The majority of business-critical applications such as Web applications, database servers, and enterprise messaging systems have been successfully virtualized, proving the benefits of virtualization for reducing cost and streamlining IT management. However, the adoption of virtualization in the area of latency-sensitive applications has been slow partly due to unsubstantiated performance concerns. By taking VoIP service as an example, this paper demonstrates that vSphere 5 brings the same virtualization benefits to latency-sensitive applications, and vSphere 5 does this while driving good performance. In particular, vSphere 5 delivers excellent out-of-the-box performance in terms of voice quality when running VoIP service. VoIP applications are characterized by latency-sensitivity that dictates audio data be delivered at regular intervals to achieve good voice quality. Irregular delivery may lead to packet drops, severely deteriorating user experience. Therefore, timely processing and delivery of audio data is critically important to VoIP service. In the virtualized environment, however, meeting this requirement for VoIP applications is more challenging due to the additional layer of scheduling virtual machines (VMs) and processing network packets. Despite such challenges, vSphere 5 is able to achieve great performance for VoIP applications thanks to the following reasons. First, vSphere 5 facilitates the highly optimized networking stack and paravirtualized device drivers to minimize virtualization overhead, adding little variance in packet delivery1. The overhead is usually in the order of tens of microseconds that are negligible, especially to VoIP applications, where packets need to be delivered at intervals of tens of milliseconds. Second, vSphere 5 gives each VM a fair share of CPU2, ensuring the predictable processing of audio data even under high CPU contention when running multiple VMs. Finally, the Network I/O Control (NetIOC) feature allows VoIP traffic to be isolated by partitioning physical network bandwidth. This helps to achieve the intended voice quality when VoIP traffic competes for shared network resources. This paper illustrates that: • Excellent out-of-the-box VoIP performance is achieved with a large number of users served by a commercial VoIP media server hosted on vSphere 5. • vSphere 5 is able to maintain great VoIP performance when running a large number of instances of VoIP server; results showed that vSphere 5 provided good performance even when running 12 instances configured with a total of 48 vCPUs on a system with 8 cores, utilizing more than 90% of the physical CPUs. • With Network I/O Control (NetIOC), vSphere 5 is able to preserve voice quality under high contention for network resources.
http://www.vmware.com/files/pdf/techpaper/voip-perf-vsphere5.pdf
- Support for connecting directly to a vSphere host (resolves Null Pointer Exception) 
