In this article we identify the common building blocks that enable some networks to provide better than best-effort transfer guarantees to the traffic they carry. We consider the role signaling plays in such a network and argue in favor of pinned routes, with a highly efficient pinning process, to improve network stability and to ease the task of maintaining QoS guarantees in the face of changing network characteristics, including failures; the use of broad QoS classes to determine the path that a particular flow should follow through the network; and providing the flexibility of specifying the detailed QoS for the flow, if needed, at any arbitrary time during the life of the flow. We conclude that a flexible signaling architecture is an essential enabling component of any QoS-aware network. We present an overview of the design and implementation of UNITE, as an example of a signaling architecture that embodies these attributes. More generally, we consider the relationship between QoS-related signaling and other protocols and mechanisms that may form part of an overall QoS-enabled network and service infrastructure.
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