The exponential growth of Internet brings to focus the need to control
such large scale networks so that they appear as coherent, almost
intelligent, organ- isms. It is a challenge to regulate such a complex
network of heterogeneous elements with dynamically changing traffic
conditions. To make such a sys- tem reliable and manageable, the
decision making should be decentralized. It is desirable to find simple
local rules and strategies that can produce coherent and purposeful
global behavior. Furthermore, these control mechanisms must be adaptive
to effectively respond to continually varying network conditions. Such
adaptive, distributed, localized mechanisms would provide a scalable so-
lution for controlling large networks. The need for such schemes arises
in a variety of settings. In this monograph, we focus on localized
approach to quality of service routing. Routing in the current Internet
focuses primarily on connectivity and typi- cally supports only the
"best-effort" datagram service. The routing protocols deployed such as
OSPF use the shortest path only routing paradigm, where routing is
optimized for a single metric such as hop count or administrative
weight. While these protocols are well suited for traditional data
applications such as ftp and telnet, they are not adequate for many
emerging applications such as IP telephony, video on demand and
teleconferencing, which require stringent delay and bandwidth
guarantees. The "shortest paths" chosen for the "best effort" service
may not have sufficient resources to provide the requisite service for
these applications.