Topic

asymmetric latency

A collection of 5 issues

DOCSIS 3.1 and NTP

Spectrum upgraded my area to DOCSIS 3.1 to offer 1G/40M service. I believe they have it configured for 1.7Gbit shared downstream (using DOCSIS 3.1) and ~100Mbit shared upstream (sharing the legacy DOCSIS 3.0 upstream channels). This is unverified because the modem (a Technicolor TC4400-AM) has

Stratum 2 NTP over a Cable Modem

Goals I have a Stratum 1 NTP server at home, and ideally I'd like to join the ntp pool as a server. The problem is, my home connection isn't up to this task. My IP is dynamic, there's an asymmetric latency built in, and my upstream is tiny. So it'd

Measuring Asymmetric latency via NTP, part 3

Part 1 [https://blog.dan.drown.org/measuring-asymmetric-latency-via-ntp/], Part 2 [https://blog.dan.drown.org/measuring-asymmetric-latency-via-ntp-part-2/] Varying round trip times Asymmetric latency changes NTP's calculated clock offsets. What do the offsets look like when two clocks are in sync (or always within ~200us) and the latency varies? SMQ clock, request

Measuring Asymmetric latency via NTP, part 2

See the first part for the math [https://blog.dan.drown.org/measuring-asymmetric-latency-via-ntp/] Let's use a third party (stratum 2) observer to compare the stratum 1 NTP clocks. Round trip times First, a graph of the $rtt times from the third party to various stratum 1 NTP clocks. This is

Measuring Asymmetric latency via NTP

Goal Learn more about the latency characteristics of my cable connection. Starting point I have a stratum 1 NTP server at home. Below is a graph of its performance. The offset between the GPS clock and the server's clock is in red. The two clocks are within +/- 50us 90%