Chapter 13. Quality of Service Introduction

This chapter covers the following topics.

• ATM

• Frame Relay

• Internet Protocol

• MPLS and MPLS-TE

• DiffServ

Quality of service (QoS) refers to the capability of a network to provide better service to selected network traffic over various networking technologies. Network service providers (NSPs) implement QoS in customer wide-area networking (WAN) technologies, such as Asynchronous Transfer Mode (ATM), Frame Relay, IP/IP-VPN (IP-based Virtual Private Networks), and MPLS, which can use any of these underlying technologies. The primary goal of QoS is to provide priority to customer traffic across a network by dedicating bandwidth, controlling jitter and latency (required by some real-time and interactive traffic), and improving loss characteristics.

The abbreviations QoS and CoS (class of service) often are used interchangeably in discussions about transport technologies. These terms are different, however, as the following definitions show:

• QoS A measure that is inviolable. It is absolute in that when QoS is implemented in a network, the service provider guarantees that they will deliver measurable performance characteristics as defined by the QoS statements in the service level agreement (SLA) between the provider and the customer.

• CoS A relative measure defined by the NSP and is unrelated to quality measurements. For example, a service provider could advertise the following transmission Classes of Service:

  - Great

  - Good

  - Fair

  - Poor

  - Carrier pigeon

Technical Note: Analyzing Network Traffic Patterns

In determining which applications require QoS, the first step is to establish which applications are mission-critical. Netflow Accounting, Network-based Application Recognition (NBAR), or QoS Device Manager (QDM) can be used to analyze the network traffic patterns, as you see here:

• NetFlow Accounting provides network traffic detail and can be used to capture traffic classification or precedence associated with each flow.

• NBAR is a classification tool that can identify traffic up to the application layer, providing per-interface, per-protocol, and bi-directional statistics for each traffic flow traversing an interface.

• QDM is a Web-based network management application that provides a graphical user interface (GUI) for configuring and monitoring advanced IP-based QoS functionality in routers.

This chapter discusses QoS networking technologies found in ATM, Frame Relay, IP, and MPLS.