Encrypted QUIC traffic complicates network management as traditional transport layer semantics can no longer be used for RTT or packet loss measurements. Addressing this challenge, QUIC includes an optional, carefully designed mechanism: the spin bit. While its capabilities have already been studied in test settings, its real-world usefulness and adoption are unknown. In this paper, we thus investigate the spin bit's deployment and utility on the web. Analyzing our long-term measurements of more than 200M domains, we find that the spin bit is enabled on ~10% of those with QUIC support and for ~50% / 60% of the underlying IPv4 / IPv6 hosts. The support is mainly driven by medium-sized cloud providers while most hyperscalers do not implement it. Assessing the utility of spin bit RTT measurements, the theoretical issue of reordering does not significantly manifest in our study and the spin bit provides accurate estimates for around 30.5% of connections using the mechanism, but drastically overestimates the RTT for another 51.7%. Overall, we conclude that the spin bit, even though an optional feature, indeed sees use in the wild and is able to provide reasonable RTT estimates for a solid share of QUIC connections, but requires solutions for making its measurements more robust.

翻译：加密的QUIC流量使网络管理复杂化，因为传统的传输层语义无法再用于RTT或数据包丢失测量。为应对这一挑战，QUIC包含一个可选且精心设计的机制：自旋比特。虽然其能力已在测试环境中得到研究，但在现实世界中的实用性和采纳情况尚不明确。因此，本文研究了自旋比特在Web上的部署与效用。通过分析对超过2亿个域名的长期测量数据，我们发现在支持QUIC的域名中约10%启用了自旋比特，在底层IPv4/IPv6主机中分别为约50%和60%。该支持主要由中型云服务提供商推动，而大多数超大规模云服务商并未实现它。在评估自旋比特RTT测量的实用性时，理论上的数据包重排问题在我们的研究中并不显著，自旋比特为使用该机制的约30.5%连接提供了准确估计，但另51.7%的连接则大幅高估了RTT。总体而言，我们得出结论：自旋比特尽管是可选功能，确实在实际中得到使用，能为相当比例的QUIC连接提供合理的RTT估计，但需要解决方案以使其测量更加稳健。