Difference between Gbps & Mpps

[Sam Pragash]

I am planning to replace a Cisco 3750E-24TD with Cisco 2960G-24TC.I wanted to make sure that 2960 will handle the load. When I went through the datasheets, I got the below queries.

What is the difference between Forwarding Bandwidth & Forwarding rate? Why they are mentioned in Gbps and sometimes in Mpps?

For Eg:

Cisco 3750E-24TD - 65.5 Mpps and

Cisco 2960G-24TC - 32 Gbps.

[Christos Papageorgopoulos]

Hi Sam,

Gbps - Giga bit per second (how many bits can be processed by the device)

Mpps - Maximum packets per second (how many packets can be processed by the device)

For Mpps is depending the size of the packet transmited.

Eg: you send the smallest frame in ethernet which are 64 bytes in size+ interframe gap, so to fill a GE port in one direction you need 10^9 / [(64+20,2)*8] = 1484560 packets per second.

so a number around of 3  Mpps(1,48*2= 2,96 ) is equivalent to 1 GE ports filled with smallest frames bidirectional.

I hope this explanation will help

[alijaan99901]

Forwarding bandwidth and forwarding rate measure different aspects of a switch’s capacity: forwarding bandwidth (Gbps) is the total data throughput the switch can handle per second, while forwarding rate (Mpps) measures how many packets per second it can process, usually based on the smallest packet size. A switch might have high bandwidth but a lower packet rate, meaning it could struggle with many small packets, or vice versa. In your example, the 3750E’s 65.5 Mpps indicates it can handle a high packet load efficiently, whereas the 2960G’s 32 Gbps shows total throughput but doesn’t guarantee the same performance with small, packet-heavy traffic, so the 2960G may not handle the same load as effectively.

[Alessio Andreoli]

Hi all,
I am sorry but I respectfully disagree with the Gbps and Mpps definitions provided above. The M of Mpps stands for Mega(million) packet per second and it is the way to size the processing capabilities of a determined platform. Generally the packet processed are set to the minimum size to provide the max overload to the CPU to analyse. Gbps instead literally means one billion(giga) of bit per second and it is the max capability of a determined link/interface. Generally speaking this capability will be never used due to the transceiver buffers and design. It is not unusual to test a gigabit link(or interface) with a multisession ds/us.

Hope this helps
Alessio

Sent from Cisco Technical Support iPad App

[Christos Papageorgopoulos]

Hi Alessio,

You are right MPPS = million packets per second

Thanks!

[Joseph W. Doherty]

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Posting

They measure two different properties.  The Gbps rating is usually the fabric/bus bandwidth, shared by all port.  Normally, it quoted for duplex bandwidth.  For example, 24 Gbps (duplex) ports would require 48 Gbps of fabric bandwidth.  As the 2960G is listed as having only 32 Gbps, the switch can not support concurrent full capacity across 24 gig ports.

PPS measures, packets per second.  Requirement varys (greatly) on packet size. 1 Gbps Ethernet requires 1.488 Mpps.  As 24 gig (duplex) ports are only switched once, Ethernet wire-rate would require 24 * 1.488 Mpps = (about) 36 Mpps.  If the switch provides a lower Mpps rating, it might not be able to support concurrent full capacity across all its ports.  Of course, if bandwidth is restricted by fabric capacity, you might check whether it could support it's full capacity.  Also, again, PPS varies (much) on packet size.  A switch that might not guarantee wire-rate for worst case might deliver wire-rate for "normal" traffic.

PS:

When looking at switches, don't forget special uplink ports, like dual 10G ports that can be found on 3750Es.