1
00:00:01,080 --> 00:00:08,189
So the phone once again is sending a layer two marking to the switch using attitude at one Q.

2
00:00:08,640 --> 00:00:18,720
The markings in binary are in the range 000 all the way to 111.

3
00:00:19,110 --> 00:00:24,870
So in binary it looks like this in decimal they'll have values like this.

4
00:00:25,260 --> 00:00:29,040
And I'll add five here because that's one used by voice.

5
00:00:29,520 --> 00:00:38,520
So an editor at one Q header has a field called a priority field or so called cos it's three bits and

6
00:00:38,520 --> 00:00:41,430
size values are in this range.

7
00:00:41,880 --> 00:00:48,980
Now in the same way when you get to a traffic light and it's red you stop or when it's green you go.

8
00:00:49,470 --> 00:00:54,120
These markings in of themselves don't mean anything.

9
00:00:54,150 --> 00:00:57,210
It's the interpretation of the marking that counts.

10
00:00:57,480 --> 00:01:02,280
We've all agreed that a red light means stop and a green light means go.

11
00:01:02,400 --> 00:01:07,950
In the same way the convention is, that voice is marked with a cost value of five.

12
00:01:08,370 --> 00:01:10,320
That's true in Cisco environments.

13
00:01:10,320 --> 00:01:14,760
If you have phones from other vendors, they may use a cost of six.

14
00:01:15,060 --> 00:01:23,010
So you need to ensure that your phones and your switches and your routers are configured to agree what

15
00:01:23,010 --> 00:01:24,330
these values mean.

16
00:01:24,600 --> 00:01:31,590
So the idea with marking is we marking packets to indicate to another device how important the data

17
00:01:31,590 --> 00:01:32,100
is.

18
00:01:32,430 --> 00:01:39,270
So when the packets are sent from switch one to switch two as an example, switch two can read the packets

19
00:01:39,270 --> 00:01:43,530
and see that they marked with a cost of five and then prioritize them accordingly.

20
00:01:43,530 --> 00:01:45,450
So prioritize them as important.

21
00:01:45,450 --> 00:01:46,500
Voice Traffic.

22
00:01:46,980 --> 00:01:55,230
Now one of the problems with ED one Q layer two markings is it requires ED one Q trunk ports.

23
00:01:55,560 --> 00:02:02,790
A link such as this between a switch and a router may be using a routed port on a switch, which means

24
00:02:02,790 --> 00:02:10,139
that ed to one Q trunking is not used if you send traffic across a cereal link as an example or a WAN

25
00:02:10,229 --> 00:02:12,870
82.1 Q Tagging is not used.

26
00:02:13,290 --> 00:02:18,120
You may as an example be using PGP or Hdl-c on a serial link.

27
00:02:18,360 --> 00:02:25,110
So layer two markings such as ADA 2 to 1 Q aren't end to end and therefore you may want to use a layer

28
00:02:25,110 --> 00:02:26,070
three marking.