QOS-Enabled Networks

Tools and Foundations

Miguel Barreiros, Peter Lundqvist

• Publisher: Wiley
• Year: 2015
• Print ISBN:
  9781119109105
• eBook ISBN:
  9781119109129
• Edition: 2
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería eléctrica y telecomunicaciones

Written by two experts in the field who deal with QOS predicaments every day and now in this 2nd edition give special attention to the realm of Data Centers, QoS Enabled Networks: Tools and Foundations, 2nd Edition provides a lucid understanding of modern QOS theory mechanisms in packet networks and how to apply them in practice. This book is focuses on the tools and foundations of QoS providing the knowledge to understand what benefits QOS offers and what can be built on top of it.

Part I
The QOS Realm

1
The QOS World

Quality of Service (QOS) has always been in a world of its own, but as the technology has been refined and has evolved in recent years, QOS usage has increased to the point where it is now considered a necessary part of network design and operation. As with most technologies, large-scale deployments have led to the technology becoming more mature, and QOS is no exception.

The current trend in the networking world is convergence, abandoning the concept of several separate physical networks in which each one carries specific types of traffic, moving toward a single, common physical network infrastructure. This is old news for the Internet and other service providers, however, a novelty in other realms such as the Data Center. The major business driver associated with this trend is cost reduction: one network carrying traffic and delivering services that previously demanded several separate physical networks requires fewer resources to achieve the same goal.

One of the most striking examples is voice traffic, which was previously supported on circuit-switched networks and is now delivered on the “same common” packet-switched infrastructure. Also, in modern Data Centers the operation of a server writing into the hard drive, the disk, is done using a networking infrastructure that is shared with other traffic types.

The inherent drawback in having a common network is that the road is now the same for different traffic types, which poses the challenge of how to achieve a peaceful coexistence among them since they are all competing for the same network resources.

Allowing fair and even competition by having no traffic differentiation does not work because different types of traffic have different requirements, just like an ambulance and a truck on the same road have different needs. There is always the temptation of simply making the road wider, that is, to deploy network resources in an over-provisioned manner following the logic that although the split of resources was not ideal, so many free resources would be available at all times that the problem would be minimized. However, this approach has some serious drawbacks. First, in certain networks, the traffic flows and patterns are not predictable making it impossible to know the required resources beforehand. Secondly, it works against the major business driver behind network convergence, which is cost reduction. And third, such over-provisioning needs to be done not only for the steady state but also to take into account possible network failure scenarios.

QOS does not widen the road. Rather, it allows the division of network resources in a nonequal manner, favoring some and shortchanging others instead of offering an even split of resources across all applications. A key point with QOS is that a nonequal split of resources implies that there cannot be “win–win” situations. For some to be favored, others must be penalized. Thus, the starting point in QOS design is always to first select who needs to be favored, and the choice of who gets penalized follows as an unavoidable consequence.

In today’s networks, where it is common to find packet-oriented networks in which different types of traffic such as voice, video, business, and Internet share the same infrastructure and the same network resources, the role of QOS is to allow the application of different network behaviors to different traffic types.

Hence, for a specific traffic type, two factors must be considered, characterizing the behavior that the traffic requires from the network and determining which QOS tools can be set in motion to deliver that behavior.

1.1 Operation and Signaling

The QOS concept is somewhat hard to grasp at first because it is structurally different from the majority of other concepts found in the networking world. QOS is not a standalone service or product but rather a concept that supports the attributes of a network by spanning horizontally across it.

QOS can be split into two major components: local operation and resource signaling. Local operation is the application of QOS tools on a particular router (or a switch, a server, or any QOS-capable device).

Resource signaling can be defined as the tagging of packets in such a way that each node in the entire path can decide which QOS tools to apply in a consistent fashion to assure that packets receive the desired end-to-end QOS treatment from the network.

These two components are somewhat similar to the IP routing and forwarding concepts. Routing is a task performed jointly by all routers in the network. All routers exchange information among them and reach a consistent agreement in terms of the end-to-end path that packets follow. As for forwarding, each router performs the task individually and independently from the rest of the network using only local information.

Routing is comparatively more complex than forwarding, because it involves cooperation among all the routers in the network. However, routing does not need to work at wire speed. Forwarding is simpler. It is a task performed by a router individually and independently. However, it must operate at wire speed.

An analogy between routing and forwarding, and QOS resource signaling and local operation, can be drawn. QOS resource signaling is somewhat analogous to the routing concept. It involves all routers in the network but has no requirement to work at wire speed. QOS local operation is analogous to the forwarding concept. Like forwarding, QOS local operation is, in concept, simpler, and each router performs it independently and individually. Also, QOS local operation must operate at wire speed.

However, there is a major difference between QOS resource signaling and routing; there are no standardized specifications (such as those which exist for any routing protocol) regarding what is to be signaled, and as a result there is no standard answer for what should be coded on all network routers to achieve the desired end-to-end QOS behavior. The standards in the QOS world do not give us an exact “recipe” as they do for routing protocols.

1.2 Standards and Per-Hop Behavior

The two main standards in the IP realm that are relevant to QOS are the Integrated Services (IntServ) and the Differentiated Services (DiffServ). IntServ is described in RFC1633 [1] and DiffServ in RFC2475 [2].

IntServ was developed as a highly granular flow-based end-to-end resource reservation protocol, but because of its complexity, it was never commonly deployed. However, some of its concepts have transitioned to the MPLS world, namely, to the Resource Reservation Protocol (RSVP).

The DiffServ model was developed based on a class scheme, in which traffic is classified into classes of service rather than into flows as is done with IntServ. Another major difference is the absence of en...

Table of contents

• Cover
• Title Page
• Table of Contents
• About the Authors
• Foreword
• Preface
• Acknowledgments
• Abbreviations
• Part I: The QOS Realm
• Part II: Tools
• Part III: Case Studies
• Index
• End User License Agreement