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A great resource for learning quality of service is the enterprise quality of service solution reference

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network design guide or R&D guide.

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At the time of this recording.

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The guide was last updated in April 2014.

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I've added the guide below the video, but you can find it by doing a search in Google, for example,

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for quality of service R&D guide.

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We are told that there's an updated version.

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If you want to buy the latest version, you'd need to purchase this book.

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End to end quality of service network design that's not required for CCNA.

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So for the CCNA course, I would simply use this document and the videos that I'm recording.

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The squad has been around for a long time, so it was originally drafted in April 2005.

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A lot of the quality of service mechanisms that we discussing haven't changed over the years.

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The reliance on some, such as link fragmentation and interleaving has been reduced as well and speeds

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have increased, but a lot of the concepts remain the same.

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So if you want to study this in more detail, have a look at this guide.

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But I'm going to summarise the details for you.

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And I'll do a demonstration to try and explain some of the options as required for the CCNA exam and

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ICI and DD two exam.

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So in the CNA exam, if I do a search for quality of service, you are expected to know basic quality

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of service concepts, including marking device trust, notarization of voice of video and data shaping

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policing and congestion management.

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These are quality of service mechanisms.

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The same topics are listed in the ICD two exam.

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So the R&D guide starts out by looking at why is quality of service important?

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What are the toolsets or mechanisms available to you?

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And there's some additional information.

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Now, quality of service is essentially important because we need to prioritize some traffic at the

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detriment of other traffic.

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As an example, if there's an emergency and an ambulance needs to take someone to hospital or reach

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someone that's injured on motorways or highways, we have dedicated lanes so that an ambulance can get

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to hospital quicker.

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We are providing a better quality of service to an ambulance than to other vehicles on the road.

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And the same is true with quality of service.

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We want to provide a higher priority or better quality of service to traffic types such as voice and

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video because of the delay requirements and other requirements that those traffic types have when compared

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to other traffic types, such as FTP or HTTP.

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Now the transmission quality of a network is determined by the following factors.

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Firstly, loss how many packets will be lost.

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Now this is important for voice conversations.

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Voice will degrade as an example when packets are lost.

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We want to have a low loss of packets in a voice conversation for FTP.

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Loss of packets isn't as important because FTP uses TCP and will simply retransmit the packets.

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But you can't retransmit voice packets.

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If voice packets are lost, they are lost and it will affect the voice quality.

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DeLay is the finite amount of time that it takes a packet to reach the receiving endpoint after being

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transmitted from the sending endpoint.

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As an example, if you're using a phone, it's the amount of time that it takes for me to speak till

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it reaches your ear.

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In other words, how long does it take for the voice to travel from me to you?

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Now the round trip delay of a voice conversation needs to be less than 300 milliseconds.

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Anything greater than that is going to affect the voice quality.

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Fttp once again can tolerate much higher delays.

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Variable delay, also called jitter is the difference in end to end delay between packets.

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So if the delay varies between packet arrival that is known as jitter, jitter can once again cause

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problems in a voice conversation.