Cisco CCNP Certification Training / ONT Exam Tutorial:
Introduction To Quality of Service (QoS)
By Chris Bryant, CCIE #12933
Even if you don't know what QoS is, you've most likely heard of it. Basically, Quality of Service is a way to give delay-sensitive traffic the attention it deserves while (hopefully) still getting "regular" traffic to its destination in a timely manner.
When you break QoS down to its very core, we're answering one question: "Which incoming data should be transmitted first?" That used to be an easy question to answer, since we didn't have a lot of time-sensitive data traveling across our network. Then again, a floppy disk used to store all the information we needed, and that's not true anymore either!
Not only do we have different data types on our network - voice and video, just to name two - but we have traffic that's much more time-sensitive than it used to be. When our network gets congested, QoS helps to ensure that the voice and video streams receive the proper level of attention, which in turn ensures that voice and video presentations are of high quality.
You've probably watched a video presentation that was more than a little choppy, or listened to streaming video that would play the stream for 30 seconds, then stop for a second or two, then pick back up. That's jitter, and our major weapon to fight jitter is QoS.
Fighting jitter isn't the only reason we configure QoS. Here are four other major reasons to use QoS:
- Provide adequate bandwidth, and guarantee it in some situations
- Provide consistent and predictable packet delivery
- Prevent delay, especially with voice and video transmission
- Prevent packet loss (especially via tail drop, which we'll address in another section)
I'll speak of "voice and video" quite a bit in this course, and while both types of data benefit from QoS, the application of QoS may be a bit different. Video tends to be more bursty than voice, particularly with video conferencing. From personal experience, I'll tell you this - video conferencing is very bursty and very hard on a network that doesn't usually carry such transmissions!
Also, network congestion is not the only problem with voice and video traffic. As you'll see in a future CCNP ONT exam tutorial, header overhead is a real problem with voice packets. We'll discuss that in detail at that time, but keep in mind that congestion and overhead are problems with voice packets.
Get ready for the ultimate in CCNP ONT exam certification training - with The Ultimate ONT Study Package! In the meantime, enjoy these ONT exam tutorials!
To your success,
Chris Bryant
CCIE #12933
chris@thebryantadvantage.com
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