1 1 00:00:00,310 --> 00:00:02,890 Encapsulation and Decapsulation. 2 2 00:00:02,890 --> 00:00:03,723 In this lesson, 3 3 00:00:03,723 --> 00:00:07,220 we're going to talk about encapsulation and decapsulation. 4 4 00:00:07,220 --> 00:00:09,450 Encapsulation is the process of putting headers 5 5 00:00:09,450 --> 00:00:12,610 and sometimes trailers around some of our data. 6 6 00:00:12,610 --> 00:00:14,000 Think about it like this. 7 7 00:00:14,000 --> 00:00:16,020 You just finished writing a letter to your grandma, 8 8 00:00:16,020 --> 00:00:17,890 and now you want to send it to her. 9 9 00:00:17,890 --> 00:00:20,620 Well, to do that, you need to put it in an envelope. 10 10 00:00:20,620 --> 00:00:22,310 Now, when you put the letter in the envelope, 11 11 00:00:22,310 --> 00:00:24,470 you're actually encapsulating it. 12 12 00:00:24,470 --> 00:00:26,280 Now, once your grandma gets that envelope, 13 13 00:00:26,280 --> 00:00:27,460 she wants to be able to read it 14 14 00:00:27,460 --> 00:00:29,330 and so she has to take the letter out of the envelope 15 15 00:00:29,330 --> 00:00:30,810 in order for her to read it. 16 16 00:00:30,810 --> 00:00:33,200 This process is known as decapsulation 17 17 00:00:33,200 --> 00:00:34,970 because we're removing the encapsulation 18 18 00:00:34,970 --> 00:00:36,610 that was applied earlier. 19 19 00:00:36,610 --> 00:00:38,440 Now, I know this is a silly example, 20 20 00:00:38,440 --> 00:00:39,840 but that's exactly what happens 21 21 00:00:39,840 --> 00:00:41,580 as we send data on our networks. 22 22 00:00:41,580 --> 00:00:44,520 It's continually being encapsulated and decapsulated 23 23 00:00:44,520 --> 00:00:47,720 as it moves up or down the layers of the OSI model. 24 24 00:00:47,720 --> 00:00:50,810 If we move down the OSI layers, from 7 to 1, 25 25 00:00:50,810 --> 00:00:52,570 we encapsulate our data. 26 26 00:00:52,570 --> 00:00:55,290 If we move upward from Layer 1 up to 7, 27 27 00:00:55,290 --> 00:00:57,320 we decapsulate our data. 28 28 00:00:57,320 --> 00:00:59,730 So let's take a closer look at how this works 29 29 00:00:59,730 --> 00:01:00,970 in the real world. 30 30 00:01:00,970 --> 00:01:05,140 In the OSI model, we use protocol data units or PDUs 31 31 00:01:05,140 --> 00:01:06,740 to transmit our data. 32 32 00:01:06,740 --> 00:01:10,010 A protocol data unit is just a single unit of information 33 33 00:01:10,010 --> 00:01:12,200 transmitted within a computer network. 34 34 00:01:12,200 --> 00:01:15,210 In the OSI model, they are simply called L, 35 35 00:01:15,210 --> 00:01:17,600 the layer number, and PDU. 36 36 00:01:17,600 --> 00:01:21,840 For example, L7 PDU is a Layer 7 PDU. 37 37 00:01:21,840 --> 00:01:23,500 This type of terminology can be used 38 38 00:01:23,500 --> 00:01:25,460 for every single layer we have, 39 39 00:01:25,460 --> 00:01:28,230 but we also have special names for the PDUs 40 40 00:01:28,230 --> 00:01:31,380 when we reach Layers 1, 2, 3, and 4. 41 41 00:01:31,380 --> 00:01:33,610 For Layer 1, we call them bits. 42 42 00:01:33,610 --> 00:01:35,900 For Layer 2, we call them frames. 43 43 00:01:35,900 --> 00:01:38,060 For Layer 3, we call it packets. 44 44 00:01:38,060 --> 00:01:41,340 And Layer 4, we call it segments if we're using TCP 45 45 00:01:41,340 --> 00:01:43,930 or datagrams if we're using UDP. 46 46 00:01:43,930 --> 00:01:45,940 Now, as a user creates data 47 47 00:01:45,940 --> 00:01:47,690 and they want to send it over a network, 48 48 00:01:47,690 --> 00:01:49,510 they're going to enter it into an application 49 49 00:01:49,510 --> 00:01:52,150 at the application layer, Layer 7. 50 50 00:01:52,150 --> 00:01:55,350 This data then has a Layer 7 header added 51 51 00:01:55,350 --> 00:01:56,640 that contains metadata 52 52 00:01:56,640 --> 00:01:58,340 with the parameters that are agreed upon 53 53 00:01:58,340 --> 00:02:00,260 by the specific application. 54 54 00:02:00,260 --> 00:02:04,100 So if you're using HTTP or you're using FTP, 55 55 00:02:04,100 --> 00:02:07,610 that's going to have specific metadata for that type of data. 56 56 00:02:07,610 --> 00:02:10,740 Then that information is going to be passed down to Layer 6 57 57 00:02:10,740 --> 00:02:12,820 where it's going to encapsulate the Layer 7 header 58 58 00:02:12,820 --> 00:02:16,220 and data together, and then add its own Layer 6 header, 59 59 00:02:16,220 --> 00:02:18,680 which contains its own metadata with information 60 60 00:02:18,680 --> 00:02:22,010 about the presentation or encryption formats being used. 61 61 00:02:22,010 --> 00:02:24,870 Next, it's going to pass this down to Layer 5 62 62 00:02:24,870 --> 00:02:26,610 where it encapsulates the Layer 6 header 63 63 00:02:26,610 --> 00:02:28,020 and the Layer 6 data 64 64 00:02:28,020 --> 00:02:30,480 and it's going to add its own Layer 5 header 65 65 00:02:30,480 --> 00:02:33,090 based on the metadata about the session. 66 66 00:02:33,090 --> 00:02:34,950 As you can see, it's like taking a letter, 67 67 00:02:34,950 --> 00:02:37,480 or in this case data, wrapping it in an envelope 68 68 00:02:37,480 --> 00:02:40,060 and then writing some information on that envelope. 69 69 00:02:40,060 --> 00:02:41,250 That's our header. 70 70 00:02:41,250 --> 00:02:42,800 When we hand it to the next person, 71 71 00:02:42,800 --> 00:02:44,200 they're going to put it in an envelope 72 72 00:02:44,200 --> 00:02:46,560 and write their own metadata on the outside of the envelope 73 73 00:02:46,560 --> 00:02:48,350 and then pass it to the next person. 74 74 00:02:48,350 --> 00:02:51,100 And we keep doing this as we go down the layers 75 75 00:02:51,100 --> 00:02:53,150 all the way down to Layer 1. 76 76 00:02:53,150 --> 00:02:57,110 Now, the headers added at Layers 4, 3, 2, and 1 77 77 00:02:57,110 --> 00:02:59,910 are very specific and they actually help ensure the message 78 78 00:02:59,910 --> 00:03:01,970 is going to reach its final destination. 79 79 00:03:01,970 --> 00:03:05,370 So let's take a look at the header that's added at Layer 4, 80 80 00:03:05,370 --> 00:03:06,850 the transport layer. 81 81 00:03:06,850 --> 00:03:08,040 Now, if you remember, 82 82 00:03:08,040 --> 00:03:10,280 the transport layer uses different protocols 83 83 00:03:10,280 --> 00:03:12,390 like TCP or UDP. 84 84 00:03:12,390 --> 00:03:15,180 The TCP header has 10 mandatory fields, 85 85 00:03:15,180 --> 00:03:17,330 totaling 20 bytes of information. 86 86 00:03:17,330 --> 00:03:20,020 This includes our source port, the destination port, 87 87 00:03:20,020 --> 00:03:22,470 the sequence number, the acknowledgement number, 88 88 00:03:22,470 --> 00:03:25,080 the TCP data offset, the reserve data, 89 89 00:03:25,080 --> 00:03:26,810 which is currently always going to be set to zero 90 90 00:03:26,810 --> 00:03:28,390 because it's not really used, 91 91 00:03:28,390 --> 00:03:32,150 the control flags, the window size, the TCP checksum, 92 92 00:03:32,150 --> 00:03:35,840 the urgent pointer, and the mTCP optional data. 93 93 00:03:35,840 --> 00:03:38,250 Now, you don't need to know all of these fields in depth, 94 94 00:03:38,250 --> 00:03:40,450 but there are a couple that are pretty important. 95 95 00:03:40,450 --> 00:03:42,660 For example, the source and destination ports 96 96 00:03:42,660 --> 00:03:44,330 are pretty important to understand 97 97 00:03:44,330 --> 00:03:45,480 because this helps determine 98 98 00:03:45,480 --> 00:03:47,500 where the information is being sent from 99 99 00:03:47,500 --> 00:03:48,970 and where it's being sent to, 100 100 00:03:48,970 --> 00:03:50,930 and allows it to go through a firewall 101 101 00:03:50,930 --> 00:03:52,790 by going to the right ports. 102 102 00:03:52,790 --> 00:03:55,380 Also, the sequence number and acknowledgment numbers 103 103 00:03:55,380 --> 00:03:57,300 are going to be used to ensure all the data 104 104 00:03:57,300 --> 00:03:59,330 is properly received by the destination 105 105 00:03:59,330 --> 00:04:01,260 when it's sent by the original transmitter. 106 106 00:04:01,260 --> 00:04:04,720 So this is also important when you're using TCP. 107 107 00:04:04,720 --> 00:04:06,930 Another important concept in the TCP header 108 108 00:04:06,930 --> 00:04:08,270 is the control flags. 109 109 00:04:08,270 --> 00:04:10,090 There are six control flags that are used 110 110 00:04:10,090 --> 00:04:12,377 to manage data flow before, during, 111 111 00:04:12,377 --> 00:04:15,320 and to stop the data communication when you're finished. 112 112 00:04:15,320 --> 00:04:17,870 You should already be familiar with the three-way handshake. 113 113 00:04:17,870 --> 00:04:20,410 That uses the SYN packet sent by the client, 114 114 00:04:20,410 --> 00:04:22,650 the SYN-ACK packet that's sent by the server, 115 115 00:04:22,650 --> 00:04:25,030 and the ACK packet that the client sends back to the server 116 116 00:04:25,030 --> 00:04:26,030 at the end. 117 117 00:04:26,030 --> 00:04:30,140 These packets are sent using the TCP flags of SYN or ACK 118 118 00:04:30,140 --> 00:04:32,190 inside your TCP header. 119 119 00:04:32,190 --> 00:04:34,240 Now, in addition to the SYN and ACK flags, 120 120 00:04:34,240 --> 00:04:38,890 there's also four others: FIN, RST, PSH, and URG. 121 121 00:04:38,890 --> 00:04:42,230 First, we have the SYN flag or synchronization flag. 122 122 00:04:42,230 --> 00:04:44,400 This is by far the most well-known flag 123 123 00:04:44,400 --> 00:04:47,410 in TCP communications because it's used to synchronize 124 124 00:04:47,410 --> 00:04:50,070 the connection during the three-way handshake. 125 125 00:04:50,070 --> 00:04:52,830 Next, we have the ACK or acknowledgement flag. 126 126 00:04:52,830 --> 00:04:55,130 This is also used during the three-way handshake, 127 127 00:04:55,130 --> 00:04:56,660 but in addition to that, 128 128 00:04:56,660 --> 00:04:58,890 we use it to acknowledge the successful receipt 129 129 00:04:58,890 --> 00:05:01,490 of all the packets during the communication. 130 130 00:05:01,490 --> 00:05:04,080 The FIN or finished packet is used to tear down 131 131 00:05:04,080 --> 00:05:06,810 the virtual connection created by the three-way handshake 132 132 00:05:06,810 --> 00:05:08,150 and the SYN flag. 133 133 00:05:08,150 --> 00:05:10,800 The FIN flag always appears when the last packets 134 134 00:05:10,800 --> 00:05:13,090 are exchanged between a client and a server, 135 135 00:05:13,090 --> 00:05:15,880 and the host is now ready to shut down that connection. 136 136 00:05:15,880 --> 00:05:19,260 Next, we have the RST flag or reset flag. 137 137 00:05:19,260 --> 00:05:21,110 This is going to be used when a client or server 138 138 00:05:21,110 --> 00:05:23,370 receives a packet that it was not expecting 139 139 00:05:23,370 --> 00:05:24,930 during the current connection. 140 140 00:05:24,930 --> 00:05:27,210 For example, if you tried to establish a connection 141 141 00:05:27,210 --> 00:05:30,040 with a server that didn't want to accept any new connections, 142 142 00:05:30,040 --> 00:05:32,850 it could send back an RST or reset flag 143 143 00:05:32,850 --> 00:05:35,570 to inform your client that it's not accepting connections 144 144 00:05:35,570 --> 00:05:38,330 and automatically reject a request. 145 145 00:05:38,330 --> 00:05:41,810 The next one we have is a PSH flag or push. 146 146 00:05:41,810 --> 00:05:43,410 Now, a push flag is used to ensure 147 147 00:05:43,410 --> 00:05:44,860 the data is given priority 148 148 00:05:44,860 --> 00:05:47,760 and is processed at the sending or receiving ends. 149 149 00:05:47,760 --> 00:05:50,100 Most often, this flag is added to a packet 150 150 00:05:50,100 --> 00:05:52,910 at the beginning or end of a data transfer. 151 151 00:05:52,910 --> 00:05:56,900 The final flag we have is URG or the urgent flag. 152 152 00:05:56,900 --> 00:05:58,970 The urgent flag is like the push flag 153 153 00:05:58,970 --> 00:06:01,970 and it identifies incoming data as urgent. 154 154 00:06:01,970 --> 00:06:04,690 Now, the main difference here between push and urgent 155 155 00:06:04,690 --> 00:06:06,260 is that push is used by the sender 156 156 00:06:06,260 --> 00:06:08,660 to indicate data with a higher priority level. 157 157 00:06:08,660 --> 00:06:09,970 Now, urgent, on the other hand, 158 158 00:06:09,970 --> 00:06:13,080 is sent to tell the recipient to process it immediately 159 159 00:06:13,080 --> 00:06:15,360 and ignore anything else that's in the queue. 160 160 00:06:15,360 --> 00:06:17,500 With urgent, this could lead to packets 161 161 00:06:17,500 --> 00:06:20,300 violating the first in first out priority order, 162 162 00:06:20,300 --> 00:06:21,460 so it needs to be used 163 163 00:06:21,460 --> 00:06:24,750 only by particular applications when necessary. 164 164 00:06:24,750 --> 00:06:27,560 Now, if you're using UDP instead of TCP, 165 165 00:06:27,560 --> 00:06:30,180 you're going to be using the User Datagram Protocol. 166 166 00:06:30,180 --> 00:06:32,610 Now, when we look at the User Datagram Protocol header, 167 167 00:06:32,610 --> 00:06:35,280 this is another transport layer or Layer 4 header 168 168 00:06:35,280 --> 00:06:37,040 that's going to be used in our networks. 169 169 00:06:37,040 --> 00:06:39,450 Remember, UDP is unreliable 170 170 00:06:39,450 --> 00:06:41,410 and it's a connectionless protocol, 171 171 00:06:41,410 --> 00:06:45,030 so its header is significantly smaller than TCP. 172 172 00:06:45,030 --> 00:06:47,520 With UDP, we only have an eight byte header 173 173 00:06:47,520 --> 00:06:50,890 instead of the 20 byte header used in TCP. 174 174 00:06:50,890 --> 00:06:53,380 UDP only has four fields that are used: 175 175 00:06:53,380 --> 00:06:56,170 the source port, the destination port, the length, 176 176 00:06:56,170 --> 00:06:57,400 and the checksum. 177 177 00:06:57,400 --> 00:06:58,840 The source and destination ports 178 178 00:06:58,840 --> 00:07:01,380 are just like the ones used in TCP. 179 179 00:07:01,380 --> 00:07:03,400 They dictate where the data is coming from 180 180 00:07:03,400 --> 00:07:05,080 and where it's going to. 181 181 00:07:05,080 --> 00:07:06,530 The length is used to indicate 182 182 00:07:06,530 --> 00:07:09,470 how many bytes the total UDP packet is, 183 183 00:07:09,470 --> 00:07:11,740 including the header and its data. 184 184 00:07:11,740 --> 00:07:14,120 The checksum is not a mandatory field, 185 185 00:07:14,120 --> 00:07:16,900 but instead it can be used to provide some validation 186 186 00:07:16,900 --> 00:07:19,670 that the UDP data being sent was actually received 187 187 00:07:19,670 --> 00:07:21,690 with some level of integrity. 188 188 00:07:21,690 --> 00:07:25,260 Next, let's move down to Layer 3, the network layer. 189 189 00:07:25,260 --> 00:07:26,780 As we move down another layer, 190 190 00:07:26,780 --> 00:07:29,840 we're going to again encapsulate the data and add a header. 191 191 00:07:29,840 --> 00:07:31,810 This time, we're going to add the IP 192 192 00:07:31,810 --> 00:07:33,690 or internet protocol header. 193 193 00:07:33,690 --> 00:07:36,160 The IP header is going to contain several fields, 194 194 00:07:36,160 --> 00:07:39,170 including the IP version, the length of the IP header, 195 195 00:07:39,170 --> 00:07:40,190 the type of service, 196 196 00:07:40,190 --> 00:07:42,860 which was defined by the standard but never really used, 197 197 00:07:42,860 --> 00:07:44,840 the total length of the packet and header, 198 198 00:07:44,840 --> 00:07:47,930 the identifier, the flags, the fragmented offset, 199 199 00:07:47,930 --> 00:07:51,150 the time to live, the protocol, the header checksum, 200 200 00:07:51,150 --> 00:07:53,560 the source IP, the destination IP, 201 201 00:07:53,560 --> 00:07:55,530 and the options and padding. 202 202 00:07:55,530 --> 00:07:57,600 Now, as we continue down the layers, 203 203 00:07:57,600 --> 00:08:00,290 we're going to reach Layer 2, the data link layer, 204 204 00:08:00,290 --> 00:08:01,880 and this is going to encapsulate the data 205 205 00:08:01,880 --> 00:08:03,960 by adding an Ethernet header. 206 206 00:08:03,960 --> 00:08:06,450 Now, this header features just a few things, 207 207 00:08:06,450 --> 00:08:09,850 including a destination MAC address, the source MAC address, 208 208 00:08:09,850 --> 00:08:12,770 the EtherType field, and an optional VLAN tag 209 209 00:08:12,770 --> 00:08:16,797 using either IEEE, 802.1q, or IEEE 802.1ad. 210 210 00:08:19,170 --> 00:08:21,840 We're going to talk more about VLANs in a separate video though 211 211 00:08:21,840 --> 00:08:23,730 because it's an important concept. 212 212 00:08:23,730 --> 00:08:25,910 So let's talk about a MAC address. 213 213 00:08:25,910 --> 00:08:28,790 A MAC address is a physical address that's used to identify 214 214 00:08:28,790 --> 00:08:31,360 a network card on your local area network. 215 215 00:08:31,360 --> 00:08:33,970 This allows our source to find our destination 216 216 00:08:33,970 --> 00:08:36,470 by using this type of Layer 2 addressing. 217 217 00:08:36,470 --> 00:08:39,430 This is what's processed by switches in your network. 218 218 00:08:39,430 --> 00:08:41,720 Now, the EtherType field is used to indicate 219 219 00:08:41,720 --> 00:08:45,130 which protocol is encapsulated in the payload event frame. 220 220 00:08:45,130 --> 00:08:48,350 So if you're using IPv4 or IPv6, 221 221 00:08:48,350 --> 00:08:51,780 this can be indicated here using the EtherType field. 222 222 00:08:51,780 --> 00:08:53,920 Now, in addition to the Ethernet header, 223 223 00:08:53,920 --> 00:08:57,670 a frame being sent at Layer 2 will also contain a payload. 224 224 00:08:57,670 --> 00:09:00,760 In Ethernet, the minimum payload is 42 bytes 225 225 00:09:00,760 --> 00:09:02,180 if VLANs are being used 226 226 00:09:02,180 --> 00:09:05,310 and 46 bytes if no VLANs are being used. 227 227 00:09:05,310 --> 00:09:07,070 Now, when you're trying to send a payload, 228 228 00:09:07,070 --> 00:09:08,890 there is a maximum size to this, 229 229 00:09:08,890 --> 00:09:12,470 known as an MTU or maximum transmission unit. 230 230 00:09:12,470 --> 00:09:13,700 When we talk about payloads, 231 231 00:09:13,700 --> 00:09:16,410 this is the data we're trying to send across the network. 232 232 00:09:16,410 --> 00:09:20,250 By default, Ethernet uses an MTU of 1,500 bytes 233 233 00:09:20,250 --> 00:09:21,940 as its maximum size. 234 234 00:09:21,940 --> 00:09:24,940 Now, if you have a payload that's larger than 1,500 bytes, 235 235 00:09:24,940 --> 00:09:27,950 then you need to allow for what's known as a jumbo frame. 236 236 00:09:27,950 --> 00:09:29,960 This just means the frame is going to be larger 237 237 00:09:29,960 --> 00:09:31,520 than 1,500 bytes. 238 238 00:09:31,520 --> 00:09:32,860 To configure this on your switch, 239 239 00:09:32,860 --> 00:09:35,070 you're going to reconfigure your MTU size 240 240 00:09:35,070 --> 00:09:37,180 or your maximum transmission unit size 241 241 00:09:37,180 --> 00:09:39,460 to larger than 1,500 bytes. 242 242 00:09:39,460 --> 00:09:42,330 All right, that was a ton of information we just covered, 243 243 00:09:42,330 --> 00:09:45,080 but let's review a couple of main concepts here. 244 244 00:09:45,080 --> 00:09:48,970 First, remember, as data moves from Layer 7 to Layer 1, 245 245 00:09:48,970 --> 00:09:51,440 we are going to encapsulate that data. 246 246 00:09:51,440 --> 00:09:54,080 So as we move down the OSI layers, 247 247 00:09:54,080 --> 00:09:55,600 we're going to encapsulate that data 248 248 00:09:55,600 --> 00:09:57,950 and add a header at each of those layers. 249 249 00:09:57,950 --> 00:09:59,950 At Layer 4, we're going to add our source 250 250 00:09:59,950 --> 00:10:01,330 and destination ports. 251 251 00:10:01,330 --> 00:10:04,980 At Layer 3, we add our source and destination IP addresses. 252 252 00:10:04,980 --> 00:10:08,540 At Layer 2, we add our source and destination MAC addresses. 253 253 00:10:08,540 --> 00:10:10,300 Now, once we get to Layer 1, 254 254 00:10:10,300 --> 00:10:12,530 we're simply transmitting our Layer 2 frames 255 255 00:10:12,530 --> 00:10:15,530 as a series of ones and zeros over the medium. 256 256 00:10:15,530 --> 00:10:17,240 When it's received by the next device, 257 257 00:10:17,240 --> 00:10:18,700 for example a switch, 258 258 00:10:18,700 --> 00:10:20,310 it's going to put the frames back together 259 259 00:10:20,310 --> 00:10:23,330 from the electrical, optical, or radio frequency signals 260 260 00:10:23,330 --> 00:10:25,380 that it received over Layer 1. 261 261 00:10:25,380 --> 00:10:28,480 Now, it's going to decapsulate the Layer 2 information 262 262 00:10:28,480 --> 00:10:30,390 by reading the Ethernet header. 263 263 00:10:30,390 --> 00:10:33,030 If the destination MAC is on one of the switch ports, 264 264 00:10:33,030 --> 00:10:34,770 it's going to send the message to it. 265 265 00:10:34,770 --> 00:10:37,460 If not, it's going to forward it to its default gateway, 266 266 00:10:37,460 --> 00:10:38,850 which is a router. 267 267 00:10:38,850 --> 00:10:42,080 This router then decapsulates the data to Layer 3, 268 268 00:10:42,080 --> 00:10:44,400 and it reads the destination IP address. 269 269 00:10:44,400 --> 00:10:45,670 If it's on its network, 270 270 00:10:45,670 --> 00:10:47,700 it's going to forward the data to that device. 271 271 00:10:47,700 --> 00:10:50,010 If not, it's going to re-encapsulate the data 272 272 00:10:50,010 --> 00:10:52,070 and send it out its default gateway. 273 273 00:10:52,070 --> 00:10:54,080 And then this process will continue 274 274 00:10:54,080 --> 00:10:56,840 until the final destination or host is found. 275 275 00:10:56,840 --> 00:10:58,540 Now, once that host is found, 276 276 00:10:58,540 --> 00:11:00,800 it's going to keep decapsulating that information 277 277 00:11:00,800 --> 00:11:02,850 all the way back up to Layer 7 278 278 00:11:02,850 --> 00:11:04,340 where its application can read 279 279 00:11:04,340 --> 00:11:06,550 and understand the underlying data. 280 280 00:11:06,550 --> 00:11:08,080 Now, we're going to cover a lot more 281 281 00:11:08,080 --> 00:11:10,110 about how this data transfer happens 282 282 00:11:10,110 --> 00:11:11,810 when we talk about switches and routers 283 283 00:11:11,810 --> 00:11:13,030 later in this course. 284 284 00:11:13,030 --> 00:11:16,233 But for now, this is the basics you need to understand.