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Particular topics that need work
New ECN Semantics (e.g. DC-TCP)
The original ECN proposals assumed that ECN signals would be sent infrequently, similar to packet-loss "signals" in prior times. Later on, proposals such as Microsoft's Data Center TCP suggested to use more fine-grained congestion signals, by marking increasing percentages of packets with ECN bits as congestion increases. BBRv2 assumes this "DC-TCP-like" form of ECN, and proposals like L4S (see below) and SCE (Some Congestion Experienced) do as well.
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This was mostly used either specifically for DNS, in particular for higher-level (e.g. Root/TLD) nameservers, or within individual administrative domains. Lately it has become more widely used, for example in CDNs. SIGCOMM 2021 had two papers about it. SWITCH has an "interesting" (in the Chinese-curse sense of the word) story about an issue with such a CDN and ECMP that might be worth documenting.
Should be updated, preferably by someone with actual experience with such systems. In particular, the TCP socket buffer tuning hints from MacOSXOSSpecific probably work as-is on *BSD. Someone should check that, and either copy/paste the Mac instructions over to the BSD topic, or unify them somehow else.
Linux OS Specific
The TCP_CONGESTION setsockopt() socket option should be documented. It is available in Linux and possibly also in FreeBSD. It allows to select the TCP congestion-control algorithm on a per-connection basis. The current Linux-specific tuning instructions only talk about setting this globally.
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