4 ms·
If you’re looking at TCP headers, you might as well go all the way to the PHY layer. Your TCP headers will get encoded by an error correcting code (good, they’l
by freyir 9y ago
If you’re looking at TCP headers, you might as well go all the way to the PHY layer. Your TCP headers will get encoded by an error correcting code (good, they’ll look random again) but then the data will be split into frames, and each frame begins with an identical preamble sequence of bits.
- bmm6o 9y ago> good, they’ll look random again They might look random, but they contain the same amount of entropy as the original data and are longer. Also, the encoding is deterministic.
- freyir 9y agoThe code itself is deterministic but usually bits are are interleaved and scrambled with a long time varying pseudorandom sequence. If you pass a short repetive sequence in, it will look random coming out.
- bmm6o 9y agoThat's interesting. I know a bit about ECC in general, but not too much about what the current state of implementations is. Do you know what the codes in use are called?
- freyir 9y agoThe scrambler's actually a separate block, usually immediately before or shortly after the encoder. It's common in wireless modems, which I'm more familiar with, but it seems like it's rare in wireline PHYs. Ethernet apparently uses an 8b10b encoding to maintain a similar number of 0s and 1s. I can't speak on entropy, but turbo codes use an internal interleaver and the codewords can be quite long, so a short repetitive input sequence turns into a very random looking output sequence. As you mentioned though, two identical input sequences would still map to identical output sequences.