SNMP network management is based on the familiar client/server model that is widely used in TCP/IP-based network applications. Each host that is to be managed runs a process called an agent. The agent is a server process that maintains the Management Information Base (MIB) database for the host. Hosts that are involved in network management decision-making may run a process called a manager. A manager is a client application that generates requests for MIB information and processes responses. In addition, a manager may send requests to agent servers to modify MIB information.
For more information on SNMP, you may want to read "Simple Network Management Protocol (SNMP)" in AIX Communications Programming Concepts. The following RFCs may also be of use: