QOS-Enabled Networks

Traffic Types (QOS-Enabled Networks) Part 3

QOS Conclusions for VOIP Because voice heavily relies upon QOS, one must calculate the bandwidth that needs to be scheduled and protected (so that resources are available when necessary) to achieve the service and quality demands. The telephony world has a term for this, Counting Erlangs , named after the Danish mathematician and telephone engineer […]

Traffic Types (QOS-Enabled Networks) Part 4

Example of Internet Radio/Video Internet radio/video is an example of a new long-session application. Essentially, it is a plain old-fashioned TCP session with a twist: you download a media file of streamed content and watch it at the same time. Playback buffering solves possible reordering and jitter issues, and the user is not aware of […]

Classifiers (QOS-Enabled Networks) Part 1

In Part One of this topic, we discussed the concept of Per-Hop Behavior (PHB), in which each router in the network independently implements its own QOS settings because no signaling is possible either between neighbors or end to end. Consistency is achieved by applying a QOS configuration on each router in the network that applies […]

Classifiers (QOS-Enabled Networks) Part 2

Mixing Different QOS Realms So far, we have discussed scenarios consisting of a single realm in which the same technology is used from the source to the destination. Single-realm networks make things easier from the perspective of classifying traffic. However, in the real world, it is common to have a mix of technologies between the […]

Policing and Shaping (QOS-Enabled Networks) Part 1

The first part of this topic presented the policer and shaper tools as black boxes and gave a high-level view of their functionalities. This topic goes one step further and takes a closer look at the fundamental mechanics of these tools. Policers are implemented using the concept of a token bucket, while shapers use leaky […]

Policing and Shaping (QOS-Enabled Networks) Part 2

Dual-Rate Token Buckets A policer can be defined to simply limit all traffic indiscriminately to a certain bandwidth, or it can be defined to be more granular. For an example of a scenario requiring greater granularity, consider that all traffic arriving from a customer should be globally policed to 10 Mbps and that the input […]

Queuing and Scheduling (QOS-Enabled Networks) Part 1

Throughout this topic, we have always referred to the queuing and scheduling tool as the star of the QOS realm, the tool that makes crystal clear the principle of benefiting some at the expense of others. In this topic, we analyze the internals of the queuing and scheduling mechanism that allow such differentiation. But first, […]

Queuing and Scheduling (QOS-Enabled Networks) Part 2

Priority Queuing For applications that are sensitive to delay and that are not able to handle packet loss, the priority queuing (PQ) scheduling algorithm provides a simple method of supporting differentiated service classes. After a classification scheme has classified the packets and placed them into different queues with different priorities, the PQ algorithm handles the […]

Queuing and Scheduling (QOS-Enabled Networks) Part 3

Priority-Based Deficit Weighted Round Robin Introducing the deficit counter allows the WRR algorithm to be aware of bandwidth and improves the fairness. But for certain traffic types, fairness is not the desired behavior. What is needed is a priority scheduling similar to PQ, but that preserves the benefits of DWRR. To achieve predictable service for […]

Advanced Queuing Topics (QOS-Enabled Networks) Part 1

This topic discusses more advanced scenarios involving over-provisioning and guaranteed rates that are used in large-scale queues to differentiate shaping rates. This topic touches on the debate about the optimal size of the queues and different memory allocation techniques. Finally, the topic details the famous (or infamous) RED (Random Early Discard ) concept. Hierarchical Scheduling […]