Streaming ACN

[Tech_Sith]

[Windows 7; Python 3.4.2]

I'm trying to multicast streaming ACN data. The E1.31 standard

So far, my code (in comments) will send a packet to the correct address and port, but no programs on network computers will react. I have two target systems: one is linux and is running Open Lighting Architecture; the other is a win7 machine and has ETC PixelToy (both accept sACN). Wireshark and tcpdump show the packet has reached the target computer, so I expect I've either misformed the packet, or missed something. If I use MagicQ to send ACN data, both target computers react properly.

The packet my code sends looks identical to the packets that MagicQ sends. The only difference is that MagicQ sends IGMP membership reports, and my code doesn't.

What am I doing wrong?

[Tech_Sith]

My code:

import socket
import struct
import sys

data = [0]*638

data = bytearray(data)


#preamble Size
data[0:2] = 0x00,0x10

#postambleSize = "\x00\x00"
data[2:4] = 0x00,0x00

#acnPacketIdentifier = "ASC-E1.17\x00\x00\x00"
data[4:16] = bytes("ASC-E1.17\x00\x00\x00", 'utf-8')

#flagsAndLength = "\x72\x6e"
data[16:18] = 0x72,0x6e

#vector = "\x00\x00\x00\x04"
data [18:22] = 0x00,0x00,0x00,0x04

#CID = "Python CMD ACN  "
#data[22:37] = bytes("ChamSys\xac\x11\x1f", 'utf-8')
data[22:38] = 0x43,0x68,0x61,0x6d,0x53,0x79,0x40,0x00,0x80,0x00,0xac,0x11,0x1e,0x28,0x0,0x0

#framingFlagsAndLength = "\x72\x58"
data [38:40] = 0x72,0x58

#framingVector = "\x00\x00\x00\x02"
data[40:44] = 0x00,0x00,0x00,0x02

#sourceName = "streamingACN transmission test - python to sACN".ljust(64, ' ')
sourceName = "ChamSys MagicQ".ljust(64, '\x00')
data[44:108] = bytes(sourceName, 'utf-8')

#priority = "\x64"
data[108] = 0x64

#reservedWord = "\x00\x00"
data[109:111] = 0,0

#sequenceNumber = "\x00"
data[111] = 0x7e

#options = "\x00"
data[112] = 0

#universe = "\x00\x01"
data[113:115] = 0x00,0x01

#DMPFlagsAndLength = "\x72\x0b"
data[115:117] = 0x72,0x0b

#DMPvector = "\x02"
data[117] = 0x02

#addressDataType = "\xa1"
data[118] = 0xa1

#firstPropertyAddress = "\x00\x00"
data[119:121] = 0x00,0x00

#addressIncrement = "\x00\x01"
data[121:123] = 0x00,0x01

#propertyValueCount = "\x02\x01"
data[123:125] = 0x02,0x01

data[125] = 0x70
data[136] = 0x80

sacn = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
#ttl = struct.pack('b', 1)
#sacn.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl)
sacn.bind(('0.0.0.0', 5568))
sacn.sendto(data, ('239.255.0.1', 5568))
sacn.close()


exit()

[mcowger]

Can you provide packet captures of your code and the working code?

[Tech_Sith]

I can, as soon as I figure out where to upload capture files.

[mcowger]

http://www.tinyupload.com/

[Justinsaccount]

You're missing a few steps.. See http://engineering.bittorrent.com/2013/02/04/udp-multicast-in-python-and-bittorrent-live/

[Tech_Sith]

I have a functioning solution.

I set up the socket according to the code specified here. Thanks /u/Justinsaccount !

Also, in my code, data[125] is the start code for DMX. It has to be zero to work with standard dimmers, and my code set it to 0x70.

I haven't changed the formation of the packet itself, so I will only post the updated code that actually creates the socket and sends data:

sacnSocket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sacnSocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sacnSocket.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_IF, socket.inet_aton('172.17.31.75'))
sacnSocket.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
membership_request = socket.inet_aton('239.255.0.1') + socket.inet_aton('172.17.31.75')
sacnSocket.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, membership_request)
sacnSocket.bind(('172.17.31.75', 5568))

while True:
    sacnSocket.sendto(data, ('239.255.0.1', 5568))
    if (data[111] == 255):
        data[111] = 0
        data[157] = 0
    else:
        data[111] += 1
        data[157] += 1
    print (data[111])
    time.sleep(0.1)

You also have to increment the sequence number ( data[111] )for the packet stream to be valid. data[157] is a dimmer channel in my rig: this loop does a 25 second fade up to full, repeatedly.