Mix network are routing protocols
that create hard-to-trace communications
by using a chain of Proxy Servers
known as mixes which take in messages
from multiple senders, shuffle them, and send them back out in random
order to the next destination (possibly another mix node).
Mix network operations breaks the link between the source of the request and the destination, making it harder for eavesdroppers to trace end-to-end communications.
Mix network was first described by David Chaum in 1981.
Mix network Applications based on this concept include anonymous remailers (such as Mixmaster) and The Onion Router (Tor).
There might be more information for this subject on one of the following: