Dirk Kutscher

How can we obtain the benefits of network-assisted multipath transport without changing Internet routing?

Our paper on "MARS: Multipath Adaptive Reliable Service has been accepted for publication at the 34th IEEE International Conference on Network Protocols (ICNP). It addresses this question by combining receiver-driven transport with lightweight overlay forwarders that safely discover additional forwarding opportunities and coordinate congestion control close to network bottlenecks.

Modern cloud services, geo-distributed AI systems, and large-scale content distribution increasingly depend on moving massive amounts of data across heterogeneous wide-area networks. Existing multipath transports, such as MPTCP and MPQUIC, can only exploit the paths visible to endpoints, while routing-based approaches require changes to network infrastructure.

At a glance, MARS augments traditional endpoint multipath with lightweight receiver-driven overlay forwarding.

MARS (Multipath Adaptive Reliable Service) explores a different direction. Rather than relying solely on endpoint scheduling or modifying Internet routing, MARS introduces lightweight, deployable forwarding assistance in an overlay network.

MARS combines receiver-driven transport with cooperating overlay forwarders that safely discover additional forwarding opportunities and react to congestion much closer to network bottlenecks—all while running as an incrementally deployable UDP overlay that requires no changes to Internet routers or routing protocols.

Key Ideas

• Safe overlay path discovery that expands usable path diversity while preventing forwarding loops, backward steering, and excessive path inflation.
• Receiver-driven congestion control coordinated with intermediate forwarders using lightweight queue feedback.
• Incremental deployment, allowing MARS to operate at endpoints alone while automatically benefiting from additional cooperating overlay forwarders.
• Robust operation under heterogeneous WAN conditions, packet loss, and transient network failures.

Results

We evaluate MARS through both large-scale ndnSIM simulations and a working Mininet prototype.

The results show that:

• MARS remains competitive even with endpoint-only deployment.
• Additional overlay forwarders expose significantly richer path diversity.
• MARS reduces worst-case 95th-percentile Flow Completion Time (FCT) by up to 81.5% compared with ECMP-limited multipath baselines.
• MARS remains robust under packet loss and quickly adapts to transient network failures.

Why It Matters

MARS demonstrates how Information-Centric Networking enables deployable receiver-driven overlay multipath without requiring changes to Internet routing. Rather than replacing today's Internet, MARS shows how lightweight receiver-driven forwarding can incrementally extend existing infrastructures with richer path diversity, faster congestion response, and improved robustness for modern WAN applications.

Reference

• Yitong Li, Xinjiao Li, Dirk Kutscher; MARS: Multipath Adaptive Reliable Service, to appear in the proceedings of the 34th IEEE International Conference on Network Protocols (ICNP); Tempe, Arizona, USA, October 05-08, 2026
• Pre-print on arxiv

Today’s transport protocols schedule packets without understanding computation. SAFS introduces receiver-driven semantic-flow scheduling, allowing distributed AI runtimes to expose computation semantics so that computation-critical communication is prioritized before pipeline bubbles can form.

Modern AI systems increasingly execute as pipelines spanning multiple GPUs, servers, and disaggregated components. In these systems, network communication is no longer just a data transfer problem – it directly determines whether expensive GPU resources remain busy or become idle.

Yet today's datacenter transports remain largely application-agnostic. They optimize congestion, flow completion time, packet priorities, or deadlines, but they do not understand why a particular communication flow matters to the computation.

The figure below illustrates the core idea behind SAFS. Conventional transport schedules communication independently of application progress, whereas SAFS uses lightweight runtime semantics to prioritize computation-critical communication before the no-bubble deadline.

Our accepted IEEE ICNP 2026 paper introduces SAFS (Slack-Aware Flow Scheduling), a transport architecture that schedules communication according to AI computation semantics.

The Key Observation

A network transfer is not harmful simply because it is delayed.

Instead, it becomes harmful only when it arrives after the downstream computation has exhausted the slack that could otherwise have hidden the communication. At that point, the delay becomes an exposed pipeline bubble, leaving GPUs idle while waiting for missing data.

This leads to a fundamentally different transport objective.

Instead of asking:

Which flow should finish first?

SAFS asks:

Which communication dependency will become the next computation bottleneck?

From Packets to Semantic Flows

SAFS introduces the notion of semantic flows.

Rather than treating network traffic as anonymous byte streams, each communication flow is associated with lightweight runtime metadata describing its role within the computation. This includes information such as:

• remaining data volume,
• a no-bubble timestamp indicating when the data must arrive,
• dependency information,
• and runtime updates as execution progresses.

Receivers use this semantic information to allocate bandwidth to the communication flows that are most critical for maintaining continuous pipeline execution.

Receiver-Driven Scheduling for AI Workloads

SAFS combines these computation semantics with a receiver-driven transport architecture.

Instead of allocating bandwidth solely according to congestion, flow size, or externally assigned deadlines, receivers compute the transmission rates required to keep each communication dependency on its no-bubble trajectory.

This allows application semantics to guide transport scheduling while existing transport mechanisms continue to provide congestion control, fairness, and reliable data delivery.

Because SAFS augments rather than replaces existing transport protocols, it can be deployed incrementally without requiring changes to AI applications or accelerator hardware.

Evaluation

We demonstrate SAFS in two representative AI environments:

• Pipeline-parallel training, where communication between pipeline stages competes with background traffic.
• Disaggregated LLM inference, where hidden-state transfers determine when feed-forward computation can begin.

Across both workloads, SAFS consistently prioritizes the communication dependencies that determine end-to-end execution performance.

Highlights include:

• Up to 38.7% lower iteration time during ZeroBubble pipeline training under background traffic.
• 38.7% lower p99 TPOT than D2TCP for large-scale disaggregated inference.
• 66.2% lower p99 TPOT than Homa.
• Zero urgent deadline misses in targeted receiver-incast microbenchmarks.

Why It Matters

SAFS explores a broader research direction:

Transport protocols should understand computation—not just packets.

This represents a fundamental shift from optimizing packet delivery toward optimizing application progress. As AI systems become increasingly distributed and disaggregated, exposing computation semantics to the transport layer enables the network to prioritize the communication that actually determines application performance.

Rather than optimizing generic network metrics, SAFS directly optimizes what distributed AI workloads ultimately care about: continuous computation, high accelerator utilization, and fewer pipeline bubbles.

Reference

Ruilong Wu, Yisu Wang, Jiaxiang Zou, Xiangsen Chen, Yixiang Zhu, Xinjiao Li, Xinyu Chen, Dirk Kutscher; SAFS: Slack-Aware Flow Scheduling for Pipelined AI Workloads; to appear at the 34th IEEE International Conference on Network Protocols (ICNP); Tempe, Arizona, USA, October 05-08, 2026

Our 2024 paper on Networked Metaverse Systems: Foundations, Gaps, Research Directions has been mentioned as one most popular and impactful papers of the IEEE Open Journal of the Communications Society (OJCOMS) 2024–2025.

References

• https://dirk-kutscher.info/publications/networked-metaverse-systems/
• Y. Zhang, D. Kutscher and Y. Cui, "Networked Metaverse Systems: Foundations, Gaps, Research Directions," in IEEE Open Journal of the Communications Society, vol. 5, pp. 5488-5539, 2024, doi: 10.1109/OJCOMS.2024.3426098.