We also wanted to reproduce the tables for various network scenarios described in the three tables in the later part of Section 4: latency distributions on high delay and high loss networks. We set out to reproduce Figure 2, which is the key-press latency distributions of SSH and Mosh over a cellular network with moderate average delay. Simulated High Packet Loss Network, 100 ms RTT Verizon LTE in Cambridge, MA (high delay network) A summary of statistics listed in the paper are shown below. Finally, Mosh showed resilience to high packet loss, as it yielded a lower median and mean latency for key presses compared to SSH, even without the benefit of predictive local echo.
While 0.9% of the keystrokes resulted in erroneous predictions, Mosh was able to correct such predictions within one RTT. For keystrokes that Mosh could not predict, its latency distribution is similar to that of SSH. In fact, about 70% of the time, Mosh was confident enough to display its prediction and give a nearly instant keystroke response time. In all mentioned cases, the authors found that Mosh offered a lower mean and median latency for key presses compared to SSH. The graph below demonstrates the results of replaying those traces over the Sprint 3G cellular connection. Finally, to test resilience to packet loss, the authors replayed the traces over a test network inducing an artificial RTT of 100 ms and a 50% round-trip packet loss probability. The authors then replayed the traces over several networks, including a Sprint 3G cellular internet connection, a Verizon LTE service, and a trans-oceanic wired link. The authors collected traces from individuals performing “typical, real-world sessions” to a remote host. SSH is one of the most used applications, but many interactive remote applications can benefit from the ideas of Mosh and the SSP protocol some that come to mind are telnet, IRC and the X window server, all of which currently operate over TCP. The user experience of SSH has two failings: firstly that it has poor performance on mobile networks, and secondly that it makes no allotment for mobility as it is based on TCP, which ties flows to the “4-tuple”, so switching networks will kill the connection. Most technical computer users have either directly or indirectly used SSH it’s the de facto protocol for spawning and interacting with a remote shell. The SSH task is a proxy to show that other interactive remote applications can make use of SSP to improve performance for users on high-delay and high-variability delay networks like cellular networks. They demonstrate that SSP has a much better keystroke response latency than existing SSH over TCP. The goal of Mosh is to serve as a better remote terminal application for mobile clients, as well as demonstrating the superiority of the State Synchronization Protocol––as opposed to TCP––for interactive mobile applications. Mosh is a remote terminal application which supports additional features, namely intermittent connectivity, roaming, and speculative echo of user keystrokes. Authors: Harrison Ho, Andrew Duffy The Goals of Mosh
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