Well...
>> IPv6 routing Several good algorithms are prohibited.
Alan Cox mentioned this to me when I pointed him to a nice trie-based
system for keeping track of routes.
>> compression Arithmetic encoding (bzip), MPEG, audio, GIF...
Oringinal bzip uses arithmetic encoding for the second stage, which works
better than the huffman encoding currently used. The same exact problem
hits jpeg, with everyone forced to use the inferior compression.
Many kinds of perceptual compression algorithms for audio and video
are patented. They remove the data that humans don't notice, and get
far better compression.
GIF compression is an old and well known problem. Lots of people
violate it though. PNG can do a better job with plain images, but
the MNG animation format is not yet well supported. I doubt this
one has many years left on it.
>> encryption Idea, RSA, some kinds of key exchange...
PGP hit some problems here. RSA (the company) holds many.
>> color management The gimp can't do it. Damn.
At least 3 patents hit us here. The gimp site has a web page about it.
>> filesystem updates We can't do delayed ordered writes.
Old AT&T patent.
>> OSPF The IETF is not happy with this one!
>> quality-of-service Multi-protocol Label Switching (MPLS) QoS
Both IBM patents. Cisco has a few nasty ones too AFAIK.
These make it hard to do some networking stuff.
>> register allocation Ever wonder why VC++ code can beat g++ code?
Various people AFAIK. Something about graph coloring...
>> PPP Can't return a useful error code to the other side.
Use grep on the kernel source. Motorola holds this one.
>> drivers/net/zlib.c Must use code with nonlinear time requirements.
2 guys hold it. Not serious. You can't do gzip with a nice time bound.
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