Demystifying Mpps

Throughput Parameter regarding switches has always been an ambiguity, finally i manage to crack it, with some help from guislar and ganesh @ Cisco Netpro.

2960-48PST-S -- 13.3 Mpps

The figure Mpps expresses the maximum number of frames per second that can be processed by the device.
It is not dependent on frame size but clearly small frames require higher packet rates.

To give you an idea of what this number says:
smallest frames in ethernet are 64 bytes in size, taking in account the preamble (8 bytes) and the minimum interframe gap (the last two counts roughly for 20.2 bytes) to fill a GE port in one direction you need
1484560 frame per second.

10^9 / [(64+20,2)*8]

where 8 is bits/byte

so a number of 13.3  Mpps is equivalent to ((13.3 M * (64+20.2) * 8 )) / 10^9 = 8.95 / 2 = 4.47 GE ports filled with smallest frames bidirectional.

on the other hand frames of max size 1518 bytes require 81264 fps to fill a GE port in one direction.

So this number expresses the forwarding capability of the device.
A non blocking device with 48 GE ports would require 2 * 1484560 * 48 as Mpps or higher.

A device like C2960 can be classified as centralized CEF forwarding.


Mpps regarding routers,

MPPS stands for million packets per second and Cisco prefers to refer throughput in MPPS.For a layer-3 switch an Mpps value is shared one. For some of the higher-end cisco routers the routing is "distributed" between multipe line-cards, in which case the PPS numbers are based on the number of line cards, bit for non-distributed architectures (Catalyst switches) the numbers are based on the routing engine, so it is the maximum number of Packets Per Second that the box can route.

and as giuslar said 2960 switches are centralized cef based forwarding.

Switching capacity vs Throuhput

Cisco Catalyst 4900 Series Switch Model Comparison for Fiber Aggregation

Feature and Description	Cisco Catalyst 4928 10 Gigabit Ethernet Switch
Switch Capacity	96 Gbps
Throughput	71 mpps

Switching capacity is some times given as  the amount of frames a switch can deal with over a given time frame and throughput on the other hand means  how much actually data can cross the switch in a given time frame.