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Lets say I have 2 switches and 2-2 devices connected to each switch.

Each device sends data to other devices in a cylic manner for example Device1 sends data at 100msec, device 2 at 200ms.

So i want to calculate the required bandwidth for each device and switch if the data size sent is approx 2000bytes.

So now in my simulation I have given bandwidth values of 10Mbps, but after certain period lets say after 1 minute of simulation.. switch buffer starts filling up and messages are getting droped.

So in my conclusion i think bandwith is the problem because messages are not sent or accepted with required bitrates.

So I want to calculate bandwith of each device and switch.enter image description here

Sanchit Jain
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  • https://www.broadcom.com/products/ethernet-connectivity/automotive/phy Just contact Broadcom. This is what you are looking for. And it is being done already. – BitTickler Aug 01 '22 at 12:47
  • Hi, thanks for the reply. actually i want to calculate it for my project work. So i am looking for some theory which can help me to calculate. – Sanchit Jain Aug 01 '22 at 13:33

1 Answers1

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2000 bytes every 100 ms is 2000 * 8 / .1 = 160 kbit/s. If you've got four such sources, you're using roughly 6.5% of a 10 Mbit/s link.

Even if each device unicasts that amount to each of the three others, that total bandwidth is only tripled. Only half of those unicasts (~1 Mbit/s) cross the switch interconnect which is your bottleneck. Also, modern Ethernet is full duplex, so a 10 Mbit/s interface can transmit 10 Mbit/s and receive 10 Mbit/s at the same time.

Of course, a better approach would be to use multicast. That way, each data chunk is only propagated through the network in a single instance.

If your network goes down after a few seconds, then the parameters above or the diagram aren't correct, or the simulation is flawed.

Zac67
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  • Thanks for the detailed Explanation. Yes I had bug in my simulink model so my buffer was full because of wrong parameters and messages were getting dropped in my Simulation. – Sanchit Jain Aug 08 '22 at 07:51
  • Hi Can you please also suggest some maths behind the selection of bandwidth of wires. for example how to select which bandwidth wire I should use and how much data rate is required for smooth network flow – Sanchit Jain Aug 09 '22 at 13:15
  • The required bandwidth is *(amount of data sent or received)/(amount of time)*. Aggregated bandwidths need to be calculated when you pass multiple sources/destinations over a single link - simply add the single bandwidths. It only becomes interesting when you can't increase the link speed on an aggregated ports any more. – Zac67 Aug 09 '22 at 13:33
  • Thanks for the answer. And could you please help me with one more question. How can I calculate the switch buffer size. – Sanchit Jain Aug 10 '22 at 10:56
  • @SanchitJain Since your used bandwidth is way below the network/link bandwidth, there's no need for switch buffering (apart from the implementation-specific amount). If there were short(!) bursts temporarily exceeding the network bandwidth, then you would ideally size the buffer to the modeled amount of burst data. – Zac67 Aug 10 '22 at 12:26
  • Hi, @Zac67 Can you also tell me if we want to calculate the total bandwidth utilization of ethernet switch then we need to calculate average bandwidth utilization of all the ports of the switch? – Sanchit Jain Aug 12 '22 at 07:39
  • @SanchitJain See comment #3, it's all there. Assuming a non-blocking switch (a given for single-chassis/non-modular switches), throughput is only limited by port speeds. – Zac67 Aug 12 '22 at 08:16
  • Thanks, And how is receding throughput calculated? Is the the data received/total time taken. for example switch has 10 ports. it received the data from different ports but sends the data through one port so individual port has its own throughput? Considering same bandwidth for all ports. – Sanchit Jain Aug 12 '22 at 09:15