Community discussions

MikroTik App
 
jo2jo
Forum Veteran
Forum Veteran
Topic Author
Posts: 971
Joined: Fri May 26, 2006 1:25 am

802.3 POE and PoE Out = Forced On ? (ie on new Omnitik 5 poe)

Sat May 20, 2017 12:00 am

On a Mt device such as the excellent / versatile new OmniTIK 5 poe (RBOmniTIKPG-5HacD ) - when the RB is powered with 802.3at (or af for that matter) - and you then plug in another 802.3af device (such as an IP camera)- How does “PoE Out = Forced ON” differ from “PoE Out = Auto ON” (or does it?) - again im only asking this in the case of 802.3 PoE being used (not passive POE).

Ive had excellent results with the OmniTIK 5 poe , and powering them via 48v DC in , and then plugging in 802.3af IP cameras into the OmniTIK. I really like this routerboard!

But Ive just always had the question of how does “PoE Out = Forced ON” work when 802.3x PoE is being used (bc the 802.3x protocol uses auto detection, so what does Forced ON mean in this scenario)


Thanks
:beep :beep :beep
 
aholmes
just joined
Posts: 19
Joined: Wed May 17, 2017 6:16 am

Re: 802.3 POE and PoE Out = Forced On ? (ie on new Omnitik 5 poe)

Mon May 22, 2017 6:22 am

Auto-On waits for an appropriate resistance to be measured across the power pins before firing up

Forced-On applies power all the time

Please correct me if I'm wrong, MT, but as far as I know the MT 802.3af/at PSE implementation isn't fully-compliant & is just taking advantage of the fact that you can apply 48V passive to 802.3af devices and they'll power right up - how this affects 802.3at devices I don't know as I don't know that MT's implementation would correctly signal 802.3at, due to the lack of a 2nd negotiation step, but most AT devices will power up anyway without negotiation.

Some Cisco devices use layer2 comms to negotiate 802.3at and these will not operate in full power mode with a non-Cisco power supply.

The Auto-On selection is basically 802.3af compliant (and kind of 802.3at compliant; won't signal correctly to some devices but will supply adequate power) while Forced-On is still basically compliant but removes the initial "device detection" stage & therefore removes protection for non-PoE-capable devices. I've not had amazing experiences with auto-on; i recommend setting forced-on on any ports you're connecting powered devices to and forced-off on ports not in use (and at least one port for management).
 
jo2jo
Forum Veteran
Forum Veteran
Topic Author
Posts: 971
Joined: Fri May 26, 2006 1:25 am

Re: 802.3 POE and PoE Out = Forced On ? (ie on new Omnitik 5 poe)

Thu Jun 15, 2017 9:01 am

Thanks, That is super helpful and informative!

The main point i took away (and didnt know) was that *any* (not all) 802.3 compliant devices will accept power if they are provided with "passive" 48v. So that does help me understand how Forced-On might work @ 48v.

I hope MT can chime in here, or update their online manual with an outline of how these new RBs are handeling 802.3 when they are powered at 48v.

(eitherway, for me, MT moving to increasingly support 802.3 in their RBs has been super helpful and is making me use more RBs in places i had always wanted to in the past, and so far with great 802.3 results)
:beep :beep :beep

Who is online

Users browsing this forum: MSN [Bot] and 59 guests