1 00:00:02,080 --> 00:00:03,919 When you're designing, building, or 2 00:00:03,919 --> 00:00:05,839 troubleshooting a network, you'll be 3 00:00:05,839 --> 00:00:08,720 using a network topology type that can 4 00:00:08,720 --> 00:00:10,960 vary depending on the technology you're 5 00:00:10,960 --> 00:00:13,120 using. If you're looking to understand 6 00:00:13,120 --> 00:00:15,280 the way the data is flowing, or you want 7 00:00:15,280 --> 00:00:18,000 to plan to create a new type of network, 8 00:00:18,000 --> 00:00:19,600 then it's useful to understand what 9 00:00:19,600 --> 00:00:22,080 these topologies might be. This is also 10 00:00:22,080 --> 00:00:23,439 useful during the troubleshooting 11 00:00:23,439 --> 00:00:25,680 process because you'll know exactly what 12 00:00:25,680 --> 00:00:27,920 flow the traffic takes to get between 13 00:00:27,920 --> 00:00:30,720 point A and point B. One of the most 14 00:00:30,720 --> 00:00:33,440 popular types of topologies is the star 15 00:00:33,440 --> 00:00:35,200 topology. You might also hear this 16 00:00:35,200 --> 00:00:37,440 referred to as a hub and spoke, where the 17 00:00:37,440 --> 00:00:39,520 hub is in the middle and the spokes are 18 00:00:39,520 --> 00:00:42,320 along the outside. This is a topology 19 00:00:42,320 --> 00:00:44,480 that you'll find on almost any network, 20 00:00:44,480 --> 00:00:47,120 regardless of the size of the network. 21 00:00:47,120 --> 00:00:49,360 And you'll also find that most devices 22 00:00:49,360 --> 00:00:51,840 are connecting back to this central hub 23 00:00:51,840 --> 00:00:54,480 of the star. For example, a switched 24 00:00:54,480 --> 00:00:57,039 Ethernet network has the Ethernet switch 25 00:00:57,039 --> 00:00:59,680 in the middle of this star. And then all 26 00:00:59,680 --> 00:01:02,960 of the devices run directly back to this 27 00:01:02,960 --> 00:01:05,040 particular switch. They're not connecting 28 00:01:05,040 --> 00:01:07,119 to each other. They're instead connecting 29 00:01:07,119 --> 00:01:09,360 back to the central switch in this star 30 00:01:09,360 --> 00:01:11,119 topology. 31 00:01:11,119 --> 00:01:12,960 Although we don't often see a ring 32 00:01:12,960 --> 00:01:16,000 topology used on our local area networks, 33 00:01:16,000 --> 00:01:17,920 it's still a topology type that's used 34 00:01:17,920 --> 00:01:20,720 quite often for wide area networks. So 35 00:01:20,720 --> 00:01:22,560 although many people will remember the 36 00:01:22,560 --> 00:01:24,799 older Token Ring technologies that we 37 00:01:24,799 --> 00:01:26,880 used to run inside of our local area 38 00:01:26,880 --> 00:01:29,200 networks, we don't generally find those 39 00:01:29,200 --> 00:01:31,439 ring networks any longer. But if you're 40 00:01:31,439 --> 00:01:33,439 connecting over a metropolitan area 41 00:01:33,439 --> 00:01:36,320 network or a wide area network, we use 42 00:01:36,320 --> 00:01:38,960 ring networks extensively. It's not 43 00:01:38,960 --> 00:01:41,439 because a ring technology somehow lends 44 00:01:41,439 --> 00:01:43,600 itself to work better over a wide area 45 00:01:43,600 --> 00:01:45,680 network. It's because we can create 46 00:01:45,680 --> 00:01:48,159 additional redundancy using the ring 47 00:01:48,159 --> 00:01:49,520 topology. 48 00:01:49,520 --> 00:01:51,759 For example, a very common way to send 49 00:01:51,759 --> 00:01:54,000 traffic over a ring network is to have 50 00:01:54,000 --> 00:01:56,640 the traffic simply go in a circle. Now, if 51 00:01:56,640 --> 00:01:58,479 we're on this wide area network and 52 00:01:58,479 --> 00:02:00,320 there's construction going on and 53 00:02:00,320 --> 00:02:02,320 someone happens to sever a fiber 54 00:02:02,320 --> 00:02:04,159 connection that's being used for this 55 00:02:04,159 --> 00:02:06,640 metropolitan area network, then we're not 56 00:02:06,640 --> 00:02:08,640 going to be able to send that traffic 57 00:02:08,640 --> 00:02:10,640 through the rest of that ring. But the 58 00:02:10,640 --> 00:02:13,200 devices that are on either side of that 59 00:02:13,200 --> 00:02:15,680 severed link recognize that traffic is 60 00:02:15,680 --> 00:02:17,599 no longer able to traverse that 61 00:02:17,599 --> 00:02:19,840 connection, and instead will loop back 62 00:02:19,840 --> 00:02:22,239 the connection on those individual 63 00:02:22,239 --> 00:02:24,560 endpoints. So instead of having data go 64 00:02:24,560 --> 00:02:26,879 around a ring, the data will instead go 65 00:02:26,879 --> 00:02:29,440 as far as it can around the ring and 66 00:02:29,440 --> 00:02:31,840 then loop back to get to the other side 67 00:02:31,840 --> 00:02:34,000 of the ring, maintaining uptime and 68 00:02:34,000 --> 00:02:36,640 availability even in the case where part 69 00:02:36,640 --> 00:02:39,519 of that ring may be severed. 70 00:02:39,519 --> 00:02:41,360 Early types of Ethernet networks were 71 00:02:41,360 --> 00:02:43,360 not switched Ethernet, but were instead 72 00:02:43,360 --> 00:02:46,480 run over coax. And this coax was quite 73 00:02:46,480 --> 00:02:48,879 simply a cable that was run down the 74 00:02:48,879 --> 00:02:51,440 middle of the room, very similar to this 75 00:02:51,440 --> 00:02:54,239 cable. This is a bus network. And although 76 00:02:54,239 --> 00:02:56,080 it was commonly used on those early 77 00:02:56,080 --> 00:02:58,319 Ethernet networks, we can still find 78 00:02:58,319 --> 00:03:01,920 modern networks that use the same bus topology. 79 00:03:01,920 --> 00:03:04,400 One problem with bus networks is that it 80 00:03:04,400 --> 00:03:06,800 is a single cable that is running either 81 00:03:06,800 --> 00:03:08,879 through the walls or down the center of 82 00:03:08,879 --> 00:03:11,120 the room. And if we happen to have a 83 00:03:11,120 --> 00:03:13,440 break in this cable, you can see 84 00:03:13,440 --> 00:03:15,599 immediately that it would suddenly 85 00:03:15,599 --> 00:03:17,519 segment the network into different 86 00:03:17,519 --> 00:03:20,400 pieces, or in some cases, cause no data to 87 00:03:20,400 --> 00:03:22,879 be transferred across the network. That's 88 00:03:22,879 --> 00:03:24,959 one of the reasons we moved away from 89 00:03:24,959 --> 00:03:27,680 bus networks for our local area networks-- 90 00:03:27,680 --> 00:03:29,760 because one single disconnect could 91 00:03:29,760 --> 00:03:33,280 cause an outage for everybody else on the network. 92 00:03:33,280 --> 00:03:35,680 In our modern automobiles, we have bus 93 00:03:35,680 --> 00:03:37,680 networks that we use extensively. These 94 00:03:37,680 --> 00:03:41,280 are Controller Area Network buses, or CAN 95 00:03:41,280 --> 00:03:43,200 bus connections, and they're used to 96 00:03:43,200 --> 00:03:45,200 connect all of the different sensors and 97 00:03:45,200 --> 00:03:47,760 controllers inside of our automobiles to 98 00:03:47,760 --> 00:03:49,840 be able to make all of our cars much 99 00:03:49,840 --> 00:03:52,480 safer to drive on the roads. 100 00:03:52,480 --> 00:03:54,640 Another popular topology, especially in 101 00:03:54,640 --> 00:03:57,040 larger networks, is to create a mesh 102 00:03:57,040 --> 00:04:00,319 between devices or a mesh between sites. 103 00:04:00,319 --> 00:04:02,480 We may have devices that are connected 104 00:04:02,480 --> 00:04:04,720 in different locations, and we might want 105 00:04:04,720 --> 00:04:06,480 to connect them all together. But instead 106 00:04:06,480 --> 00:04:08,480 of having a single connection to a 107 00:04:08,480 --> 00:04:10,720 particular site, we may want to create 108 00:04:10,720 --> 00:04:12,799 multiple connections to mesh these 109 00:04:12,799 --> 00:04:15,760 together. That way, if we do lose any one 110 00:04:15,760 --> 00:04:17,840 of these network links, we're able to 111 00:04:17,840 --> 00:04:20,320 work around that problem by simply using 112 00:04:20,320 --> 00:04:22,800 one of the redundant connections. 113 00:04:22,800 --> 00:04:25,040 You'll commonly use this type of mesh 114 00:04:25,040 --> 00:04:26,960 design if you're creating redundancy or 115 00:04:26,960 --> 00:04:28,800 fault tolerance, or perhaps you're 116 00:04:28,800 --> 00:04:30,800 designing a load-balanced network and you 117 00:04:30,800 --> 00:04:32,479 can use different parts of the network 118 00:04:32,479 --> 00:04:34,000 to share that load. 119 00:04:34,000 --> 00:04:36,479 Probably the most common place to find a 120 00:04:36,479 --> 00:04:38,960 wired mesh network is over a wide area 121 00:04:38,960 --> 00:04:41,120 network, where you can create multiple 122 00:04:41,120 --> 00:04:43,040 links to other sites so that you can 123 00:04:43,040 --> 00:04:45,120 have a primary connection from one site 124 00:04:45,120 --> 00:04:47,040 to the other, and then a backup or 125 00:04:47,040 --> 00:04:49,120 secondary connection that you can use if 126 00:04:49,120 --> 00:04:51,440 you run into problems. 127 00:04:51,440 --> 00:04:53,040 When you start combining these different 128 00:04:53,040 --> 00:04:55,440 topologies together, you create a hybrid 129 00:04:55,440 --> 00:04:58,000 network. A hybrid network is more than 130 00:04:58,000 --> 00:05:00,320 one of these topology types all working 131 00:05:00,320 --> 00:05:02,320 together. For example, you might have 132 00:05:02,320 --> 00:05:04,240 three remote sites all connecting 133 00:05:04,240 --> 00:05:06,320 devices together using a switched 134 00:05:06,320 --> 00:05:08,720 Ethernet or star network. And then you 135 00:05:08,720 --> 00:05:10,639 may be connecting those together over a 136 00:05:10,639 --> 00:05:14,880 wide area network that uses a ring topology. 137 00:05:14,880 --> 00:05:16,560 If you're using a wireless network, you 138 00:05:16,560 --> 00:05:18,560 may be communicating in a number of 139 00:05:18,560 --> 00:05:20,880 different ways. If you're using an access 140 00:05:20,880 --> 00:05:22,880 point, you're probably communicating over 141 00:05:22,880 --> 00:05:25,280 an infrastructure connection. This means 142 00:05:25,280 --> 00:05:27,039 that all of the devices on your network 143 00:05:27,039 --> 00:05:29,039 are communicating through an access 144 00:05:29,039 --> 00:05:31,199 point. This is probably the most common 145 00:05:31,199 --> 00:05:33,600 way to use wireless connections, but it's 146 00:05:33,600 --> 00:05:35,840 not the only way to communicate over a 147 00:05:35,840 --> 00:05:37,759 wireless link. If you just have two 148 00:05:37,759 --> 00:05:40,000 devices and there's no access point that 149 00:05:40,000 --> 00:05:42,240 you can use, you can connect directly 150 00:05:42,240 --> 00:05:45,280 from one device to another using ad hoc 151 00:05:45,280 --> 00:05:47,520 networking. You don't need an access 152 00:05:47,520 --> 00:05:49,520 point or any other type of wireless 153 00:05:49,520 --> 00:05:51,440 infrastructure. You simply have 154 00:05:51,440 --> 00:05:53,759 one device communicate directly to another 155 00:05:53,759 --> 00:05:56,639 device over this wireless connection. 156 00:05:56,639 --> 00:05:58,800 And if you've added Internet of Things 157 00:05:58,800 --> 00:06:01,120 devices, which are commonly wireless 158 00:06:01,120 --> 00:06:03,680 devices that control our lights, our door 159 00:06:03,680 --> 00:06:06,080 locks, or the air conditioning systems, 160 00:06:06,080 --> 00:06:08,000 then you're probably using a mesh 161 00:06:08,000 --> 00:06:10,400 network where all of these devices can 162 00:06:10,400 --> 00:06:12,639 communicate to all the other devices 163 00:06:12,639 --> 00:06:14,960 simultaneously to create an 164 00:06:14,960 --> 00:06:17,680 interconnected mesh of communication 165 00:06:17,680 --> 00:06:21,120 between all of these IoT devices. 166 00:06:21,120 --> 00:06:23,039 One of the advantages of these mesh 167 00:06:23,039 --> 00:06:25,840 wireless networks is that it allows many 168 00:06:25,840 --> 00:06:28,080 devices to communicate to each other, 169 00:06:28,080 --> 00:06:30,560 even if those devices are very far apart 170 00:06:30,560 --> 00:06:32,720 from each other. This also allows the 171 00:06:32,720 --> 00:06:35,440 mesh network to self-heal. So if you turn 172 00:06:35,440 --> 00:06:37,680 off one of those IoT devices, the 173 00:06:37,680 --> 00:06:40,000 remaining devices will self-heal and 174 00:06:40,000 --> 00:06:42,880 redesign themselves into a mesh network 175 00:06:42,880 --> 00:06:46,313 that will allow them to continue the communication.