The course only covers one network layer protocol - the Internet Protocol (IP). This is the most widely used network layer protocol for wide area networks. A number of other protocols have also been used. These include:
A network, such as Ethernet, may support a number of different network player protocols, each is identified by a protocol type field in the data link layer header (i.e. the link layer service access point). A single computer may also support more than one protocol, by implementing more than one parallel protocol stack. Each sender inserts the correct protocol type values into the link layer frames that it sends. An Ethernet network interface card will ensure that only received packets of the correct type are forwarded to each protocol entity (this is refered to as "protocol demultiplexing").