# Lower-Latency Screen Updates over QUIC with Forward Error Correction
## 7 Concluding Remarks  
In this paper, we described the design and implementation of a partial-order delivery system over QUIC, for workloads with a sequence of updates, which contain messages without strict ordering dependencies. For example, a typical VNC runs over the TCP, whose totally ordered delivery adds unnecessary blocking time. Unmodified QUIC supports a kind of partial ordering, based on streams, which does not fit the screen updates workload. Also, we combined our partial ordering design with FEC to further improve latency and reduce blocking time by not waiting proportionally to the RTT for retransmissions.  
We used two different synthetic workloads: (1) Streaming updates: The sender sends a sequence of updates without gap such as the frames of a video. (2) Non-streaming updates: The sender sends each update after an input (request) from the client. Through our evaluation with a range of parameters (e.g., packet-loss rate, RTT, bandwidth, and CCA) on the Emulab testbed, we showed that our proposal achieved latency improvements compared to total delivery for both workloads.  
For the baseline setting (0.5% loss, 100 ms RTT, 100 Mbps, BBR), with the streaming workload, we could reduce the 99-percentile of message-blocking time by 230 ms compared to total delivery (Figure 9) (0.4 ms v.s. 230 ms). And with the non-streaming workload, we could reduce the 99-percentile of update response time by 50% compared to total delivery (Figure 18) (162 ms v.s. 325 ms). These improvements grew as we increased the packet-loss rate and RTT.  
We started with synthetic workloads to establish the basic benefits of adding partial ordering and FEC to QUIC for low-latency applications. Admittedly, real-world scenarios will be more complicated due to contention between multiple data streams and scalability issues. Shared networks, like the wider Internet outside of testbeds such as Emulab, have multiple users, multiple protocols in use (e.g., TCP, UDP, CUBIC CCA, and BBR CCA), and multiple applications.  
One contribution of our empirical analysis is quantification of the benefits of partial ordering and FEC for both the CUBIC and BBR CCAs, with BBR benefiting even more than CUBIC from FEC. Given the fundamental differences (e.g., loss-based vs. measurement-/model-based designs) between CUBIC and BBR, it was not obvious beforehand what would be the benefit of our proposals. Furthermore, with the growth in the use of BBR due to Google's engineering efforts, that result is useful for future QUIC-based use cases.  
As well, real-world scenarios that push the scalability of networked applications (e.g., larger numbers of users, concurrent VNC sessions, and competing data streams) are of particular interest. Contention for networks, especially at bottleneck links, result in more packet loss, complicated bursty loss patterns, and greater chances of even retransmitted packets being lost. Our current results establish a baseline benefit from partial ordering and FEC across a range of network parameters (e.g., packet-loss rate, bottleneck bandwidth, CCA protocol, etc.), and we plan on future experiments with more dynamic and high-contention scenarios.  
Methodology, N.E.; software, N.E.; experiments, N.E.; writing--original draft preparation and editing, N.E.; Methodology, N.E.; writing--review and editing, P.L.; supervision, P.L. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding. The APC was funded by Dr. [PERSON].  
The implementation and workloads supporting the conclusions of this article will be made available by the authors upon request.