How to compare internal performance of different switches?

[fred2k3]

As per this thread I am trying to find a couple of entry level backbone switches to aggregate about 5 or 6 Catalyst 2960X-48TS-L switches.  I am on a budget, and also trying to keep this simple, no stacking, no SFP (since the up-link ports on the 2960Xs are the same speed as the 1GbE Ethernet ports anyway).

The advise I've been given is that make sure the backbone switches I buy have a better backplane speed than then edge / client switches so they can cope with the switching load, which makes sense, but I'm finding it very difficult to compare the various Cisco switches on this (can't see backplane speed anywhere in the datasheets).  I have found "Switching Bandwidth" and "Switching Capacity" on the datasheets for the 2960X and the 3650 - is this what I should be looking at?

If so, I'm still confused because the specifications are laid out very differently between the 2 series.  It says the switching bandwidth for the 2960X is 216 Gbps, and for the 3650 it says the switching capacity is 176 Gbps on 48-port models (non-multigigabit models), which is lower.  So are bandwidth and capacity different things?  Also, what is "forwarding performance"?

[Leo Laohoo]

When it comes to Cisco-branded switches, it is always "you get what you paid for". 2960X will always have lower performance and capacity compare to the others.

[Joseph W. Doherty]

Most current and recent Cisco Enterprise class switches have a fabric and forwarding capacity (the capacity to move some number of frames/packets per second) that can support all their ports at wire rate. (BTW, for Cisco switches, a full capacity fabric would be all the bandwidth of all ports - duplex, e.g. 48 gig ports would need a 96 gig fabric. Forwarding capacity is generally quoted for minimum size Ethernet (64 bytes) which requires [about] 1.488 Mpps per gig, e.g. 48 gig ports would need about 72 Mpps.)

However, as Leo notes, you get what you pay for. Buffer RAM and other features vary widely between switches that are all "wire-rate" capable.

Since price varies too, ideally you need to determine what your network's expected capacity requirements are to find switches that can meet those needs without overspending for capacity you'll never use.