def METHOD_NAME(test, params, env):
    """
    Test for network bandwidth in libvirt.
    1. Preparation:
        * Init variables from params.
        * Keep a backup for vmxml and networkxml.
        * Build a file with dd command.
    2. Edit vmxml and networkxml to control the bandwidth.
    3. Verify the bandwidth with scp.
    4. Clean up.
    """
    # get the params from params
    vm_name = params.get("main_vm", "avocado-vt-vm1")
    vm = env.get_vm(vm_name)
    inbound_average = params.get("LNB_inbound_average", "512")
    inbound_peak = params.get("LNB_inbound_peak", "512")
    inbound_burst = params.get("LNB_inbound_burst", "32")
    outbound_average = params.get("LNB_outbound_average", "512")
    outbound_peak = params.get("LNB_outbound_peak", "512")
    outbound_burst = params.get("LNB_outbound_burst", "32")
    config_type = params.get("LNB_config_type", "network")
    bandwidth_tolerance = float(params.get("LNB_bandwidth_tolerance", "20")) / 100
    file_size = params.get("LNB_verify_file_size", "10")
    nic1_params = params.object_params('nic1')
    # We assume this test is for a guest using default network.
    nettype = 'network'
    netdst = 'default'
    vm_xml = VMXML.new_from_inactive_dumpxml(vm_name)
    vm_xml_backup = vm_xml.copy()
    # This test assume that VM is using default network.
    # Check the interfaces of VM to make sure default network
    # is used by VM.
    interfaces = vm_xml.get_devices(device_type="interface")
    # interface which is using default network.
    default_interface = None
    for interface in interfaces:
        if interface.source == {nettype: netdst}:
            default_interface = interface
            break
    if not default_interface:
        test.cancel("VM is not using default network,"
                    "skip this test.")
    bandwidth_inbound = {'average': inbound_average,
                         'peak': inbound_peak,
                         'burst': inbound_burst}
    bandwidth_outbound = {'average': outbound_average,
                          'peak': outbound_peak,
                          'burst': outbound_burst}
    network_xml = NetworkXML.new_from_net_dumpxml("default")
    network_xml_backup = network_xml.copy()
    tmp_dir = data_dir.get_tmp_dir()
    file_path = os.path.join(tmp_dir, "scp_file")
    # Init a QemuImg instance.
    cmd = "dd if=/dev/zero of=%s bs=1M count=%s" % (file_path, file_size)
    process.METHOD_NAME(cmd, shell=True)
    try:
        if config_type == "network":
            network_xml.bandwidth_inbound = bandwidth_inbound
            network_xml.bandwidth_outbound = bandwidth_outbound
            network_xml.sync()
        elif config_type == "interface":
            devices = vm_xml.devices
            for index in range(len(devices)):
                if not (devices[index].device_tag ==
                        default_interface.device_tag):
                    continue
                if devices[index].mac_address == default_interface.mac_address:
                    bound = {'inbound': bandwidth_inbound,
                             'outbound': bandwidth_outbound}
                    default_interface.bandwidth = default_interface.new_bandwidth(**bound)
                    devices[index] = default_interface
                    break
            vm_xml.devices = devices
            vm_xml.sync()
        elif config_type == "portgroup":
            if nettype != 'network':
                test.cancel("Portgroup is only applicable with "
                            "virtual network")
            # Add a portgroup into default network
            portgroup_name = "test_portgroup"
            portgroup = PortgroupXML()
            portgroup.name = portgroup_name
            portgroup.bandwidth_inbound = bandwidth_inbound
            portgroup.bandwidth_outbound = bandwidth_outbound
            network_xml.portgroups = [portgroup]
            network_xml.sync()
            # Using the portgroup in VM.
            devices = vm_xml.devices
            for index in range(len(devices)):
                if not (devices[index].device_tag ==
                        default_interface.device_tag):
                    continue
                if devices[index].mac_address == default_interface.mac_address:
                    default_interface.source = {nettype: netdst,
                                                'portgroup': portgroup_name}
                    devices[index] = default_interface
                    break
            vm_xml.devices = devices
            vm_xml.sync()
        else:
            test.cancel("Unsupported parameter config_type=%s." %
                        config_type)
        # SCP to check the network bandwidth.
        if vm.is_alive():
            virsh.destroy(vm_name)
        vm.start()
        vm.wait_for_login()
        time_before = time.time()
        vm.copy_files_to(host_path=file_path, guest_path="/root")
        time_after = time.time()
        speed_expected = int(inbound_average)
        speed_actual = (10 * 1024 // (time_after - time_before))
        if not (abs(speed_actual - speed_expected) <=
                speed_expected * bandwidth_tolerance):
            test.fail("Speed from host to guest is %s.\n"
                      "But the average of bandwidth.inbound is %s.\n"
                      % (speed_actual, speed_expected))
        time_before = time.time()
        vm.copy_files_from(host_path=file_path, guest_path="/root/scp_file")
        time_after = time.time()
        speed_expected = int(outbound_average)
        speed_actual = (10 * 1024 // (time_after - time_before))
        if not (abs(speed_actual - speed_expected) <=
                speed_expected * bandwidth_tolerance):
            test.fail("Speed from guest to host is %s.\n"
                      "But the average of bandwidth.outbound is %s\n"
                      % (speed_actual, speed_expected))
    finally:
        if os.path.exists(file_path):
            os.remove(file_path)
        network_xml_backup.sync()
        vm_xml_backup.sync()