with snmpget api, the agent returns the value associated 
with the OID (or OIDs) specified in the original request.
The snmpgetnext api is  similar, but the agent returns the 
value associated with the next (valid) OID
eg:
snmpgetnext('192.168.40.134',
                   'public',
                   'SNMPv2-MIB::sysUpTime.0');
will give the output:
STRING: user@hostname