What are peer to peer architectures
<p>I am confusing about the classification of peer to peer architectures.<br>
Are they structured and unstructured or the centralization levels(decentralized centralized and hybrid).<br> 
I searched a lot on the web but i didn't find any good results everyone says his opinion .<br>
All what i need to know is what are those classifications .<br>
Thanks for any suggestions.</p>