QoS-Sensitive Flows: Issues in IP Packet Handling

Imagine a network technology that routinely loses information, experiences variable and unpredictable delay in data delivery, and makes no distinction between applications with different communication requirements. Next, imagine that the use of this technology is growing exponentially and that, even as networks become increasingly congested, its applications are being extended to global-scale voice and video. This scenario describes the situation we face in supporting real-time applications over an IP-based infrastructure. Such applications involve data flows that have quality-of-service (QoS) requirements. A QoS-sensitive data flow cannot readily tolerate the effects of packet loss, delay (and delay variation, or jitter), and fluctuations in network throughput. In this article, we examine the problems in attempting to make the existing IP infrastructure do what it was never designed to do—provide QoS support for integrated services to both real-time and non-real-time applications. We concentrate on the issues and principles concerning router modification for IP packet handling.