The Hercules file transfer system demonstrates that high-speed file transfers are possible with SCION. This video shows an early demonstration. In collaboration between ETH and SWITCH, we could achieve machine-to-machine file transfers of close to 100 Gbps from Bern to Lugano across the SWITCH network. 

Hercules is a data transfer application that takes advantage of SCION for increased data transfer rates.
In contrast to traditional data transfer solution such as FTP or Gridftp that suffer from the drawbacks of TCP, Hercules implements a congestion control mechanism called PCC which is more efficient for high latency, high throughput connections as well as a retransmission scheme which improves memory locality and access patterns based on RBUDP.
It also bypasses the operating network stack using a feature in recent Linux kernels called AF_XDP for increased performance.

On top of that it can also make use of the clean multipath feature provided through the SCION architecture and make use of local backup links.

Measurements on the SCI-ED connection between ETHZ and CSCS show efficient use of the connection, using a single path:

and the improvement by using two paths in parallel:

Within the Switch Network even higher throughput rates were reached (over 90Gbps on a link limited to 100Gbps), as show in the following graph:

Key insights for the increased throughput was that the sending rate should only be reduced when the link is congested, and congestion is only one cause for packet loss.
Furthermore since we are running over SCION and do not use TCP offloading, it is more efficient to bypass the OS network stack entirely using AF_XDP.

Aggregating the available bandwidth provided by disjoint links further improves the throughput achievable.
Thus, Hercules is able to provide high throughput on a regular 2RU server even without hardware acceleration.

To learn more about the background of SCION, please check out the talks at SCION Day.

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