1 00:00:00,830 --> 00:00:03,350 So in this lecture I will have two computers. 2 00:00:03,350 --> 00:00:07,340 Both are using the Ubuntu operating system on it and have ROS two installed. 3 00:00:07,610 --> 00:00:12,710 Basically, we're going to have one computer, run a publisher and see ways we can configure our network 4 00:00:12,710 --> 00:00:17,510 so that the second computer can receive ROS communications from it. 5 00:00:18,020 --> 00:00:23,600 Both computers are connected to the same router, in this case via ethernet cable. 6 00:00:24,200 --> 00:00:26,990 You can also do this over wi fi if you want it as well. 7 00:00:27,470 --> 00:00:31,850 So you can't see the modem since it's off camera, but it essentially looks like this. 8 00:00:34,750 --> 00:00:39,680 So here I am on my main Linux machine, which I have been recording all the previous lectures on. 9 00:00:39,700 --> 00:00:45,290 First thing I will do is confirm to you that the two devices I will be using are on the same network. 10 00:00:45,310 --> 00:00:50,860 We can check this by either going into our network settings and viewing our connection details. 11 00:00:50,860 --> 00:00:54,280 So in this case I'm connected via Ethernet, so if I head over to here. 12 00:00:55,100 --> 00:00:59,330 You can see my IPV four address which my router assigned to my device. 13 00:00:59,510 --> 00:01:04,130 Or alternatively, if you want it to do this in a terminal environment, you could open up a terminal 14 00:01:04,310 --> 00:01:06,620 and run IP a. 15 00:01:07,510 --> 00:01:14,680 And in this case, this is my Ethernet adapter, which shows my IPV four address we saw earlier. 16 00:01:14,710 --> 00:01:19,120 The main thing to keep in mind is that we want to be on the same subnet, so we want to have the same 17 00:01:19,120 --> 00:01:20,300 three sets of digits. 18 00:01:20,300 --> 00:01:22,500 So 19216 8.50. 19 00:01:22,510 --> 00:01:26,710 This would be different depending on your computer and router configuration. 20 00:01:26,800 --> 00:01:31,320 So now go ahead and clear the screen and start a ROS node. 21 00:01:31,330 --> 00:01:35,860 You can start one of the nodes we've made in section four, but for simplicity, I'll run the example 22 00:01:35,860 --> 00:01:37,510 talker and listener nodes. 23 00:01:37,510 --> 00:01:40,570 We ran back when we first installed Ros to Humble. 24 00:01:42,980 --> 00:01:45,320 Okay, So we see that this node is running, it's going to start printing. 25 00:01:45,320 --> 00:01:50,450 So let's head over to our second device to try and subscribe to the values being published. 26 00:01:51,470 --> 00:01:52,970 All right, So here I am on my second device. 27 00:01:52,970 --> 00:01:56,390 So first thing I'm going to do is verify that I'm on the same network subnet. 28 00:01:56,390 --> 00:02:02,030 So again, you could open up your settings and here I am in my network and we see I'm on that same 19216 29 00:02:02,030 --> 00:02:04,310 8.50 subnet. 30 00:02:04,310 --> 00:02:09,950 And again, you could do the same exact thing in terminal with IP A and on this device I have lots of 31 00:02:09,950 --> 00:02:15,800 virtual connectors, but here we're interested in my ethernet connection, which here we see is on the 32 00:02:15,800 --> 00:02:18,140 19216850 subnet. 33 00:02:18,470 --> 00:02:23,990 So I'll go ahead and clear this and let's try and subscribe to the messages coming in from that Hello 34 00:02:23,990 --> 00:02:24,500 world node. 35 00:02:24,500 --> 00:02:29,780 We started on the first computer, so I'm going to go ahead and run the corresponding listener node. 36 00:02:33,820 --> 00:02:39,060 And here we get our hello messages printing, which are being published by the other computer. 37 00:02:39,070 --> 00:02:44,890 And if I go ahead and show both computers on the screen right now, I can go ahead and stop the talker 38 00:02:44,890 --> 00:02:49,570 node on the first computer and we stop receiving messages on the second one. 39 00:02:49,570 --> 00:02:52,210 And of course, I could go ahead and restart the node. 40 00:02:53,600 --> 00:02:58,490 And we see the corresponding messages printing again to the subscriber on this second computer. 41 00:02:59,030 --> 00:02:59,660 Och great. 42 00:02:59,660 --> 00:03:04,590 We have two devices on the same local network with ROS nodes able to communicate with each other. 43 00:03:04,610 --> 00:03:09,350 So I will go ahead and stop these nodes from running and clear the screen. 44 00:03:10,230 --> 00:03:11,900 Do the same thing on my second device. 45 00:03:15,860 --> 00:03:22,460 Now, what happens if we had multiple robots which ran the same task and Ross nodes on the same network? 46 00:03:22,550 --> 00:03:27,890 Well, we could implement different names for each similarly named topic and node. 47 00:03:28,130 --> 00:03:34,340 Or we could instead create a separate domain for the ROS nodes to communicate across on the same network. 48 00:03:34,370 --> 00:03:38,390 We can do this by setting a domain ID in each set of environments. 49 00:03:38,390 --> 00:03:40,280 We want to communicate with each other. 50 00:03:40,880 --> 00:03:46,190 You can find out more information about domain IDs on the ROS Docs page, but we will jump straight 51 00:03:46,190 --> 00:03:48,470 into implementing it on these two computers. 52 00:03:50,120 --> 00:03:54,030 All we need to do is export a Ross domain ID environment variable. 53 00:03:54,050 --> 00:03:57,770 This will generally be within the values of one and 101. 54 00:03:57,770 --> 00:04:05,210 So for example, I can set the ROS domain ID of my first computer to a value of one while I set the 55 00:04:05,210 --> 00:04:07,970 domain ID on the second computer to two. 56 00:04:11,580 --> 00:04:14,820 Now let's try rerunning our ROS nodes on each computer. 57 00:04:22,780 --> 00:04:27,910 So this time we see nothing happens on our listener side, even though the networks and nodes remain 58 00:04:27,910 --> 00:04:28,840 unchanged. 59 00:04:29,260 --> 00:04:35,920 So if I were to go ahead and stop the listener node on the second computer and I'll go ahead and instead 60 00:04:35,920 --> 00:04:41,770 export the domain ID to match my first computer, which was one, and rerun the listener node. 61 00:04:42,550 --> 00:04:47,260 Now I'm getting those Hello world messages that are being published by the first computer. 62 00:04:50,460 --> 00:04:53,850 So I'll go ahead and stop these nodes and clear the screen. 63 00:04:57,840 --> 00:05:01,260 You can also use this feature on the same computer. 64 00:05:01,260 --> 00:05:05,160 So on my first computer, I can go ahead and open up a second terminal. 65 00:05:05,490 --> 00:05:09,360 And if I set the domain ID to something that does not match, for example, three. 66 00:05:12,180 --> 00:05:16,290 Just remind you, this first terminal has a domain ID of one, so I can actually echo that. 67 00:05:22,880 --> 00:05:23,370 So there we go. 68 00:05:23,390 --> 00:05:25,970 We see we have a domain ID value of one. 69 00:05:25,970 --> 00:05:29,810 And so here we have a cross domain value of three. 70 00:05:31,490 --> 00:05:33,140 So we're on the same exact computer. 71 00:05:33,140 --> 00:05:39,080 But if I go ahead and run that publisher and now I run the listener on this terminal. 72 00:05:45,030 --> 00:05:50,070 We can see no messages are received unless I were to change the domain ID to match. 73 00:05:54,090 --> 00:05:55,650 And now we get our Hello world messages. 74 00:05:55,650 --> 00:06:02,820 So again, this can work on the same local host instance as well as across your local network on your 75 00:06:02,820 --> 00:06:03,450 router. 76 00:06:05,380 --> 00:06:11,740 So with that you can see how you can interact with other computers running ROS on a local network connection 77 00:06:11,740 --> 00:06:18,400 and how you can set up ROS domain IDs to have better control over which ROS nodes are able to communicate 78 00:06:18,400 --> 00:06:20,470 with each other on the same network.