should avoid maintaining redundant state information for non-
      member nodes, reducing state maintenance burden and ensuring that
      state updates do not introduce additional latency that affects AI
      task efficiency.

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3.5.  Simplicity

   Simplicity is a foundational architectural principle for multicast in
   AIDCs, directly enabling the microsecond-timescale low-latency
   transmission in large-scale AIDC networks.  Complexity in the control
   or data plane manifests as variable latency, unpredictable jitter,
   and an inability to meet the strict performance bounds of AI
   workloads.  Therefore, multicast in AIDCs should be governed by the
   following overarching simplicity requirements:

   *  Control plane simplicity: The multicast control plane should be
      architecturally simple to maintain core functions like multicast
      routing, minimizing signaling interaction overhead and control
      processes.  It should avoid complex state synchronization and
      protocol negotiation processes, to reduce network operation and
      maintenance complexity.

   *  Data plane simplicity: The multicast data plane needs to be highly
      efficient and simple, including efficient member identification
      and forwarding adapting to sparse and dynamic multicast
      characteristics, and optimized packet processing mechanisms.
      These ensure minimal forwarding and processing overhead, meeting
      the low-latency transmission requirements of AI workloads.

4.  Gap Analysis

   To address the gaps between multicast requirements in AIDCs and
   existing technologies, typical multicast technologies are first
   introduced, followed by an analysis of their capabilities against key
   requirements.

4.1.  Typical Multicast Technologies

   Protocol Independent Multicast (PIM) is a widely deployed multicast
   routing protocol that operates independently of underlying unicast
   routing protocols.  It supports dense mode (PIM-DM) [RFC3973] and
   sparse mode (PIM-SM) [RFC7761].  PIM-SM builds unidirectional shared
   trees rooted at a Rendezvous Point per group and it optionally
   creates shortest-path trees per source.

   Multipoint extensions for Label Distribution Protocol (mLDP)
   [RFC6388] constructs the P2MP or multipoint-to-multipoint (MP2MP)
   Label Switched Paths (LSPs) in Multiprotocol Label Switching (MPLS)
   networks without interacting with or relying upon any other multicast
   tree construction protocol.

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   Segment Routing Point-to-Multipoint (SR-P2MP) [RFC9960] enables the
   creation of P2MP trees for efficient multi-point packet delivery in a
   Segment Routing (SR) domain.  It requires the routing module of the
   controller or ingress node to calculate and determine the path of the
   multicast traffic, and the data plane can reuse existing SR unicast
   forwarding mechanisms.

   Bit Indexed Explicit Replication (BIER) [RFC8279] is a stateless
   multicast technology that eliminates the need for explicit tree
   construction.  Instead, the set of intended receivers is encoded as a
   BitString within the packet header.  Intermediate BIER Forwarding
   Routers (BFRs) replicate packets based on the BitString, without
   maintaining any per-flow or per-tree state.

4.2.  Gap Analysis Against Requirements

   The support of typical multicast technologies for multicast
   requirements in AIDCs is summarized in Table 1.

   +==========+=============+===========+========+==========+==========+
   |Technology|Interactivity|Reliability|Dynamics|Sparseness|Simplicity|
   +==========+=============+===========+========+==========+==========+
   |   PIM    |     Poor    |    Poor   |  Poor  |   Good   |   Poor   |
   +----------+-------------+-----------+--------+----------+----------+
   |   mLDP   |     Poor    |    Poor   |  Poor  |   Good   |   Poor   |
   +----------+-------------+-----------+--------+----------+----------+
   | SR-P2MP  |     Poor    |  Moderate |Moderate|   Good   | Moderate |
   +----------+-------------+-----------+--------+----------+----------+
   |   BIER   |     Poor    |  Moderate |  Good  | Moderate |   Good   |
   +----------+-------------+-----------+--------+----------+----------+

                           Table 1: Gap Analysis

   Interactivity: These multicast technologies can support best-effort
   P2MP data delivery, but none of them can natively support the reverse
   MP2P forwarding or even aggregation to achieve bidirectional
   interactivity.

   Reliability: These multicast technologies fail to meet the lossless
   requirement of AIDC networks.  The reliability of PIM and mLDP
   basically relies on routing convergence and multicast tree
   reconstruction.  Although some fast detection and recovery mechanisms
   [RFC9186][RFC9860][RFC7715] can be adopted to accelerate failure
   recovery, their tree-based architectures often keep the failure
   impact domain tree-level.  In contrast, BIER and SR-P2MP can
   effectively reuse unicast’s reliability capabilities such as Fast
   ReRouting, and control the failure domain within the damaged
   receivers, demonstrating good reliability.

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   Dynamics: PIM and mLDP adjust multicast trees via control signals,
   leading to slow convergence that struggles to handle high-frequency
   member changes.  SR-P2MP dynamically recalculates forwarding trees
   via a controller, which needs global recalculating and result
   distribution.  BIER only requires updating the BitString in packets,
   enabling faster responses to member changes and exhibiting good
   dynamics.

   Sparseness: PIM, mLDP, and SR-P2MP natively support sparse multicast
   scenarios.  These protocols maintain mappings between multicast group
   identifiers and multicast members.  They identify individual members
   using discrete IP addresses or dedicated identifiers, and data
   packets carry only group identifiers instead of full member
   information.  By contrast, standard BIER does not pre-establish
   bindings between multicast groups and member sets.  It encodes all
   nodes in a BIER sub-domain into a fixed-length BitString, where each
   bit corresponds to one BFR.  Even with only a small number of sparse
   members, the full BitString sized for the entire sub-domain must be
   transmitted.  This causes excessive bandwidth overhead and degraded
   forwarding performance.  To improve BIER’s adaptability for sparse
   multicast member scenarios, optimization solutions have been
   proposed, such as Unmasked BIER [I-D.zzhang-bier-unmasked-bier].

   Simplicity: PIM and mLDP require the maintenance of complex multicast
   tree states and signaling mechanisms, resulting in high operational
   complexity and poor simplicity.  SR-P2MP reuses the SR unicast
   forwarding plane, with the control plane relying on a controller,
   leading to moderate complexity but still requiring additional tree
   management logic.  BIER, on the other hand, eliminates the need for
   explicit multicast tree construction, with no per-flow state at
   intermediate nodes, resulting in better simplicity.  Moreover,
   simplicity still needs further optimization to meet the ultra-high
   performance requirements of AI networks.

   In summary, the most critical common gap is the lack of native
   support for efficient, scalable bidirectional interactivity, which is
   the cornerstone for implementing closed-loop acknowledgement and
   congestion control.  Furthermore, no single multicast technology
   excels in all dimensions: some lack reliability, dynamics or
   simplicity (PIM, mLDP, SR-P2MP), others are inefficient for sparse
   groups (BIER).  Consequently, merely deploying or combining these
   existing technologies is insufficient to meet the stringent demands
   of AIDC workloads.  This gap analysis underscores the need for either
   a new architecture designed from the ground up for AIDCs or
   significant extensions to existing technologies.

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5.  IANA Considerations

   TBD.

6.  Security Considerations

   TBD.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

7.2.  Informative References

   [RFC3973]  Adams, A., Nicholas, J., and W. Siadak, "Protocol
              Independent Multicast - Dense Mode (PIM-DM): Protocol
              Specification (Revised)", RFC 3973, DOI 10.17487/RFC3973,
              January 2005, <https://www.rfc-editor.org/info/rfc3973>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

   [RFC6388]  Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
              Thomas, "Label Distribution Protocol Extensions for Point-
              to-Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
              <https://www.rfc-editor.org/info/rfc6388>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

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   [RFC9186]  Mirsky, G. and X. Ji, "Fast Failover in Protocol
              Independent Multicast - Sparse Mode (PIM-SM) Using
              Bidirectional Forwarding Detection (BFD) for Multipoint
              Networks", RFC 9186, DOI 10.17487/RFC9186, January 2022,
              <https://www.rfc-editor.org/info/rfc9186>.

   [RFC9860]  Liu, Y., McBride, M., Zhang, Z., Xie, J., and C. Lin,
              "Multicast-Only Fast Reroute (MoFRR) Based on Topology
              Independent Loop-Free Alternate (TI-LFA) Fast Reroute",
              RFC 9860, DOI 10.17487/RFC9860, October 2025,
              <https://www.rfc-editor.org/info/rfc9860>.

   [RFC7715]  Wijnands, IJ., Ed., Raza, K., Atlas, A., Tantsura, J., and
              Q. Zhao, "Multipoint LDP (mLDP) Node Protection",
              RFC 7715, DOI 10.17487/RFC7715, January 2016,
              <https://www.rfc-editor.org/info/rfc7715>.

   [RFC9960]  Parekh, R., Ed., Voyer, D., Ed., Filsfils, C., Bidgoli,
              H., and Z. Zhang, "Segment Routing Point-to-Multipoint
              Policy", RFC 9960, DOI 10.17487/RFC9960, April 2026,
              <https://www.rfc-editor.org/info/rfc9960>.

   [I-D.zzhang-bier-optimized-use-in-aidc]
              Zhang, Z. J., Xu, X., Zhang, Z., Tantsura, J., Mahale, A.,
              and Q. Zhang, "Optimized Use of BIER in AIML Data
              Centers", Work in Progress, Internet-Draft, draft-zzhang-
              bier-optimized-use-in-aidc-01, 16 March 2026,
              <https://datatracker.ietf.org/doc/html/draft-zzhang-bier-
              optimized-use-in-aidc-01>.

   [I-D.zhang-rtgwg-llmmoe-multicast]
              Zhang, Z., Duan, W., Xu, X., and Y. Liu, "Multicast use
              case in LLM MoE", Work in Progress, Internet-Draft, draft-
              zhang-rtgwg-llmmoe-multicast-02, 13 April 2026,
              <https://datatracker.ietf.org/doc/html/draft-zhang-rtgwg-
              llmmoe-multicast-02>.

   [I-D.liu-multicast-for-computing-storage]
              Liu, Y. and X. Geng, "Multicast for Computing and
              Storage", Work in Progress, Internet-Draft, draft-liu-
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Authors' Addresses

   Junye Zhang
   China Mobile
   China
   Email: zhangjunye@chinamobile.com

   Weiqiang Cheng
   China Mobile
   China
   Email: chengweiqiang@chinamobile.com

   Kefei Liu
   China Mobile
   China
   Email: liukefei@chinamobile.com

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