In a datacenter, can I be able to use switches of cisco in some parts and juniper products too ? I mean in the active side ??can I be able to link both to do a single functionality ?
It is certainly possible to mix brands.
There are pros and cons to doing so, on the one hand mixing vendors reduces the risk of a single bug taking down everything and puts you in a stronger negotatings position when it comes to buying stuff. On the other hand mixing brands can expose interoperability bugs, may limit the use of some features and requires you to maintain familiarity with both.