So the phone once again is sending a layer two marking to the switch using attitude at one Q.
The markings in binary are in the range 000 all the way to 111.
So in binary it looks like this in decimal they'll have values like this.
And I'll add five here because that's one used by voice.
So an editor at one Q header has a field called a priority field or so called cos it's three bits and
size values are in this range.
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.
These markings in of themselves don't mean anything.
It's the interpretation of the marking that counts.
We've all agreed that a red light means stop and a green light means go.
In the same way the convention is, that voice is marked with a cost value of five.
That's true in Cisco environments.
If you have phones from other vendors, they may use a cost of six.
So you need to ensure that your phones and your switches and your routers are configured to agree what
these values mean.
So the idea with marking is we marking packets to indicate to another device how important the data
is.
So when the packets are sent from switch one to switch two as an example, switch two can read the packets
and see that they marked with a cost of five and then prioritize them accordingly.
So prioritize them as important.
Voice Traffic.
Now one of the problems with ED one Q layer two markings is it requires ED one Q trunk ports.
A link such as this between a switch and a router may be using a routed port on a switch, which means
that ed to one Q trunking is not used if you send traffic across a cereal link as an example or a WAN
82.1 Q Tagging is not used.
You may as an example be using PGP or Hdl-c on a serial link.
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
three marking.