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CPqD / ofsoftswitch13

OpenFlow 1.3 switch.
http://cpqd.github.com/ofsoftswitch13
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Influence of package dropping to tcp links when using meter table #301

Closed Rovanstian closed 4 years ago

Rovanstian commented 4 years ago

Hello~

I am trying to use meter table to limit the bandwidth of tcp links. As far as I've known, tcp cannot tolerant a high package dropping rate. But when I test it with a ftp program, it works without any performance degradation or deadlock.

Does meter table really drop the packages? Dose meter table have a buffer?

ederlf commented 4 years ago

How are you using it?

It should drop if the rate goes above the one you specified.

Rovanstian commented 4 years ago

Firstly, thanks for your time, @ederlf ~

I am using it with action type "drop" and it does function well.

I tested a simple ftp service between two hosts on mininet with a meter band limiting the bandwidth to 1Mbps. It takes me about 80s to receive a 10MB file.

Actually, what's confusing me is why dropping packages frequently won't influence the performance of a TCP link. Can TCP natively tolerant a high package loss rate like 50% or even higher?

I thought when the bandwidth is set to a low level, the actual throughput of the tcp link would be way lower than this bandwidth, isn't that right?

ederlf commented 4 years ago

How are you limiting it? If you check the flow, can you see if it is matching? What do the meter statistics say?