1 1 00:00:00,560 --> 00:00:02,490 Wireless considerations. 2 2 00:00:02,490 --> 00:00:05,500 In this video, we're going to discuss wireless considerations 3 3 00:00:05,500 --> 00:00:06,580 that you need to think about 4 4 00:00:06,580 --> 00:00:09,220 as you start to troubleshoot your wireless networks. 5 5 00:00:09,220 --> 00:00:11,110 We're going to begin by discussing antennas, 6 6 00:00:11,110 --> 00:00:13,900 their placement, their type, and their polarization. 7 7 00:00:13,900 --> 00:00:15,970 Then, we're going to cover channel utilization, 8 8 00:00:15,970 --> 00:00:17,930 site surveys and the types of information 9 9 00:00:17,930 --> 00:00:19,520 that those things can help us with 10 10 00:00:19,520 --> 00:00:21,080 as we troubleshoot our networks. 11 11 00:00:21,080 --> 00:00:23,780 Finally, we're going to talk about wireless access points 12 12 00:00:23,780 --> 00:00:27,560 or AP association times, and how association actually works. 13 13 00:00:27,560 --> 00:00:29,970 First, let's talk all about antennas. 14 14 00:00:29,970 --> 00:00:32,030 Antennas can come in multiple different types, 15 15 00:00:32,030 --> 00:00:34,200 and each one has its own purpose. 16 16 00:00:34,200 --> 00:00:36,350 By default, most wireless access points 17 17 00:00:36,350 --> 00:00:38,300 are going to use omnidirectional antennas. 18 18 00:00:38,300 --> 00:00:39,790 And normally they're going to be located 19 19 00:00:39,790 --> 00:00:41,600 in a vertical form factor. 20 20 00:00:41,600 --> 00:00:43,250 Now for a vertical antenna, 21 21 00:00:43,250 --> 00:00:45,670 the radiation pattern for the radio frequency waves 22 22 00:00:45,670 --> 00:00:47,540 is going to extend outward in all directions, 23 23 00:00:47,540 --> 00:00:49,280 away from that antenna and away 24 24 00:00:49,280 --> 00:00:52,450 from the wireless access point at an equal power level. 25 25 00:00:52,450 --> 00:00:54,390 As the radio waves travel further and further 26 26 00:00:54,390 --> 00:00:55,300 from that antenna, 27 27 00:00:55,300 --> 00:00:57,220 the signal is going to get lost a little bit 28 28 00:00:57,220 --> 00:00:59,790 and the power and strength is going to decrease. 29 29 00:00:59,790 --> 00:01:01,850 Now, if you're monitoring this from your client, 30 30 00:01:01,850 --> 00:01:04,960 you're going to see that you have more negative RSSIs 31 31 00:01:04,960 --> 00:01:07,070 as you go further from the wireless access point 32 32 00:01:07,070 --> 00:01:08,460 and it's antenna. 33 33 00:01:08,460 --> 00:01:09,340 Now, for example, 34 34 00:01:09,340 --> 00:01:11,530 let's say you're sitting right next to the antenna. 35 35 00:01:11,530 --> 00:01:14,490 You might have an RSSI of negative 30 to negative 40 36 36 00:01:14,490 --> 00:01:17,450 decibels, but if you move out a hundred feet away, 37 37 00:01:17,450 --> 00:01:20,040 that signal strength may now be at an RSSI 38 38 00:01:20,040 --> 00:01:23,250 of negative 65 or negative 70 decibels. 39 39 00:01:23,250 --> 00:01:25,330 Another type of antenna you might come across 40 40 00:01:25,330 --> 00:01:28,750 is known as a dipole antenna or a bi-directional antenna. 41 41 00:01:28,750 --> 00:01:30,070 With a dipole antenna, 42 42 00:01:30,070 --> 00:01:32,320 the antenna is going to produce a radio-frequency wave 43 43 00:01:32,320 --> 00:01:34,070 that extends outward in two directions, 44 44 00:01:34,070 --> 00:01:35,630 away from the antenna. 45 45 00:01:35,630 --> 00:01:36,880 With a dipole antenna, 46 46 00:01:36,880 --> 00:01:38,640 you're normally going to see a higher RSSI 47 47 00:01:38,640 --> 00:01:39,720 in the client device, 48 48 00:01:39,720 --> 00:01:42,050 even when it's located further from the access point, 49 49 00:01:42,050 --> 00:01:44,480 because this antenna can now focus its power 50 50 00:01:44,480 --> 00:01:48,180 in only two directions instead of the entire 360 degrees 51 51 00:01:48,180 --> 00:01:51,600 around itself, like an omnidirectional antenna produces. 52 52 00:01:51,600 --> 00:01:53,570 So if you need the radio frequency waves 53 53 00:01:53,570 --> 00:01:55,040 to only go in two directions, 54 54 00:01:55,040 --> 00:01:57,240 a dipole is going to be a good option for you, 55 55 00:01:57,240 --> 00:01:59,850 but they're not heavily used in wireless networks 56 56 00:01:59,850 --> 00:02:01,430 for the most part. 57 57 00:02:01,430 --> 00:02:04,410 Next, we have this thing known as a Yagi antenna. 58 58 00:02:04,410 --> 00:02:07,180 Now a Yagi antenna is the type of unidirectional antenna 59 59 00:02:07,180 --> 00:02:10,400 that sends the radio frequency waves only in one direction. 60 60 00:02:10,400 --> 00:02:12,260 Due to this focusing of the radio frequency 61 61 00:02:12,260 --> 00:02:13,580 in a singular direction, 62 62 00:02:13,580 --> 00:02:15,790 a Yagi antenna can send the radio frequency waves 63 63 00:02:15,790 --> 00:02:18,480 further in a single direction using less power 64 64 00:02:18,480 --> 00:02:20,510 than an omnidirectional antenna will. 65 65 00:02:20,510 --> 00:02:22,860 Normally you're going to see a Yagi antenna used 66 66 00:02:22,860 --> 00:02:24,380 when you're trying to connect to different sites 67 67 00:02:24,380 --> 00:02:25,940 using a wireless link. 68 68 00:02:25,940 --> 00:02:26,800 For example, 69 69 00:02:26,800 --> 00:02:28,450 you may want to connect to office buildings 70 70 00:02:28,450 --> 00:02:30,560 on a college campus using a wireless link 71 71 00:02:30,560 --> 00:02:32,960 instead of running a buried fiber optic cable. 72 72 00:02:32,960 --> 00:02:33,820 In this case, 73 73 00:02:33,820 --> 00:02:36,440 you're going to use a Yagi antenna to do that. 74 74 00:02:36,440 --> 00:02:39,450 Finally, we have a parabolic grid or disc antenna. 75 75 00:02:39,450 --> 00:02:41,780 These antennas are unidirectional antennas, 76 76 00:02:41,780 --> 00:02:43,300 just like a Yagi antenna is, 77 77 00:02:43,300 --> 00:02:45,340 but they're built a little bit differently. 78 78 00:02:45,340 --> 00:02:48,050 Now, parabolic grid antennas are most commonly used 79 79 00:02:48,050 --> 00:02:49,700 for site-to-site applications 80 80 00:02:49,700 --> 00:02:50,680 where you need to connect buildings 81 81 00:02:50,680 --> 00:02:53,640 over a longer distance than you would with a Yagi antenna. 82 82 00:02:53,640 --> 00:02:54,910 Like a Yagi antenna, 83 83 00:02:54,910 --> 00:02:57,040 a parabolic antenna is going to allow the radio wave 84 84 00:02:57,040 --> 00:02:58,920 to be transmitted in only one direction, 85 85 00:02:58,920 --> 00:03:01,230 making it a unidirectional antenna. 86 86 00:03:01,230 --> 00:03:03,310 Now, when it comes to placing your antennas, 87 87 00:03:03,310 --> 00:03:04,340 this is going to be dependent 88 88 00:03:04,340 --> 00:03:05,620 on where you're going to place them 89 89 00:03:05,620 --> 00:03:07,390 inside or outside of your building 90 90 00:03:07,390 --> 00:03:09,570 to create the coverage that you desire. 91 91 00:03:09,570 --> 00:03:11,130 If you're setting up a site-to-site 92 92 00:03:11,130 --> 00:03:12,760 or building-to-building connection, 93 93 00:03:12,760 --> 00:03:14,810 you're going to want to use a unidirectional antenna 94 94 00:03:14,810 --> 00:03:17,080 like a parabolic or Yagi antenna. 95 95 00:03:17,080 --> 00:03:18,600 Now you're going to take that and mount it 96 96 00:03:18,600 --> 00:03:20,000 on the outside of your building. 97 97 00:03:20,000 --> 00:03:22,140 And usually you're going to attach it to the roof 98 98 00:03:22,140 --> 00:03:23,650 and make sure there's a clear line of sight 99 99 00:03:23,650 --> 00:03:26,510 between both antennas on each of those buildings. 100 100 00:03:26,510 --> 00:03:28,420 Now, one of the common issues you're going to experience 101 101 00:03:28,420 --> 00:03:30,480 with wireless antennas for a site-to-site or 102 102 00:03:30,480 --> 00:03:32,550 building-to-building connection is that the connection 103 103 00:03:32,550 --> 00:03:36,810 may deteriorate and slow down or completely stop over time. 104 104 00:03:36,810 --> 00:03:37,770 If this occurs, 105 105 00:03:37,770 --> 00:03:39,250 you need to ensure that both the antennas 106 106 00:03:39,250 --> 00:03:41,190 still have a clear sight between them. 107 107 00:03:41,190 --> 00:03:43,630 For example, maybe you have two office buildings 108 108 00:03:43,630 --> 00:03:45,550 and they are only one or two stories high. 109 109 00:03:45,550 --> 00:03:47,830 You've gone ahead and installed the antennas in the fall. 110 110 00:03:47,830 --> 00:03:49,260 And there was no issues at all. 111 111 00:03:49,260 --> 00:03:51,310 You had a perfectly clear line of sight, 112 112 00:03:51,310 --> 00:03:53,080 but it's been about six months, 113 113 00:03:53,080 --> 00:03:55,690 and now the seasons have changed and spring appears 114 114 00:03:55,690 --> 00:03:56,770 and your wireless connection 115 115 00:03:56,770 --> 00:03:58,590 may start to be affected by trees 116 116 00:03:58,590 --> 00:04:00,100 because they've sprouted new leaves 117 117 00:04:00,100 --> 00:04:02,020 and they are now blocking your line of sight clearly 118 118 00:04:02,020 --> 00:04:03,780 between those two buildings. 119 119 00:04:03,780 --> 00:04:06,490 Similarly, if in the winter time there's a lot of snow, 120 120 00:04:06,490 --> 00:04:08,100 this can also block your signal, 121 121 00:04:08,100 --> 00:04:10,120 or if it rains heavily in the summer, 122 122 00:04:10,120 --> 00:04:11,840 you could also have a deteriorating signal 123 123 00:04:11,840 --> 00:04:13,410 because the water droplets will block 124 124 00:04:13,410 --> 00:04:16,480 the wireless communication between these two antennas. 125 125 00:04:16,480 --> 00:04:18,300 So if you're working with antennas, 126 126 00:04:18,300 --> 00:04:19,560 you need to think about these things 127 127 00:04:19,560 --> 00:04:21,120 when you're working outside. 128 128 00:04:21,120 --> 00:04:21,953 Now, on the other hand, 129 129 00:04:21,953 --> 00:04:23,670 if you're working inside your building, 130 130 00:04:23,670 --> 00:04:25,650 you're going to be more likely to use omni-directional 131 131 00:04:25,650 --> 00:04:28,350 or unidirectional patch antennas to control the signal 132 132 00:04:28,350 --> 00:04:30,280 being radiated by your wireless networks, 133 133 00:04:30,280 --> 00:04:31,720 to each of your clients. 134 134 00:04:31,720 --> 00:04:33,150 With omnidirectional antennas, 135 135 00:04:33,150 --> 00:04:34,930 it's going to be common to place this on the ceiling 136 136 00:04:34,930 --> 00:04:37,100 in the middle of the office or classroom. 137 137 00:04:37,100 --> 00:04:38,900 For a unidirectional patch antenna, 138 138 00:04:38,900 --> 00:04:39,900 you're usually going to place this 139 139 00:04:39,900 --> 00:04:42,450 on the outer wall of the building facing inward, 140 140 00:04:42,450 --> 00:04:44,840 thereby directing all those radiofrequency waves 141 141 00:04:44,840 --> 00:04:47,810 back inward towards the office or the classrooms. 142 142 00:04:47,810 --> 00:04:49,840 Now, the last thing we need to discuss with antennas 143 143 00:04:49,840 --> 00:04:52,000 is the concept of polarization. 144 144 00:04:52,000 --> 00:04:54,630 Polarization is the orientation of the electric field 145 145 00:04:54,630 --> 00:04:57,400 or transmissions that are occurring from that antenna. 146 146 00:04:57,400 --> 00:05:00,450 Basically, as the radio frequency waves leave the antenna, 147 147 00:05:00,450 --> 00:05:02,240 how is it going to be oriented? 148 148 00:05:02,240 --> 00:05:04,750 Every antenna has a polarization associated with it. 149 149 00:05:04,750 --> 00:05:06,160 And for wifi networks, 150 150 00:05:06,160 --> 00:05:07,480 our intent is usually you're going to have 151 151 00:05:07,480 --> 00:05:11,290 a vertical or horizontal polarization associated with them. 152 152 00:05:11,290 --> 00:05:13,960 Now, most wifi clients that have external antennas 153 153 00:05:13,960 --> 00:05:16,090 are going to use vertical polarization, 154 154 00:05:16,090 --> 00:05:17,850 but your wireless access point 155 155 00:05:17,850 --> 00:05:20,610 could use vertical or horizontal polarization 156 156 00:05:20,610 --> 00:05:22,780 depending on what type of antenna it has. 157 157 00:05:22,780 --> 00:05:24,550 Now, if you see a problem with some clients 158 158 00:05:24,550 --> 00:05:26,120 getting a poor RSSI, 159 159 00:05:26,120 --> 00:05:28,250 even though they're pretty close to your access point, 160 160 00:05:28,250 --> 00:05:30,900 this may indicate you have a polarization issue. 161 161 00:05:30,900 --> 00:05:31,870 If this is the case, 162 162 00:05:31,870 --> 00:05:32,980 I want you to try flipping 163 163 00:05:32,980 --> 00:05:34,640 the wireless access point antenna 164 164 00:05:34,640 --> 00:05:36,070 to allow the clients to better connect 165 165 00:05:36,070 --> 00:05:39,160 to that device if they support bending the antenna upwards, 166 166 00:05:39,160 --> 00:05:40,743 or if you're using wireless access points 167 167 00:05:40,743 --> 00:05:42,400 that are sitting on the floor, 168 168 00:05:42,400 --> 00:05:44,700 you want to make sure you're using vertical polarization 169 169 00:05:44,700 --> 00:05:47,480 and radiating antennas to increase your coverage area. 170 170 00:05:47,480 --> 00:05:48,790 If you're using horizontal, 171 171 00:05:48,790 --> 00:05:50,140 it's going to keep sending those radio waves 172 172 00:05:50,140 --> 00:05:51,220 out horizontally 173 173 00:05:51,220 --> 00:05:53,570 right along the floor and up to the desk level 174 174 00:05:53,570 --> 00:05:55,020 where everybody else is working. 175 175 00:05:55,020 --> 00:05:58,370 Remember, most wifi networks use vertical polarization. 176 176 00:05:58,370 --> 00:06:00,070 So your intentions should be sticking upward 177 177 00:06:00,070 --> 00:06:01,930 if you're using an omnidirectional antenna 178 178 00:06:01,930 --> 00:06:03,720 with your wifi networks. 179 179 00:06:03,720 --> 00:06:06,300 All right, next, we have channel utilization. 180 180 00:06:06,300 --> 00:06:09,040 Channel utilization is a statistic or measure of the amount 181 181 00:06:09,040 --> 00:06:10,740 of airtime utilization that occurs 182 182 00:06:10,740 --> 00:06:12,630 for a particular frequency or channel. 183 183 00:06:12,630 --> 00:06:14,700 If there's a higher rate of channel utilization, 184 184 00:06:14,700 --> 00:06:16,690 then that means there's more traffic being transmitted 185 185 00:06:16,690 --> 00:06:18,540 over that particular frequency. 186 186 00:06:18,540 --> 00:06:20,470 In order to have a fast wireless network, 187 187 00:06:20,470 --> 00:06:24,060 you want to keep your channel utilization under around 30%. 188 188 00:06:24,060 --> 00:06:26,020 Now, channel utilization is not something 189 189 00:06:26,020 --> 00:06:27,410 you alone can control though, 190 190 00:06:27,410 --> 00:06:29,040 because there's lots of these different channels 191 191 00:06:29,040 --> 00:06:31,630 that overlap with other people in that area. 192 192 00:06:31,630 --> 00:06:33,240 And so the same channels and frequencies 193 193 00:06:33,240 --> 00:06:36,350 can be used by your network and other networks too. 194 194 00:06:36,350 --> 00:06:38,620 For example, let's say you're running a wireless B 195 195 00:06:38,620 --> 00:06:40,800 or wireless G or wireless N network, 196 196 00:06:40,800 --> 00:06:43,580 and you're operating in the 2.4 gigahertz spectrum. 197 197 00:06:43,580 --> 00:06:45,010 We are going to be using the same channels 198 198 00:06:45,010 --> 00:06:48,190 that everybody else is, channels one, six, and 11. 199 199 00:06:48,190 --> 00:06:49,980 Now, if you have a large office building, 200 200 00:06:49,980 --> 00:06:51,460 this won't be a big problem for you 201 201 00:06:51,460 --> 00:06:52,560 because nobody else is going to be 202 202 00:06:52,560 --> 00:06:54,550 in the same general area as we are. 203 203 00:06:54,550 --> 00:06:56,440 But if you're in a crowded office building 204 204 00:06:56,440 --> 00:06:58,830 or a shopping mall or an apartment building, 205 205 00:06:58,830 --> 00:07:00,590 this can easily start to have a lot of 206 206 00:07:00,590 --> 00:07:01,960 different wireless networks operating 207 207 00:07:01,960 --> 00:07:04,790 on the same channels as ours in the same location. 208 208 00:07:04,790 --> 00:07:07,230 Now, when wireless access points and wireless clients 209 209 00:07:07,230 --> 00:07:08,560 are operating on the same channel 210 210 00:07:08,560 --> 00:07:09,640 and all of those things are in 211 211 00:07:09,640 --> 00:07:11,100 the same range of each other, 212 212 00:07:11,100 --> 00:07:13,700 they're going to begin to form a single broadcast domain, 213 213 00:07:13,700 --> 00:07:15,550 similar to an ethernet hub. 214 214 00:07:15,550 --> 00:07:17,740 All of the devices can hear each other's transmissions. 215 215 00:07:17,740 --> 00:07:20,210 And if any two devices transmit at the same time, 216 216 00:07:20,210 --> 00:07:23,230 their radio signals will collide and it becomes garbled, 217 217 00:07:23,230 --> 00:07:26,510 which results in data corruption or a complete frame loss. 218 218 00:07:26,510 --> 00:07:28,340 If there's an excessive amount of collisions, 219 219 00:07:28,340 --> 00:07:30,610 data will never be retransmitted successfully, 220 220 00:07:30,610 --> 00:07:33,620 and the wireless network could become unusable. 221 221 00:07:33,620 --> 00:07:37,370 So to avoid collisions 802.11 wireless devices use a 222 222 00:07:37,370 --> 00:07:39,030 listen before they speak approach 223 223 00:07:39,030 --> 00:07:40,900 when they're accessing the wireless medium, 224 224 00:07:40,900 --> 00:07:42,330 which is the radio frequency, 225 225 00:07:42,330 --> 00:07:46,610 following the CSMA CA or collision avoidance techniques. 226 226 00:07:46,610 --> 00:07:48,480 Now with this, devices are going to perform 227 227 00:07:48,480 --> 00:07:51,020 a clear channel assessment or CCA 228 228 00:07:51,020 --> 00:07:53,140 by first listening to see if another device 229 229 00:07:53,140 --> 00:07:55,150 is actively transmitting on the channel 230 230 00:07:55,150 --> 00:07:56,820 before they attempt to send their own frames 231 231 00:07:56,820 --> 00:07:58,490 on that given frequency. 232 232 00:07:58,490 --> 00:08:00,835 Now, when a device detects another transmission in progress, 233 233 00:08:00,835 --> 00:08:02,940 it's going to perform a random back-off 234 234 00:08:02,940 --> 00:08:05,210 for a short period of time after which 235 235 00:08:05,210 --> 00:08:07,310 it's going to perform another CCA check 236 236 00:08:07,310 --> 00:08:09,140 before it attempts to transmit. 237 237 00:08:09,140 --> 00:08:10,980 If the channel is clear after the check, 238 238 00:08:10,980 --> 00:08:12,830 that device will be able to access the channel 239 239 00:08:12,830 --> 00:08:14,220 and send some data. 240 240 00:08:14,220 --> 00:08:16,770 Now, as the number of devices needing to transmit frames 241 241 00:08:16,770 --> 00:08:18,520 starts increasing on a channel, 242 242 00:08:18,520 --> 00:08:20,480 this is going to cause congestion to occur 243 243 00:08:20,480 --> 00:08:21,820 to the point where devices can spend 244 244 00:08:21,820 --> 00:08:25,130 a lot more time waiting to be able to send something. 245 245 00:08:25,130 --> 00:08:26,530 This results in slower speeds, 246 246 00:08:26,530 --> 00:08:28,000 because devices have to wait longer 247 247 00:08:28,000 --> 00:08:29,640 before they can send their data. 248 248 00:08:29,640 --> 00:08:30,980 This is the negative effect 249 249 00:08:30,980 --> 00:08:32,770 of having high channel utilization 250 250 00:08:32,770 --> 00:08:34,170 and at least a slower throughput 251 251 00:08:34,170 --> 00:08:35,890 for our network devices. 252 252 00:08:35,890 --> 00:08:37,480 Now, how do we solve this problem 253 253 00:08:37,480 --> 00:08:39,390 of over channel utilization? 254 254 00:08:39,390 --> 00:08:40,880 Well, first we're going to start 255 255 00:08:40,880 --> 00:08:42,650 by conducting a site survey. 256 256 00:08:42,650 --> 00:08:45,190 Now a site survey also known as a wireless survey 257 257 00:08:45,190 --> 00:08:46,850 is the process of planning and designing 258 258 00:08:46,850 --> 00:08:49,070 a wireless network to provide a wireless solution 259 259 00:08:49,070 --> 00:08:51,030 that will deliver the required wireless coverage, 260 260 00:08:51,030 --> 00:08:53,920 the data rates, network capacity, roaming capability, 261 261 00:08:53,920 --> 00:08:57,090 and quality of service that your organization desires. 262 262 00:08:57,090 --> 00:08:58,360 As part of the wireless survey, 263 263 00:08:58,360 --> 00:09:01,570 you need to determine where each access point is located, 264 264 00:09:01,570 --> 00:09:03,331 what power level it's using to transmit 265 265 00:09:03,331 --> 00:09:06,430 by using its effective isotropic radiated power, 266 266 00:09:06,430 --> 00:09:09,220 or EIRP, the overlapping coverage areas 267 267 00:09:09,220 --> 00:09:10,560 for your wireless access points, 268 268 00:09:10,560 --> 00:09:13,070 and the other wireless access points in clients 269 269 00:09:13,070 --> 00:09:15,470 that may be operating in the same or general area 270 270 00:09:15,470 --> 00:09:16,870 or channels as you. 271 271 00:09:16,870 --> 00:09:19,140 Now by using this site survey information, 272 272 00:09:19,140 --> 00:09:21,110 you can determine if you need to change the channels 273 273 00:09:21,110 --> 00:09:24,170 you're using to a less busy, less utilized channel, 274 274 00:09:24,170 --> 00:09:26,250 or if you may need to upgrade your networks 275 275 00:09:26,250 --> 00:09:28,450 to a new frequency band altogether. 276 276 00:09:28,450 --> 00:09:30,220 After all, if you decide to upgrade 277 277 00:09:30,220 --> 00:09:33,770 to a wireless N, wireless AC or wireless AX network, 278 278 00:09:33,770 --> 00:09:35,930 and you start using the five gigahertz spectrum, 279 279 00:09:35,930 --> 00:09:38,450 this gives you 24 non-overlapping channels 280 280 00:09:38,450 --> 00:09:41,270 instead of the three in the 2.4 gigahertz spectrum. 281 281 00:09:41,270 --> 00:09:43,890 So there's going to be a lot less overall utilization 282 282 00:09:43,890 --> 00:09:47,420 on each of those 24 channels in the five gigahertz spectrum. 283 283 00:09:47,420 --> 00:09:48,850 By conducting a site survey, 284 284 00:09:48,850 --> 00:09:50,860 you can better understand the wireless environment 285 285 00:09:50,860 --> 00:09:52,290 in and around your networks. 286 286 00:09:52,290 --> 00:09:54,530 And this is going to allow you to configure your devices, 287 287 00:09:54,530 --> 00:09:56,250 to use the less utilized channels, 288 288 00:09:56,250 --> 00:09:58,760 ensure there's proper coverage for all of your work areas 289 289 00:09:58,760 --> 00:10:01,400 and ensure your wireless network is not being blocked 290 290 00:10:01,400 --> 00:10:03,530 or interfered with by physical obstacles 291 291 00:10:03,530 --> 00:10:04,980 within the building. 292 292 00:10:04,980 --> 00:10:06,360 Finally, we need to talk about 293 293 00:10:06,360 --> 00:10:08,800 wireless access point association times. 294 294 00:10:08,800 --> 00:10:10,730 Now when a wireless client attempts to connect 295 295 00:10:10,730 --> 00:10:14,410 to a wireless network, it goes through a seven step process. 296 296 00:10:14,410 --> 00:10:16,320 First, the wireless client is going to send 297 297 00:10:16,320 --> 00:10:19,900 a probe request to discover any 802.11 wireless networks 298 298 00:10:19,900 --> 00:10:21,980 in the general location that it's in. 299 299 00:10:21,980 --> 00:10:24,350 Essentially, it's going to send a broadcast message 300 300 00:10:24,350 --> 00:10:28,833 to the BSS ID of F F F F F F F F F F F F. 301 301 00:10:30,110 --> 00:10:31,813 And all the access points in that area 302 302 00:10:31,813 --> 00:10:33,610 that are using the same frequency, 303 303 00:10:33,610 --> 00:10:35,448 either 2.4 gigahertz or five gigahertz 304 304 00:10:35,448 --> 00:10:37,860 will respond to that client. 305 305 00:10:37,860 --> 00:10:40,550 Second, any access points that receive this probe 306 306 00:10:40,550 --> 00:10:42,700 will check to see if they can support the data rate 307 307 00:10:42,700 --> 00:10:45,150 that the client is now requesting in that probe. 308 308 00:10:45,150 --> 00:10:47,910 For example, if I'm a wireless AC access point 309 309 00:10:47,910 --> 00:10:50,380 and you just requested to communicate using wireless B, 310 310 00:10:50,380 --> 00:10:51,790 I'm going to ignore your request 311 311 00:10:51,790 --> 00:10:53,570 because I'm operating at five gigahertz 312 312 00:10:53,570 --> 00:10:55,970 and you're operating at 2.4 gigahertz. 313 313 00:10:55,970 --> 00:10:58,230 But if we both support wireless N 314 314 00:10:58,230 --> 00:11:00,020 then I can respond with a probe response 315 315 00:11:00,020 --> 00:11:03,200 that provides my SS ID, my supported data rates, 316 316 00:11:03,200 --> 00:11:05,630 my encryption type, if I'm using wireless security, 317 317 00:11:05,630 --> 00:11:08,820 and other capabilities of my particular access point. 318 318 00:11:08,820 --> 00:11:10,420 Third, our wireless client 319 319 00:11:10,420 --> 00:11:13,770 will then send a low level 802.11 authentication frame 320 320 00:11:13,770 --> 00:11:14,910 to the access point, 321 321 00:11:14,910 --> 00:11:16,920 and this will begin the authentication handshake 322 322 00:11:16,920 --> 00:11:19,470 between my client and the access point. 323 323 00:11:19,470 --> 00:11:21,400 Fourth, the access point receives 324 324 00:11:21,400 --> 00:11:23,210 this authentication frame and responds 325 325 00:11:23,210 --> 00:11:25,620 with an acknowledgement to continue the handshake. 326 326 00:11:25,620 --> 00:11:27,960 If the wireless access point receives anything other 327 327 00:11:27,960 --> 00:11:29,970 than an authentication or a probe request 328 328 00:11:29,970 --> 00:11:31,220 from this client, though, 329 329 00:11:31,220 --> 00:11:33,400 it's going to send a de-authentication frame 330 330 00:11:33,400 --> 00:11:35,520 and break the communication with this client 331 331 00:11:35,520 --> 00:11:37,360 because this client is not yet part 332 332 00:11:37,360 --> 00:11:39,250 of my authenticated network. 333 333 00:11:39,250 --> 00:11:41,310 Fifth, the wireless client is going to choose 334 334 00:11:41,310 --> 00:11:43,270 the access point it wants to associate with 335 335 00:11:43,270 --> 00:11:45,080 and sends an association request 336 336 00:11:45,080 --> 00:11:47,860 using the encryption and 802.11 capabilities 337 337 00:11:47,860 --> 00:11:50,190 that are supported by that access point. 338 338 00:11:50,190 --> 00:11:52,400 Sixth, the access point is going to process 339 339 00:11:52,400 --> 00:11:53,690 the association request, 340 340 00:11:53,690 --> 00:11:56,550 if the information sent matches its own capabilities, 341 341 00:11:56,550 --> 00:11:59,120 and then an association ID is being created 342 342 00:11:59,120 --> 00:12:01,830 for this wireless client and this access point, 343 343 00:12:01,830 --> 00:12:03,400 and the access point is going to respond 344 344 00:12:03,400 --> 00:12:06,040 with an association response of success. 345 345 00:12:06,040 --> 00:12:08,490 This way, the client knows it is now fully connected 346 346 00:12:08,490 --> 00:12:10,350 to this wireless access point. 347 347 00:12:10,350 --> 00:12:12,830 Seventh, now that the client is fully connected 348 348 00:12:12,830 --> 00:12:15,500 and associated, it can begin to connect any data transfer 349 349 00:12:15,500 --> 00:12:17,540 it needs to, and utilize the wireless network 350 350 00:12:17,540 --> 00:12:19,370 and its associated devices. 351 351 00:12:19,370 --> 00:12:21,770 Now, that's how everything is supposed to operate, 352 352 00:12:21,770 --> 00:12:24,170 but sometimes you're going to see a wireless network 353 353 00:12:24,170 --> 00:12:26,080 that has a really long association time 354 354 00:12:26,080 --> 00:12:27,720 for an end user's client. 355 355 00:12:27,720 --> 00:12:30,100 This is because the client has to scan the airwaves, 356 356 00:12:30,100 --> 00:12:32,350 find the access points it might want to connect to, 357 357 00:12:32,350 --> 00:12:33,780 request the association, 358 358 00:12:33,780 --> 00:12:35,240 authenticate to the access point, 359 359 00:12:35,240 --> 00:12:38,510 and then contact the DHCP server to get an IP address, 360 360 00:12:38,510 --> 00:12:40,750 prior to being able to actually use that wireless network 361 361 00:12:40,750 --> 00:12:42,750 connection that we just established. 362 362 00:12:42,750 --> 00:12:44,600 This process can take just a few seconds 363 363 00:12:44,600 --> 00:12:46,310 in a not heavily loaded network, 364 364 00:12:46,310 --> 00:12:48,320 but it can take up to 30 to 60 seconds 365 365 00:12:48,320 --> 00:12:49,810 if you have a busier network. 366 366 00:12:49,810 --> 00:12:51,680 To speed up the association process, 367 367 00:12:51,680 --> 00:12:54,360 clients should be located in a high signal strength area. 368 368 00:12:54,360 --> 00:12:57,420 Those with the highest RSSI during the association process 369 369 00:12:57,420 --> 00:12:59,170 are going to give us a stronger strength 370 370 00:12:59,170 --> 00:13:01,270 and that's going to drastically reduce the wait time 371 371 00:13:01,270 --> 00:13:02,533 during this association.