Virtualization has fundamentally changed the data center network. The last hop of the network is no longer handled by a physical network switch, but rather is typically performed in software inside the server to switch among virtual machines hosted by that server.

This paper presents mechanisms and optimizations to reduce the overhead of network interface virtualization when using the driver domain I/O virtualization model. The driver domain model provides benefits such as support for legacy device drivers and fault isolation. However, the processing overheads incurred in the driver domain to achieve these benefits limit overall I/O performance. This paper demonstrates the effectiveness of two approaches to reduce driver domain overheads. First, Xen is modified to support multi-queue network interfaces to eliminate the software overheads of packet demultiplexing and copying. Second, a grant reuse mechanism is developed to reduce memory protection overheads. These mechanisms shift the bottleneck from the driver domain to the guest domains, improving scalability and enabling significantly higher data rates. This paper also presents and evaluates a series of optimizations that substantially reduce the I/O virtualization overheads in the guest domain. In combination, these mechanisms and optimizations increase the maximum throughput achieved by guest domains from 2.9Gb/s to full 10 Gigabit Ethernet link rates.

This paper characterizes the impact that the use of UDP versus TCP has on the performance and scalability of the OpenSER SIP proxy server. The session initiation protocol (SIP) is an application-layer signaling protocol that is widely used for establishing voice-over-IP (VoIP) phone calls. SIP can utilize a variety of transport protocols, including UDP and TCP. Despite the advantages of TCP, such as reliable delivery and congestion control, the common practice is to use UDP. This is a result of the belief that UDP's lower processor and network overhead results in improved performance and scalability of SIP services. This paper argues against this conventional wisdom. This paper shows that the principal reasons for OpenSER's poor performance using TCP are caused by the server's design, and not the low-level performance of UDP versus TCP. Specifically, OpenSER's architecture for handling concurrent calls is responsible for most of the difference. Moreover, once these issues are addressed, OpenSER's performance using TCP is much more competitive with its performance using UDP.