TalkTalk and DSCP and 19 second latency

This page is about in interesting problem that was reported to us, by a customer, in December 2021.

TL;DR

For some reason, TT's kit is reading IP DSCP marks from IPv4 packets inside PPPoE, and then putting them in a funny queuing setup which results in latency quickly increasing to over 19 seconds.

The Problem

Our customer moved house in early 2021 and we provided a VDSL line, a FireBrick FB2900. The VDSL was supplied over TalkTalk backhaul. At the same time the customer installed a set of new Aruba access points to cover his new house in Wi-Fi.

The Wi-Fi itself works very well. But since the install the customer soon noticed problems with some 'real time' applications such as webRTC, Google Stadia, Nest Camera video streaming. The problem was with latency, which was caused delays with the live streaming of video and audio.

The customer put this down to something odd on their network until they finally decided to investigate further.