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Unicast or Multicast


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OK so I've been searching and searching and trying to find a simple answer so maybe you can help.  I get the 6 universes in Multicast and 12 universes in Unicast.  What is the difference between Unicast and Multicast and the pros and cons between them?

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In a nutshell, Multicast sends all commands (packets) to all controllers. Unicast sends commands (packets) to a specific controller. Unless you're into dozens of universes, multicast should work just fine. However, In Unicast, each controller only gets the packets meant for that controller. My first year, I had only a couple of controllers for a pixel tree, but, I still ran in Unicast. IMHO, it only takes a few more minutes per controller to set the IP address and then the Network properties in LOR, so why not use Unicast. Less chance of overloading the E1.31 network.

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One more item. If you are sharing your E1.31 traffic with your normal home LAN, and you use WiFi for all or some of your normal traffic, use unicast. Under those conditions, using multicast can choke your WiFi. And you don't want to have your wife mad because she can't watch Netflix!

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Actually unicast can easily choke a home LAN system as well! 

In unicast each packet has an individual address added to get to the correct device.

The good news is that there are no acknowledgements being sent out in uni or multicast,

The bad news is because of that the data is being continually sent out blindly. 

The best avenue is to spend $10 or $15 to purchase a second NIc card (network interface card), put it in an open slot in your pc, and use that for your display, leaving your primary NIC for your home LAN.

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You would need a LOT of unicast controllers to choke a lan.     Each packet is less than 700 bytes.   At 50ms (20 packets/sec), that's 280Kb/sec per universe.   On a 100MB network, that's well over 350 universes.  (that's theory though,  reality would be less)   That said, I think LOR sends out a lot faster than 50ms.  Maybe 10ms?   Thus, traffic is higher due to that.

 

What kills the WIFI is the multicast.   Multicast gets sent out to every device on the network, and the WIFI spec says the unicast has to go out over the lowest speed of all the devices so everything gets throttled down to a very slow speed.  Also, if a device is "asleep"  (ipad sleeping), it has to wait.   802.11n handles multicast better, but that would require ALL the devices be 802.11n.  One g/b/a device and your still stuck.    Unicast gets to go to the one wifi device as fast as it can and doesn't affect the other devices at all.

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dkulb,

You are correct that it would take a LOT of E1.31 universes to choke a 100Mb LAN, however we're talking about WiFi.  Not counting the newer multi-band WiFi protocols that really are fast, the WiFi is far slower that a 100Mb LAN.  Take a drive around a residential area with a Wifi sniffer and see how many 802.11b access points there are still in service - now you're talking really pretty slow.  Add your wife streaming Netflix and the kid playing an on-line game (both over the WiFi), and your throughput starts getting hammered.  Don't forget about the neighbor who just happens to be on the same channel as you (since you both just used the default) and is watching You-Tube all evening, and it gets even worse.  Just for good measure, the other neighbor's video baby monitor is also using the same radio frequencies and it WILL affect your WiFi.

 

BTW, LOR E1.31 sends a packet every 22 mSec so that comes out to about 45 times per second - at least every times I have watched it with Wireshark.  You missed on your math, but it does come out to about a quarter megabit per second per universe.

 

<soapbox mode on>

  My personal opinion here.  Wireless is great WHEN you need wireless, but in almost all cases, a cable will work better if you don't need wireless.  That applies to phones, keyboards and mice, LAN connectivity, video, and I'm sure a few others I did not mention).

</soapbox mode off>

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I used to work on teams that developed routers and I'm afraid my friends would make fun of me for using multicast in a unicast application because I was too lazy to specify the IP address.

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Perhaps I could have been a little more clear. I was primarily responding to Jim's post concerning wireless routers.

I personally use unicast, but then I tend to be a purist....

 

Bottom line, use a second NIC card, and avoid ALL of the added data traffic on your LAN. You can then run uni or multicast and not worry about it!

 

For a person first starting out multicast helps avoid many of the communication problems we have seen folks post about over the last few years. 

 

I can see no reason not to use a second card, which is important to those of us running a lot of universes, even using unicast! Let's assume a fully wired system for the moment. Even with a fully wired system running unicast, if you like to stream HD movies at the same time your display is running you can run into buffering issues. 

 

That can certainly create some family issues! Ask me how I know  ;)

Edited by Greg Young
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Thanks everyone for the insight.  Switched over to Unicast and a funny thing happened, it was easier to use.  I was having problems finding the controller and working the lights with Multicast.  Now it pops up every time.

 

I am planning on keeping my show computer separate from my home network just for piece of mind as far as it getting bogged down.  I am planning on using 2 Sandevices e6804's with plans to expand in the future, so can I just use an old router (not connected to my home network)  to hook them to the show?  I plan to wire them directly and not use Wi-Fi.

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I am planning on keeping my show computer separate from my home network just for piece of mind as far as it getting bogged down.  I am planning on using 2 Sandevices e6804's with plans to expand in the future, so can I just use an old router (not connected to my home network)  to hook them to the show?  I plan to wire them directly and not use Wi-Fi.

 

Yes, you can use your old router.  A couple of notes about that however:

1)  Some home type routers will not play DHCP server if there is no connection on the WAN side.  Solution is to use Static IP for your PC on that LAN (the SanDevices already will be static).

2)  Make sure you log into the router and turn off the WiFi (assuming it has WiFi).

3)  Although not an absolute requirement, make sure that the LAN side of the router has a static address in the IP address range you are using for your E6804s and PC.  That way you CAN log into the router should you need to change something later (see note 2 above also).

4)  Your IP range for your E1.31 network and your home network MUST have different IP address ranges.  Example:  If your normal home LAN assigns addresses in the 192.168.1.nnn range, you can't also use 192.168.1.nnn  range for your E1.31 LAN.  You could however use 192.168.0.nnn addresses for your E1.31 - or do like me and use 192.168.131.nnn because I can remember it that way :)

 

Note for the IP purists here.  Yes, you could use different parts of 192.168.1.nnn provided a subnet mask smaller than 255.255.255.0 is used - but that is beyond most people here...

 

If you have any questions about this, feel free to ask.

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