# File lib/snmp/pdu.rb, line 261
    def sys_up_time
        varbind = @varbind_list[0]
        if varbind && (varbind.name == SYS_UP_TIME_OID)
            return varbind.value
        else
            raise InvalidTrapVarbind, "Expected sysUpTime.0, found " + varbind.to_s
        end
    end