Hello Ismael,
some more information's.
Nsight is independent from the other mentioned systems.
In short words Nsight is for analytics and visibility in wireless networks with WING.
Extreme Management Center (XMC or EMC) formally known as NetSight (not Nsight!!!) is the basis for all other systems (without NSight because NSight is idependent). XMC delivers the database to store and bring together the data of the other system. The configuration for all system is done on XMC. Furthermore XMC is an open and in the most function vendor independent network management and monitoring system for wired and wireless devices (managed via SNMP and SSH)
Extreme Control formally NAC is an appliance for network access control via MAC, 802.1x and other authentication protocols. Basis is Radius server but there are much more functions then in an standard radius server. The configuration is done via XMC and all data a reported to XMC, too.
Extreme Analytics formally Purview is an appliance to aggregate Flow data (like Tim mentioned) and help to monitor and analyze network traffic to have a view whats going on in your network. The management is done via XMC, too.
=>XMC works standalone, all other components are optional and can't work without XMC.
Best regards
Stephan
Regards
Stephan