Improving Network Clock Synchronization by Marking Congestion

2026-04-14

AI Summary

Network congestion induces delay jitter in time synchronization packets, significantly degrading the clock synchronization accuracy of protocols such as NTP and PTP. This work proposes a lightweight congestion marking mechanism that leverages existing unused fields in IP, PTP, or NTP headers to tag synchronization packets experiencing queuing delays on programmable switches (Tofino platform), without requiring deep packet inspection or protocol modifications, thereby preserving backward compatibility. At the receiver, statistical filtering strategies—combining minimum RTT and median delay estimates—effectively discard congestion-affected packets. Experimental results demonstrate that the proposed approach improves synchronization accuracy by over 80% in single-hop scenarios and reduces clock offset estimation error by 30%–80% in multi-hop environments, achieving up to a 90% performance gain over conventional filtering methods.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Machine Learning: Hardware-aware ML
• Search and Optimization: Distributed Search

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Responsible Web: Measurement, analysis, and circumvention of Web censorship

Abstract

Achieving consistent time across devices in distributed systems often involves exchanging timestamped messages over a network. Precise time synchronization is crucial for applications such as cellular networks, industrial automation, and transactional databases. However, delay variation in synchronization packets-often caused by congestion from competing traffic-degrades synchronization accuracy. Detecting whether a packet experienced congestion can help improve synchronization through filtering and statistical methods. We propose an in-network congestion indication and filtering mechanism for synchronization messages used in protocols such as the Network Time Protocol (NTP) and Precision Time Protocol (PTP). Network devices mark packets that experienced queuing, allowing clocks to correct errors caused by varying delays. Our approach requires only simple changes at switches or routers, avoiding deep packet inspection or protocol modifications. The method is backward compatible, using standard but currently unused fields in IP, PTP, or NTP headers. We implement our method on a Tofino P4 target and demonstrate an improvement of over 80% in synchronization performance over a single hop. Moreover, we show that the performance of traditional statistical filters, such as min-RTT and median-delay, is improved by 90% over the one-hop hardware setup. We further demonstrate the effectiveness of our proposed method across multiple hops, both analytically and through simulation. Congestion marking improves the root-mean-squared clock offset estimation error by 30% to 80%, depending on network conditions and filtering techniques.

Problem

• clock synchronization
• network congestion
• delay variation
• timestamped messages
• synchronization accuracy

Innovation

• congestion marking
• clock synchronization
• network time protocol
• in-network signaling
• delay filtering