Some chip makers have hidden latency and jitter issues from common tests
tl;dr: The Intel Puma 6 and Puma 7 chipsets have a performance issue in a part of the packet processing that is specific to TCP/IP, which went undetected for awhile because "ping" packets are not TCP/IP. Modems that use the affected chipset will have high jitter under load (especially load consisting of many short connections), and will suffer denial of service when sent traffic with many different port numbers. Additionally, under a previous firmware (but according to a commenter on https://www.reddit.com/r/news/comments/7fjvvt/hundreds_of_mi... not on the most recent firmware), a timed process would briefly block throughput every 2 seconds, adding to jitter issues. DSLReports has created a tool which checks for this at http://www.dslreports.com/tools/puma6 .