Problem with delivery / looking for alternative

RouterOS General
1

Hi guys, I have an issue and hope someone could jump in.

I have a network of some 42 WiFi (cAP) devices. For powering I choose CRS328-24P-4S+RM, however local distributor can not deliver the switches (2).

I would have to wait december for switches to maybe arrive. I asked MT for help, but they told me they have production issues.

Due to situation (looming deadline), the distributor offered me either Aruba Instant On 1930 24G Class4 PoE 4SFP/SFP+ 195W Switch or Planet GS-4210-24P2S. Never worked with either.

As I see, Aruba is more than 2x and Planet about 20-30% weaker unit than MikroTik. - Would they be suitable for my installation?

The cables would all be quite long, good part of them at full UTP length with a patch cable on either side of the infrastructure cable.

2

I use ubiquiti EdgeSwitch as a decently priced alternative - however 20+ cAP’s on a single switch has a max power draw of over 500W (not including the power the switch needs), you can obviously account for much less continuous but if you are playing safe you’d have to go up to 48 port 750W versions (in ubiquiti land) or perhaps split the 42 APs over 3 switches instead.

Edit - I’ll eat my words here and say the 24W was based on max consumption on the passthrough port has well, the unit itself has max consumption of 130W so 300W would be about what you need to stay comfortable power limits during things like power outage/full boot time.

The Aruba only looks to have <200W so would not be my pick

3

Thanks. Is there a way to Calculator PoE requirements in wome way?

4

Or you may use the passive injectors bundled with the cAP ac for those 6 cAPs that exceed the power budget of each switch. It is definitely not nice, but you only need a forking DC cable and a 80 W power supply at 24 to 48 V. Or even an AC extension cord with 12 free outlets if there’s a supply shortage even for the AC/DC converters.

5

Guys, are you sure I will run power poor? - It is not one switch to support all the cAPs, but two!

cAP uses 4W max, meaning max 4 x 21 per switch. That is about 84W + losses, which I factor in as 20% max on a good wire, so ~ 100W.

Aruba (favourite compared to planet) can churn out 195W class 4 (at/af).

I played with this: http://poe-world.com/Calculator/poe-calc.php a bit and I can’t get losses to amount for that much. :-I

The main issue I am concerned about is long term stability. If I get a weaker device I could run into problems.

6

My advice: do not use only “one” PoE switch, but distribute the load over several points, and not in the same “room”.

7

Yes, the older 2.4ghz only cAP only uses 4W, if that is the model you are implementing then 100% your calculations are correct - mine above are with accounting for 13W max consumption of the cAP AC (dual band cAP), so you’ll be find based on that info. Aruba is quite expensive for what it is though.

Also 48 ports with 42 cAP’s being installed doesn’t leave much headroom if you account for 2 uplinks per switch for redundancy, so it may be beneficial to jump straight to 48 port switches anyway that way you have growth options if required.

8

Thanks. I have only one Cap AC device, so I guess I am fine. From what I see, calculating in power req to +15-20% watts total is a good indication..

That said, that MikroTik switch is a real powerhouse with its 450W of power delivery. Arubas are expensive as hell. 8-I About 1000 EUR+ for the same performance. As for the Planet I was also offered, they do provide higher power, but I had numerous problems with their switches in the past, so no way I would install that.

9

I fell into the same rabbit hole, no way it came to my mind you might be installing actual cAPs (2,4 GHz only, 4 W only, single FastEthernet port only) these days.

Ask your distributor also about TP-link PoE switches like TL-SG2428P, here the price of this model is comparable with the CRS you’ve chosen, for less functionality (no L3 capability AFAIK).

10

2.4 GHz was fine for the purpose, as there are no other radio sources and I could put as many as I needed on the ceiling. I even did a pilot with 5 modules to see how it worked in one row, and it was fine. The price would be quite up for the ac version, so I skipped that.