In this paper we present a framework for the emerging Internet Quality of Service (QoS). All the important components of this framework, i.e., Integrated Services, RSVP, Differentiated Services, Multi-Protocol Label Switching (MPLS) and Constraint Based Routing are covered. We describe what Integrated Services and Differentiated Services are, how they can be implemented, and the problems they have. We then describe why MPLS and Constraint Based Routing have been introduced into this framework, how they differ from and relate to each other, and where they fit into the Differentiated Services architecture. Two likely service architectures are presented, and the end-to-end service deliveries in these two architectures are illustrated. We also compare ATM networks to router networks with Differentiated Services and MPLS. Putting all these together, we give the readers a grasp of the big picture of the emerging Internet QoS. It is becoming apparent that several service classes will likely be demanded. One service class will provide predictable Internet services for companies that do business on the Web. Such companies will be willing to pay a certain price to make their services reliable and to give their users a fast feel of their Web sites. Whether mechanisms are even needed to provide QoS is a hotly debated issue. People arguing against QoS mechanisms say that fibers and Wavelength Division Multiplexing (WDM) will make bandwidth so abundant and cheap that QoS will be automatically delivered. People arguing for QoS mechanisms say that no matter how much bandwidth the networks can provide, new applications will be invented to consume them all. Therefore, mechanisms will still be needed to provide QoS. This argument is beyond the scope of this paper. Here we simply note that, even if bandwidth will eventually become abundant and cheap, it is not going to happen soon. For now, some simple mechanisms are definitely needed in order to provide QoS on the Internet. Our view is supported by the fact that all the major router/switch vendors now provide some QoS mechanisms in their high-end products [13] [14] [15] [16][17][18]. The Internet Engineering Task Force (IETF) has proposed many service models and mechanisms to meet the demand for QoS. Notably among them are the Integrated Services/RSVP model [4, 7] , the Differentiated Services (DS) model [22, 23] The Integrated Services model is characterized by resource reservation. For real-time applications, before data are transmitted, the applications must first set up paths and reserve resources. RSVP is a signaling protocol for setting up paths and reserving resources. In Differentiated Services, packets are marked differently to create several packet classes. Packets in different classes receive different services. MPLS is a forwarding scheme. Packets are assigned labels at the ingress of a MPLS-capable domain. Subsequent classification, forwarding, and services for the packets are based on the labels. Traffic Engineering is the process of arranging how traffic flows through the network. Constraint Based Routing is to find routes that are subject to some constraints such as bandwidth or delay requirement. Although there are many papers on each of Integrated Services, RSVP, Differentiated Services, MPLS, Traffic Engineering and Constraint Based Routing, to the best of the authors' knowledge, they are never discussed together in a single paper. As a result, it is difficult for readers to understand the relationships among them and to grasp the big picture of the QoS framework. In this paper, we give an introduction to Integrated Services, RSVP, Differentiated Services, MPLS, Traffic Engineering and Constraint Based Routing. We describe how they differ from, relate to, and work with each other to deliver QoS on the Internet. Through this, we intend to present the readers a clear overview of Internet QoS. The organization of the rest of the paper is as follows. In Sections 2-3, we describe Integrated Services, RSVP and Differentiated Services, their characteristics, mechanisms, and problems. A likely Differentiated Services architecture and the complete process for delivering end-to-end services in this architecture are also presented. MPLS and a service architecture based on MPLS are described in Section 4. In Section 5, we de-
More specifically, a first effort to give a global overview of Internet QoS is presented in REF .
Internet QoS: A big Picture
IEEE Network
Computer Science