QoS vs Traffic shaping, what is the difference?

Quality of Service is a level of quality you wish to provide to a service. Traffic shaping is the method you accomplish it. In the consumer market the terms are tossed around interchangeably. That's the best I can explain it.
 
Shaping falls under the umbrella of QoS. They're not really comparable. You could consider the difference between policing and shaping though.
 
QoS: marking IP packets in order to properly place them in the desired queue (RTP, voice signaling, etc). This allows you to carve out a dedicated piece of your overall bandwidth to reserve for these queues.

Shaping: limiting the flow of packets that traverse a particular interface in order to prevent that interface from becoming congested. For example, if you have a Gig interface, but the bandwidth that traverses that interface is only 100Mb, then you would flood traffic to that interface without shaping.
 
cgram23 said:
QoS: marking IP packets in order to properly place them in the desired queue (RTP, voice signaling, etc). This allows you to carve out a dedicated piece of your overall bandwidth to reserve for these queues.

Shaping: limiting the flow of packets that traverse a particular interface in order to prevent that interface from becoming congested. For example, if you have a Gig interface, but the bandwidth that traverses that interface is only 100Mb, then you would flood traffic to that interface without shaping.
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Not at all. QoS isn't marking, marking is one of the many things covered under the umbrella of QoS. Maybe you're thinking of CoS?

And what you described is more policing than shaping.
 
AMD_Gamer said:
damn this is confusing.
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The way I see the differences without having deep studies into the subject (later in my CCNP career lol) is that QoS is more or less letting the traffic through although giving higher priority to certain types of traffic to create an overall smooth experience on the network. So if your network is heavily saturated time critical bandwidth applications wouldn't suffer because packets would have a higher priority to them (i.e. Voice, Streaming video).

High link saturation is going to raise latency which will affect some services, the goal is to prioritize them enough that even under full load you wont notice huge performance hits so long as they aren't prolonged periods. Very time consuming to get down a science.

Traffic shaping more or less is defining certain types of traffic that eats up a lot of those link resources. For instance you might not want all 100 employees using the popular YouTube service since videos take up such a large amount of bandwidth. This is especially true if you're running VOIP for the employees and maybe a database server that requires very low latency for accuracy. I could be off, but that's kind of the way I look at it. Just in my CCNA studies I've learned there are some really major differences without going into much detail because literally there are Cisco courses dedicated to the subject (many seem to hate them too lol). More or less I see it as allowing all traffic alas with specific priorities v.s. limiting other types of traffic and their impact on network resources.

Maybe that kind of makes it a little easier to understand? I'm sure I'm wrong in the way I look at things and someone will correct me. There's just so much to networking as is it's hard to find the time to master all those intriguing subjects.
 
Shaping is, as mentioned, a component of QoS, but it is ALSO something that can stand alone.

Shaping is a way of buffering traffic temporarily and discarding packets when appropriate to prevent congestion or impose a limit upon the amount of bandwidth a connection uses. This is commonly used BY QoS when traffic is prioritized, as different classes of traffic are given bandwidth limits.

However, you can shape traffic without it being QoS. If you only have one class of traffic, there is no prioritization, but shaping can still occur. Involve multiple classes of traffic, and you have QoS.

QoS is, as mentioned, a deep subject, and commonly misunderstood by network administrators (I know, I spend all day explaining it to people). QoS can provide traffic priority, traffic bandwidth, involve different methods for queueing traffic, varying buffer depths for traffic, and so on.

A lot of people tell me "your QoS is wrong, we are dropping too many packets, you need to give X class more bandwidth and/or larger buffers". It's frustrating trying to explain to them the dynamic bandwidth-sharing nature of QoS, the consequences of TCP buffer bloat, IP-range tagging, random detect drops, or fair-queueing a class of traffic. Even so, there's aspects of QoS that I don't fully understand.

About a year ago I made a blog post on setting up QoS, so here it is if anyone is interested:

http://sean-the-electrofreak.blogspot.com/2012/05/im-back-today-im-posting-how-to-on-qos.html
 
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Vito_Corleone said:
How do you figure? That's like saying you can use OSPF without it being routing. QoS is just a generic term for a subset of technologies.
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Well, I guess if you want to go by the formal definition of QoS... but I don't really consider it QoS unless you're dealing with more than one class of traffic. If you use OSPF only to form an adjacency between two IPs of a /30 either side of a point-to-point, is it really routing? Not the best example, I know, but hopefully you see my point.
 
I've never heard anyone define QoS by how many groups of traffic are touched. "QoS" is just a group of technologies used to treat subsets of traffic different from other subsets of traffic. Policing, shaping, marking, etc, etc, fall under the QoS umbrella (I feel like a broken record). Saying policing (or shaping, marking, etc) isn't QoS, or that they're the "same thing", is false. These technologies are just different facets of QoS as a whole.

Your analogy doesn't really work for me. So, in your scenario, you have used a routing protocol to form a routing adjacency between two routers. If you aren't routing any packets, you aren't actually using the technology. If I turn on a router with all of its interfaces down, is it no longer a router? Doesn't make sense.
 
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