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Wireless Networks Thread, POE sanity check - Mode A vs Mode B in Technical; Which is more commonly supported for power delivery (switches) and endpoint kit (access points, cameras)? From reading around it would ...
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    POE sanity check - Mode A vs Mode B

    Which is more commonly supported for power delivery (switches) and endpoint kit (access points, cameras)? From reading around it would appear that Mode A is the more flexible and so should be more prevalent, but I need a sanity check.

    This post brought to you by "that POE switch is disturbingly cheap, I wonder what's wrong with it".

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    From what I understand Mode A should be more prevalent - certainly anything supporting gigabit speeds and PoE seems to use Mode A (Power over Ethernet - Wikipedia, the free encyclopedia)

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    pete (7th February 2011)

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    The PSE, not the powered device (PD), decides whether power mode A or B shall be used. PDs that implement only Mode A or Mode B are disallowed by the standard. in theory then your device supplying the power should be capable of both ways.

    Ben

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    Quote Originally Posted by Soulfish View Post
    From what I understand Mode A should be more prevalent - certainly anything supporting gigabit speeds and PoE seems to use Mode A (Power over Ethernet - Wikipedia, the free encyclopedia)
    Anything that is gigabit and requires poe has to use mode a as there are no spare pairs for mode b operation.

    Ben

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    pete (7th February 2011)

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    Beware of classes too, there are some issues with how switches negotiate power with devices. For example, one 24 port switch may have a total of 140 watts power to give to devices. If your devices are class 0 (don't negotiate and usually use draw the full 15.4 watts regardless of what they actually need) or class 3 (high power, always draw 15.4 watts) then you'll run out of POE by port 10...

    Other switches, usually the more expensive ones, have a full 15.4 watts available on each individual port, so you'll have no issues expanding later! Might be cheaper using a separate injector and swtich. PowerDsine stuff is nice and reliable.

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    pete (7th February 2011)

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    Cheers, that's what I hoped. Spotted a ~200 Not-Linksys-any-more-it's-a-Cisco-really-guv 8-port Gigabit POE switch (SRW2008MP-EU) that can deliver 15.4w port for an outbuilding and was wondering what was wrong with it.

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