The end user switches in the past have only offered Ethernet connections to the users but we are now encouraging users to consider FastEthernet connections for their workstations to the network. The Ethernet network is useful only if communications software and applications are available which can build on the the physical layer and primitive software services incorporated in the Ethernet standard. OSI Model Protocols define standards used for communications. Ethernet is one protocol. In this model protocols are built on top of each other in a vertical stack with protocols running on one device communicating with a peer protocol running on another device.
Protocols provide services to higher level protocols and make requests from lower level protocols.
Thus a protocol has 3 defined interfaces - the services IT provides, the requests it makes and the communications with a peer. The OSI stack defines 7 layers, with each layer providing defined services. These layers, from the highest to the lowest are the Application, Presentation, Session, Transport, Network, Datalink and Physical layers. Communication proceeds as follows between an application on a sending node and an application on a receiving node. A message is generated by an application on the sending node and packaged by the highest layer protocol into a packet.