So what is the Cisco quality of service toolset?
The R&D guide discusses the following mechanisms or quality of service tool sets that allow you to implement
quality of service.
This is what is emphasized in the Q&A exam.
The exam talks about marking device trust, prioritization, shaping policing and congestion management.
And if you look at the mechanisms listed in the R&D guide, we have classification and marking policing
and markdown scheduling.
Link Specific tools.
And there are some additional options, such as order quotas and call it mission control.
Here's a graphic showing the quality of service tool set.
Now these mechanisms apply to differentiated services or serve into service has its own mechanisms and
best effort to essentially doesn't have these mechanisms.
It simply treats all traffic the same.
Firstly, we have admission control.
Will your call, as an example, be permitted across the IP network?
If there's oversubscription of a link, a voice call may need to take an alternate path.
Classification and marking is essentially looking at traffic types and putting them into classes.
So is it a voice traffic?
If it is, then it goes into a certain class.
Is it a video traffic?
Then it would go into a different class.
Is it FTP?
FTP would go into third class?
We have policing and markdown.
If you're sending too much traffic, your traffic could be dropped or the quality of service given to
you could be lowered.
Then we have scheduling, which includes queuing and dropping.
We have traffic shaping and link specific mechanisms.
We'll start off with classification and marking.
When you send a package with FedEx or DHL, that package needs to be marked for next day delivery or
urgent delivery or standard delivery.
A label gets put onto the package to indicate how important that package is when the package is sent
from one depot to another.
They don't open the package to determine the quality of service that that package would get.
They look at the label and the label determines the quality of service that the package gets.
In the same way, when a telephone sends packets into a network.
It needs to mark those packets as important so that every switch and router along the path can treat
the packet differently when compared to, say, FTP sent by a PC.
So when packets are forwarded from the phone to the first switch, it needs to indicate using some kind
of marking or label or field that the packet is important.
It needs to be treated better than, say, an FTP packet.
When switch one sends the packet to switch two, it needs to indicate to that switch that the packet
is important.
And in the same way, when the second switch sends the packet to the router, it needs to indicate to
the broader that the packet is of great importance.
Now this introduces the concept of a trust boundary.
Who do we trust in the network?
As an example, does the router trust switch to the switch to trust switch one as an example.
If these devices trust the markings that they receive from each other or the quality of service settings
that they receive from one another, then the trust boundary ends over here.
In other words, the switch doesn't trust the phone and the switch doesn't trust the PC.
If, however.
The switch did trust the phone.
The trust boundary would be extended to the phone, as is the case with a lot of IP phones.
We could have a PC connected to a phone.
So we could connect the PC to the back of the phone, and in that case, the trust boundary would end
at the phone.
In other words, the switches and the router trust the phone, but they don't trust the PC.
So if the PC sends traffic to the phone, telling the phone that its traffic is important, the phone
will not trust those markings, all those values, and would override them in the same way.
Switch one doesn't trust the markings or values sent by the PC, but it would trust the markings or
values sent by the phone.
And again, switch two would trust what switch one tells it and the writer would trust switch to.
As an analogy, if you go to the airport and your ticket says that you have a first class ticket, you
will be treated differently to someone who has a economy class ticket.
But the people at the airport won't accept a ticket that you've just made up.
So if you just printed out your own ticket, they're not going to trust that unless they can reference
it officially.