I don't know your equipment specifically, but I think you are referring to a modern, switched Ethernet network. If so, you should be using layer 2 switches (also called multiport bridges) inside that Ethernet domain, as opposed to layer 1 "hubs" or coaxial daisy chained topology. And you should have hosts each connected to their own dedicated switch port, one host per port, in the layer 2 switches.

Given this setup, you should never see "collisions." Collisions only occur if multiple hosts share the physical layer, as they would with the old Ethernet "hubs" or even older coaxial Ethernet daisy chains.

In the old days, "collisions" were used in the shared medium to throttle back the data rate. If two or more hosts began transmitting at the same time, they would detect the collision in that broadcast domain, they would back off, and then try again after a random wait interval.

With layer 2 bridges, instead, each host has a dedicated link to the bridge. No chance for collisions per se. Your host sends the entire message into a switch buffer. If the switch is transmitting another Ethernet frame upstream when your host finishes sending data, your data will be temporarily held in a queue in the switch. Your host won't even notice this. As soon as the switch has finished sending previous Ethernet frames in the queue, it will transmit your frame upstream.

So, you should never see collisions or dropped frames, unless (a) the bandwidth of the layer 2 switch has been exceeded (causing overflow of queues), unless (b) you have mistakenly configured the host to use "full duplex" while the switch is set to "half duplex" or "auto," or the other way around (duplex mismatch is a common problem), or unless (c) there is some kind of cable or switch hardware fault.

Best bet is to always use auto settings for speed and duplex.

Note that these days, the normal way switches operate is to always buffer the entire Ethernet frame, before relaying it. No point playing games with beginning to transmit before the source host has finished, as very often, the speed used in different switch ports will vary.

There could be several reasons why you are not observing any dropped packets, Tx/Rx errors, or collisions in your Mininet network:

While it is possible for a network to operate without any dropped packets, Tx/Rx errors, or collisions, it is unlikely to occur in a real-world scenario with high network traffic volume. However, it is always a good practice to monitor network statistics to ensure that the network is performing optimally.

Dear Tabarak Yassen,

I hope this will answer your question.

If the traffic intensity is low, the contention mechanism will face no challenge and will be able to resolve the collisions, and hence no drop or error will happen. In this case, the accurate measure is the delay encountered by the transmitted packets and the packet inter-reception time (PIR).