Mixing HogNet and ArtNet

rosswillrosswill Registered User, Hog Beta
I think I know the answer but would appreciate an expert one:

I want to know the issues with mixing HogNet and ArtNet on the same network, ie plugging both active outputs of the Fullboar or DP8K into the same Gigaswitch (one which does not support separate vlan's).

Thanks Ross


  • edited January 2009
    There's no easy answer to this question. In many cases it will work just fine, but it's also prone to flaking out when you can least afford it (See Footnote 1)

    Art-Net is a very rude network protocol which depends heavily on broadcast packets. Network broadcasts are the equivilant of shouting in a large room and hoping the right person will hear you; It works fine when only a few people do it, but when everyone starts shouting, noone can hear anything.

    Using only broadcast works fine for Art-Net because it doesn't matter if a few percent of the packets get dropped; The next packet will come along in 30 milliseconds or so and cleanup whatever was missing.

    Hog-Net depends on getting all of it's traffic through in a timely fashion. Delays, dropped packet and retransmisions will quickly start to impair your performance.

    Numerically, 16 universes of Art-Net is about 4 megabits/second. On a 100 or 1000mbit network, that's not a lot of traffic percentage-wise, but something about heavy broadcast traffic brings out the weakest links in the network. For example, some switches can only handle broadcast and multicast traffic at the rate of their slowest port; and will drop everything else. Thus, that one older Art-Net node with a 10mbit connection hobbles the entire system.

    Mixing Art-Net and Hog-Net over wireless links can be a disaster. Wireless networks are iffy for running a real-time protocol like Hog-Net in the best of times, and a heavy broadcast load only makes it worse.

    If you do need to mix the two, I strongly recommend using Unicast for all of your Art-Net traffic. This takes a lot more configuration up front, but segments traffic much more effectively. For example, unicasting to rack of media servers on a gigabit switch shouldn't cause any problems.

    There are all kinds of network configuration changes you can make to improve the performance of mixed networks, but most of these changes require relatively high-end switches and advance configuration skills. That's why the DP8000 and RHFB have separate ports for the two, it's easy to remember "everything on this switch is Art-Net, and that switch is Hog-Net".

    I'll provide a few ideas here for those with advanced networking skills.
    1: In the switch, prioritize any traffic for which the ingress port goes to a Hog-Net device. (L2 or L3 QOS/TOS fields)
    2: Severely limit what traffic can go over wireless links.
    3: Make use of VLANs and Tagged VLANs for trunks.
    4: Disable Spanning Tree Protocol or strictly limit which ports participate in it.
    5: Configure IGMP snooping.
    Finally, if you're doing a large system where you must mix traffic, give yourself plenty of extra time for testing and configuration.

    Footnote 1: Art-Net only sends changes in the data, so under light loads it will handle many universes. But, when you do a big transition (think hitting blackout) everything suddenly comes alive and blasts out full data all at once. That's why the Hog's Art-Net defaults to sending full data all the time; It's technically a violation of the standard, but if there's an overload problem on the network I'd rather you see it constantly rather than just during big transitions.

    Footnote 2: The PRG Series 400 distros use Art-Net for their internal DMX handling. If you plan to put your DPs at Dimmer beach using the 400's networking, talk to me or some of the tech. services folks at PRG who've worked with Hog-Net a lot *before* you go in pre-production. You have to configure it slightly differently to avoid mixing traffic.
  • rosswillrosswill Registered User, Hog Beta
    edited January 2009
    Many thanks for taking the time to answer so thoroughly Eric. I'm sure many of us can learn something from this. Lots of interesting points covered. I have had issues with PRG switches in the past. Perhaps you have explained this mystery.

    Thanks again,

  • srautanesrautane Registered User, Hog Beta
    edited January 2009
    Thanks Eric! That was very interesting to read, very helpful.
  • Joe BleasdaleJoe Bleasdale Registered User
    edited January 2009
    srautane wrote:
    Thanks Eric! That was very interesting to read, very helpful.

    Seconded! This will prove interesting when I am playing with Art-Net out put in the near future.
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