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The Internet and the Internet Protocol (IP) were designed to provide a best-effort, fair datagram delivery service. With the tremendous increase in traffic volume, and the introduction of new real-time, multimedia, and multicasting applications, the traditional Internet protocols and services are woefully inadequate. The first step to fixing this problem was the introduction of the Integrated Services Architecture (ISA) and the related RSVP reservation protocol.
ISA and RSVP are intended to support quality of service (QoS) offering in the Internet and in private internets. Although ISA in general and RSVP in particular are useful tools in this regard, these features are relatively complex to deploy. Further, they may not scale well to handle large volumes of traffic because of the amount of control signaling required to coordinate integrated QoS offerings and because of the maintenance of state information required at routers.
As the burden on the Internet grows, and as the variety of applications increases, there is an immediate need to provide differing levels of QoS to different traffic flows. The differentiated services (DS) architecture is designed to provide a simple, easy-to-implement, low-overhead tool to support a range of network services that are differentiated on the basis of performance. Several key characteristics of DS contribute to its efficiency and ease of deployment:
Although DS is intended to provide a simple service based on relatively simple mechanisms, the set of RFCs related to DS is relatively complex. In his book Differentiated Services for the Internet, Kalevi Kilkki has done an admirable job of presenting both the forest and the trees of this important new Internet facility.
Part I of the book provides background, including a look at traffic management on the Internet prior to the introduction of DS and the way in which the DS working group tackled the problem. Part II looks at the use of DS within a single network domain. This part begins with a detailed look at the overall framework for DS. In addition to looking at the defined services, Kilkki provides the technical background that explains the choices made. Among the technical issues explored are the efficiency of statistical multiplexing under various assumptions, the issue for predictability of quality, and a comparison of service models for guaranteed service and relative service. The book then moves on to look at the user interface to DS, including overall service models available to various applications, ways to request a specific service, and pricing structure. Finally, Part II goes "under the hood" to look at how differentiated services are implemented. Issues addressed include tools for traffic handling in boundary nodes, tools for traffic handling in interior nodes, and network operation and management issues.
Part III deals with the use of DS across multiple domains and the interworking issues that are raised. Among other issues, Kilkki covers interoperability between a pure best-effort domain and a DS domain, mappings between differentiated services and integrated services, and the implementation of DS in ATM-based networks. The book includes examples of how DS can be used in specific configurations.
Differentiated Services for the Internet is well-organized, well-written, and packs in a lot of detail. I recommend it for anyone interested in this topic.
-- William Stallings
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