I have currently a router in my office network which has maximum input rate of around 12 Mbps, and output rate of 27 Mbps on its uplink port to the ISP.

Now we want to replace this old router with new Cisco ISR. So we have to specify what throughput is needed for purchase. How can I calculate that?

  • Following on the excellent response by @Zac67, some more information would help. What sort of uplink/connection is provided by your ISP? Is it some DSL/etc type of connection? – user4565 Feb 6 '20 at 18:31
  • It is optical connection from ISP network. – Shyamkkhadka Feb 7 '20 at 5:18
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer. – Ron Maupin Dec 17 '20 at 15:13

You need to determine the average and peak workloads and estimate their change over the lifetime of the router.

For instance, you might have 50 total users with on average 15 users surfing online with a demand for 1 Mbit/s each, 5 Mbit/s if video is involved, or 20 Mbit/s when there's heavy cloud usage. Obviously, your Internet uplink has to be scaled equivalently.

In addition to router throughput you need to make sure that it can also support the required sessions for all users, assuming you're using NAT. I calculate roughly with 25 sessions per (light) user.

Requirements for throughput and concurrent sessions can vary extremely. Between light web access and a power user, demand can easily differ more than one order of magnitude (10x).

Running a public server in your network needs to be estimated separately, depending on its use.

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