Before we get too far, let's define protocols.  A protocol is the transmission format of data between network devices. 

Protocols vary according to purpose, speed, transmission efficiency, utilization of resources, ease of setup, compatibility, and ability to travel between different Local Area Networks (LANs).

A network utilizing more then one type of protocol defined as a multiprotocol network.  TCP/IP, IPX/SPX, NetBIOS, and AppleTalk are amongst the most commonly used protocols today, with TCP/IP leading as the most popular.