How Do I Size A Switch?

Are there any guidelines to picking the right switch for a system, when dealing with bandwidth not power?

What specifications on a switch spec sheet actually help determine if the switch can handle the number of camera and configuration needed?

A camera configuration calculator (like from Exacq) can be used to get a rough estimate of the total camera data rate, but how is that number used to make sure the switch can handle those cameras?


The spec you're looking for is most commonly listed as backplane, fabric, switching capacity, or total bandwidth (at least those are the ones I've seen, there are probably others). It's a rating of how much data the switch can actually move around internally.

I'll generally look for something that has the requisite number of ports for a job (and number of PoE ports), then management features (if required), and then consider budget... that will generally net two or three options, and the deciding factor then becomes backplane - the bigger the better.

Note that some switches list it in (mega/giga)bytes per second, others list it by packets per second, so make sure when looking at specs, that you're comparing apples to apples.

Example from a local retailer's website: Cisco SG300-28PP (24 GbE PoE ports, two GbE uplink ports, two GbE combo ports, Layer 3 management, retail $720) lists "Switching capacity: 56 Gbps" while the SF200-24P (24 x 10/100 PoE ports, plus two GbE combo uplink ports, Layer 2 management, retail $325) lists "Switching capacity : 6.55 Mpps". Sounds like a LOT LOT less, until you factor in that they're measuring 64-byte packets; Cisco lists the 200 as 8.8 Gbps. (Note: their SG200-28xx series all list 52 Gbps, so the 28-port gigabit models are pretty close in performance whether they do L2 or L3.)

Someone will probably bring up power budget as a spec to look for as well... for me, that's not a concern, as we're not installing any cameras that pull over 5-6W... I think the P3384-VEs are rated up to 12W with the heater, but we don't enable that).

As with everything else, of course, consider the specs that suit your own needs.