Many production datacenters nowadays service multiple applications with dynamically allocated network bandwidth, and some applications are time-critical so their data transfers or flows are constrained by deadlines. To meet deadlines, several flow scheduling schemes for datacenter networks are proposed, but most of them are unaware of bandwidth variations, leading to suboptimal throughputs. In this paper, we present a flow scheduling scheme, called UBAS, to improve deadline-meeting throughputs for time-critical applications with uncertain time-varying bandwidth allocations. First, we model an optimization problem of scheduling deadline-constrained flows under uncertain time-varying bandwidth allocations to maximize the expected deadline-meeting throughput. The problem is NP-hard. Then, we propose an approximation algorithm under a mild condition for the problem in a special case, where bandwidth allocations are certain, as well as a conditional approximation algorithm for the problem in general. To adapt to practice, scalable and online variants of the algorithm are also presented. In evaluation, we conduct simulations based on a real traffic trace in a production datacenter. The results demonstrate that, with severe practical settings, UBAS still achieves nearly optimal deadline-meeting throughputs. Moreover, the throughput improvements of UBAS against existing bandwidth-agnostic schemes are more substantial when the variance of bandwidth allocations over time increases.

Virtual cluster is a useful resource descriptive model, in terms of virtual machines (VMs) and link bandwidth, for many data center applications that require predictable performance. Bandwidth-constrained data centers often use reservation schemes to statically allocate underlying physical resources to virtual clusters. However, due to highly varying workloads, existing reservation schemes may place VMs improperly, causing a waste of bandwidth reservation and eventually leading to rejecting new virtual cluster requests even the VM capacity is sufficient. In this paper, we propose a mechanism to detect and rectify such bandwidth-wasting VM placements via VM reshuffling. To compute a new VM placement accommodating new requests as many as possible, we formulate an optimization problem, with the objective of minimizing the reservations of limited bandwidth. The problem is NP-hard. We propose two efficient algorithms for a practical special case and the general case of the problem respectively. To evaluate our mechanism, we conduct simulation with the settings close to real data center environments. The results show that our mechanism with VM reshuffling achieves a significant reduction in rejecting virtual cluster requests and increases data center throughput over various high loads.

Meeting flow deadlines is crucial for a business running its interactive applications in a shared datacenter. Current deadline-aware transport protocols fall short in terms of throughput and fairness, when datacenter tenants compete for network capacity by their deadline-sensitive traffic. This paper presents an admission control mechanism to work with a deadline-aware transport protocol. Following pay-as-you-use paradigm, we model a revenue-maximizing problem for the mechanism to admit a right fraction of deadline-constrained traffic to the underlying transport layer, while respecting per-flow fairness by an economic notion, envy-free pricing. To tackle fast-changing traffic, we propose a greedy algorithm for the problem in the mechanism, which can easily adopt a batch processing method to mitigate the incurred overhead. By packet-level simulation, we demonstrate that the admission control mechanism sustains high application throughput and good revenues in heavy traffic loads. In addition, we present two service policies, each of which is demonstrated to have a desirable service property in dynamic environments.

Increased network bandwidth is making desktop video conferencing an attractive application for an increasing number of computer users. Unfortunately, two competing standards for video conferencing signaling are in use, H.323 and SIP. In this paper we look at the interoperability between these two standards by developing a conferencing gateway that supports conferences involving both SIP and H.323 clients. By appropriately translating between H.323 and SIP operations, our prototype gateway supports basic multi-party video conferencing between NetMeeting (an H.323 client) and VIC (a SIP client) without modifications to the clients. However, our experiments also show that seamless interoperation would require changes to the client implementations and the standards.