What is the principle difference between the SGMP and the SNMP?
The Simple Gateway Management Protocol (SGMP) was the precursor to the Simple Network Management Protocol (SNMP). It was designed to manage only objects of relevance to Gateways (Routers); for example the number of Gateway ports. This capability was considered sufficient at the time. Today, SNMP can manage objects relevant to any device that has an SNMP agent installed.