What is the difference between these NGINX's modules?

I'm reading the documentation, I found these NGINX's modules:

• HttpLimitReqModule
• HttpLimitZoneModu开发者_StackOverflow社区le

What are the differences? They are pretty similar to me, no?

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HttpLimitReqModule is supposed to limit the request rate (number of requests per given time), while HttpLimitZoneModule is used to limit the number of simultaneous connections.