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Colloquium - Sahu

Supporting Heterogeneous Services in the Internet
Sambit Sahu
University of Massachusetts
4/13/2000
11:00am-12:00pm

The rapid growth of the Internet has been accompanied by an evolution of new applications, ranging from simple data services to complex applications such as IP telephony, video on demand, and interactive multimedia communication. These new applications require an end-to-end IP architecture that can support multiple levels of service while preserving the scalability and simplicity of the current so-called ``best-effort'' Internet service model. I examine and propose network and end-system support for these cutting-edge applications.

In the first part of the talk, I focus on scalable network support for providing different classes of services to multimedia applications. In particular, I focus on the achievable services and limitations of the recently proposed differentiated services (diffserv) architecture in which simple mechanisms are used within the network core and more complicated functionality is possible only at the network edge. First I determine the mechanisms at the network core that are best suited to provide service differentiation. In order to do so, I compare the ability of proposed diffserv mechanisms in providing delay and loss differentiation across service classes. Next I examine the impact of diffserv mechanisms on the applications that use TCP congestion control protocol. I present a simple and yet accurate analytical model for TCP when ``profile-based'' marking is used at the network edge for providing service differentiation. Using this model, I examine whether it is possible to provide rate guarantees to TCP flows by solely setting the profile parameters at the network edge. I find that it is not always easy to regulate or guarantee the rate achieved by a TCP flow using this approach. I derive conditions that determine what rates are achievable and provide insights for choosing appropriate profile parameters for these achievable services. These observations are validated in a testbed implementation using PCs running modified Linux kernel.

In the second part of my talk, I focus on the end-system and propose solutions for handling the variable resource requirements of multimedia streaming applications. I show that commonly used round-based scheduling techniques for transferring data between the disk and the network interface are not well suited for the retrieval of multimedia streams. I propose lazy-EDF scheduling and show that it minimizes the server buffer and disk bandwidth requirements. Simulation studies with MPEG traces demonstrate the significant performance gains possible under lazy-EDF.

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