Editing Tunneling protocol (section)

== {{Anchor|TCP meltdown}}TCP meltdown problem ==
{{expand-section|date=September 2024}}
Tunneling a TCP-''encapsulating'' payload (such as [[Point-to-Point Protocol|PPP]]) over a TCP-based connection (such as SSH's port forwarding) is known as "TCP-over-TCP", and doing so can induce a dramatic loss in transmission performance — known as the ''TCP meltdown problem''<ref>{{cite web
| url=http://sites.inka.de/bigred/devel/tcp-tcp.html
| title=Why TCP Over TCP Is A Bad Idea
| first=Olaf
| last=Titz
| date=2001-04-23
| archive-url=https://web.archive.org/web/20220103191127/http://sites.inka.de/bigred/devel/tcp-tcp.html
| access-date=2023-01-03| archive-date=2022-01-03
}}</ref><ref>{{cite conference
| bibcode=2005SPIE.6011..138H
| title=Understanding TCP over TCP: effects of TCP tunneling on end-to-end throughput and latency
|author1=Honda, Osamu |author2=Ohsaki, Hiroyuki |author3=Imase, Makoto |author4=Ishizuka, Mika |author5=Murayama, Junichi | s2cid=8945952
|book-title=Performance, Quality of Service, and Control of Next-Generation Communication and Sensor Networks III
| volume=6011
| date=October 2005
| doi=10.1117/12.630496
| citeseerx=10.1.1.78.5815
| editor1-last=Atiquzzaman
| editor1-first=Mohammed
| editor2-last=Balandin
| editor2-first=Sergey I
}}</ref> which is why [[virtual private network]] (VPN) software may instead use a protocol simpler than TCP for the tunnel connection. TCP meltdown occurs when a TCP connection is stacked on top of another. The underlying layer may detect a problem and attempt to compensate, and the layer above it then overcompensates because of that, and this overcompensation causes said delays and degraded transmission performance.