PoE Gig-E RJ45 SFP (mini-gbic)

[Randyman]

Hello. I’m not sure if this is the correct sub-forum or not. Apologies.

I have a Cisco CBS110-24T unmanaged switch that has two mini-gbic SFP ports. This is the “compact” version of the switch without onboard PoE (the PoE model is a full 1RU, and I have space restrictions in this home install).

Is there a mini-gbic SFP module available that would simply give me a copper RJ45 gig-e port with PoE delivery for one of the two mini-gbic ports on this switch?

This would allow me to eliminate the external PoE injector for the single WiFi-AP I have that requires PoE. I can’t seem to locate a compatible SFP with PoE, and I’d prefer not to upgrade to the larger and more expensive CBS110-24TT switch model that has onboard PoE (mainly because of the size restrictions mentioned above). 

Thanks!

Randy V.

[balaji.bandi]

no i do not believe that support as per your requirement.

[Leo Laohoo]

No one has ever developed a TX optics that can also support PoE. 

The best option is to get a power injector.

[Randyman]

Hello and thanks for the replies!

@balaji.bandi  - Yes indeed - The 24T does not have "native" PoE.  The 24TT model does, but is a larger 1RU unit that won't fit with the current installation restraints.  The 24T is a compact unit and one of the few I found that has 24x gig-e ports in such a compact form factor (but again, no PoE).

@Leo Laohoo  - Of course we can't send power over fiber / optics (maybe one day lol).  I was looking got a copper Gig-E / RJ45 mini-gbic SFP that might also have PoE included.  I'm not sure what voltage specs are presented at the mini-gbic SFP port, but I assumed there would be a copper gig-E RJ45 SFP that also passes PoE - one that might be compatible with my CBS110-24T.

So no one makes copper RJ45 gig-e SFP's that include PoE?

I'm using a standalone PoE injector now - but I'd like to get rid of it if I can find a suitable SFP.  It will make the installation cleaner and much easier to dress...

Thanks for all of your responses - and enjoy the rest of your weekend.

Randy V.

[balaji.bandi]

So no one makes copper RJ45 gig-e SFP's that include PoE?

None at this moment in the market.

I'm using a standalone PoE injector now - but I'd like to get rid of it if I can find a suitable SFP.  It will make the installation cleaner and much easier to dress...

Get PoE Switch to fix this issue. ( SFP not going to solve your problem you need a device that has a port that can give PoE.

Look at the Model which support  (Power over Ethernet (PoE)

https://www.cisco.com/c/en/us/products/collateral/switches/business-350-series-managed-switches/datasheet-c78-744156.html

[Ethan Grinnell]

I was curious if this is even possible with the SFP+ specification. It's not, not even close.

I believe that the most recent specification can be found here: https://www.snia.org/technology-communities/sff/specifications?combine=8431 or directly downloaded here: https://members.snia.org/document/dl/25891

SFP+ runs at 3.3V with a maximum permitted power of 1.5W (Power level II) per voltage pin. There are 2 voltage supply pins ( VccT and VccR [Transmitter and receiver voltages]). That gives only 3.0W as the absolute maximum that SFP+ port could supply to a module. An addendum increases that to 2.0W per pin, still at 3.3V (4.0W total). There's just no way to get 48V@30W to power a PoE+ 802.3at device via a SFP+ port. The only way I could think to make that work would be to have an external power adapter to the SFP+ module, which is asking a lot for something to small. Here's the power supply requirements table from the SFP+ addendum.

 

[Joseph W. Doherty]

Even if transceiver specs way above transceiver module's needs (to support PoE [especially the later PoE wattage standards]) unlikely there would be much market demand (considering typical usage of uplink ports).

Further consider switch would likely need larger power supply, etc.

I.e., you're likely to possibly always be limited to using a power injector or a switch with PoE ports, by design.  (Also for APs, mGig PoE ports, currently, might be your "best" choice.)

[Ethan Grinnell]

We're pretty much saying the same thing.

Though, it doesn't matter how strong the SFP+ host's power supply is, it could run on a nuclear power plant. Per the standard, the VCC pins on the SFP+ port are limited to the absolute maximum of 660mA sustained @3.3V, not a chance of powering a PoE device from that and the SFP module as well. Cisco's SFP-10G-T-X takes 2.5W just to power the SFP.

[Joseph W. Doherty]

"We're pretty much saying the same thing."

Laugh, well that wasn't my intention.

If what I wrote seemed that way, my bad.

[Randyman]

OP with an update:

I re-configured and expanded my Network/Server area from a "small nook" to a much larger area of a spare room (including all new runs of CAT6).  So the 1/2 rack space limitations I required from the unmanaged CBS110-24T in my "nook" were no longer needed.

I ended up being able to fit a full-size 1RU Ubiquiti USW-Enterprise-24-PoE switch with PoE+ and 2.5Gig ports in my setup.  Now, my two NAS' and two desktops saturate the 2.5Gig connections, and I have 24 ports of PoE+ on tap!  I added 3 more PoE devices since the initial post (two more UniFi AP's and a PTZ camera) - so this seemed to be a sensible investment.  Plus, being a managed switch, I split my IOT devices on their own VLAN/WiFi.

I was able to return the unmanaged CBS110-24T (and a TP-Link 5-port 2.5Gig switch) as I was within the Amazon return period, and only paid a few hundred dollars to upgrade to a superior setup.  About the cost of a few PoE injectors or a small unmanaged PoE switch and dramatically improved my entire network as a result...

Nice to see people still clarifying the initial Oct '21 inquiry for me!  Grazie

[Joseph W. Doherty]

Thanks for the update.  Always nice to know how it turned out.