1
00:00:00,600 --> 00:00:02,490
What is quality of service?

2
00:00:03,969 --> 00:00:11,560
Quality of service is providing a better quality to certain applications at the detriment of other applications.

3
00:00:11,800 --> 00:00:19,180
In the same way that on the roads certain vehicles are prioritized over others, such as ambulances

4
00:00:19,180 --> 00:00:20,190
or buses.

5
00:00:20,200 --> 00:00:25,510
We are prioritizing certain traffic types, in other words, making sure that they go to the front of

6
00:00:25,510 --> 00:00:29,580
the queue as an example versus other traffic types.

7
00:00:29,590 --> 00:00:34,150
Certain traffic types such as voice or video are delay sensitive.

8
00:00:34,180 --> 00:00:41,530
They can't handle a lot of delay, so they'll be prioritized over traffic types that can handle delay

9
00:00:41,530 --> 00:00:43,270
such as FTP.

10
00:00:43,450 --> 00:00:46,100
It's also called managed unfairness.

11
00:00:46,120 --> 00:00:52,390
We are introducing unfairness into the network, prioritizing certain traffic types over other traffic

12
00:00:52,390 --> 00:00:52,990
types.

13
00:00:53,200 --> 00:01:00,610
As an example, a very important phone call from the CEO would be prioritized over someone watching

14
00:01:00,610 --> 00:01:03,860
YouTube videos for the CCNA exam.

15
00:01:03,880 --> 00:01:08,740
You need to be aware of three traffic types and their traffic characteristics.

16
00:01:08,980 --> 00:01:10,540
Firstly, we have data.

17
00:01:10,690 --> 00:01:14,270
Data traffic is generally bursty and greedy.

18
00:01:14,290 --> 00:01:20,890
That's not always the case, but generally data applications such as FTP will grab as much bandwidth

19
00:01:20,890 --> 00:01:21,940
as they can.

20
00:01:22,390 --> 00:01:29,440
If you give an FTP application two megabits per second, it'll take two megabits per second.

21
00:01:29,470 --> 00:01:34,020
If you give it four megabits per second, it's going to take four megabits per second.

22
00:01:34,030 --> 00:01:36,970
So data is bursty and greedy.

23
00:01:37,390 --> 00:01:39,510
It's sometimes smooth and benign.

24
00:01:39,520 --> 00:01:43,240
In other words, it doesn't grab all the bandwidth that you give it.

25
00:01:43,240 --> 00:01:47,050
But in a lot of cases, data applications are bursty and greedy.

26
00:01:47,590 --> 00:01:49,810
They also tend to be drop insensitive.

27
00:01:49,840 --> 00:01:54,430
In other words, if a packet is dropped, it doesn't matter because it's retransmitted.

28
00:01:54,700 --> 00:01:59,810
A lot of data applications use TCP, which re transmits data.

29
00:01:59,830 --> 00:02:03,220
If packets go missing, it's also delay insensitive.

30
00:02:03,250 --> 00:02:09,009
So as an example, if packets are delayed by 500 milliseconds, it's not a major problem.

31
00:02:09,039 --> 00:02:12,490
Now, this really depends on the type of data sent.

32
00:02:12,670 --> 00:02:15,820
There are two major categories of data applications.

33
00:02:15,820 --> 00:02:20,920
We have interactive data applications and non-interactive data applications.

34
00:02:21,430 --> 00:02:24,160
Telnet, as an example, is interactive.

35
00:02:24,490 --> 00:02:32,140
A large delay will degrade the user experience, but if you downloading a file using FTP delay isn't

36
00:02:32,140 --> 00:02:33,160
that important.