Author Topic: Network Switches - Multicast v. Unicast  (Read 1416 times)

Offline L1011

  • Jr. Member
  • **
  • Join Date: Dec 2015
  • Location: NH
  • Posts: 86
  • Kudos: 0
Network Switches - Multicast v. Unicast
« on: December 16, 2015, 04:38:16 AM »
I'm curious what types of switches you folks use for your displays.  I read on one of the (excellent) Powerpoint presentations to be sure your network switch features IGMP Snooping. Easy enough so far.... but....when comparing Unicast v. Multicast setups, Unicast seems to give me a lot more flexibility in terms of number of E1.31 controllers.

So why use Multicast instead of Unicast?  What's the advantage?

Thanks!

Newbie for 2016 using FPP, F16v2r, F4v2, and WS2811 bullet pixels.

Offline gadgetsmith

  • Hero Member
  • *****
  • Join Date: Apr 2014
  • Location: Charlton, NY
  • Posts: 989
  • Kudos: 14
Re: Network Switches - Multicast v. Unicast
« Reply #1 on: December 16, 2015, 06:12:42 AM »
Two I can think of.
1) Easier setup. All info gets sent to all controllers, so no need to worry about sending the correct channels to the correct IP addresses.
2) ARP. Unicast is actually a two way communication. It sends data back to the source to verify it's received (at least this is how I understand it works from the things I've read, but I'm certainly no expert). See dkulps explaination below.  If a controller is off for  some reason, or your using wireless devices, you have to think about that added traffic. Multicast has no ARP, which I think is why some people refer to multicast as "spray and pray". ☺

3) Personal Preference. They both work, given that your network switches handle multicast, so it really comes down to this.

For me it's unicast, as something in my network interferes with multicast, plus I get more universes out if a 682 controller in unicast mode.
« Last Edit: December 16, 2015, 06:46:51 AM by gadgetsmith »

Offline dkulp

  • Developer
  • ******
  • Join Date: Sep 2013
  • Location: Framingham, MA
  • Posts: 1,586
  • Kudos: 92
    • KulpLights.com
Re: Network Switches - Multicast v. Unicast
« Reply #2 on: December 16, 2015, 06:34:14 AM »

#2 isn't correct.   Unicast is still a send and pray.   What the ARP is is a lookup at the beginning to figure out where to send the packet.   Ethernet needs to lookup what device owns the particular IP address so an ARP request is issued before the first packet.   The problem, as you mentioned, is if the device isn't up, it periodically sends out additional arp requests and waits for responses which can create pauses. 

Offline gadgetsmith

  • Hero Member
  • *****
  • Join Date: Apr 2014
  • Location: Charlton, NY
  • Posts: 989
  • Kudos: 14
Re: Network Switches - Multicast v. Unicast
« Reply #3 on: December 16, 2015, 06:51:19 AM »
Thanks for that.  So is it the ethernet part of the controllers that respond to the ARP request, or is it everything (routers, switches, etc) ?  That's why I was referring to it as "two way" communication as something needs to respond to the request, not good wording on my part.

Offline Gilrock

  • Sr. Member
  • ****
  • Join Date: Dec 2013
  • Location:
  • Posts: 329
  • Kudos: 8
Re: Network Switches - Multicast v. Unicast
« Reply #4 on: December 16, 2015, 06:56:57 AM »
I just switched my show FPP back to unicast last night.  The main reason was I wanted to connect my show router to the internet so my FPP's can get time but I don't want multicast traffic flooding my house network.  I was able to leave all my controllers still on DHCP because I have the show router setup to give specific IP addresses out to each MAC address of the controllers.

I'm really sure if the router sends the multicast data out the yellow internet port so if someone can tell me how to make sure that data stays within the show network I'd be glad to switch back to multicast.

Offline gadgetsmith

  • Hero Member
  • *****
  • Join Date: Apr 2014
  • Location: Charlton, NY
  • Posts: 989
  • Kudos: 14
Re: Network Switches - Multicast v. Unicast
« Reply #5 on: December 16, 2015, 02:29:42 PM »
I run an Ethernet cable from my home network to the wan side of my show router.  I have 32 universes of multicast for my show, and have never seen any of it on my home network.  I'm just using the basic router settings, nothing special. You'd be able to see multicast traffic on your home network simply by looking at the status leds on any switch on your home network side... they would all be blinking like crazy if multicast was present.

Offline Gilrock

  • Sr. Member
  • ****
  • Join Date: Dec 2013
  • Location:
  • Posts: 329
  • Kudos: 8
Re: Network Switches - Multicast v. Unicast
« Reply #6 on: December 16, 2015, 02:34:18 PM »
Yeah I had thought about just trying it and seeing if it works and maybe Wireshark a PC on the home network side.

Offline AussiePhil

  • Sr. Member
  • ****
  • Join Date: Dec 2014
  • Location:
  • Posts: 495
  • Kudos: 11
Re: Network Switches - Multicast v. Unicast
« Reply #7 on: December 16, 2015, 03:21:09 PM »
Unicast should be used if you have wireless access points on your show network.

Nothing stops you using a mix of unicast/multicast traffic.

Unicast will impact your display if any destination is not available or fails during show time. This alone should make people think about when to use unicast.

Multicast has further benefits.
- multiple controllers can receive the same universes allowing for easy duplication of effects/elements
- controller management ip's don't have to even be on same ip range as show.... this might seem dumb but I transitioned from 10.x.x.x to 192.168.33.x for my show network but a couple of the J1sys controllers are still on 10.x.x.x but are happily processing the multicast traffic and controlling lights. (didn't need to adjust config)
- sender configuration is easier as you just say, output x number of universes, this may not be a big deal when you have a couple of controllers but for larger numbers of controllers it's a pain to configure unicast.

the second also allows you to have preconfigured spares ready to be plugged in without having to change management ip addresses. 

Multicast will impact your network if you are not proactive in isolating the multicast traffic

 

Back to top