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?

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.