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New Member

Throughput and Backplane Capacity

hi,

a Cisco 3560 switch (WS-C3560-24PS-S) has following scalability feautes

Throughput : 6.6 Mpps

Backplane Capacity : 8.8 Gbps

Can anyone explain this ?

thank in advance.

regards

Rajib

7 REPLIES
Silver

Re: Throughput and Backplane Capacity

hi!

The backplane capacity would indicate how much bandwidth is available for data between the modules. So a maximum of 8.8 Gbps data can flow between the modules / or to the CPU and back. So this is one of the things affecting the performance of the device.

Throughput on the other hand is in terms of packets per second. It is the maximum rate at which the device can process the packets.so a throughput of 6.6Mpps means that the device can process only 6.6 million packets per second.

So in situations where all the traffic is made up of very small packets - say 64 byte packets. It is possible that the through put capacity is reached through 6.6 Mpps and hence traffic is dropped. The backplane capacity might not be exhausted yet as 6.6Mpps*64 byte doesnot equate 8.8Gbps.

as the avg. packet size goes on increasing, the same number of packets account for more bandwidth and can exhaust the backplane capacity and drops can occour.

Therefore the performance of a device will be determined by combination of number of packets per sec and the size of the packet.

Regards,

Niranjan

(pls rate helpful posts)

New Member

Re: Throughput and Backplane Capacity

Hi Niranjan

This is very helpful to me. So I think most of the time it is 64byte data, I think I need to concentrate on switch performance in mpps. So if I am considering 32Gbps backplane then it takes 500mpps to exhaust that backplane right? (32g/64byte)

Now how do I know how many mpps are processed on my network. I do not have a Cisco switch at this stage but wanted to get after doing this evaluation. I have a Linksys SR2016 and I cannot monitor anything on that and the performance is slow. I dont know its backplane or switch performance.

Actually my problem is the latency issues on my LAN and we have files sized few hundred Megs and somefiles are Gigs. So can you please suggest which switch I can go for?

Initially I thought to go for 2960G-24 which processes 35.7mpps with 32Gig backplane but after the calculation I see only 2Gbps backplane is utilized with 35.7mpps and I thought to concentrate on mpps rather than backplane.

Am I thiking right?

And is there any advantage in using Cisco switches rather than Linksys or Netgear Gig switches considering only the performance and backplane speeds.

Thanks

Venkat

Super Bronze

Re: Throughput and Backplane Capacity

"So if I am considering 32Gbps backplane then it takes 500mpps to exhaust that backplane right? (32g/64byte)"

No, a 32 Gbps backplane, if doing 64 byte Ethernet sized frames, will fill at 31.25 Mpps. (Cisco appears to spec backplane bandwidths for full duplex, and remember to convert the frame into its bits size, 512.)

"Initially I thought to go for 2960G-24 which processes 35.7mpps with 32Gig backplane but after the calculation I see only 2Gbps backplane is utilized with 35.7mpps and I thought to concentrate on mpps rather than backplane. "

Assuming the 35.7 Mpps is quoted for 64 byte Ethernet frames, it would support 18.3 gig, internally, or 24 gig on the ports. But because the backplane only supports 16 Gbps, duplex (32), the bottleneck on the 2960G-24 would be the backplane.

An example of an Ethernet "wire speed" or "line rate" switch is the 4948, 48 gig Ethernet ports, rated at 72 Mpps and 96 Gbps fabric.

PS:

Gig Ethernet Wire Speed

Packet Size (Bytes) 64 128 256 512 1024 1518

Theoretical Maximum Kpps 1488 845 453 235 120 81

Silver

Re: Throughput and Backplane Capacity

hi Rajib,

Guess Joseph's that would answer all your questions. He has pinpointed the caveats exactly. Cisco always uses the numbers as full-duplex for marketing.

Cheers!

New Member

Re: Throughput and Backplane Capacity

Thanks for the explanation. Can you please respond to these below?

Now how do I know how many mpps are processed on my network. I do not have a Cisco switch at this stage but wanted to get after doing this evaluation.

And is there any advantage in using Cisco switches rather than Linksys or Netgear Gig switches considering only the performance and backplane speeds.

Thanks

Sarat

Super Bronze

Re: Throughput and Backplane Capacity

"Now how do I know how many mpps are processed on my network."

If the device you're using now has any type of "smarts", if it supports mini-RMON, you might be able to acquire some stats that way. Otherwise, you might check the stats on the devices using the network.

"And is there any advantage in using Cisco switches rather than Linksys or Netgear Gig switches considering only the performance and backplane speeds. "

Usually features is one major difference. Low end devices often are unmanageable. Also, performance specifications are often not published for many low end switches, but some public Internet sites publish benchmark results.

New Member

Re: Throughput and Backplane Capacity

Thanks for that

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