A great resource for learning quality of service is the enterprise quality of service solution reference
network design guide or R&D guide.
At the time of this recording.
The guide was last updated in April 2014.
I've added the guide below the video, but you can find it by doing a search in Google, for example,
for quality of service R&D guide.
We are told that there's an updated version.
If you want to buy the latest version, you'd need to purchase this book.
End to end quality of service network design that's not required for CCNA.
So for the CCNA course, I would simply use this document and the videos that I'm recording.
The squad has been around for a long time, so it was originally drafted in April 2005.
A lot of the quality of service mechanisms that we discussing haven't changed over the years.
The reliance on some, such as link fragmentation and interleaving has been reduced as well and speeds
have increased, but a lot of the concepts remain the same.
So if you want to study this in more detail, have a look at this guide.
But I'm going to summarise the details for you.
And I'll do a demonstration to try and explain some of the options as required for the CCNA exam and
ICI and DD two exam.
So in the CNA exam, if I do a search for quality of service, you are expected to know basic quality
of service concepts, including marking device trust, notarization of voice of video and data shaping
policing and congestion management.
These are quality of service mechanisms.
The same topics are listed in the ICD two exam.
So the R&D guide starts out by looking at why is quality of service important?
What are the toolsets or mechanisms available to you?
And there's some additional information.
Now, quality of service is essentially important because we need to prioritize some traffic at the
detriment of other traffic.
As an example, if there's an emergency and an ambulance needs to take someone to hospital or reach
someone that's injured on motorways or highways, we have dedicated lanes so that an ambulance can get
to hospital quicker.
We are providing a better quality of service to an ambulance than to other vehicles on the road.
And the same is true with quality of service.
We want to provide a higher priority or better quality of service to traffic types such as voice and
video because of the delay requirements and other requirements that those traffic types have when compared
to other traffic types, such as FTP or HTTP.
Now the transmission quality of a network is determined by the following factors.
Firstly, loss how many packets will be lost.
Now this is important for voice conversations.
Voice will degrade as an example when packets are lost.
We want to have a low loss of packets in a voice conversation for FTP.
Loss of packets isn't as important because FTP uses TCP and will simply retransmit the packets.
But you can't retransmit voice packets.
If voice packets are lost, they are lost and it will affect the voice quality.
DeLay is the finite amount of time that it takes a packet to reach the receiving endpoint after being
transmitted from the sending endpoint.
As an example, if you're using a phone, it's the amount of time that it takes for me to speak till
it reaches your ear.
In other words, how long does it take for the voice to travel from me to you?
Now the round trip delay of a voice conversation needs to be less than 300 milliseconds.
Anything greater than that is going to affect the voice quality.
Fttp once again can tolerate much higher delays.
Variable delay, also called jitter is the difference in end to end delay between packets.
So if the delay varies between packet arrival that is known as jitter, jitter can once again cause
problems in a voice conversation.