4 ms·
Two things I've learned working with SPE in its 100 Mb and 1 Gb configurations for a few years: 1) PoDL is substantially lighter, smaller, and simpler (though
by addaon 3y ago
Two things I've learned working with SPE in its 100 Mb and 1 Gb configurations for a few years:
1) PoDL is substantially lighter, smaller, and simpler (though not necessarily cheaper) at 1 Gb than at 100 Mb, due to the increased frequency separation. Just like with other Ethernet protocols, the lowest frequency of comms is basically DC; it's only statistically brought above that by the scrambler, but there's no useful true lower bound. Having an order of magnitude more separation, such as it is, allows a more reasonably sized filter to stomp over less (ideally, approximately none) of the data.
2) Only the 1 Gb protocol includes FEC, 100 Mb is a simpler, non-error-correcting encoding. This means that even though the maximum frequency on the twisted pair goes up by an order of magnitude to ~660 MHz, requiring better cabling, better twist spacing, etc... it allows a "sloppier" job at both high and low frequencies, since the FEC really does hide a few errors. This can be spent on even worse filters for PoDL, on frequency-specific interference (e.g. an RF amp running nearby), etc.
Basically, I was surprised to find that 1 Gb was not only not more challenging at the system design level, it was often simpler. (I haven't played with 10 Mb in either of its two incarnations seriously yet.)
- wmf 3y agoPoDL = Power over Data Line. I guess this is similar but incompatible to PoE.
- addaon 3y agoSimilar in purpose, extremely different in implementation, since PoE-supporting Ethernets (e.g. 100base-TX) are magnetically coupled, but PoDL-supporting Ethernets (e.g. 100base-T1) are capacitively coupled.
- monocasa 3y agoI mean, isolation transformers like in regular amd PoE Ethernet are a form of capacitive coupling.
- unsung 3y agoThe windings in isolation transformers are inductively coupled through the magnetic field in the core. There's often a shield between the two windings to reduce any capacitive coupling.
- deleted 3y ago[deleted]
- MMoe 3y agoThe industry standard for SPE is moving towards a transformer as well, because to get 1,5kV in isolation from a capacitor requires large components. A transformer is a lot smaller and provides common mode rejection.
- gumby 3y ago> PoDL is substantially lighter, smaller, and simpler (though not necessarily cheaper) at 1 Gb than at 100 Mb, This was one of those wonderful "oh of course" points for me: when you read something and it's blindingly obvious, but until reading it my intuition pointed the other way (easier to deal with lower frequencies rather than unnecessarily high data rates).
- madengr 3y ago[dead]