Sejun Song

Probabilistic approach to switched Ethernet for real-time control applications

Switched Ethernet combines Ethernet and ATM switching technology. The authors propose a probability based admission control algorithm over switched Ethernet to provide real time capability for control applications. The main contribution of the paper is providing an efficient means of estimating the queuing possibilities and the corresponding queuing delays inside the switch for periodic control system application. The approach enables switched Ethernet admission control without sophisticated packet scheduling in switches or middleware on hosts. The algorithm is analyzed and implemented to verify its feasibility.

Outage Analysis of a University Campus Network

Understanding outage and failure characteristics of a network is important to assess the availability of the network, determine failure source for trouble-shooting, and identify weak areas for network availability improvement. However, there has been virtually no failure measurement and analysis on access networks. In this paper, we carry out an in-depth outage and failure analysis of a university campus network using a rich set of both node outage and link failure data. We investigate the aspects of spatial and temporal localities of failures and outages, the relation of link failure and node outage, and the impact of the hierarchical and redundant network design on outage. We find most of link failure events are not caused by node failures; frequent link up-down events may not lead to the corresponding nodes outage; for access layer switches that connect to end hosts, their link up-down events exhibit periodic patterns.

Energy efficient virtual network embedding for green data centers using data center topology and future migration

We formulate energy efficient virtual network embedding that incorporates energy costs of operation and migration for nodes and links.We prove the NP-hardness of the problem and develop a heuristic algorithm to minimize the energy consumption.We consider a practical intra-DC architecture to further improve energy efficiency.We conduct extensive evaluations and comparisons with existing algorithms to show that the proposed algorithm substantially saves energy consumption and allows high acceptance ratios. With the rapid proliferation of data centers, their energy consumption and greenhouse gas emissions have significantly increased. Some efforts have been made to control and lower energy consumption of data centers such as, proportional energy consuming hardware, dynamic provisioning, and virtualization machine techniques. However, it is still common that many servers and network resources are often underutilized, and idle servers spend a large portion of their peak power consumption.We first build a novel model of virtual network embedding in order to minimize energy usage in data centers for both computing and network resources by taking practical factors into consideration. Due to the NP-hardness of the proposed model, we develop a heuristic algorithm for virtual network scheduling and mapping. In doing so, we specifically take the expected energy consumption at different times, virtual network operation and future migration costs, and a data center architecture into consideration. Our extensive evaluation results show that our algorithm could reduce energy consumption up to 40% and take up to a 57% higher number of virtual network requests over other existing virtual mapping schemes.

Protocol independent multicast group aggregation scheme for the global area multicast

IP multicast is an important enabling service for the current and future Internet. With the explosive growth of the Internet, a challenging issue facing IP multicast is scalability, in particular, the problem of multicast forwarding state and control explosion. In this paper, we propose a new methodology to address the multicast scalability problem for backbone domains-multicast tunneling with branch filtering (MTBF). This multicast group aggregation scheme is designed on top of the inter-domain protocol architecture such as MASC/BGMF, and is independent of any underlying intra-domain multicast protocols. It aggregates multicast groups by constructing bolder router (BR)-based multicast routing trees and forwards data by using an encapsulation technique called multicast tunneling (MT). The feasibility and performance of our scheme is demonstrated through analysis and simulations.

NQAR: network quality aware routing in error-prone wireless sensor networks

We propose a network quality aware routing (NQAR) mechanism to provide an enabling method of the delay-sensitive data delivery over error-prone wireless sensor networks. Unlike the existing routing methods that select routes with the shortest arrival latency or the minimum hop count, the proposed scheme adaptively selects the route based on the network qualities including link errors and collisions with minimum additional complexity. It is designed to avoid the paths with potential noise and collision that may cause many non-deterministic backoffs and retransmissions. We propose a generic framework to select a minimum cost route that takes the packet loss rate and collision history into account. NQAR uses a data centric approach to estimate a single-hop delay based on processing time, propagation delay, packet loss rate, number of backoffs, and the retransmission timeout between two neighboring nodes. This enables a source node to choose the shortest expected end-to-end delay path to send a delay-sensitive data. The experiment results show that NQAR reduces the end-to-end transfer delay up to approximately 50% in comparison with the latency-based directed diffusion and the hop count-based directed diffusion under the error-prone network environments. Moreover, NQAR shows better performance than those routing methods in terms of jitter, reachability, and network lifetime.

Using RTT Variability for Adaptive Cross-Layer Approach to Multimedia Delivery in Heterogeneous Networks

A holistic approach should be made for a wider adoption of a cross-layer approach. A cross-layer design on a wireless network assumed with a certain network condition, for instance, can have a limited usage in heterogeneous environments with diverse access network technologies and time varying network performance. The first step toward a cross-layer approach is an automatic detection of the underlying access network type, so that appropriate schemes can be applied without manual configurations. To address the issue, we investigate the characteristics of round-trip time (RTT) on wireless and wired networks. We conduct extensive experiments from diverse network environments and perform quantitative analyses on RTT variability. We show that RTT variability on a wireless network exhibits greatly larger mean, standard deviation, and min-to-high percentiles at least 10 ms bigger than those of wired networks due to the MAC layer retransmissions. We also find that the impact of packet size on wireless channel is particularly significant. Thus through a simple set of testing, one can accurately classify whether or not there has been a wireless network involved. We then propose effective adaptive cross-layer schemes for multimedia delivery over error-prone links. They include limiting the MAC layer retransmissions, controlling the application layer forward error correction (FEC) level, and selecting an optimal packet size. We conduct an analysis on the interplay of those adaptive parameters given a network condition. It enables us to find optimal cross-layer adaptive parameters when they are used concurrently.

Reliability and Scalability Issues in Software Defined Network Frameworks

Software Defined Network (SDN) structure has been proposed for its flexibility in deployment and management. As an implementation of SDN structure, OpenFlow protocol decouples data plane and control plane so that flexible and programmable installation and management of forwarding rules are allowed. However, on the other hand, the decoupled structure raises additional computational and network resources consumption that even may lead to fatal disasters. In this study, we examine the issues of reliability and scalability of SDN under disaster scenarios on a GENI test-bed. Observations from our experiments show that more attention should be paid to improve the reliability and scalability of SDN and its frameworks.

Application Oriented Dynamic Resource Allocation for Data Centers Using Docker Containers

Docker offers an opportunity for further improvement in data centers’ (DCs) efficiency. However, existing models and schemes fall short to be efficiently used for Docker container-based resource allocation. We design a novel application oriented Docker container (AODC)-based resource allocation framework to minimize the application deployment cost in DCs, and to support automatic scaling while the workload of cloud applications varies. We then model the AODC resource allocation problem considering features of Docker, various applications’ requirements, and available resources in cloud data centers, and propose a scalable algorithm for DCs with diverse and dynamic applications and massive physical resources.

SuVMF: software-defined unified virtual monitoring function for SDN-based large-scale networks

Traffic and resource monitoring is the essential function for large-scale enterprises, service providers, and network operators to ensure reliability, availability, and security of their resources. For this reason, many large-scale enterprises and providers have been investing in various standalone dedicated monitoring solutions. However, they find the cost of a dedicated standalone appliance per-feature prohibitive, inflexible, slow to install and difficult to maintain. Network Function Virtualization (NFV)-based virtualization trends represent an attractive opportunity for such stakeholders trying to meet the above requirements while controlling OPEX and CAPEX. Although there are many advantages that virtualization of monitoring function brings, some challenges remained to be solved are ensuring scalability and performance of single or distributed multiple virtual monitoring functions and flexibility and easiness of virtual functions lifecycle management. In this paper, to address such problems, we propose a novel architecture of software-defined unified virtual monitoring function for SDN-based large-scale networks (SuVMF). SuVMF is an essential component to build a scalable, reliable, secure and high-performance SDN architecture by providing intelligent control and monitoring management abstraction and filtering layer. In this paper, we present design, implementation, and evaluation results of SuVMF.

Topology and migration-aware energy efficient virtual network embedding for green data centers

With the rapid proliferation of data centers, their energy consumption and green house gas emissions have significantly increased. Some efforts have been made to control and lower energy consumption of data centers such as proportional energy consuming hardware, dynamic provisioning and virtual-ization machine techniques. However, it is still common that many servers and network resources are often underutilized, and idle servers spend a large portion of their peak power consumption. We first built a novel model of a network virtualization in order to minimize energy usage in data centers for both computing and network resources by taking practical factors into consideration. Due to the NP-hardness of the proposed model, we have developed a heuristic algorithm for virtual network scheduling and mapping, considering expected energy consumption at different times, a data center architecture, and virtual network migration, as well as operation costs. Our evaluation results show that our algorithm could reduce energy consumption up to 40%, and take up to 57% higher number of virtual network requests over other existing virtual mapping schemes.