Charles Shen

On TCP-based SIP server overload control

The Session Initiation Protocol (SIP) server overload management has attracted interest since SIP is being widely deployed in the Next Generation Networks (NGN) as a core signaling protocol. Yet all existing SIP overload control work is focused on SIP-over-UDP, despite the fact that TCP is increasingly seen as the more viable choice of SIP transport. This paper answers the following questions: is the existing TCP flow control capable of handling the SIP overload problem? If not, why and how can we make it work? We provide a comprehensive explanation of the default SIP-over-TCP overload behavior through server instrumentation. We also propose and implement novel but simple overload control algorithms without any kernel or protocol level modification. Experimental evaluation shows that with our mechanism the overload performance improves from its original zero throughput to nearly full capacity. Our work leads to the important general insight that the traditional notion of TCP flow control alone is incapable of managing overload for time-critical session-based applications, which would be applicable not only to SIP, but also to a wide range of other common applications such as database servers.

The impact of TLS on SIP server performance

Securing Voice over IP (VoIP) is a crucial requirement for its successful adoption. A key component of this is securing the signaling path, which is performed by the Session Initiation Protocol (SIP). Securing SIP can be accomplished by using Transport Layer Security (TLS) instead of UDP as the transport protocol. However, using TLS for SIP is not yet widespread, perhaps due to concerns about the performance overhead. This paper studies the performance impact of using TLS as a transport protocol for SIP servers. We evaluate the cost of TLS experimentally using a testbed with OpenSIPS, OpenSSL, and Linux running on an Intel-based server. We analyze TLS costs using application, library, and kernel profiling and use the profiles to illustrate when and how different costs are incurred. We show that using TLS can reduce performance by up to a factor of 17 compared to the typical case of SIP-over-UDP. The primary factor in determining performance is whether and how TLS connection establishment is performed due to the heavy costs of RSA operations used for session negotiation. This depends both on how the SIP proxy is deployed and what TLS operation modes are used. The cost of symmetric key operations such as AES, in contrast, tends to be small. Network operators deploying SIP-over-TLS should attempt to maximize the persistence of secure connections and will need to assess the server resources required. To aid them, we provide a measurement-driven cost model for use in provisioning SIP servers using TLS. Our cost model predicts performance within 15% on average.

A VoIP Privacy Mechanism and its Application in VoIP Peering for Voice Service Provider Topology and Identity Hiding

Voice Service Providers (VSPs) participating in VoIP peering frequently want to withhold their identity and related privacy-sensitive information from other parties during the VoIP communication. A number of existing documents on VoIP privacy exist, but most of them focus on end user privacy. By summarizing and extending existing work, we present a unified privacy mechanism for both VoIP users and service providers. We also show a case study on how VSPs can use this mechanism for identity and topology hiding in VoIP peering.

BIM and sensor-based data management system for construction safety monitoring

Purpose This research aims to investigate the integration of real-time monitoring of thermal conditions within confined work environments through wireless sensor network (WSN) technology when integrated with building information modelling (BIM). A prototype system entitled confined space monitoring system (CoSMoS), which provides an opportunity to incorporate sensor data for improved visualization through new add-ins to BIM software, was then developed. Design/methodology/approach An empirical study was undertaken to compare and contrast between the performances (over a time series) of various database models to find a back-end database storage configuration that best suits the needs of CoSMoS. Findings Fusing BIM data with information streams derived from wireless sensors challenges traditional approaches to data management. These challenges encountered in the prototype system are reported upon and include issues such as hardware/software selection and optimization. Consequently, various database models are explored and tested to find a database storage that best suits the specific needs of this BIM-wireless sensor technology integration. Originality value This work represents the first tranche of research that seeks to deliver a fully integrated and advanced digital built environment solution for automating the management of health and safety issues on construction sites.

Measurement and Evaluation of ENUM Server Performance

ENUM is a DNS-based protocol standard for mapping E.164 telephone numbers to Internet Uniform Resource Identifiers (URIs). It places unique requirements on the existing DNS infrastructure, such as data scalability, query throughput, response time, and database update rates. This paper measures and evaluates the performance of existing name server implementation as ENUM servers. We compared PowerDNS (PDNS), BIND and Navitas. Results show that BIND is not suitable for ENUM due to its poor scaling property. Both PDNS and Navitas can serve ENUM. However, Navitas turns out to be highly optimized and clearly outperforms PDNS in all aspects we have tested. We also instrumented the PDNS server to identify its performance bottleneck and investigated ways to improve it.

Routing dynamics measurement and detection for next step Internet signaling protocol

A next step in signaling (NSIS) protocol is currently under standardization by the Internet Engineering Task Force (IETF) to support various applications that need to manipulate control information along the flow path. This paper addresses the NSIS protocol and IP routing interaction problem. We conducted routing measurement experiments to characterize the current Internet path dynamics, and discussed the impact of the observations on NSIS protocol design. The focus of our study is route change. We introduce NSIS-affecting route changes and define them in typical NSIS deployment models. With the NSIS deployment models in mind, we evaluate the simple packet TTL monitoring route change detection method. Finally, we propose a new route change detection method based on one-way-delay monitoring and provide preliminary evaluation.

Multistakeholder Conflict Minimization–Based Layout Planning of Construction Temporary Facilities

AbstractThe layout planning of construction temporary facilities (CTFs) is a specific construction site layout problem. Despite considerable research undertaken to determine satisfactory layouts of...

Open Data Landscape: A Global Perspective and a Focus on China

Governments are producing significant public data that, if made open, is expected to create enormous social and commercial value as well as improve the civil governance. Unleashing the true power of open public data requires a much better understanding of its ecosystem than is known currently. This paper surveys the global open data landscape by taking into account the Open Data Barometer (ODB) ranking system and its three sub-indexes - readiness, implementation and impact. These indexes are compared and analyzed on the basis of income levels of the ODB ranked countries. Finally, using air quality open data, data availability in developing countries like China is compared with countries of better practices such as UK and US. The comparison helps in understanding the current situation and barriers in opening data in China.

Application Layer Feedback-based SIP Server Overload Control

A SIP server may be overloaded by emergency-induced call volume, “American Idol” style flash crowd effects or denial of service attacks. The SIP server overload problem is interesting especially because the cost of serving and rejecting a SIP session could be in the same neighborhood. For this reason, the built-in SIP overload control mechanism based on generating rejection messages could not prevent the server from entering congestion collapse at heavy load. The SIP overload problem calls for a pushback control solution in which the potentially overloaded receiving server may notify its upstream sending servers to have them send only the amount of load within the receiving server’s processing capacity. The pushback framework can be achieved by SIP application layer rate-based feedback or window-based feedback. We propose three new window-based feedback algorithms and evaluate them together with two existing rate-based feedback algorithms. We compare the different algorithms in terms of number of tuning parameters and performance under both steady and dynamic load. Furthermore, we identify two categories of fairness requirements for SIP overload control, namely, user-centric and provider-centric fairness. With the introduction of a new double-feed SIP overload control architecture, we show how the algorithms can meet those fairness criteria.

SEM-Based Value Generation Mechanism from Open Government Data in Environment/Weather Sector

Environmental issues are harmful effects of human activities on the biophysical environment. More and more citizens are engaged in the open data movement for different purposes, in particular, emerging private companies are being built on Open Government Data (OGD) to predict extreme weather events for environmental protection, to satisfy more social requirements (e.g. job creation) and to make economic profits, simultaneously. Emerging companies are utilizing OGD to generate values. Building on a synthesis of the OGD literature and established theories of value generation, we develop a structural equation modelling (SEM)-based model to explore the causal relationship between OGD and value generation. This study constructs the conceptual structural equation model and lays a foundation for the upcoming research.