-: Wide Area Network Technologies. 2 2
Now, I'm going to break this lesson into two parts 3 3
because there are so many technologies 4 4
that we have to talk about, 5 5
and so, it's going to be this lesson and the next one. 6 6
Now, the first one we want to talk about 7 7
is a dedicated leased line. 8 8
I mentioned this in the last lesson. 9 9
This is a point-to-point connection between two sites, 10 10
and you're going to get all the bandwidth all of the time 11 11
which is really good. 12 12
If you see something like a T1, an E1, a T3, 13 13
or an E3, or other dedicated circuits, 14 14
that's what we're talking about. 15 15
Now, when you get this digital circuit, 16 16
it's going to be measured in 64 kilobit per second channels 17 17
called a DS0, or a Digital Signal 0. 18 18
Based on the type of connection you buy, for example, 19 19
you're going to get more or less of these DS0s. 20 20
So, if you buy a T1, you're going to get 24 21 21
of these 64-kilobit channels. 22 22
Now, on your location, 23 23
you're going to get a device that looks like a modem, 24 24
and this is actually called a CSU/DSU, 25 25
a channel service unit/data service unit. 26 26
It's used to terminate the digital signal 27 27
in your location from the phone company, 28 28
and then, you tie that into your router 29 29
to be able to connect it to your network. 30 30
Now, for exam day, I want you to remember 31 31
T1s and E1s are dedicated leased lines 32 32
and they use CSUs and DSUs to connect to your network. 33 33
Now, some students say, "Why do I have to learn this? 34 34
It's really old. 35 35
Nobody uses them anymore." 36 36
Well, there's still a lot of people that do use these, 37 37
and as a network technician, 38 38
you may come across a CSU/DSU in the field. 39 39
Just last year, I came across a couple of them 40 40
as I was doing some consulting work. 41 41
So they do still exist even though most people 42 42
are migrating away from them. 43 43
Now, what are some examples of digital signal levels? 44 44
Well, this is going to depend 45 45
on the carrier signal you're using. 46 46
If you're using something like a T1, 47 47
or a T3, or an E1, or an E3, 48 48
then, you're going to have an associated signal with it. 49 49
A T1 is going to be a DS1. 50 50
A T3 is going to be a DS3. 51 51
Now, E1 and E3, those are European standards, 52 52
where T1 and T3 are American standards. 53 53
Now, these don't fall into this digital signaling measurement 54 54
when you're dealing with those European standards, though. 55 55
You're going to see the number of channels 56 56
that you're going to get, 57 57
and how many voice channels or data channels 58 58
of 64 kilobits each that you're going to have 59 59
and the speed is right there. 60 60
Now, what from this chart should you memorize? 61 61
Well, you should know that a T1 and a T3 62 62
and an E1 speed are important to know. 63 63
So, if you remember a 1.544 megabit per second, that is a T1. 64 64
44.736 megabits per second, or about 45 megabits per second, 65 65
is a T3. 66 66
And if you have an E1, 67 67
that's going to be a two-megabit connection. 68 68
Now, if you remember that, you're going to do fine on test day. 69 69
And remember, this is a multiple choice exam, 70 70
so, if you remember 1.5-ish, 45-ish, and two-ish, 71 71
that's going to be close enough to get you the right answer. 72 72
Next, we have metro ethernet. 73 73
Now, service providers are beginning to get away 74 74
from these T1s, and E1s, and T3 connections 75 75
because those CSU/DSUs are just 76 76
kind of cumbersome to work with, 77 77
and it's a really old technology. 78 78
So, they've been starting to migrate 79 79
towards what's called metro ethernet. 80 80
This is where the service provider 81 81
gives you an ethernet jack in your building, 82 82
and you simply plug it into your router. 83 83
Now, these are less expensive and much more common 84 84
than using a specialized serial port 85 85
like you'd see in a CSU and DSU. 86 86
The technology used by the service provider 87 87
really doesn't matter to me as a customer, right? 88 88
All I care about is the fact that I have this ethernet jack 89 89
that I can plug into my router, 90 90
and as long as I can do that, 91 91
I don't really care what's behind it 92 92
and I let the service provider worry about it. 93 93
So, give me something as simple as an RJ45, 94 94
I plug it in my router, and I get online. 95 95
It's a win for me as a customer, 96 96
and it allows the service provider 97 97
to change the backbone anytime they want 98 98
and I don't even have to see it. 99 99
That's one of the big benefits of metro ethernet. 100 100
Next, we have a PPP connection, 101 101
which is the Point-to-Point Protocol. 102 102
This is commonly used as a Layer 2 protocol 103 103
that we use on top of one of these dedicated leased lines. 104 104
So, whether we're using metro ethernet, 105 105
a T1, an E1, T3, an E3, a cable modem, 106 106
a DSL, any of these things, 107 107
we can actually use these other 108 108
different protocols on top of it, 109 109
and PPP is what we use at Layer 2. 110 110
Then, we can use other protocols at Layer 3, 111 111
like IPX or IP, on top of them. 112 112
Now, most of the time in your networks, 113 113
you're probably going to be using IP 114 114
because TCP/IP is what we all use these days, 115 115
but each Layer 3 protocol could run 116 116
its own instance of PPP under the Link Control Protocol, 117 117
which manages the link and does some basic 118 118
error-checking for you. 119 119
So, I can run different levels and different IP or IPXs 120 120
over the same connection. 121 121
Now, this is also going to do what we call 122 122
a multilink interface for you, 123 123
and that will allow multiple physical connections 124 124
to be bounded together 125 125
to give you a single, logical interface. 126 126
So, much like I could do link aggregation in my switches, 127 127
I could do the same thing where I buy two or three T1s, 128 128
bind them together, and that will give me more speed. 129 129
So, a single T1 is about 1.5 megabits per second. 130 130
If I buy three of them, I have 4.5 megabits per second. 131 131
And I can put them all together using this aggregation, 132 132
and bind them all together 133 133
under a single, logical interface. 134 134
It'll also allow me to do looped link detection 135 135
to find any kind of errors that I have. 136 136
It also allows me to do error detection 137 137
by checking my frames 138 138
and perform basic authentication over the link 139 139
to make sure I'm authorized to use 140 140
this point-to-point connection. 141 141
These are all some of the benefits of PPP. 142 142
Now, the way it does this is with three different mechanisms, 143 143
depending on which one you're going to choose. 144 144
Now, the authentication can be done using PAP, 145 145
which is the Password Authentication Protocol. 146 146
You could also be using the Challenge-Handshake 147 147
Authentication Protocol, or CHAP. 148 148
Or you could be using Microsoft CHAP, which is their version 149 149
of the Challenge-Handshake Authentication Protocol. 150 150
Now, because Microsoft seems to not follow 151 151
the standards everybody else does, 152 152
they make up their own, and this is known as MS-CHAP. 153 153
Now, I like to say a little tongue-in-cheek about Microsoft 154 154
but Microsoft actually made a better implementation 155 155
of the old CHAP protocol, 156 156
which is why they have MS-CHAP, instead. 157 157
Now, when we talk about PAP, how does it work? 158 158
Well, PAP performs a one-way authentication 159 159
between the client and the server. 160 160
On my basic diagram, 161 161
you're going to see I have a client on one side 162 162
and a server right around the other. 163 163
Now, the credentials are sent in the clear, 164 164
from the client to the server. 165 165
Basically it says, "Here's my username and my password." 166 166
The server then comes back and says, 167 167
"I acknowledge it and I let you in." 168 168
Now, the bad thing about PAP 169 169
is that it was sent in clear-text, 170 170
which means anybody on that network 171 171
could read the authentication and steal it from you. 172 172
So, there had to be a better way, 173 173
and that's where CHAP came in. 174 174
CHAP is the Challenge-Handshake Authentication Protocol, 175 175
and it performs a one-way authentication 176 176
using a three-way handshake. 177 177
Essentially, when you want to connect to a router, 178 178
in this case the server's router, 179 179
it starts doing a challenge. 180 180
It essentially says, "Hey, who are you?" 181 181
and then the client says, "Well, I'm this person, 182 182
and here's my username and password." 183 183
And then the router checks the hash credentials 184 184
sent as the username and password, 185 185
and if that matches its stored version in the server, 186 186
it's going to send a success or failure message. 187 187
The benefit of this is that there was no password sent 188 188
in clear-text over the network. 189 189
Instead, it just sent a hash of that credential. 190 190
Now, Microsoft server does essentially the same thing 191 191
except there's also a two-way authentication here, 192 192
so, the client has to verify the server 193 193
and the server verifies the client. 194 194
For the exam, I want you to remember 195 195
that PAP is sent in the clear, 196 196
which is a huge security risk. 197 197
CHAP and Microsoft CHAP are actually 198 198
going to have the credentials hashed first, 199 199
and they're going to make it a more secure way of doing PAP, 200 200
with Microsoft CHAP being the most secure. 201 201
Now, the next thing we need to talk about 202 202
is PPP over ethernet, 203 203
or Point-to-Point Protocol over ethernet. 204 204
This was commonly used with DSL modems, 205 205
and it actually took your PPP protocol 206 206
that we would use over a T1 connection 207 207
and encapsulates those with frames 208 208
so it can use it over ethernet at layer two. 209 209
Now, if you're using metro ethernet, 210 210
this is likely what you're going to be using, as well. 211 211
This allows authentication to occur over ethernet, 212 212
using something like PAP, CHAP, or MS-CHAP. 213 213
Next, we have DSL which is a digital subscriber line. 214 214
Now, when I first started building networks 215 215
back in the late 1990s and early 2000s, 216 216
DSL was all the rage. 217 217
It was everywhere because it was a really inexpensive way 218 218
to get high-speed data to our end users, 219 219
and small offices, and home offices. 220 220
Now, instead of having to pay for a T1 connection, 221 221
which could cost you 1,000 or $2,000 a month, 222 222
you could actually go ahead and get a DSL connection 223 223
for 50 or $100 a month. 224 224
Now, there is three different types of DSL. 225 225
You have ADSL, SDSL, and VDSL. 226 226
ADSL is Asymmetric DSL. 227 227
That means there's a different speed 228 228
on the download versus the upload. 229 229
The maximum download speed 230 230
was about eight megabits per second 231 231
according to the current textbooks, 232 232
although there were some that were getting 233 233
a little bit faster than that. 234 234
The upload speed was equivalent to a T1, 235 235
at about 1.544 megabits per second. 236 236
So, I have eight megs down, one and a half up. 237 237
Now, why would it be okay 238 238
to have different uploads and download speeds? 239 239
Well, this went back to the 80/20 rule. 240 240
When you're online, do you upload more or download more? 241 241
If you're like most people, 242 242
you download a lot more than you upload. 243 243
For example, when you're watching this video, 244 244
you selected the video with your mouse, 245 245
and you told the server what you wanted to watch. 246 246
That may have been just a couple of kilobits in size. 247 247
Then the video sent you back 100, 248 248
or 200, or 300 megabytes in size, 249 249
and it's a really large file 250 250
and you're downloading all of that. 251 251
So, your upload was very, very small, 252 252
but your download was a lot, 253 253
and for most users, they upload very little, 254 254
but they download a lot of information. 255 255
And so, ADSL maximizes the download 256 256
and minimizes your uploads. 257 257
Now SDSL, or Symmetric DSL, works just like a T1. 258 258
You'd have an equal upload and download speed. 259 259
The speeds are much slower here for symmetric, 260 260
but they were dedicated access 261 261
so you're pretty much guaranteed 262 262
to get that speed all of the time. 263 263
With ADSL, if there is a lot of people online at the time, 264 264
it could slow down your speeds. 265 265
Now, ADSL is very popular with home users, 266 266
and it started getting a lot more funding, 267 267
and because of that, ADSL speeds increased quickly 268 268
and got into those one and a half megabits per second, 269 269
and then four megabits per second, 270 270
and then eight megabits per second, 271 271
and they kept going up from there. 272 272
When they first came out, all of this was very slow. 273 273
We were talking about DSL speeds 274 274
of 256 kilobits per second, or half a meg per second. 275 275
As advancements in technology went though, 276 276
they kept moving more and more towards ADSL, 277 277
and most people abandoned the symmetric DSL. 278 278
Now, the last type of DSL we have 279 279
is known as the Very High Bit-Rate DSL. 280 280
This is where you could get very, very high speeds. 281 281
In fact, you could have downloads 282 282
as high as 50 megabits per second or more 283 283
and uploads over 10 megabits per second or more. 284 284
The big limitation here though 285 285
was your distance from what's known as the DSLAM. 286 286
Now, what is a DSLAM? 287 287
Well, this is the point of presence 288 288
that's owned by the telephone company. 289 289
With Variable DSL, you had to be within 4,000 feet 290 290
from that DSLAM, which is less than a mile. 291 291
Now, not all home users or offices could get VDSL 292 292
because most of them were within 18,000 feet, 293 293
and if you're within 18,000 feet, you could get ADSL. 294 294
But, if you are lucky and you're within 4,000 feet, 295 295
you could then use VDSL and get those higher speeds. 296 296
Again, because DSL started declining 297 297
in popularity in recent years 298 298
as more people moved towards cable and fiber, 299 299
that's what ended up happening. 300 300
And so, DSL didn't get a lot more DSLAMS put in, 301 301
and it ended up fading away 302 302
as we started moving towards cable and fiber, 303 303
which we're going to talk about in the next lesson.