-: In the last lesson, we just finished talking about DSL. 2 2
And I mentioned that there was a decline in popularity, 3 3
because cable modems and fiber modems started taking over. 4 4
So let's talk about cable modems for a moment. 5 5
Cable modems use the cable TV network, 6 6
which is made up of a hybrid fiber-coax solution, 7 7
known as HFC, 8 8
and this is the type of distribution network it has. 9 9
If you see the term HFC on the exam, 10 10
remember we're talking about cable modems here. 11 11
Now cable TV can write on top of it, 12 12
but so can our internet signals. 13 13
And so this mixture of coax and fiber cables 14 14
made it very fast. 15 15
They're specific frequency ranges 16 16
that are used for upstream and downstream transmissions, 17 17
as determined by a standard called DOCSIS, 18 18
which is Data-Over-Cable Service Interface Specification. 19 19
D-O-C-S-I-S. 20 20
So again, for the exam, 21 21
anytime you see HFC or D-O-C-S-I-S, 22 22
I want you to think about the answer 23 23
being something to do with cable modems. 24 24
Now, upstream, these use between five and 42 megahertz, 25 25
and downstream, they use between 50 and 860 megahertz. 26 26
Don't worry about those frequencies for the exam, 27 27
just remember the terms HFC and DOCSIS 28 28
are associated with cable modems, and you'll do fine. 29 29
Now, these systems can transmit and receive 30 30
over the current cable TV infrastructure, 31 31
which is already rolled out to most of America 32 32
and many other places worldwide. 33 33
And this made it a very quick sell to get cable modems 34 34
into the marketplace, 35 35
and they offered increased speed over DSL, 36 36
which made them even more popular. 37 37
Now, the next one we have, 38 38
is what's known as a satellite modem. 39 39
I've already mentioned satellites a little bit, 40 40
but I want to go a little bit more in-depth here, 41 41
because now we're talking about the technology itself 42 42
and not just the concept. 43 43
Satellite modems are used in remote, rural, 44 44
or disconnected locations. 45 45
Like if you're out to sea or you're in some farmland 46 46
in the middle of nowhere. 47 47
Now satellite modems provide us with relatively fast speeds, 48 48
like a DSL modem, 49 49
but not nearly as speeds of cable or fiber. 50 50
Now, the bad thing about satellite, 51 51
is that it provides us with very low usage caps. 52 52
Now, what I mean by that is, 53 53
if you're going to do a lot of streaming video services, 54 54
satellite is probably not the right answer for you, 55 55
because they may only let you have 56 56
five or 10 gigabytes per month of service, 57 57
and after that, you'd end up having to pay a lot more money. 58 58
If you end up watching a couple hours of Netflix, 59 59
you can quickly use a gigabyte or more of data, 60 60
and so this is a concern. 61 61
Now, there are some other issues with using satellite 62 62
that you have to be concerned with, 63 63
and one of them is the delay. 64 64
You have to realize that when you're going from up 65 65
to a satellite and down, 66 66
you're not just going across the country, 67 67
but you're actually going all the way out to space. 68 68
And if you have your satellite terminal 69 69
going all the way up to space, 70 70
and then all the way down to a ground station, 71 71
that adds up time. 72 72
Every time the satellite has to go up and down 73 73
from the satellite, 74 74
there's about a quarter of a second right off the bat delay. 75 75
So if you're trying to do something like 76 76
Voice over IP over satellite, 77 77
you're going to have this kind of echo-y sound, 78 78
because there's a delay in your voice. 79 79
It's like, hey, hey, 80 80
how, how, 81 81
are, are, 82 82
you, you? 83 83
It just gets really annoying. 84 84
Well, when you have that connectivity 85 85
versus no connectivity, it really is better than nothing. 86 86
But if you have another choice, 87 87
you probably want to choose something other than satellite. 88 88
Now, the other issue with satellite 89 89
is that there's weather issues too. 90 90
Anytime you have a big thunderstorm or a snowstorm, 91 91
that's putting interference 92 92
between your satellite dish and the satellite in space, 93 93
and this can cause issues and cause loss of service. 94 94
Also, if the ground station that you're connecting to, 95 95
has rain delays in their area or snow in their area, 96 96
that can actually cause service issues for you, 97 97
even if you have good weather in your area. 98 98
Now, the next one we need to talk about, 99 99
is what's known as the Plain Old Telephone Service or POTS. 100 100
POTS runs on what's called the PSTN, 101 101
or the public switched telephone network. 102 102
This consists of all the telephone carriers 103 103
from around the globe. 104 104
I can make a phone call from my house to my neighbor's house 105 105
or from my house to the other side of the world, 106 106
and it's still running on the PSTN using POTS service. 107 107
This is what we call analog phone service, 108 108
and it's all based on beeps and bops. 109 109
Now these analog connections can be voiced when I'm talking, 110 110
or it can be data that's being converted from ones and zeros 111 111
into a modulation of that sound using those beeps and bops. 112 112
This is how PSTN works. 113 113
Now, these are often called dial-up connections 114 114
or POTS connections. 115 115
Now, if you're an older person like me, 116 116
you might've used a dial-up modem back in the day. 117 117
You might remember the dial-up modems 118 118
have a maximum bandwidth of 53.3 kilobits per second, 119 119
which means they're really slow. 120 120
The reason for this, 121 121
is the phone system worked on these T1 channels, 122 122
and each one is only 64 kilobits per second. 123 123
And so essentially, 124 124
POTS ran over the same technology as a T1 connection, 125 125
or 1/24th of a T1 connection. 126 126
So when you made a phone call, you only had access to 64k, 127 127
and part of that was being eaten up by overhead, 128 128
so you got a maximum of 53.3 kilobits per second. 129 129
Now I just gave you a lot of information about dial-up, 130 130
and you really don't need to memorize all the specifics 131 131
because honestly, most people don't use dial-up anymore. 132 132
In fact, if you're still running dial-up, 133 133
you're not watching this video, 134 134
because it's just not fast enough, right? 135 135
It's too darn slow for anything you really want to do 136 136
on the real internet nowadays. 137 137
But you may find it in some very specialized, 138 138
unique situations, 139 139
or what we call legacy systems in your network. 140 140
Now legacy system means it's an old system, 141 141
but we still need it for some critical function, 142 142
and it just can't work on the internet itself, 143 143
so it still relies on something like a dial-up modem. 144 144
Now for the home and office user, 145 145
you're just not going to find these dial-up modems anymore, 146 146
because most people just don't use them. 147 147
You may find something known as ISDN though, 148 148
which is the Integrated Service Digital Network. 149 149
Now, I mentioned this briefly when we talked about 150 150
circuit switch technologies, 151 151
because ISDN is a great example 152 152
of a circuit switch technology. 153 153
It supports taking multiple 64k bearer channels 154 154
and putting them together. 155 155
So it works a lot like dial-up, 156 156
but you could bind those channels together 157 157
and get speeds up to a T1 connection. 158 158
Now, again, this is an older technology, 159 159
designed to carry voice, video, or data 160 160
over these B channels, these bearer channels. 161 161
They also had D channels, which were data or delta channels, 162 162
that existed for signaling, 163 163
that was able to do control measures. 164 164
Now we're not going to go too in-depth into ISDN here, 165 165
because honestly, you're probably never going to run across one 166 166
in the real world here in 2020, 167 167
because most people have already moved to cable, or fiber, 168 168
or even a T1 connection. 169 169
But if you work for some organizations, 170 170
they may have some legacy thing out there 171 171
that still has an ISDN. 172 172
I actually ran into one about six months ago, 173 173
when I was doing some contracting. 174 174
So it is something you may come across, but not likely. 175 175
Now these again, were popular back in the late 90s. 176 176
And when we dealt with T1s, they work the same kind of way. 177 177
They had two different circuits, they had BRIs and PRIs. 178 178
BRIs are Basic Rate Interface, 179 179
and PRIs are Primary Rate Interface. 180 180
With the Basic Rate Interface for ISDN, 181 181
it would give you 128 kilobits per second 182 182
by tying two B channels together. 183 183
PRI, on the other hand, would give you about T1 speeds 184 184
by taking 23 B channels, putting them together, 185 185
and then using one as a data channel. 186 186
Now, the next technology we want to talk about, 187 187
is frame relay. 188 188
And this is losing market share as well, 189 189
due to the cheapness of cable and DSL. 190 190
Frame relay was where we were able to use virtual circuits. 191 191
If I had two branch offices and a headquarters, 192 192
I could connect them through point-to-point, 193 193
or point to multi-point as shown in this diagram. 194 194
Now, this is a point to multi-point connection, 195 195
and they were low-cost and widely available. 196 196
It provided always on or on-demand, 197 197
depending on how much you wanted to pay, 198 198
and these were considered a Layer 2 technology. 199 199
Now frame relay was really great for a long time, 200 200
but because of the lower cost of fiber, cable, and DSL, 201 201
most small business environments switched away 202 202
from frame relay and into one of those solutions instead. 203 203
Next, we have SONET, 204 204
and SONET is a Synchronous Optical Network. 205 205
It is a Layer 1 technology that uses fiber as its media. 206 206
Now, this is fast, really, really fast. 207 207
Now, when we talk about T1 connections, 208 208
we were talking about 1.5 megabits per second. 209 209
When we talked about a T3 connection, 210 210
we were talking about 45 megabits per second. 211 211
When I'm talking about SONET, 212 212
I'm talking about speeds of 155 megabits per second 213 213
to start with, 214 214
and then they go up 215 215
all the way to 10 gigabits per second or more. 216 216
SONET uses Transport Layer 2 encryption, 217 217
like ATM or Asynchronous Transfer Mode, 218 218
to do all the shaping of those frames 219 219
and really send stuff around 220 220
really, really fast, 221 221
because it's all fiber, 222 222
and it can go really long distances too, 223 223
of 20 to 250 kilometers or more. 224 224
Now the physical topology of this, 225 225
can be either a bus or a ring. 226 226
I've seen this implemented as what's known as a FDDI ring, 227 227
a fiber distribution ring, 228 228
which has two counter-rotating rings for redundancy. 229 229
ATM then rides on top of SONET, 230 230
and this is the Layer 2 way of shaping those frames 231 231
and sending them over the network, 232 232
much like we'd use Ethernet over copper cabling. 233 233
Now this is going to use two different things. 234 234
We can either have the permanent virtual circuits or PVCs, 235 235
or we can use switched virtual circuits, SVCs. 236 236
It's like frame relay, 237 237
except all the frames have a fixed-length, 238 238
and we call these cells, 239 239
and we can move them around really, really fast 240 240
because they're all fixed rate. 241 241
And as we move them around, 242 242
it's known as a protocol data unit. 243 243
Now because they're all fixed-length, 244 244
and they have the shortened header, 245 245
which is only five bytes in size, 246 246
this is going to save us a lot of time 247 247
and makes things much, much faster. 248 248
As you can see here on the diagram, 249 249
I broke out what an ATM header looks like for you. 250 250
Again, you don't have to memorize 251 251
all of these pieces and parts, 252 252
but do realize that ATM has a fixed header of five bytes, 253 253
and a payload of 48 bytes, 254 254
giving us a 53-byte cell for ATM, 255 255
and because it's the same each and every time, 256 256
it's really easy and really fast for us to move it around. 257 257
When we look at ATM virtual circuits, 258 258
they are designated in two different ways. 259 259
The user-network interface or UNI, 260 260
is what connects the ATM switches to the end points. 261 261
Then we have these network node interfaces, 262 262
and we connect the ATM switches together using those. 263 263
Again, you don't need to know this in too much depth, 264 264
except to know that if you see the terms ATM, 265 265
when it comes to testing day, 266 266
you need to realize that deals with fiber 267 267
and SONET networks. 268 268
The next one we have is what's known as MPLS, 269 269
or Multiprotocol Label Switching. 270 270
Now Multiprotocol Label Switching, 271 271
is going to support multiple protocols on the same network. 272 272
MPLS is not something you're going to use in your networks, 273 273
but it is something that your service provider uses 274 274
as the backbone for their networks. 275 275
This can support frame relay and ATM 276 276
on the same MPLS backbone, 277 277
and because this is all using switching and labeling 278 278
to transfer things around, 279 279
it is extremely fast and works really well 280 280
for backbone networks. 281 281
This allows traffic to be dynamically routed 282 282
based on low conditions and path availability. 283 283
Now, using this label switching, it is much more efficient 284 284
than standard logical Layer 3 IP addressing. 285 285
And so it makes really quick work 286 286
of all the routing and switching for us, 287 287
as we take things around the globe. 288 288
Again, this is used by backbone service providers, 289 289
not us in our own networks. 290 290
If you're working for a large telecom company, 291 291
you may run into MPLS, 292 292
but in your own small office, or home office, 293 293
or medium-sized business, you're not going to see MPLS. 294 294
MPLS is something the customer 295 295
doesn't even know that exists half the time. 296 296
It all happens behind the scenes at the service provider. 297 297
Now, the last one we want to talk about is DMVPN. 298 298
And this is the Dynamic Multipoint Virtual Private Network. 299 299
This allows the internet itself, 300 300
to be used as a WAN connection for us 301 301
between two different sites and use it 302 302
for secure communication. 303 303
You can create a VPN tunnel 304 304
with authentication and encryption, 305 305
so the user on the unsecured network 306 306
can't even see what you're doing. 307 307
For example, if I have a couple of regional offices, 308 308
I can connect them together over a VPN, 309 309
instead of buying dedicated point-to-point connections. 310 310
This allows me to buy maybe a cable modem or a DSL 311 311
in that regional office for 50 or 100 dollars a month, 312 312
instead of having to buy a dedicated T1 connection 313 313
between my head office and my regional office, 314 314
that can cost me thousands. 315 315
This saves me a lot of time, and a lot of money, 316 316
and I can connect remote users with low cost, 317 317
without dedicated or leased line access. 318 318
Now we're going to talk a lot more about VPNs 319 319
in their own lecture, 320 320
when we get into the network security section 321 321
later on in the course. 322 322
Now, I also want to talk about data rates here. 323 323
When we talk about data rates, 324 324
there are a couple of things that you just have to memorize. 325 325
And so this chart is one that you should add to your notes. 326 326
Bandwidth can be measured in kilobits per second, 327 327
megabits per second, or gigabits per second. 328 328
ATM and SONET are measured by optical carriers, 329 329
known as OC connections. 330 330
They start out with OC-1, 331 331
which is 51.84 megabits per second, 332 332
and everything else becomes a multiple of it. 333 333
So if you have an OC-3, that is three times 51.84. 334 334
If you're using an OC-12, it's 12 times 51.84. 335 335
And so here on the chart, 336 336
I'm going to show you a couple that you need to memorize. 337 337
First, frame relay goes from 56 kilobits per second, 338 338
which is a dial-up connection, 339 339
all the way up to a T1 connection 340 340
of 1.5 megabits per second. 341 341
A T1 connection is 1.5 megabits per second. 342 342
A T3 is 45 megabits per second. 343 343
An E1 and an E3 are shown here on the board as well, 344 344
and both of those are European standards. 345 345
It's two megabits connection for an E1, 346 346
and 34 megabit connection for an E3. 347 347
The last two we have are both fiber networks. 348 348
ATM, which can be anywhere from an OC-3 up to an OC-12, 349 349
and SONET, which can use anything from an OC-1, 350 350
all the way up to an OC-3072, 351 351
which is 160 gigabits per second, 352 352
which is really quite fast. 353 353
Now, do you have to memorize 354 354
all the decimal points like this, 355 355
the 1.544 for a T1 and things like that? 356 356
As I said before, no. 357 357
Remember, this is a multiple choice exam. 358 358
If you see one that looks close, 359 359
that's going to be the right answer. 360 360
So put this in your notes, 361 361
look it over a couple of times before test day, 362 362
and you should do just fine 363 363
when you get these questions on the exam.