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TalkTalk and DSCP and 19 second latency: Difference between revisions
TalkTalk and DSCP and 19 second latency (view source)
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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.
=in depth=
= The Problem =▼
== Home network ==
the cusotmer's home network is fairly typical, eg:
WiFi devices <-> Aruba AP22 <-> FireBrick 2900 <-> Huawei HG612 (bridge mode)
There are also a number of devices wired in via a switch and the FireBrick.
▲== 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 customer put this down to something odd on their network until they finally decided to investigate further.
== The cause
pcaps revelealed that the Aruba access point was marking some traffic with the DSCP flag CS6
== Things that were tried==
===...that didn't make a difference===
* Disabling the "QoS" setting on the HG612 in bridge mode (still observe high latency)
* Reducing the "speed" of the PPPoE connection from the FB2900 to 85% of sync speed, hoping to avoid buffer-bloat anywhere in the me-to-A&A direction (still observe high latency)
* Using other wireless devices (I can repro the problem with the "live view" of some Nest Cameras and with web-based Stadia on a Chromebook)
* Dumping packets on the WAN interface of the FB2900 (I've confirmed that the FB2900 itself isn't introducing the extra latency)
===...that did make a difference===
* Connecting the phone, running Stadia, via wired ethernet (high latency goes away because the problematic QoS marking has gone, DSCP field = 0)
* Setting a special feature on AAISP and the FireBrick - 'IP over LCP' - this sends the IP traffic as control frames. (high latency goes away)
== The cause of the latency==
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