Throughput, fabric speed and marketing numbers

Reading through various vendors numbers for their fabric speed it gets a little confusing. For instance: http://ift.tt/2hIS21e

This is a pretty simple system, it has 2 line cards with 480 Gbps of Full-Duplex throughput per card. What becomes a little confusing is that the total system throughput is 1.92 Tbps, which I assume is all duplexes in/egressing the fabric.

When sizing up these systems is it always generally a case of just doing the math which is simply working up from the card and making sure all the numbers check out for the equipment facing ports? (e.g. 480 Gbps, 480 in/out over 2 cards = 1920 Gbps)

Realistically the unit can only handle 480 Gbps of Full-duplex traffic from the port perspective as the inputs have to match the outputs.

A simple example of a switch with 2 line cards of which the interfaces are 1 Gbps each. My system will be able to achieve 1 Gbps Full-Duplex traffic. But each of those cards will need 1 Gbps into the backplane (2 Gbps) and if we wanted to say that each of those 1 Gbps links into the backplane needs in/egress traffic that's 4 Gbps. Which I assume 4 Gbps is the marketing number used on the quoted system throughput?

• I assume this is more of a problem on systems in which the fabric isn't at line rate to the interfaces like older equipment cat4500/6500?
• Is this just a typical annoyance because there is no real definitive way to say "this does linerate" without just adding up all the speeds and feeds?
• In regards to a sizing exercise (like if you were sizing this for a client) would you have to work backwards to end up with my calculation of 480 Gbps in order to realise if the device suits your needs? Anything above this number doesn't seem to represent a useful value for traffic transiting between networks.

Edit: I guess I was really after figuring out what real world traffic could be pushed through the device.

(slots / 2) * linecard speed = Maximum transit traffic through device?