Chapter 9. Quality of Service

Quality of service (QoS) is an important aspect of any IP service offering. QoS helps define an important component of the service level agreement (SLA): packet delivery. The guaranteed and timely delivery of packets is necessary for applications, such as voice and video. The unsatisfactory delivery of packets results in an undesired user experience that might eventually result in a negative perception of the network. The existing user experience of the Internet has defined a grade of service called best effort. This Internet grade of service is usually assumed to be best effort packet delivery with no security or bandwidth guarantees but providing ubiquitous presence. Packets are delivered to the destination if they can be with no regard for delay, jitter, or even guarantee of delivery. This might be enough for most applications we commonly use, such as web browsing, e-mail, and Internet chat.

On the other hand, when it comes to the delivery of business-critical traffic, in most cases, best effort delivery of traffic is no longer sufficient. Many applications require bandwidth guarantees, and some also require delay and jitter guarantees. Any service delivered with MPLS must also be capable of delivering QoS to meet the needs of business-critical applications. Applications, such as voice and video, have stringent requirements with respect to jitter and packet loss. These days, highly efficient codecs are used that can mask some delay and jitter with buffering, encoding, and decoding techniques. Nevertheless, despite these efficient codecs, bandwidth, delay, and jitter guarantees from the network are still needed for better quality of experience (QoE).

This chapter discusses the QoS requirements and the available QoS tools and techniques of an IP network. It also explains how the IP QoS can be further enhanced using MPLS components.