Public Switched Telephone Network Research Articles

QoS-aware path switching for VoIP traffic using SCTP

Voice over Internet protocol (VoIP) has been a prevalent multimedia service nowadays. It allows us to transmit voice data over IP networks. However, quality of service (QoS) is a major challenge to VoIP services. It must provide similar quality to traditional public switched telephone network or cellular phone services. Therefore, QoS related protocols have become important for real-time applications. Multi-protocol label switch (MPLS) is one of the important techniques to improve the network performance from QoS point of view. It employs label swapping to speed up packet forwarding. However, when a large number of users utilize VoIP services, the network congestion issue still exists. It causes delay, jitter and packet loss that affect VoIP QoS. In this paper, we propose a QoS-aware path switching strategy by using stream control transmission protocol (SCTP) in MPLS network to improve the VoIP traffic. This was done by employing SCTP selective acknowledgment mechanism to report the transmission parameters of primary path and to determine the criteria to switch to backup path. Simulation results show significant improvement in VoIP QoS.

Leveraging Broadband Access Expansion for PSTN Migration: A Case Study for Converged Fixed Access

Service providers (SPs) across the globe are initiating programs to transform their existing networks into all-Internet Protocol (IP) networks. Expanding both the reach and speed of broadband access in order to provide rich IP services has proven to be a sound business strategy that future-proofs SP investment and lays a strong foundation for a successful transformation. However, for fixed operators, the broadband access expansion initiative has focused mainly on enabling higher-speed data and video service offerings, rather than evolving or migrating the public switched telephone network (PSTN) voice network. This paper discusses industry perspectives on strategies adopted by SPs for evolving their PSTN voice network. In addition, it presents a case study of a fixed operator synergistically leveraging its broadband access expansion program for PSTN voice migration, in order to minimize its overall transformation costs. © 2012 Alcatel-Lucent.

UHF와 PSTN간 단대단 디지털 음성보안통신

전술무선통신망의 급격한 증가로 이기종망간 단대단 음성보안통신은 매우 중요한 보안이슈가 되어왔다. 일반적으로 고비도의 단대단 음성보안통신은 사용자 통신단말에 고비도의 암호알고리즘을 적용함으로써 가능하나, 이는 이기종망간 암호화된 데이터를 직접 전송할 수 없는 문제점을 필수적으로 야기시킨다. 다시 말해, 서로 다른 전술통신망 사이에 위치하는 망연동 게이트웨이에서 암호화 데이터에 대한 복호화 및 재암호화와 같은 부가절차가 필연적으로 요구된다. 본 논문에서는 이기종 전술통신환경에서 게이트웨이에서의 복호화 및 재암호화에 따른 문제점을 해결하고, 최적의 단대단 음성보안체계를 수립하기 위해 UHF와 PSTN 통신망간 단대단 음성보안통신 메커니즘을 제안하고 기존 메커니즘 대비 제안 메커니즘의 성능을 비교, 분석한다. 제안된 메커니즘은 망연동 게이트웨이에서의 복호화 및 재암호화에 따른 부가지연이 전혀 없고, 이기종망간 우수한 연동특성을 가진다. With the widely applications of tactical radio networks, end-to-end secure speech communication in the heterogeneous network has become a very significant security issue. High-grade end-to-end speech security can be achieved using encryption algorithms at user ends. However, the use of encryption techniques results in a problem that encrypted speech data cannot be directly transmitted over heterogeneous tactical networks. That is, the decryption and re-encryption process must be fulfilled at the gateway between two different networks. In this paper, in order to solve this problem and to achieve optimal end-to-end speech security for heterogeneous tactical environments, we propose a novel mechanism for end-to-end secure speech transmission over ultra high frequency (UHF) and public switched telephone network (PSTN) and evaluate against the performance of conventional mechanism. Our proposed mechanism has advantages of no decryption and re-encryption at the gateway, no processing delay at the gateway, and good inter-operability over UHF and PSTN.

A dynamic traffic allocation model of voice over internet protocol and public switched telephone network

PurposeCorporations with multiple national and international sites rely on telecommunication services such as public switched telephone network (PSTN) to deal with their customers and with vendors. Over the last few years, the cost of using PSTN for telecommunication has increased, thus adding considerable cost to business. The infrastructure of the internet is well placed now, and the continued growth of information technologies have made it cost effective to route voice calls over the internet, known as voice over internet protocol (VoIP). The purpose of this paper is to advance research, strategies and a predictive decision model that analyzes the cost of routing voice‐based traffic either via VoIP network or PSTN. This predictive decision model is based on the beta‐binomial distribution, and it computes the cost differential in tariff with respect to choice of routing the voice traffic between the VoIP network and the PSTN.Design/methodology/approachA call supported by the PSTN involves the establishment of an end‐to‐end circuit that is maintained for the duration of the call. A call supported by VoIP technology, by contrast, involves the transmission of many individual packets over an IP network. The cost of a VoIP call thus depends in part on the number and size of the packets that must be transmitted, i.e. the bandwidth required.FindingsGreat savings are realized when optimal number of calls would be routed through CCS vendors, as determined by the VoIP allocation model. The available bandwidth on the internet is capable of supporting VoIP at much cheaper rate than the expensive PSTN. Business could still buy into PSTN service if they require secured telecommunication services.Originality/valueThe paper tackles one of the most critical problems of minimizing the burden and costs of telecommunications by PSTN and VoIP.

The Effects of Legacy Pricing Regulation on Adoption of Broadband Service in the United States

We examine and document the effect of policy-relevant factors on broadband adoption. We focus on the role of the price of basic local service on broadband adoption, to determine whether and to what extent legacy telephone policies and associated pricing distortions interfere with the contemporary goal of increased broadband adoption. Legacy universal service policy suppressed basic local telephone rates for residential customers in some areas to below-cost levels, subsidized by a variety of other revenue sources, including switched access revenues, prices for non-basic features, and business rates. The economic theory supporting this policy was that lower prices for basic local service would encourage adoption of basic local service, encouraging universal connection to the public switched telephone network. Today, however, there is effectively universal subscription to some form of local telephone service, which may include wireless or wireline services that are provided at unregulated prices; and policy goals are transitioning away from promoting basic local service to promotion of universal broadband adoption.We hypothesize that subsidized prices for basic residential services depress broadband adoption decisions. There are two reasons that we anticipate such an effect. First, broadband service and stand-alone traditional voice service are economic substitutes insofar as consumers can use broadband for voice service by purchasing an over-the-top VoIP service. Second, some customers may purchase a stand-alone voice line only or primarily for dial-up Internet access, for which broadband service is a substitute. Hence, for both reasons, we would expect to find a positive relationship between the price of basic local service and broadband adoption, meaning that where basic local service prices are lower, broadband adoption is lower. Intuitively, the logic is that, for a given price of broadband, the higher is the price of stand-alone voice service, the lower is the price hurdle to adopting broadband instead. We test this theory using quarterly household-level data from the first quarter 2006 through the second-quarter 2010 for over 70,000 household observations. The data are from the nationwide TNS surveys and bill samples. Using a multinomial logit specification, we find that higher prices for basic local service are in fact associated with higher rates of broadband adoption, controlling for availability of broadband service, broadband expenditures, household income, age of the head of household, size of household, population density of the household’s location, race, and other factors. We find that the demographic variables have largely the expected effects consistent with the literature. We also find that once other demographic and price variables are controlled for, there is not a “rural” divide - that is, a household’s propensity to adopt broadband service is higher, all else equal, in less densely populated areas, controlling for income, broadband availability, and other factors. Our results regarding the pricing variables are consistent with the hypothesis that promoting legacy policy goals of universal voice service by holding retail prices of basic local service artificially low impedes the achievement of current policy goals of universal broadband adoption. We believe our results are important because, unlike the numerous demographic variables that are known to be correlated with broadband adoption, the price of basic local service is, in many areas, subject to regulatory control and is therefore a policy variable. Our results suggest that relieving restrictions on prices of basic local service would promote the federal policy of universal broadband adoption.

Beyond Africa’s Cellular Phone Euphoria

The cellular phone has been described as God’s gift to Africa, previously the least connected continent in the world. The euphoria about the capability of the technology for connection, scalability, affordability and ubiquity has been greatest in the context of the cellular phone. Photos abound of people of all walks of life – from cattlemen in Uganda to Somali pirates on a boat on the Indian Ocean – holding mobile phones in stark contrasts with their surroundings. The stories and photos are so common that it would appear as if the estimated 1.2 billion people in African all have cell phones. This is not so, though at 65% penetration rate, the statistics are impressive in a continent where many countries had no reliable public switched telephone networks as recently as ten years ago. Also, the euphoria is not without foundation as studies have shown a positive relationship between the cellular phone and socioeconomic and political development in Africa. There is also evidence that the technology can stimulate economic growth across socioeconomic sectors from the basic micro level to large scale businesses. For instance, unemployed youths, without much investment capital, in many African countries have started businesses with just a cell phone. While these cases are undoubtedly prevalent on the continent, this paper moves beyond the anecdotes to examine the connections between information and communication technologies (ICTs) and the United Nations Millennium Development Goals (MDGs). This is rooted in the assumption that access to the technologies are strategic to the achievement of the MDGs, though many countries are lagging behind in many of the targets. Indeed, it is unlikely that many African countries will achieve these goals by the target date of 2015 as evidence from Nigeria and Ghana indicates. This then raises critical questions concerning policies deliberately aimed at expanding universal access to ICTs as an approach to achieving the MDGs. We address these questions and conclude with a discussion of the opportunities and challenges in the process, as well as policy recommendations.

Quality of experience evaluation of voice communication: an affect-based approach

AbstractVoice communication systems such as Voice-over IP (VoIP), Public Switched Telephone Networks, and Mobile Telephone Networks, are an integral means of human tele-interaction. These systems pose distinctive challenges due to their unique characteristics such as low volume, burstiness and stringent delay/loss requirements across heterogeneous underlying network technologies. Effective quality evaluation methodologies are important for system development and refinement, particularly by adopting user feedback based measurement. Presently, most of the evaluation models are system-centric (Quality of Service or QoS-based), which questioned us to explore a user-centric (Quality of Experience or QoE-based) approach as a step towards the human-centric paradigm of system design. We research an affect-based QoE evaluation framework which attempts to capture users' perception while they are engaged in voice communication. Our modular approach consists of feature extraction from multiple information sources including various affective cues and different classification procedures such as Support Vector Machines (SVM) and k-Nearest Neighbor (kNN). The experimental study is illustrated in depth with detailed analysis of results. The evidences collected provide the potential feasibility of our approach for QoE evaluation and suggest the consideration of human affective attributes in modeling user experience.

The Mixed Blessing of a Deregulatory Endpoint for the Public Switched Telephone Network

Receiving authority to dismantle the wireline public switched telephone network (“PSTN”) will deliver a mixture of financial benefits and costs to incumbent carriers. Even if these carriers continue to provide basic telephone services via wireless facilities or the Internet, they will benefit from the likely substantial relaxation of common carriage duties, no longer having to serve as the carrier of last resort and having the opportunity to decide where and what services they will provide going forward. On the other hand, incumbent carriers may have underestimated the substantial financial and marketplace advantages they also will lose in the deregulatory process. Incumbent carriers often obscure or dismiss as insignificant the substantial privileges and benefits accruing from their status as telecommunications service providers. Common carrier responsibilities include duties to interconnect with other carriers, provide service on transparent and nondiscriminatory terms and offer some low margin services. But this legal status also guarantees wireline local exchange carriers access to billions of dollars in annual universal service funding, zero or low cost access to rights of way and radio spectrum, accelerated depreciation and other tax benefits, the ability to vertically integrate throughout the “food chain” of telecommunications services and dominant status in the administration of telephone numbers, standard setting and other policy issues. Incumbents will strive to capture deregulatory benefits while retaining the many benefits previously reserved for common carriers. This paper will identify the potential problems resulting from an FCC decision to grant authority for telecommunications service providers to discontinue PSTN services. The paper also will consider whether in the absence of common carrier duties, carriers providing telephone services, including Voice over the Internet Protocol (“VoIP”), voluntarily will agree to interconnect their networks. The paper will examine Internet peering and other types of network interconnection with an eye toward assessing whether a largely unregulated marketplace can ensure ubiquitous access to PSTN replacement services. The paper concludes that private carrier interconnection models and information service regulatory oversight may not solve all disputes, or foreclose price discrimination for functionally the same type of service. Recent Internet interconnection and television program carriage disputes involving major players such as Comcast, Level 3, Fox and Cablevision, point to the possibility of increasingly contentious negotiations that could result in balkanized telecommunications networks with reversed or reduced progress in achieving universal service goals. The paper also concludes that rural access to VoIP and other voice communications services could end up costing significantly more than what urban residents pay, an efficient, but politically risky outcome.

User-Profile Framework against a Spit Attack on VoIP Systems

Spam over Internet Telephony is becoming a large problem of the Voice over IP Architectures. Voice over IP has become a valid alternative to the Public Switched Telephone Network and it has a new paradigm for providing telephony services at a lower cost and higher flexibility. In the meantime, with Voice over IP the privacy becomes so hard and the benefits introduced are as strong as the security problems, like Spam over Internet Telephony. People have more attention on the spam voice issue, because of the great danger of this threat. Thus, in this paper we want to propose and introduce a new protection model against Spam over Internet Telephony attack, through a user-profile framework. This framework allows to identify the optimal countermeasures to be taken against this threat, according to the user assessment, that receives a certain number of calls during an observation period. We define general profiles based on certain parameters, and with a user-profile matching we can identifies the best security path which must be applied.

The Case for Reforming Regulation of PSTN Voice Services

Abstract Have competitive conditions in the voice services market changed sufficiently to justify lifting most current economic and social regulation on the public switched telephone network (PSTN)? Yes, argues Richard Clarke, describing in detail the ongoing changes in the supply and demand structures of the voice market and their impact on reducing the economic power of the traditional incumbent local exchange carriers (ILECs). Based on this argument, and on evolving technology, Clarke notes that both the PSTN and the voice services it supports are “inexorably going away,” to be replaced by new services and technologies, making current regulatory requirements superfluous.

The Case for Reforming Regulation of PSTN Voice Services

Abstract Have competitive conditions in the voice services market changed sufficiently to justify lifting most current economic and social regulation on the public switched telephone network (PSTN)? Yes, argues Richard Clarke, describing in detail the ongoing changes in the supply and demand structures of the voice market and their impact on reducing the economic power of the traditional incumbent local exchange carriers (ILECs). Based on this argument, and on evolving technology, Clarke notes that both the PSTN and the voice services it supports are “inexorably going away,” to be replaced by new services and technologies, making current regulatory requirements superfluous.

Speech over VoIP Networks: Advanced Signal Processing and System Implementation

Speech communication using the Voice over Internet Protocol (VoIP) is very common today. The underlying network channel may be the public switched telephone network (PSTN channel), satellite channels or cellular wireless channels to name a few. The packetization of speech and its transmission through packet switched networks, however, introduce numerous impairments such as delay, jitter, packet loss and decoder clock offset, which degrade the quality of the speech. We present an overview of the challenges and a description of the advanced signal processing algorithms used to combat these impairments and render the perceived quality of a VoIP conversation to be as good as that of the existing telephone system. We also present an example of a speech coder designed for packet-switched networks and discuss the possibilities for hardware implementations.

PRETTY (Private Telephony Security) - Securing the Private Telephony Infrastructure

Private Branch Exchanges (PBXs) are privately owned equipment that serve the communication needs of a private or public entity making connections among internal telephones and linking them to other users in the Public Switched Telephone Network (PSTN) or other communication networks. Even if the core public network is operating normally, unintentional or targeted damages and attacks in PBXs can cause significant instability and problems. Furthermore, interception of calls is a very sensitive issue that affects all of us. In that sense, it is not an exaggeration to state that PBXs are part of a nation’s critical infrastructure. Much has been said and done regarding data communication security but PBXs have been left unprotected, forgotten and waiting to be attacked. This contribution outlines a targeted, centralized project in order to both educate the users and secure their telephony systems. It compromises of educational, policy, auditing, technical, documentation, hardware and software solutions and actions that could be implemented under a joint project.

The Mixed Blessing of a Deregulatory Endpoint for the Public Switched Telephone Network

The Mixed Blessing of a Deregulatory Endpoint for the Public Switched Telephone Network

Extraction of Electronic Evidence from VoIP: Identification & Analysis of Digital Speech

The Voice over Internet Protocol (VoIP) is increasing in popularity as a cost effective and efficient means of making telephone calls via the Internet. However, VoIP may also be an attractive method of communication to criminals as their true identity may be hidden and voice and video communications are encrypted as they are deployed across the Internet. This produces a new set of challenges for forensic analysts compared with traditional wire-tapping of the Public Switched Telephone Network (PSTN) infrastructure, which is not applicable to VoIP. Therefore, other methods of recovering electronic evidence from VoIP are required. This research investigates the analysis and recovery of digitised human voice, which persists in computer memory after a VoIP call. This paper outlines the ongoing development of a software tool, the purpose of which, determines how remnants of digitised human speech from a VoIP call may be identified within a forensic memory capture based on how the human voice is detected via a microphone and encoded to a digital format using the sound card of a personal computer. This digital format is unencrypted whist stored in Random Access Memory (RAM) before it is passed to the VoIP application for encryption and transmission over the Internet. Similarly, an incoming encrypted VoIP call is decrypted by the VoIP application and passes through RAM unencrypted in order to be played via the speaker output. A series of controlled tests were undertaken whereby RAM captures were analysed for remnants of digital audio after a VoIP audio call with known conversation. The identification and analysis of digital audio from RAM attempts to construct an automatic process for the identification and subsequent reconstruction of the audio content of a VoIP call. This research focuses on the analysis of RAM captures acquired using XWays Forensics software. This research topic, guided by a Law Enforcement Agency, uses X-Ways Forensics to simulate a RAM capture which is achieved covertly on a target machine without the user's knowledge, via the Internet, during or after a VoIP call has taken place. The authors assume no knowledge of the technique implemented to recover the covert RAM capture and are asked to base their analysis on a memory capture supplied in the format of a file with a ‘.txt’ extension. The methods of analysis described herein are independent of the acquisition method applied to RAM capture. The goal of this research is to develop automated software that may be applied to a RAM capture to identify fragments of audio persisting in RAM after a VoIP call has been terminated, using time domain and signal processing technique, frequency domain analysis. Once individual segments of audio have been identified, the feasibility of reproducing audio from a VoIP call may be determined.

An efficient relay node selection scheme to improve the performance of P2P-based VoIP applications in Chinese internet

Peer-to-peer (P2P) systems have been widely deployed and used to provide voice-over-IP (VoIP) service in the Internet. However, the current best-effort Internet cannot readily provide the service guarantees that meet the quality standards achieved in the public switched telephone network (PSTN). To address this problem, many studies have demonstrated that exploiting path diversity is a promising approach, such as multi-homing and overlay routing. In this paper, we focus on the overlay scenario and bring forward a previously unexplored approach that exploits the properties of delay space of Internet to select relay node to enhance the performance of P2P-based VoIP applications in Chinese Internet. By conducting intensive Internet measurements, we analyze the properties of delay space of Chinese Internet and show these properties can be readily exploited to select relay node with as small a cost as possible. Exploiting these properties we bring forward an efficient relay node selection scheme to improve the performance of P2P-based VoIP applications in Chinese Internet. Our intensive evaluation by trace-driven simulation shows our scheme is highly efficient and easy to be implemented.

Communication Software Design of Remote Monitoring System for Motor Excitation Parameters Based on PSTN

Based on the remote maintenance of motor exciation, this paper discusses the function design and solution method of communication software which is used in remote monitoring system of motor exciation. It mainly introduces the process of data transmission founded on the Public Switched Telephone Network (PSTN) and key problems of the implementation of communication MSComm control in VC++.

Amenazas y defensas de seguridad en las redes de próxima generación

El advenimiento de las redes de próxima generación (NGN) es una realidad en el desarrollo de las telecomunicaciones. Si bien su introducción constituye un salto tecnológico, también representa un enorme reto desde el punto de vista de la seguridad. El presente artículo realiza un análisis integral sobre aspectos relacionados con la seguridad de estas redes. Inicialmente, se abordan las amenazas que se heredan de las redes telefónicas públicas conmutadas (PSTN), las redes de datos de protocolos de Internet (IP) y las redes de televisión, así como la forma en que éstas se combinan, para obtener las amenazas propias de las NGN. Luego, se analizan los mecanismos de defensa de las redes que convergen en las NGN para proponer los mecanismos de defensa aplicables a estas últimas, los principios de su combinación, así como los requerimientos de las herramientas de seguridad. El análisis presentado constituye un importante primer paso para organizar y hacer homogéneo el trabajo de seguridad en NGN.

Supporting NGNs Core Software Services: A Hybrid Architecture and its Performance Analysis

In the last few years telco providers are striving to migrate their services from the traditional Public Switch Telephone Network to so called Next Generation Networks (NGNs) based on standard IP connectivity. This switch is expected to produce a cost degression of 50% for CAPital EXpenditure, while OPerating EXpences remains fairly stable due to network management and energy costs. At the same time, the instantiation of new telco services (Voice over IP, video conferencing, etc.) and the support of third party applications (such as support to smartphone applications, etc.) are expected to produce a big increase of the load of a telco provider at the core level. The goal of this work is to show how management and energy costs can be effectively reduced by leveraging autonomic approaches to move some NGN services toward the telco network edge while still providing Quality of Service (QoS) levels comparable with those provided by a traditional fully-managed infrastructure. This is done by taking into consideration the increase of the load of such services that is expected to raise by one order of magnitude in the near future. Specifically, we propose a hybrid architecture letting telco administrators reduce the number of servers in the provider managed network by exploiting home devices in the computation and by organizing them in a self-configuring Peer to Peer system; in this way it is possible to reduce the overall system and operational costs. Our claims are supported by an experimental study based on both simulations and theoretical models that analyze the trade-off between the number of servers and home devices in order to guarantee a service within QoS constraints. Experiments are carried out on a realistic model that abstracts the lookup procedures within the NGN of a big telco provider (i.e., finding the IP address of a given unique user profile).

Privacy in VoIP Networks: Flow Analysis Attacks and Defense

(A short version of this paper appears in IEEE INFOCOM 2009: http://www.research.ibm.com/people/i/iyengar/INFOCOM2009-kanon.pdf.) Peer-to-peer VoIP (voice over IP) networks, exemplified by Skype, are becoming increasingly popular due to their significant cost advantage and richer call forwarding features than traditional public switched telephone networks. One of the most important features of a VoIP network is privacy (for VoIP clients). Unfortunately, most peer-to-peer VoIP networks neither provide personalization nor guarantee a quantifiable privacy level. In this paper, we propose novel flow analysis attacks that demonstrate the vulnerabilities of peer-to-peer VoIP networks to privacy attacks. We then address two important challenges in designing privacy-aware VoIP networks: Can we provide personalized privacy guarantees for VoIP clients that allow them to select privacy requirements on a per-call basis? How to design VoIP protocols to support customizable privacy guarantee? This paper proposes practical solutions to address these challenges using a quantifiable k-anonymity metric and a privacy-aware VoIP route setup and route maintenance protocols. We present detailed experimental evaluation that demonstrates the performance and scalability of our protocol, while meeting customizable privacy guarantees.