Sending “random” traffic through Mininet network

Question

I want to test a data center routing algorithm using Mininet. The traffic needs to conform to certain parameters:

1. It should consist of "files" of various sizes (note that these don't actually have to be files; traffic generated in, eg, iperf is OK, as long as the size is controllable);
2. The file sizes should be drawn from a particular distribution;
3. The source/destination host pairs between which data is sent should be selected randomly for a given file;
4. The interval between when a file is sent and its successor is sent should be random; and
5. If a huge file gets sent between two hosts that takes a long time to transfer, it should still be possible to send data between other hosts in the network.

Points 1-4 are taken care of. I've been struggling with #5 for days and I can't get it working properly. My initial thought was to spawn subprocesses/threads to send iperf commands to the hosts:

while count < 10:
    if (count % 2) == 0:
        host_pair = net.get("h1", "h2")
    else:
        host_pair = net.get("h3", "h4")

    p = multiprocessing.Process(target=test_custom_iperf, args=(net, host_pair, nbytes))
    p.daemon = True
    p.start()

    time.sleep(random.uniform(0, 1))

The command test_custom_iperf is modeled after the Python Mininet API's version of iperf to include the -n transfer size parameter:

client, server = host_pair
print client, server

output( '*** Iperf: testing TCP bandwidth between',
        client, 'and', server, '\n' )

server.sendCmd( 'iperf -s' )

if not waitListening( client, server.IP(), 5001 ):
    raise Exception( 'Could not connect to iperf on port 5001' )

cliout = client.cmd( 'iperf -c ' + server.IP() + ' -n %d' % nbytes )
print cliout

server.sendInt()
servout = server.waitOutput()

debug( 'Server output: %s\n' % servout)
result = [ net._parseIperf( servout ), net._parseIperf( cliout ) ]
output( '*** Results: %s\n' % result )

Making this non-blocking has been extremely difficult. I need to be able to send the server.sendInt() command, for some reason, and to do this I need to wait for the client's command to finish.

I'd appreciate any advice on what I can try to make this work!

Answer 1

I took a hint from here and used Mininet's host.popen() module to send the data around. Hopefully this helps someone else:

def send_one_file(file_dir, host_pair, files): 

    src, dst = host_pair  # a tuple of Mininet node objects

    # choose a random file from files
    rand_fname = random.sample(files, 1)[0]
    rand_path = os.path.join(file_dir, rand_fname)

    port = random.randint(1024, 65535)

    # Start listening at the destination host
    dst_cmd = 'nc -l %d > /home/mininet/sent/%s.out' % (port, rand_fname)
    print os.path.getsize(rand_path)
    dst.popen( dst_cmd, shell=True )

    # Send file from the source host
    src_cmd = 'nc %s %s < %s' % (dst.IP(), port, rand_path)
    src.popen( src_cmd, shell=True )

Then the parent function calls send_one_file() at random intervals:

def test_netcat_subprocess_async(net, duration):

    file_dir = "/home/mininet/sf_mininet_vm/data/MVI_0406_split"
    files = os.listdir(file_dir)

    start_time = time.time()
    end_time = start_time + duration

    # Transfer for the desired duration
    while time.time() < end_time:
        # Choose a pair of hosts
        host_pair = random.sample(net.hosts, 2)

        test_send_one_file_netcat(file_dir, host_pair, files)

        interval = random.uniform(0.01, 0.1)
        print "Initialized transfer; waiting %f seconds..." % interval
        time.sleep(interval)

This works without any of the problems I experienced with multiprocessing or threading (breaking the network after the session is over, blocking when it shouldn't, etc.).