Quality of Service for Converged Data and Voice over IP Networks

The datacom and telecom industries are going through a stage of unprecedented change, as new communication ecosystems evolve from isolated, application-specific networks. The industry is moving beyond telecommunications as a utility service, towards a converged voice and data network based on Ethernet protocol and Internet protocol (IP). Quality of service (QoS) has been a feature of voice communication networks almost since their inception. The extension of traditional voice QoS methods to data communication networks and the Internet has been a longstanding research topic, although for many years it was not considered a critical issue due to the inherent differences between data and voice traffic and the relatively low cost of overprovisioning bandwidth. In particular, over-provisioning of network bandwidth has been common practice since the earliest fiber-optic local-area networks (LANs) were deployed, and bandwidth on an optical network was found to be very economical. This practice has extended into widearea networks (WANs) and metropolitan-area networks (MANs), despite the initially higher capital equipment cost. Over-provisioned networks are considered simpler to manage (since there is no QoS mechanism to be configured), easier to troubleshoot, and resistant to certain types of denial of service (DoS) attacks from the network edge. Typically, such networks will not exhibit problems unless there is an unexpected, sustained burst of traffic (exceeding perhaps 60 percent of the provisioned network capacity) or if there is a network failure that significantly increases the load on a particular network segment beyond its nominal design parameters. However, the cost of over-provisioning has increased with the migration to higher data rates (10–40 Gbps in many networks), which offsets any savings in operational or management costs. Since overprovisioning does not scale well to larger, higher-data-rate networks, alternative approaches to providing QoS have received increased attention.