-: Ethernet fundamentals. 2 2
In this section of the course, 3 3
we're going to cover Layer 2 of the OSI Model 4 4
in much more depth by digging into Ethernet fundamentals. 5 5
As we go through this section, 6 6
we're going to be touching on domain one, 7 7
networking fundamentals, 8 8
domain two, network implementations, 9 9
domain four, network security, 10 10
and domain five, network troubleshooting. 11 11
We're going to cover a lot of stuff 12 12
across a lot of domains here. 13 13
Now we're going to cover objectives 1.3, 2.1, 2.3, 14 14
4.4, and 5.5. 15 15
Objective 1.3, is to summarize the types of cables 16 16
and connectors, 17 17
and explain which is the appropriate type for a solution, 18 18
as we talk about our Ethernet standards. 19 19
Objective 2.1, is going to be to compare and contrast 20 20
various devices, their features, 21 21
and their appropriate placement on the network. 22 22
Objective 2.3, is given a scenario, 23 23
configure and deploy common Ethernet switching features. 24 24
And objective 4.4, is to compare and contrast 25 25
remote access methods and security implementations. 26 26
Finally, objective 5.5 is given a scenario, 27 27
troubleshoot general networking issues. 28 28
So without further delay, let's dive right into 29 29
Ethernet fundamentals, and I'm going to warn you, 30 30
this is a bit of a longer video, 31 31
because there's a lot of stuff we need to know. 32 32
Now in early computer networks, 33 33
there were so many different networking technologies 34 34
out there, and each of them was competing 35 35
for a piece in the market share. 36 36
There wasn't much standardization 37 37
among the different types either, 38 38
and so if you were using Ethernet, 39 39
it didn't talk with other types of networks. 40 40
Now, when I first started working with computer networks, 41 41
we had lots of different things out there, 42 42
including Ethernet, Token Bus, 43 43
Token Ring, Fiber Distributed Data Interface or FDDI, 44 44
Local Talk, Apple Talk, as well as others 45 45
that were all fighting to be the dominant market leader. 46 46
Well, there was one clear winner in these Layer 2 wars, 47 47
and that was Ethernet for our local area networks. 48 48
In this entire section of the course, 49 49
we're going to focus specifically on Ethernet, 50 50
because it's just that important. 51 51
Now Ethernet has gotten extremely popular, 52 52
so much so that if you don't understand Ethernet, 53 53
you really don't understand the way 54 54
today's modern networks operate. 55 55
Ethernet has been with us a long time. 56 56
Originally, it was run over coaxial cables, 57 57
using BNC connectors and vampire taps. 58 58
And these networks were called 10BASE2 and 10BASE5 59 59
Ethernet networks, also nicknamed ThinNet and ThickNet, 60 60
because of the relative size of their coaxial cables. 61 61
Now, the great thing about these networks 62 62
is they could cover a really long distance, 63 63
up to 200 meters with the 10BASE2 networks, 64 64
and 500 meters with a 10BASE5 networks. 65 65
Now for the Network Plus exam, 66 66
you don't need to memorize anything about 10BASE2 67 67
or 10BASE5 networks anymore, 68 68
because they're old and antiquated and likely, 69 69
you're never going to see them. 70 70
Now, the only reason I'm even talking about them, 71 71
is because I want you to understand 72 72
where Ethernet came from, 73 73
because these were the first networks that used Ethernet 74 74
and it was introduced in the early 1980s. 75 75
Over time, though, 76 76
we migrate to what is known as 10BASE-T Ethernet, 77 77
and Ethernet became associated 78 78
with this twisted pair cabling 79 79
that could run 10 megabit per second networks over it. 80 80
Now this twisted pair cabling, 81 81
is known as Cat 3 or Category 3 wiring. 82 82
These twisted pairs could be unshielded or shielded, 83 83
and they were cheaper and easier to use 84 84
than the older 10BASE2 or 10BASE5 coaxial networks. 85 85
The only real disadvantage to the new 10BASE-T network, 86 86
was it could only cover distance of up to 100 meters, 87 87
before they need to have their signal repeated 88 88
by a switch or a hub. 89 89
Now I know that 10 megabits per second here, 90 90
doesn't sound like a lot of speed. 91 91
But back in the 1980s, this was super fast. 92 92
After all, a dial-up modem in those days 93 93
was lucky to reach speeds of 300 bits per second. 94 94
So this internal network of 10 megabits per second, 95 95
was a really fast speed. 96 96
That's 10,000 bits per second. 97 97
It was lightning fast to users back then. 98 98
Now the big question, when it comes to network devices, 99 99
especially when they start operating at these speeds, 100 100
is how are they going to access the network and communicate? 101 101
And this is really one of the core questions 102 102
that Ethernet had to answer. 103 103
Should the network be deterministic 104 104
or should it be contention-based? 105 105
Now, if you're going to use deterministic means, 106 106
this is going to be where network access 107 107
is going to be very organized and orderly. 108 108
Some of the competing technologies like token bus 109 109
and token ring networks, 110 110
use this deterministic style of network access. 111 111
If a device wanted to transmit data under the network, 112 112
the device had to wait its turn, 113 113
waiting for an electronic token to get to it, 114 114
and that way they would know it was its turned to transmit. 115 115
Now let's pretend for a moment, 116 116
we're all sitting in a classroom together. 117 117
There we are, 118 118
you, me, and 20 to 25 other students, 119 119
all sitting in this room. 120 120
Now, if everybody talked at once, what would happen? 121 121
Nobody could hear or understand anything. 122 122
We'd have a whole bunch of collisions 123 123
as we call them in the networking world, 124 124
as everyone tries to talk over each other. 125 125
Instead, we need to create a deterministic system 126 126
to determine who's going to speak at any given time 127 127
in my classroom. 128 128
So, whenever I was teaching in a classroom, 129 129
I would tell my students, you have to raise your hand, 130 130
and then I'm going to call on you, 131 131
and then it's your turn to talk, 132 132
that's deterministic. 133 133
Since I was the instructor, 134 134
I was handing out the token, in this case, 135 135
calling on somebody, 136 136
and then they were given this virtual token 137 137
and they could speak until they gave that virtual token 138 138
back to me and said they were done, 139 139
or at any time, I could tell them to stop talking, 140 140
and I could take back that virtual token and speak myself, 141 141
because again, I'm the instructor, 142 142
I'm the one in charge in the room. 143 143
Now, if you use the token ring or a token bus network, 144 144
that is essentially how they operated. 145 145
The great thing about this is there are zero collisions, 146 146
because nobody's going to talk over each other. 147 147
They all wait their turn. 148 148
That's the great thing about using a deterministic network. 149 149
Now, the other way we can determine 150 150
who gets access to the network, 151 151
is by using what's known as contention-based networks. 152 152
Now contention-based networks are very chaotic. 153 153
Unlike my classroom example, which was very deterministic, 154 154
and I get to be in charge of telling everyone 155 155
when and how long they can talk, 156 156
a contention-based model, 157 157
is more like when you go to the pub on Friday night 158 158
with your friends. 159 159
Maybe you're hanging out with five of your friends, 160 160
and you're sitting around a table there 161 161
and you're having some drinks. 162 162
Now normally, people know how to interact 163 163
in these situations and they carry on a conversation, right? 164 164
We've all been there before. 165 165
There isn't somebody in your group who says, 166 166
hold on, Alex, it's Tamara's turn to talk now, 167 167
or okay Tamara, you have 90 seconds, 168 168
now, it's John's turn, let's switch. 169 169
It doesn't work that way. 170 170
I don't know about you, but if I had friends like that, 171 171
I think I would leave that conversation 172 172
and find me some new friends. 173 173
Now, instead, we actually have a natural way of talking 174 174
with each other, right? 175 175
Each of us, more or less, 176 176
take some time to tell our stories, 177 177
and the flow of conversation naturally just happens. 178 178
I pick up the conversation when there's a space, 179 179
and I fill it in with some of my stories, 180 180
and then somebody else picks up the conversation, 181 181
and says their stories or what they want to talk about. 182 182
This is contention-based. 183 183
Essentially, as you're sitting there, 184 184
you hear a gap in the conversation and you begin to speak. 185 185
If somebody else is speaking, 186 186
you listen until you find an appropriate time 187 187
for you to transmit, or in this case say, 188 188
whatever it is you wanted to add to that conversation. 189 189
Now, the problem with using 190 190
a contention-based method like this, 191 191
is that you can have collisions. 192 192
Have you ever been at the pub, 193 193
and you're having a conversation with some friends 194 194
and all of a sudden you hear that gap in the conversation, 195 195
and you go to speak and you find that somebody else speaks 196 196
at the exact same time as you? 197 197
Well, that's a collision. 198 198
You both transmit at the same time. 199 199
When that occurs, you both spoke over each other 200 200
and nobody around you could hear what was being said, 201 201
because it mumbled together. 202 202
So likely, one of you paused, 203 203
let the other one finish their story, 204 204
and then try talking again. 205 205
Now, because of this natural way of having a conversation 206 206
can lead to people talking over each other, 207 207
and therefore creating collisions, 208 208
some people also might take up more time than others. 209 209
And there's other issues like that 210 210
when we deal with these contention-based models. 211 211
They can be very chaotic. 212 212
And oddly enough, this is how Ethernet chose to work. 213 213
Ethernet, unlike token ring, 214 214
actually chose to use a contention-based network. 215 215
Now, why would they do that? 216 216
Well, because contention-based networks have lower overhead. 217 217
This means you don't have to pass around 218 218
this electronic token, 219 219
and this way you can make full use 220 220
of all the bandwidth in the network, 221 221
because anyone can talk at any time. 222 222
Now I know this may seem odd, 223 223
but it's actually a good thing. 224 224
You see, in some of these traditional 225 225
deterministic networks, 226 226
you would actually split up the communication 227 227
into chunks of time. 228 228
For instance, 229 229
let's say we have eight devices on our network. 230 230
We could say that everybody gets one-eighth of a second 231 231
to communicate. 232 232
And then they're going to pass the token 233 233
to the next network's device. 234 234
That device is going to communicate 235 235
for their eighth of a second, 236 236
and we keep doing that as we go in a circle. 237 237
So if every one second, 238 238
you can only transmit one-eighth of a second. 239 239
That is it for a 10 megabit per second network, 240 240
you're going to get to transmit 1.25 megabits per second, 241 241
not the full 10. 242 242
Now effectively, we've just cut down the network speed 243 243
by a factor of eight, because most of the time, 244 244
these devices don't have anything to communicate, 245 245
but we still gave them the time period. 246 246
Think about when you and your friends 247 247
are sitting around the table at the pub again. 248 248
And if I said that each you had to take turns 249 249
and can only speak for one minute, 250 250
some of your friends will be able to fill that minute 251 251
and then run out of time, 252 252
and others wouldn't be able to fill them in at all. 253 253
They would tell a quick one-line joke, 254 254
and then sit there for 45 seconds of silence. 255 255
This is the difference between the way people communicate. 256 256
For that reason, deterministic models 257 257
can waste a lot of resources and we'd be sitting in silence. 258 258
So Ethernet chose instead, 259 259
to use contention-based networks, 260 260
to maximize the efficiency of the network, 261 261
by allowing anyone to use all the bandwidth at any time 262 262
for as long as they need it. 263 263
But if any network device can transmit at any time 264 264
on the network, how are we going to prevent collisions? 265 265
Well, the way Ethernet approaches this, 266 266
is by using something known as CSMA/CD. 267 267
This stands for Carrier Sense Multiple Access 268 268
with Collision Detection. 269 269
Now, what exactly is that? 270 270
Well, just like when you're sitting around the table 271 271
at the pub, with all your friends, 272 272
you first listened and waited for the gap in conversation. 273 273
Once you heard that, you then tried to speak. 274 274
Now, if two of you spoke at the same time, you simply say, 275 275
oh, I'm sorry, we must have spoken over each other. 276 276
Let's try again, and then we wait and we try again. 277 277
That's the idea here. 278 278
Well, in Ethernet, we do the same thing using CSMA/CD. 279 279
Let's break down each part of this 280 280
and explain it a little bit. 281 281
The CS or carrier sense part of this, 282 282
means that the Ethernet 283 283
needs to be able to do carrier sensing. 284 284
Now, a carrier is essentially the line 285 285
we're going to communicate on. 286 286
This means that it's going to listen to the network 287 287
and determine if there's a signal already being transmitted. 288 288
Now, this is known as carrier sensing. 289 289
Carrier is just this fancy word in electronics 290 290
for a signal that carries information or data. 291 291
So we're going to try to sense if that data 292 292
is currently being transmitted, 293 293
or to use our pub example, 294 294
we're going to see, is there a gap in the conversation? 295 295
Now, if there is a gap, 296 296
this is where the MA part of CSMA/CD comes into play. 297 297
MA stands for multiple access. 298 298
All that means is that there are many different devices 299 299
that all have the ability to access, listen to, 300 300
and transmit to that network at the same time. 301 301
So Ethernet is going to have lots of devices on the network, 302 302
and they're all going to be able to listen before they speak. 303 303
That is the CSMA part of CSMA/CD. 304 304
Now we get to the important part, the CD part, 305 305
collision detection. 306 306
Since of all these devices are listening to the network, 307 307
if they detect a collision has occurred, 308 308
when they are transmitting something, 309 309
then those two devices who are both talking over each other 310 310
can decide who's going to transmit their data now, 311 311
and who's going to wait to retransmit. 312 312
To simplify this process, 313 313
Ethernet uses a clever method to determine 314 314
who gets to transmit first. 315 315
Essentially, if a collision is detected, 316 316
both Ethernet devices will stop transmitting 317 317
and pick a random number and then wait to retransmit. 318 318
So if you and your friend both talk over each other 319 319
at the pub, you might have a standing rule 320 320
that you both will stop what you're doing, 321 321
pick a random number, 322 322
and then count up to that number in your head, 323 323
and if nobody is speaking yet, you can then start to talk. 324 324
This is exactly what Ethernet devices do 325 325
when they detect a collision. 326 326
They stop transmitting, 327 327
they pick a random number, and they count. 328 328
This is known as a random back-off timer, 329 329
and it allows the two devices 330 330
to attempt to retransmit again, 331 331
when their timers hit zero. 332 332
Think of it this way. 333 333
Have you ever been walking down a hallway at work 334 334
and somebody is coming from the other direction, 335 335
it might be a small hallway and you walk up to each other, 336 336
and you kind of do that little dance 337 337
where I go left and you go right, 338 338
and you go right and I'll go left, 339 339
and you really don't say anything, 340 340
but you just kind of figure it out? 341 341
Well, if so, you're smack dab in the middle 342 342
of a CSMA/CD collision. 343 343
So what should you do? 344 344
Well, what I usually do, is exactly what Ethernet does. 345 345
I stop and I count to three, 346 346
and then I look and see if the other person 347 347
has walked around me, or if they're still in front of me. 348 348
If they haven't walked around me, I'll walk around them. 349 349
It effectively ends that little dance, 350 350
and the collision is over inside the hallway. 351 351
That's the same idea here with Carrier Sense Multiple Access 352 352
Collision Detection. 353 353
So let's take a look at how this looks on a network. 354 354
Here's the example where I have six devices on the network 355 355
using a bus, just to make it easier for us to see. 356 356
Yes, you could use a star, a bus, a ring, 357 357
or any topology you really want with Ethernet. 358 358
So from my illustration, and to make it graphically easy, 359 359
we're going to use a bus. 360 360
Now here we have six devices 361 361
and they're all sharing the same wire. 362 362
If your number four wants to talk to number five, 363 363
and they want to communicate over this network segment, 364 364
that means there's no problem, 365 365
because nobody else is talking right now. 366 366
But what happens if number two 367 367
wants to talk to number one right now? 368 368
Well, carrier sensing shows us that the line is clear. 369 369
So two transmits and one receives. 370 370
There's no problem here. 371 371
Now, what happens if both three and number five 372 372
are both going to try talking at the same time? 373 373
They listen to the carrier, 374 374
they didn't hear anybody else talking, 375 375
and they both started transmitting. 376 376
Well, this causes a collision, 377 377
just as we can see here with the red X. 378 378
So now we've detected a collision. 379 379
What do we do? 380 380
Well, three and five are both going to stop, 381 381
and they're going to pick a random number 382 382
to serve as their random back-off timer. 383 383
Now, in the case of three, it chose to wait 30 milliseconds. 384 384
In the case of five, it chose 150 milliseconds. 385 385
So what happens next? 386 386
Well, 30 milliseconds goes by, 387 387
number three listens to the carrier, 388 388
and it doesn't detect anybody else transmitting, 389 389
so it starts to transmit. 390 390
At the same time, number five is still waiting, 391 391
because only 30 milliseconds have passed 392 392
and they chose to wait 150 milliseconds. 393 393
So they still have 120 milliseconds on their back-off timer. 394 394
Now, what happens if it takes number three, 395 395
300 milliseconds to transmit everything? 396 396
Well, number five is going to wait for its back-off timer 397 397
of 150 milliseconds, and then when its timer hit zero, 398 398
it listens to the carrier again. 399 399
This time though, it hears somebody transmitting, 400 400
in this case, it's number three. 401 401
So it's just going to wait until it hears an open spot 402 402
in the conversation, and then it will transmit, 403 403
in this case, it should be when number three 404 404
is done transmitting about 180 milliseconds from now. 405 405
Now when number three is done communicating 406 406
and the carrier seems clear for transmission, 407 407
number five will transmit. 408 408
If someone else happens to be transmitting at the same time, 409 409
again, we have a collision, 410 410
both choose a random back-off timer, 411 411
they wait and the cycle repeats, 412 412
until everybody transmits everything they want to send. 413 413
Now, I know this may seem like a bad way of doing things, 414 414
because as networks get busier and busier 415 415
and you have more clients, 416 416
you're going to have a lot more collisions. 417 417
And guess what, you would be exactly right. 418 418
The more devices you have communicating 419 419
on a single network segment, 420 420
the more collisions you're going to have. 421 421
Each area of the network that shares a single segment 422 422
is known as a collision domain. 423 423
In this example, 424 424
we had six devices all sharing a single bus cable. 425 425
That made up our collision domain. 426 426
With Ethernet, anytime you have devices on the same cable, 427 427
or they're all connected to the same hub, 428 428
you are sharing the same collision domain. 429 429
Because of this, all of the devices need to operate 430 430
in half duplex mode, 431 431
because they have to listen and then talk. 432 432
They can't do both at the same time. 433 433
If a device talks and listens at the same time, 434 434
they simply hear themselves, 435 435
and think somebody else is transmitting. 436 436
So they cannot operate in full duplex, 437 437
where they can listen and talk at the same time. 438 438
If you're using a hub or a shared network segment, 439 439
you have to be able to listen to prevent those collisions. 440 440
For this reason, we need to keep collision domains 441 441
very small inside our networks. 442 442
If you have a large collision domain, 443 443
there is a high probability of collisions, 444 444
and each collision requires that data to be retransmitted 445 445
again, waiting for a back-off timer to pass, 446 446
and this is going to minimize your bandwidth. 447 447
This is going to slow down the entire network segment. 448 448
Now, if you have a hub with four devices, 449 449
it probably won't be a major issue, 450 450
but if you're using a hub with 24 or 48 ports, 451 451
the collisions can bring your network to a screeching halt. 452 452
Think about it this way. 453 453
If we're going to go to the pub 454 454
and we take a group of four friends, 455 455
we can make that conversation work. 456 456
Everyone can listen for the gaps and they can transmit, 457 457
and we won't have too many people talking over each other. 458 458
But if we go at the same time with 20 to 25 people, 459 459
we're going to have entirely too many collisions 460 460
and it just won't work. 461 461
So we need to break that larger group into smaller groups. 462 462
For my pub example, 463 463
we may do this by breaking up our 20 to 25 friends 464 464
into groups of four or five people 465 465
and sit them each at a different table. 466 466
This breaks down 467 467
our large single collision domain of 20 to 25 people 468 468
into five to six smaller collision domains 469 469
of four to five people each. 470 470
In our networks, we do the exact same thing 471 471
to break down collision domains by using Ethernet switches. 472 472
This drastically increases the scalability of our networks 473 473
by creating a lot of different collision domains. 474 474
Remember, lots of collision domains is good, 475 475
because you have less people in each one. 476 476
Every single switch port 477 477
is actually considered its own collision domain. 478 478
You can see here with my switch in the center, 479 479
I have four collision domains. 480 480
There is one in between each computer and the switch itself. 481 481
Now, if I was using a hub, 482 482
all four devices and the hub 483 483
are all part of that single collision domain. 484 484
So I have five devices in one collision domain. 485 485
But by simply replacing the hub with a switch, 486 486
I can increase the speed of my network, 487 487
because now nobody else is talking on that switch port, 488 488
except the device that I cabled to it. 489 489
Therefore, the switch port now can operate 490 490
in full duplex mode. 491 491
After all, it's my only device on that network segment, 492 492
so there's no chance of collision. 493 493
It's like I can just ignore the fact that I had to listen. 494 494
If I'm sitting in my room alone, 495 495
I can talk all I want and I will never have a collision, 496 496
because nobody's here to interrupt me. 497 497
I don't have to listen before I transmit. 498 498
I can just keep talking. 499 499
I have a full-time dedicated channel 500 500
between my device and my switch. 501 501
So I'm allowed to now operate in full duplex mode, 502 502
transmitting my data faster, 503 503
getting more bandwidth out of this connection, 504 504
and ensuring there are no collisions. 505 505
All right, now that we covered 506 506
the basics about Ethernet networks, 507 507
let's dive into the different ways 508 508
that we classify Ethernet. 509 509
These are known as the Ethernet standards, 510 510
and they take the form of a number, 511 511
the word base, and then one or two letters. 512 512
For example, earlier I mentioned that we use 10BASE-T 513 513
for our Cat 3 Ethernet networks. 514 514
10BASE-T is the slowest version of Ethernet, 515 515
and only operates at 10 megabits per second, 516 516
and for up to a distance of 100 meters. 517 517
I already covered the basics of copper Ethernet standards 518 518
in the lesson on copper cabling, but in this lesson, 519 519
we're going to do a quick review of those standards, 520 520
as we say, which Ethernet standard goes for each one, 521 521
and then we're going to talk about the Ethernet standards 522 522
for fiber optic cables too. 523 523
So let's do a quick review of copper Ethernet standards. 524 524
We're going to start with the slowest 525 525
and move our way upward to the fastest. 526 526
First, we have 10BASE-T, 527 527
which operates at 10 megabits per second, 528 528
over Cat 3 cables. 529 529
This is known as Ethernet. 530 530
Second, we have 100BASE-TX, 531 531
which operates at 100 megabits per second, 532 532
over Cat 5 cables. 533 533
This is known as fast Ethernet. 534 534
Third, we have 1000BASE-T, 535 535
which operates at 1000 megabits per second 536 536
or one gigabit per second, 537 537
over either Cat 5e or Cat 6 cables. 538 538
This is called gigabit Ethernet. 539 539
Fourth, we have 10GBASE-T, 540 540
which operates at 10 gigabits per second over Cat 6, 541 541
Cat 6a, and Cat 7 cables. 542 542
This is known as 10 gigabit Ethernet, go figure. 543 543
And fifth, and finally, we have 40GBASE-T, 544 544
which operates at 40 gigabits per second over Cat 8 cables. 545 545
This of course is known as 40 gigabit Ethernet. 546 546
As you can see, 547 547
they stopped getting creative with the names after Cat 5. 548 548
Now, when it comes to distances, 549 549
remember most copper cabling used by Ethernet 550 550
can only go up to 100 meters before the signal attenuates, 551 551
and you can no longer maintain signal integrity. 552 552
The only two exceptions to this rule are Cat 8, 553 553
which only goes 30 meters, 554 554
and Cat 6, which only goes 55 meters, 555 555
if you want to reach the full 556 556
10 gigabits per second of speed, 557 557
otherwise, you can go up to 100 meters with Cat 6, 558 558
if you stick to a one gigabit per second speed. 559 559
Now, remember when I say speed, 560 560
I'm really talking about bandwidth. 561 561
Bandwidth is measured about how many bits 562 562
the network can transmit in one second, 563 563
known as a bit per second. 564 564
We can get up to megabits, 565 565
and then that's millions of bits per second, 566 566
or gigabits, which is billions of bits per second, as well. 567 567
Depending on the type of cable, 568 568
this is going to determine the capacity 569 569
for the bandwidth of your network. 570 570
So if you replace all your old Cat 3 cables and switches, 571 571
with newer Cat 7 ones, 572 572
you're going to increase your bandwidth 573 573
from 10 megabits per second to 10 gigabits per second, 574 574
making it 1000 times faster. 575 575
Now, let's switch from copper to fiber 576 576
and talk about the different Ethernet standards that we use 577 577
with fiber cables. 578 578
Unlike copper, fiber can go further than just 100 meters. 579 579
Now multi-mode fibers can reach distances 580 580
of 200 to 500 meters or more, 581 581
and single-mode fibers can reach distances 582 582
of up to 40 kilometers, 583 583
before you have to repeat that signal. 584 584
First, we have 100BASE-FX. 585 585
This is going to operate at 100 megabits per second, 586 586
over multi-mode fiber, 587 587
and it can reach a distance up to two kilometers. 588 588
Now this is a bit special because normally, 589 589
multi-mode isn't going to be able to go this far, 590 590
but this particular multi-mode range that's being used, 591 591
is actually going to border on the single-mode range 592 592
when we talk about the actual light source, 593 593
and this is why the distance is longer for 100BASE-FX 594 594
even though it technically uses multi-mode fibers. 595 595
Now second, we have 100BASE-SX, 596 596
which is going to operate at 100 megabits per second, 597 597
over single-mode fiber, 598 598
but it's going to use a shorter wavelength than 100BASE-FX, 599 599
which makes it cheaper to produce, 600 600
because it's going to use LEDs as the light source 601 601
instead of a laser. 602 602
100BASE-SX is going to operate at 100 megabits per second 603 603
at distance of up to 300 meters using a multi-mode fiber. 604 604
Third, we have 1000BASE-SX, 605 605
which operates at 1000 megabits per second, 606 606
or one gigabit per second, over multi-mode fiber, 607 607
using nanometer near-infrared wavelengths. 608 608
1000BASE-SX can reach distances of 200 to about 550 meters. 609 609
Fourth, we have 1000BASE-LX, 610 610
which is going to operate at 1000 megabits per second, 611 611
or one gigabit per second, over a single-mode fiber. 612 612
Now, 1000BASE-LX is going to use a long wavelength laser 613 613
as its light source, 614 614
and this means it can go further distances 615 615
of up to five kilometers. 616 616
1000BASE-LX is a bit strange though, 617 617
because you can also use it 618 618
with multi-mode fibers if you want to. 619 619
If you use it with the cheaper multi-mode fiber, 620 620
then the speed is going to remain the same, 621 621
but your distance is going to drop down to about 550 meters. 622 622
Fifth, we have 10GBASE-SR. 623 623
Now, this is going to operate at 10 gigabits per second 624 624
over multi-mode fiber. 625 625
SR stands for short range. 626 626
Because this uses a multi-mode fiber, 627 627
it's going to limit your maximum distance 628 628
to about 400 meters. 629 629
And sixth, we have 10GBASE-LR, 630 630
which operates at 10 gigabits per second, 631 631
over a single-mode fiber. 632 632
Now, LR stands for long reach, 633 633
because it uses a single-mode fiber 634 634
that can reach distances of up to 10 kilometers. 635 635
All right, when it comes to fiber Ethernet standards, 636 636
you don't have to memorize the fact 637 637
that there are 200 meters, or 500 meters, 638 638
or five kilometers, or 10 kilometers, or 40 kilometers. 639 639
What is important is to remember their relative distances. 640 640
When it comes to distances, 641 641
you really need to memorize just a few key things. 642 642
First, copper cables have a maximum distance of 100 meters. 643 643
Second, if you're using Cat 6, 644 644
you're going to be using it at 100 meters, 645 645
then you need to limit your speed to one gigabit per second, 646 646
instead of 10 gigabits per second. 647 647
Third, if you're using Cat 6 and you're under 55 meters, 648 648
you can increase your speed to 10 gigabits per second, 649 649
instead of one gigabit per second. 650 650
Fourth, if you're dealing with multi-mode fiber, 651 651
you're going to be dealing with shorter distances. 652 652
That means something around 200 to 500 meters. 653 653
Fifth, if you need longer distances, 654 654
you have to use single-mode fibers. 655 655
This is where we start talking about things 656 656
in kilometers and distance instead of meters. 657 657
So we're talking two or 10 or 40 kilometers. 658 658
For the exam, 659 659
you may see questions about specific cable lengths 660 660
or limitations when it comes to copper. 661 661
But for fiber, they're only going to ask you about the fact 662 662
that multi-mode distances are longer than copper, 663 663
but shorter than single-mode. 664 664
Now this is where you have to figure out 665 665
which cable you're going to use. 666 666
Copper is great for short distances. 667 667
Fiber, if you need short distances, 668 668
you're going to use multi-mode, 669 669
and if you need long distances, 670 670
you're going to use single-mode. 671 671
Now, another thing they're going to test you on 672 672
in regards to fiber, 673 673
is whether a fiber Ethernet standard 674 674
is going to use multi-mode or single-mode fibers. 675 675
For example, you might see a question like this. 676 676
You're a network technician, 677 677
and you need to select an Ethernet standard 678 678
that will allow you to connect your main office 679 679
to your branch office that's located at 35 kilometers away, 680 680
which of the following should you use? 681 681
10GBASE-T, 682 682
1000BASE-SX, 683 683
10GBASE-LR, 684 684
or 1000BASE-T? 685 685
So is this question really asking 686 686
about the length of the cable and memorizing the distances? 687 687
Well no, not really. 688 688
Instead, it's asking you about a single-mode cable 689 689
and being able to figure out which of these is single-mode, 690 690
because we know copper cables are less than 100 meters 691 691
and multi-mode cables are less than 500 meters 692 692
with modern fiber cables. 693 693
So if you can remember that 1000BASE-LR 694 694
is a single-mode cable, you've got your answer. 695 695
Now, is there an easy way to memorize which cables 696 696
are single-mode and which are multi-mode? 697 697
Well, I personally use a little memory to help me do this. 698 698
Remember, we covered six different types of fiber cables 699 699
in this lesson, right? 700 700
We covered 100BASE-FX, 100BASE-SX, 1000BASE-SX, 701 701
1000BASE-LX, 10GBASE-SR, and 10GBASE-LR. 702 702
Now, you may remember, 703 703
that I said that 100BASE-LX was special, right? 704 704
The reason it was special, 705 705
is because you could use either single-mode 706 706
or multi-mode fiber with it. 707 707
So the rest of them though, 708 708
we have a really simple little saying 709 709
that'll help us remember which ones are single, 710 710
and which ones are multi-mode, 711 711
and it goes like this, 712 712
S is not single. 713 713
That's it. 714 714
If you remember that S is not single, 715 715
it will tell you whether or not that fiber 716 716
is a single-mode or multi-mode fiber based on its name. 717 717
So if you see an S there in the fiber Ethernet standard, 718 718
like 100BASE-SX, 1000BASE-SX, 10GBASE-SR, 719 719
you know it's using a multi-mode fiber, 720 720
because it's short range. 721 721
So every time you see S in the name, 722 722
remember S is not single. 723 723
Therefore, if there's an S in the name, 724 724
it must be a multi-mode fiber. 725 725
If you don't see the S, it's used for longer distances. 726 726
This rule holds true for most everything out there, 727 727
except the 1000BASE-LX, 728 728
because this one works with both single-mode 729 729
and multi-mode fibers. 730 730
All right, in this lesson, 731 731
we covered just a few of the Ethernet fiber standards, 732 732
specifically, the ones you're going to be asked about 733 733
on the Network Plus exam, 734 734
but be aware there are many others out there, 735 735
including things like 1000BASE-EX, 10GBASE-ER, 736 736
100GBASE-LR4, 100GBASE-ER4, and many others. 737 737
But for the exam, you only need to know 738 738
the six that we covered in this lesson.