What is the difference between qos and traffic shaping

From this example, 8, bits is our Bc required to maintain a CIR of 64Kbps over a period of 1 second, at msec time interval. We can also calculate Bc using that formula above i.

Note : Remember that while Tc is usually expressed in msec, when used in that calculation, it is converted to seconds. For example, msec is 0. So in the case of traffic shaping and using our example, if a packet of bytes which is bits arrives at time 0sec, it will be sent without any delay because there are enough tokens bits in the bucket.

However, if another bytes packet arrives within the same time interval, that packet will be delayed until the next interval. One more term we will talk about before going back to our lab is the Excess Burst Be.

Also noticed that I have applied the policy map in the outbound direction. On Cisco devices, traffic shaping can only be applied outbound. We can view our configuration using the show policy-map command:. We can also view the status of our traffic shaping using the show policy-map interface command:. As you can see, some packets have already been matched because we are using the class-default class map. However, also notice that the average round-trip time has gone up to ms from ms when we did it with traffic policing.

This tells us that some packets are being delayed. We can confirm this using the show policy-map interface command:. Note : In this case, we still lost packets. A better alternative will be to use a CIR less than e. In our labs so far, we have not used the Be value. If you want to enable this value, there are certain things to keep in mind:. Let us change the configuration on our devices to match these settings. For the policing, we are transmitting packets that conform, transmitting packets that exceed but reclassifying them to a lower DSCP value Best Effort , and dropping all packets that violate.

As you can see, even though some of those packets exceeded, they were still transmitted without issues. You can play around with higher ping packet sizes till you find the one that causes a violation. This brings us to the end of this article where we have looked at two QoS features that are often used in a complementary manner.

While traffic policing is usually used to enforce a hard rate limit, traffic shaping is used to conform to that rate limit by delaying packets in a buffer. Owokade thank you very much for in detail an simple explanation of QoS techniques. I am trying to reproduce this case scenario on my GNS3 setup and would like to include measurement graphs in my paper.

Did You manage to extract graphs shown in this article with some monitoring software attached to GNS3, or You just draw them on your own? Including them would be very helpful and would improve my paper a lot. Nice write-up. To convert bits to bytes you simply divide the bits by 8 not 8 bits.

Your email address will not be published. Notify me of followup comments via e-mail. You can also subscribe without commenting. This site uses Akismet to reduce spam. Eickst said:. Liger88 2[H]4U. Joined Feb 14, Messages 2, Electrofreak [H]ard Gawd. Joined Aug 5, Messages 1, 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. 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.

Last edited: May 26, Electrofreak 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. I've never heard anyone define QoS by how many groups of traffic are touched.

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.

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