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StatusCompleted
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Status date2025-12-09
The main objectives of the project are as follows:
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Design novel Congestion Control (CC) mechanisms for the QUIC transport protocol, which deliver acceptable performance over both satellite and terrestrial networks.
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Prove the effectiveness of the new mechanisms in relevant GEO/NGSO scenarios.
Both verification and validation campaigns are performed to show that the designed solution satisfies the technical requirements and to evaluate the effectiveness compared to existing options. A goal is to attain similar or higher performance than can be achieved using a PEP with TCP. A set of demonstration campaigns use commercial satellite links for both GEO (e.g., Eutelsat Konnect, SES ASTRA) and NGSO (Starlink), and consider migration scenarios (satellite to terrestrial network switching).
The key results of the project are contributing to the Internet Engineering Task Force (IETF), the principal Internet standards development organisation.
The recently defined QUIC protocol (RFC9000) has been widely deployed across the Internet. This uses TLS 1.3 to encrypt the end-to-end communication. This prevents using techniques to mitigate the differences introduced in satellite systems (e.g., PEPs) and therefore introduces performance limitations (RFC9065). Instead, the project proposes to change the QUIC sender to optimise transfers over satellite using the QUIC transport protocol.
An update to the QUIC sender congestion control has been designed and analysed. This provides effective performance over satellite systems: increasing the throughput and reducing data transfer time. The improvement is delivered across a wide range of applications using satellite systems, and targets performance close to, or better than, that offered by current TCP-PEP solutions, even when end-to-end security is employed.
The new congestion control mechanism has been proposed for standardisation within the IETF. This update can be implemented in Internet servers providing a demonstrable benefit when used over or migrating to a NGSO and GEO satellite network.
The project has implemented the congestion control mechanism in two QUIC stacks: A fork of the CloudFlare Quiche, and a fork of Picoquic. These implementations have been validated and then evaluated using a range of applications operating over commercial satellite links for both GEO (e.g., Hylas, Eutelsat Konnect, SES ASTRA) and NGSO (Starlink). A range of non-satellite paths have also been evaluated and many also experience benefit, as well as considering migration scenarios where the path changes between satellite to terrestrial networks. Configuration and KPI recording is implemented through a web-interface (GUI).
The project has three phases:
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Phase 1: Definition of a technical baseline and preliminary validation of the mechanisms using simulation campaigns in ns-3. This was used to derive the initial design.
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Phase 2: Development of a consolidated technical baseline in a real-world QUIC implementation followed by in-depth analysis over emulation testbeds.
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Phase 3: Demonstration over real-satellite services using real applications.
All phases have been completed: The project has finalised a technical specification (called Careful Resume), supported by simulation analysis and evaluation. This has been shown to significantly improve the performance and reliability of the Internet, especially for users of high-bandwidth-delay-product paths – such as those provided by some cellular services and by broadband satellite providers.
The project has successfully contributed an Internet-Draft (draft-ietf-tsvwg-careful-resume) specifying Careful Resume to the IETF TSVWG working group. This has been adopted as a work item and is currently progressing towards publication as an IETF Standards Track RFC.
During Phase 2, three independent implementations of Careful Resume were developed and integrated into different QUIC stacks:
In addition, the qvis tool was extended to support the detailed analysis of Careful Resume behaviour, facilitating deeper performance insights across test campaigns.
The Phase 3 demonstrations over commercial GEO and LEO satellite links confirmed that Careful Resume achieves PEP-level performance for encrypted traffic, significantly improving throughput and reducing transmission times without compromising end-to-end encryption.
Careful Resume was evaluated over both geostationary (GEO) and low Earth orbit (LEO) satellite paths using real commercial networks.
Over a GEO satellite connection (Eutelsat Konnect), the results show that QUIC with Careful Resume achieves nearly identical transmission times to those of the operator’s proprietary TCP PEP, which is only applicable to unencrypted HTTP/2 traffic. In contrast, conventional encrypted transports such as unmodified QUIC (HyStart) or VPN-based connections exhibit significantly longer transfer durations.
On a LEO satellite path (Starlink), Careful Resume again outperforms both TCP and unmodified QUIC, demonstrating its ability to quickly adapt to the higher capacity and lower delay variations typical of LEO systems.
To demonstrate end-user relevance, additional experiments were performed with current web browsers. In these tests, Careful Resume substantially reduced webpage loading times and achieved ramp-up rates comparable to those of PEP-assisted TCP connections.
Overall, the results confirm that Careful Resume provides PEP-level performance for encrypted traffic over both GEO and LEO satellite links, significantly improving throughput and responsiveness without breaking end-to-end encryption.
This method can be used with any web content, and is therefore applicable to other forms of media delivered over QUIC (such as streaming video).
