Can Power Over Ethernet be daisy chained?

I am planning a wireless network that will involve a wireless radio modem that must be mounted pretty far from my house on a post (Needs line of sight to work) and then getting the signal back over to the house using an outdoor wireless access point(something like this, for example).

Both the modem and the WAP can be powered by Power over Ethernet and I was wondering if I can chain them.

For example, can I replace this configuration...
Cat5 -> PoE Injector -> Cat5 -> WAP -> Cat5 --> PoE Injector-> Cat5 -> Modem

With this configuration...
Cat5 -> PoE Injector -> Cat5 -> WAP -> Cat5 -> Modem

Is this possible? Also, Is one of these two configurations a bad idea for some reason?

power-over-ethernet

JohnFx

Posted 2011-08-12T22:56:27.473

Reputation: 1 299

what's a wireless radio modem? do you mean what i've heard is called a range extender that extends the range of your WAP. – barlop – 2011-08-13T01:15:38.347

the configuration you describe has cables on both sides of your WAP so not making use of wireless and who would an ethernet over mains plug, have cat5 cables on both sides, it can only have one side with cat5.. you have me baffled. This "Cat5 --> PoE Injector-> Cat5 -" is something you'd add if your WAP cannot reach your modem. – barlop – 2011-08-13T01:23:33.313

1@barlop It's not Ethernet over mains, it's power over Ethernet. The WAP is used for wireless - it links with the remote wireless device. – sblair – 2011-08-13T02:16:34.797

@barlop - It is used by WISP providers. In my example it is the subscriber module for the Motorola Canopy System (http://www.canopy-wireless-solutions.com/Products/PMP/Specifications/24Specficiations/2450SMBC.shtml)

– JohnFx – 2011-08-13T15:16:38.207

Answers

Generally no, because in switched Ethernet, all links are point-to-point. There should be one power sourcing equipment (PSE) device (e.g., an injector) per powered device (PD). It would be up to the switching fabric in the switch (in your case the Ethernet switch in the WAP) to support this.

An exception is the relatively new Cisco PoE passthrough [PDF] range of devices which:

can draw power from an upstream (PoE+/PoE-capable) switch or a router in the wiring closet, to power itself and to drive power downstream to the IP devices connected to it.

Another option is a HP IntelliJack Gigabit switch, which can power up to two devices, but only if supplied by a 802.3at-2009 (PoE+) source (or a local DC supply, as described in the manual PDF).

HP IntelliJack Gigabit switch

sblair

Posted 2011-08-12T22:56:27.473

Reputation: 12 231

Apparently it's possible. There's a manufacturer of surveillance cameras that offers daisy-chained PoE cameras. I don't know to what extent their solution follows the standards, I assume they have added some proprietary "hacks" to make it all work.

VIVOTEK is pleased to launch a revolutionary series of daisy-chain PoE network cameras, IB8367-R, IB8367-RT and IB8338-HR. The three uniquely-designed network cameras allow for both PoE input and output as well as direct connection with other PoE network cameras without an additional power source, thereby facilitating long-distance surveillance system implementation in factory areas, parking lots, crossroads, and outdoor sidewalks.

http://www.vivotek.com/vivotek-embedded-poe-extender-design-r-series-network-camera-revolutionary-invention-accelerates-the-evolution-of-outdoor-and-long-distance-surveillance-applications/

ximo

Posted 2011-08-12T22:56:27.473

Reputation: 63