Kenneth Finnegan

@KWF

Engineer who loves to play with electronics, software, and bits.

San Jose, CA
blog.thelifeofkenneth.com
Vrijeme pridruživanja: ožujak 2008.
4.849 fotografija ili videozapisa Fotografije i videozapisi

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  1. proslijedio/la je Tweet
    prije 9 sati

    the only reason anyone ever does tweets on this hellsite is to get responses are are just their name in all caps / followed by a full stop

    10 proslijeđenih tweetova 49 korisnika označava da im se sviđa
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  2. prije 2 sata

    I feel like awk doesn't get enough love for all it's capabilities beyond just extracting a subset of a line's fields.

    11 korisnika označava da im se sviđa
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  3. prije 3 sata

    Twitter... You know what to do. 🤓

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  4. prije 14 sati

    People talk about how amazing it is that the Internet works because of "DNS" or "MTU discovery" or "BGP route security" But shit; just try and set up a peering session with Amazon and you'll understand how amazing this is.

    1 reply 4 korisnika označavaju da im se sviđa
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  5. prije 14 sati

    Only in networking have I experienced email threads which go on for YEARS with MONTHS between replies. It's amazing.

    9 korisnika označava da im se sviđa
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  6. prije 16 sati

    Moar art!

    1 reply 3 korisnika označavaju da im se sviđa
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  7. 4. velj

    Just imagine how much easier free wifi would be if no one had ever come up with the ToS click portal.

    6 korisnika označava da im se sviđa
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  8. proslijedio/la je Tweet
    4. velj

    Gelatin art

    46 replies 6.952 proslijeđena tweeta 13.175 korisnika označava da im se sviđa
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  9. 4. velj

    The only IC inside the connector is just a bog standard I2C EEPROM, which has the standard SFP memory map coded into it to identify itself as a 10G DAC cable of a certain length. This is why you tend to see more switches support third party DACs than actual optics; it's simple!

    2 proslijeđena tweeta 32 korisnika označavaju da im se sviđa
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  10. 4. velj

    Here's the bottom side of the PCB where the twinax lands on the PCB, and then the two differential pairs are routed out to the SFP connector. Notice how each pair has a ground pin on both sides of it! That's to help protect the signal integrity through the SFP connector

    1 reply 2 proslijeđena tweeta 22 korisnika označavaju da im se sviđa
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  11. 4. velj

    This should really emphasize why DACs save so much power! They're so simple! The 10Gbps signal literally just launches from the SFP connector PCB into the twinax, and lands on the other end!

    2 proslijeđena tweeta 22 korisnika označavaju da im se sviđa
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  12. 4. velj

    What the heck! The circuit board is potted in resin! I guess that makes a lot of sense since it really controls the spacing and routing of the twinax landing on the PCB, since it literally can't move. Good protection from those damn monkeys yanking on the cables in the DC!

    2 proslijeđena tweeta 22 korisnika označavaju da im se sviđa
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  13. 4. velj

    Let's pop off the lid! Look at that kapton, baby!

    1 reply 1 proslijeđeni tweet 21 korisnik označava da mu se sviđa
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  14. 4. velj

    Before we crack it open, here's the bottom view of the SFP+ connector. Note how it's designed to be hot-swap by the GND/power pins being longer than the signal lines. The bottom side is the low speed signals like Loss of Signal (LOS) and the I2C bus for telemetry/module ID.

    1 reply 3 proslijeđena tweeta 18 korisnika označava da im se sviđa
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  15. 4. velj

    Here you can see how I cut open the shield on one of the pieces of twinax to expose the two center conductors. Just like coax, but there's two conductors in the middle!

    1 reply 1 proslijeđeni tweet 14 korisnika označava da im se sviđa
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  16. 4. velj

    DAC cables are awesome because they save all the power and connectors needed to convert the signal into light, run it into a fiber, etc etc, with the downside that it is a relatively thick/stiff cable, and has a very limited range of only 5m. Great for connecting servers to ToRs

    1 proslijeđeni tweet 18 korisnika označava da im se sviđa
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  17. 4. velj

    DAC cables aren't Ethernet over copper like you're used to for 4x twisted pair. They're meant to plug into SFP+ cages, and instead of converting the differential signal into light and back, just pipe it straight to the other host over twinax.

    1 reply 3 proslijeđena tweeta 21 korisnik označava da mu se sviđa
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  18. 4. velj

    Unfortunately, while some of these are held together by a spring or the EMI gasket, this one is held together by two rivets, so we need to get violet.

    1 proslijeđeni tweet 17 korisnika označava da im se sviđa
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  19. 4. velj

    Today, let's take apart one end of a 10Gbps Ethernet Direct Attach Copper cable!

    9 replies 81 proslijeđeni tweet 235 korisnika označava da im se sviđa
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  20. 4. velj

    Today, in "silly things off eBay that are kind of genius," an adapter to make a male USB-A device plug into USB-C!

    3 proslijeđena tweeta 60 korisnika označava da im se sviđa
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