POE sanity check - Mode A vs Mode B

[pete]

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".

[Soulfish]

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)

[plexer]

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

[plexer]

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

[ben604]

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.

[pete]

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.