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We propose and compare alternative protocols, architectures, and controls for providing long distance (LD) voice services over asynchronous transfer mode (ATM) and Internet protocol (IP)-based networks. ATM standards and products are already mature enough for high-quality voice transport over a multiservice network infrastructure. The main design choices we must make are related to voice processing at the synchronous transfer mode (STM)-ATM interface, signaling protocols, and appropriate use of permanent virtual circuits (PVCs) and switched virtual circuits (SVCs). We compare the various alternatives along these dimensions. High-quality LD voice service over IP backbones is still a challenge. We propose different alternatives for providing such a service over a managed, multiservice IP network. First we consider a simple architecture involving line-speed forwarding, priority scheduling for voice over data, connection admission controls (at signaling gateways), and virtual provisioning servers. We then enhance the simple architecture to add hierarchical bandwidth guarantees, scheduling, and buffer management made available by emerging Layer 3/Layer 4 IP switches. We show that the basic and enhanced architectures allow integration of LD voice service with the best-effort service and multiservice virtual private networks (VPNs), respectively.

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SUMMARYVoice over Internet protocol (VoIP) is a technology that enables the transmission of voice over an IP network. Recent years have witnessed heavy investment in this area in the commercial world. For VoIP to replace Public Switched Telephone Network (PSTN), it should provide voice quality comparable to circuit-switched PSTN networks. This paper addresses the mechanisms to guarantee VoIP quality of service (QoS). The focus is given to the call admission control, which blocks voice calls when the required resources are not available to guarantee the QoS for the call. We review call admission control approaches that can be applied to VoIP, and describe the advantages and disadvantages of each approach. In the second part of the paper, we present a measurement-based admission control scheme that achieves QoS in an efficient and scalable manner. The scheme uses voice traffic load measurements at each router link to compute link-level blocking policies for new call attempts. Then, these policies are translated into pathlevel blocking policies, which are applied to new call set-up requests. The performance of the scheme is presented for single and multiple-priority voice calls.