How can I estimate ethernet performance?

Question

I need to think about performance limitations of 100 mbps ethernet (including scenarios with up to ~100 endpoints on the same subnet) and I'm wondering how best to go about estimating the capacity of the network. Are there any rules of thumb for this?

The reason I ask is that I am working on some back-of-the-envelope level calculations about performance limitations, so it doesn't need to be incredibly accurate. I just haven't been through this exercise before and was hoping to gain some insight from those who have. Mark Brackett's answer (as of 1/26) is along the lines of what I am looking for.

Answer 1

If you're using switches (and, honestly, who isn't these days) - then I've found 80% of capacity a reasonable estimate. Usually, it's really about 90% because of TCP overhead - but 80% accounts for occasional retransmits.

If it's a single collision domain (hubs), then you'd probably be around 30% with moderate activity on those 100 nodes. But, it'd be pretty variable based on the traffic generated. And anyone putting 100 nodes in a single CD these days would no doubt be shot - so I don't think you'll actually run into those IRL.

Edit: Note that these numbers are for a relatively healthy network - one that is generally defined as working. Extremely excessive broadcasts or other anomalous traffic patterns have been known to bring a network to it's knees.

Answer 2

Use WANem

WANem is a Wide Area Network Emulator, meant to provide a real experience of a Wide Area Network/Internet, during application development / testing over a LAN environment.

You can simulate any network scenario using it and then test your application's behaviour using it. It is open-source and is available with sourceforge.

Link : WANem - The Wide Area Network emulator