CC_HTCP(4)

💅 CC_HTCP — H-TCP Congestion Control Algorithm

okay so bestie, welcome to the Kernel Interfaces Manual, section 4 🎀 this is cc_htcp, the H-TCP Congestion Control Algorithm, and she is literally built different. let's get into it ✨

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🦋 NAME 🦋

cc_htcp — the H-TCP Congestion Control Algorithm. that's her. that's the whole name. periodt 💅

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🌸 DESCRIPTION 🌸

so the H-TCP congestion control algorithm was designed to give you increased throughput in fast and long-distance networks. main character energy fr fr 🔥

and the way that she's thoughtful?? she attempts to maintain fairness when she's competing with legacy NewReno TCP in those lower speed scenarios where NewReno is actually able to operate adequately. like, she's not gonna steamroll the old guard, she's gonna share the vibe check 🤝

here's the tea on how the congestion window moves: the congestion window is increased as a function of the time elapsed since the last congestion event ⏳

and the window increase algorithm?? it operates like NewReno for the first second after a congestion event, and then — after that one second — she switches to a high-speed mode based on a quadratic increase function 🚀 not me transitioning into my high-speed era after exactly one second.

ngl the implementation was done in a clean-room fashion 🙈 and it's based on the Internet Draft and other documents referenced in the “SEE ALSO” section below. no copying, all original, we love to see it 💖

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✨ MIB Variables ✨

the algorithm exposes these tunable variables in the net.inet.tcp.cc.htcp branch of the sysctl(3) MIB 👑

• adaptive_backoff — controls use of the adaptive backoff algorithm, which is designed to keep network queues non-empty during congestion recovery episodes 🫶. the default is 0 (disabled).
• rtt_scaling — controls use of the RTT scaling algorithm, which is designed to make congestion window increase during congestion avoidance mode invariant with respect to RTT 🌀. the default is 0 (disabled).

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🔍 SEE ALSO 🔍

go read these besties, they're all iconic 👇

• cc_chd(4)
• cc_cubic(4)
• cc_hd(4)
• cc_newreno(4)
• cc_vegas(4)
• mod_cc(4)
• tcp(4)
• mod_cc(9)

and the ✨ literature ✨:

• D. Leith and R. Shorten, H-TCP: TCP Congestion Control for High Bandwidth-Delay Product Paths, http://tools.ietf.org/id/draft-leith-tcp-htcp-06.txt.
• D. Leith, R. Shorten, and T. Yee, “H-TCP: A framework for congestion control in high-speed and long-distance networks”, Proc. PFLDnet, 2005.
• G. Armitage, L. Stewart, M. Welzl, and J. Healy, “An independent H-TCP implementation under FreeBSD 7.0: description and observed behaviour”, SIGCOMM Comput. Commun. Rev., 3, 38, 27-38, July 2008.

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💖 ACKNOWLEDGEMENTS 💖

development and testing of this software were made possible in part by grants from the FreeBSD Foundation and Cisco University Research Program Fund at Community Foundation Silicon Valley. shoutout, we love funding that actually funds 🫶✨

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📜 HISTORY 📜

the cc_htcp congestion control module first appeared in FreeBSD 9.0 🌈

the module was first released in 2007 by James Healy and Lawrence Stewart whilst they were working on the NewTCP research project at Swinburne University of Technology's Centre for Advanced Internet Architectures, Melbourne, Australia 🦘 which was made possible in part by a grant from the Cisco University Research Program Fund at Community Foundation Silicon Valley. more details are available at:

http://caia.swin.edu.au/urp/newtcp/

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👑 AUTHORS 👑

the cc_htcp congestion control module was written by James Healy <jimmy@deefa.com> and Lawrence Stewart <lstewart@FreeBSD.org> 💅

this manual page was written by Lawrence Stewart <lstewart@FreeBSD.org> and David Hayes <david.hayes@ieee.org> ✍️

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and that's the whole page bestie 🎀 this one's a Debian situation, dated September 15, 2011 — so yes she's an older queen but she still ate, no cap 💜⭐ bye pookie 🦋