Home About us Contact
|
Home About us Contact | ||
|
|
||
Telephone Network (telephone + network)
Selected AbstractsCall admission control for voice over IPINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2006Huseyin Uzunalioglu Abstract Voice over Internet protocol (VoIP) is a technology that enables the transmission of voice over an IP network. Recent years have witnessed heavy investment in this area in the commercial world. For VoIP to replace Public Switched Telephone Network (PSTN), it should provide voice quality comparable to circuit-switched PSTN networks. This paper addresses the mechanisms to guarantee VoIP quality of service (QoS). The focus is given to the call admission control, which blocks voice calls when the required resources are not available to guarantee the QoS for the call. We review call admission control approaches that can be applied to VoIP, and describe the advantages and disadvantages of each approach. In the second part of the paper, we present a measurement-based admission control scheme that achieves QoS in an efficient and scalable manner. The scheme uses voice traffic load measurements at each router link to compute link-level blocking policies for new call attempts. Then, these policies are translated into path-level blocking policies, which are applied to new call set-up requests. The performance of the scheme is presented for single and multiple-priority voice calls. Copyright © 2006 John Wiley & Sons, Ltd. [source] Network-magnetotelluric method and its first results in central and eastern Hokkaido, NE JapanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2001Makoto Uyeshima Summary A new field observation technique based on the magnetotelluric (MT) method has been developed to determine deep and large-scale 3-D electrical conductivity distributions in the Earth. The method is named ,Network-MT', and employs a commercial telephone network, to measure voltage differences with long dipole lengths ranging from 10 to several tens of kilometres. This observation configuration enables us to obtain the telluric field distribution with nearly continuous coverage over a target region. Response functions are estimated between the respective voltage differences and the horizontal magnetic fields at a reference point. Owing to the long electrode spacing, the observed responses are relatively free from the effects of small-scale near-surface heterogeneity with a scalelength shorter than the typical electrode spacing. Therefore, physically meaningful direct comparison between the observations and model responses is feasible even if the fine-scale features of near-surface heterogeneity are ignored. This extensively reduces the difficulty, especially in 3-D MT interpretation. The first Network-MT experiment was performed in central and eastern Hokkaido, NE Japan, in 1989. It took about five months to complete all of the measurements, and used 209 dipoles to cover the target area of 200(EW) × 200(NS) km2. The long electrode spacing enabled us to obtain the voltage differences with a high signal-to-noise ratio. For 175 dipoles, the squared multiple coherency between the voltage difference and the horizontal magnetic field at Memambetsu Geomagnetic Observatory was determined to be more than 0.9 in the period from 102 to 104 s. 193 MT impedances were computed in tensor form by linear combination of the response functions. The estimated impedances generally possessed smooth period dependence throughout the period range. No drastic spatial change was observed in the characteristics of the tensors for neighbouring sites, and some regional trend could be detected in the spatial distribution. Thus, we confirmed the merit of the Network-MT method, that its responses are little affected by small-scale near-surface structures. The regional feature of the response implied a significant influence of the coast effect, and was well correlated with the regional geological setting in Hokkaido. Conventional Groom,Bailey tensor decomposition analysis revealed that the target region is not regionally one- or two-dimensional. Therefore, we developed a 3-D forward modelling scheme specially designed for the Network-MT experiment, and tried to reproduce the Network-MT responses directly. In the 3-D model, a realistic land,sea distribution was considered. The resistivity of sea water was fixed to be 0.25 , m and, as a first trial of 3-D modelling, the resistivity of the land was assumed to be uniform and its value was determined to be 200 , m by a simple one-parameter inversion. Overall agreements between the observations and the best-fit model responses indicated the importance of the 3-D coast effect in the target region. However, there remained significant discrepancies, especially in the phase of the responses, which provide a clue to determining a regional deep 3-D structure. [source] On-line Monitoring of Nocturnal Home HemodialysisHEMODIALYSIS INTERNATIONAL, Issue 1 2003SJA Stokvis Background. Nocturnal home hemodialysis (NHD, 6,7 times weekly 6,8 hours) is a promising dialysis modality. On-line distant monitoring is complicated and expensive, and its usefulness should be evaluated. Methods. Since December 2001, 15 patients were included in a Dutch NHD project (,Nocturne'). So far, 3 patients received a renal transplant. Patients are assisted by their spouses. The dialysis machine is connected through the public telephone network by a bedside node and routers to the server in a call center. All patients received a dedicated ISDN-connection. Alarms produced by the machine are detected in the call center. For each type of alarm, a period is defined during which the patient can solve the problem. When the alarm continues after this period, the call center will notify the patient. Results. During 4 months, approximately 900 alarms in 1300 dialysis treatments were produced. In only 11 of 900 cases, the partner had to wake up the patient because he/she did not hear the alarm. The call center had to call 13 times, always because the patient resumed sleeping after the end of the treatment. No intervention because of serious problems was required. A majority of patients and personnel consider on-line monitoring nevertheless important as it gives a sense of safety. Additionally, nurses use the real-time connection frequently to check running dialysis treatments. Also, the system enables automatic saving of important treatment data in an electronic patient file. The experience so far is used to design a so-called ,secure bitpipe' for homecare applications, with emphasis on privacy, safety, security and effectivity. Conclusion. On-line monitoring of NHD may not be crucial, but enables good coaching of patients and gives a sense of safety. [source] AUTOMATICALLY OPERATING RADARS FOR MONITORING INSECT PEST MIGRATIONSINSECT SCIENCE, Issue 4 2002Alistair Drake Abstract, Over the last three decades, special-purpose "entomological" radars have contributed much to the development of our understanding of insect migration, especially of the nocturnal migrations at altitudes of up to , 1 km that are regularly undertaken by many important pest species. One of the limitations of early radar studies, the difficulty of maintaining observations over long periods, has recently been overcome by the development of automated units that operate autonomously and transmit summaries of their observations to a base laboratory over the public telephone network. These relatively low-cost Insect Monitoring Radars (IMRs) employ a novel "ZLC" configuration that allows high quality data on the migrants' flight parameters and identity to be acquired. Two IMRs are currently operating in the semi-arid inland of eastern Australia, in a region where populations of migrant moths (Lepidoptera) and Australian plague locusts Chortoicetes terminifera (Orthoptera) commonly originate, and some examples of outputs from one of these units are presented. IMRs are able to provide the data needed to characterize a migration system, i.e. to estimate the probabilities of migration events occurring in particular directions at particular seasons and in response to particular environmental conditions and cues. They also appear capable of fulfilling a "sentinel" role for pest-management organisations, alerting forecasters to major migration events and thus to the likely new locations of potential target populations. Finally, they may be suitable for a more general ecological monitoring role, perhaps especially for quantifying year-to-year variations in biological productivity. [source] Modeling and simulation of mixed traffic on a prioritized shared mediumINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 1 2003Jeffrey J. Evans Network access systems (NAS) such as digital loop carriers (DLC) are increasingly utilizing a shared medium, such as Hybrid Fiber Coax (HFC) to provide point-to-multi-point access from the public switched telephone network (PSTN) to the end user (consumer). New services, such as direct access to the packet switched network (PSN, WWW) have been added to DLC equipment in such a way as to provide for a prioritized set of services over a shared medium in an effort to take advantage of otherwise unused bandwidth. The introduction of such services requires the modeling and analysis of these network access systems. This becomes complex when considering the variability in different service type traffic characteristics. This work identifies a traffic engineering problem of prioritized circuit switched and packet switched (PSTN/PSN) traffic over the same shared medium as it may relate to "perceived" quality of service (QoS). Copyright © 2002 John Wiley & Sons, Ltd. [source] Trunking of TDM and narrowband services over IP NetworksINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 1 2003Dr James Aweya The recent interest in IP as the vehicle for transporting TDM and narrowband services stems from the possibility of using a common transport network for voice, video, and data, and the flexibility with which new services can be introduced. A key step in the evolution of networks towards a ,broadband' IP-based environment is the ,graceful' interworking of the IP networks with the existing networks and services, particularly with the circuit switched telephone network. A ,graceful' interworking approach is one whose complexity is minimal and preserves the user's perceived quality of service (QoS). To interwork with a circuit switched network whose services are pre-dominantly time-sensitive, the IP network must essentially behave as a transparent ,link' in the end-to-end connection. This paper presents an overview of the main technical problems to be addressed when trunking TDM and narrowband services over IP networks. Copyright © 2002 John Wiley & Sons, Ltd. [source] The Environmental Impact of Getting the NewsJOURNAL OF INDUSTRIAL ECOLOGY, Issue 3-4 2002A Comparison of On-Line, Newspaper Information Delivery, Television Summary The environmental impact associated with reading an on-line and a printed newspaper is analyzed and compared with respective parts of a television (TV) broadcast. Two reference units were chosen for comparison to account for differences between media in presentation and consumption (reading or watching a news item) and consumption of the daily news as a whole. The environmental impact is assessed using life-cycle assessment (LCA). Key drivers of the environmental impact for both electronic delivery systems are energy consumption and power generation. Not only do the manufacturing of the products and their use have an environmental impact, but so does the use of the necessary infrastructure, that is, energy consumption of the telephone network or data transfer via Internet. Printing of on-line information also turned out to be important. In the case of the printed newspapers, energy consumption is again important, here for the manufacturing of pulp and paper. Complete printed newspapers (the form in which they are typically purchased) have a very high environmental burden relative to watching the TV news or reading on-line news, even if the propensity to extend TV viewing is taken into consideration. [source] An over-current protection module for telephone network line cards,an analysis of electro-thermal propertiesQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 5 2002Marina Santo Zarnik Abstract In this paper the results of a finite-element analysis of the electro-thermal behaviour of an over-current protection thick-film hybrid module are presented. The module was designed for protecting the line card of a telephone network against an abnormal surge of current, resulting from accidental shorts between adjacent power feed lines. The switching time of the device is crucial to its effectiveness as a protective element. A transient finite-element thermal analysis was performed in order to predict the dynamic temperature states at the critical points of the circuit design and to evaluate the influence on the switching characteristics. A comparison between simulated and practical results is given. Copyright © 2002 John Wiley & Sons, Ltd. [source] IMS network signaling peering: Challenges and proposalBELL LABS TECHNICAL JOURNAL, Issue 4 2008Jean-Philippe Joseph IP Multimedia Subsystem (IMS) network peering is a key enabler that will help accelerate deployment of next-generation IMS-based networks. Today's early deployments of dispersed IMS networks require public switched telephone network (PSTN)/public land mobile network (PLMN) bridges for network interconnection between IMS islands. The PSTN/PLMN bridging arrangement is inefficient, however, in that it results in unnecessary settlements for the carriers. It further impedes the implementation of rich multimedia and Voice over IP (VoIP)-related services that require end-to-end Internet Protocol (IP) connectivity. Last, it perpetuates the reliance on the existing PSTN/PLMN network for voice calls among subscribers served by different IMS-based carriers. This paper analyzes in detail the IMS peering challenges from the perspective of Session Initiation Protocol (SIP) signaling peering. It discusses issues related to the routing of SIP messages, and addressing, address resolution, and discovery of peering points for IMS signaling peering. It further establishes that a new routing algorithm is needed that will allow signaling peering points to dynamically discover the "best" transit network among others for reaching a destination. In closing, it presents a high-level IMS signaling routing process that includes, among other benefits, support for number portability as a key function for inter-carrier IMS peering. © 2008 Alcatel-Lucent. [source] Advanced IMS client supporting secure signalingBELL LABS TECHNICAL JOURNAL, Issue 4 2008Ramana Isukapalli With recent advances in core and access networks and the availability of increased bandwidth and sophisticated devices for end users, there is an increased demand for client applications running on mobile devices, such as laptops and handheld devices, to support real time applications like Voice over Internet Protocol (VoIP) and streaming video, apart from traditional applications like web browsing. This paper presents a prototype IP Multimedia Subsystem (IMS) client, which serves as a VoIP client to set up calls between Internet Protocol (IP) devices and interworks with circuit-switched networks to deliver calls to public switched telephone network (PSTN) phones. It implements supplementary services (including call waiting, call transfer, and call forwarding); supports multimedia ringing, short message service/multimedia messaging service (SMS/MMS), audio/video conferencing, and peer-to-peer video; and it can deliver a call to a user (as opposed to a device) by simultaneously ringing multiple devices registered by the user. Further, to address various security concerns, the client supports Hypertext Transfer Protocol (HTTP) digest authentication using Message Digest 5 (MD5) cryptographic function authentication and key agreement (AKA) and can create secure tunnels to the core network using IP security (IPsec). © 2008 Alcatel-Lucent. [source] Optimal availability and security for IMS-based VoIP networksBELL LABS TECHNICAL JOURNAL, Issue 3 2006Himanshu Pant Consumers are continuously looking for ways of improving their productivity, simplifying their tasks, and streamlining communications both domestically and globally. This has resulted in the need to support different applications and thus the ongoing process of migrating many network services from traditional circuit-switched networks to Internet Protocol (IP) to converged networks. The circuit-switched public switched telephone network (PSTN) was a closed network where cyber-security threats were not amajor issue. With the advent of converged networks and IP-based services, service providers, government, and enterprises are concerned about the growing security threat. The new networks and equipment will be subject to many types of threats and their vulnerabilities may expose mission critical applications and infrastructure to risk. Realization of these threats can lead to service outage. Today's communications service provider must decide how to treat the effects of security breaches so as to minimize service downtime. This paper highlights amethodology, with examples to identify the effect of security-related failures and the critical design factors to be considered when modeling service reliability. The ITU-T X.805 standard (now also ISO standard 18028-2), based on the Bell Labs security model, is used to evaluate potential high impact threats and vulnerabilities. The analysis uses the Bell Labs domain technique known as security domain evaluation. One of the critical outputs provides a prioritized understanding of the threats the network is exposed to and the vulnerabilities in the security architecture. The next step in themethodology includes incorporating the threats (vulnerabilities) identified in a reliability model and quantifying the corresponding service degradation. In this paper, these concepts are applied to IP Multimedia Subsystem (IMS)-based VoIP (Voice over IP) networks. Using reliability metrics, our analysis shows that reliability models are optimistic if we do not consider security. We demonstrate how reliability models can be enhanced to take security issues into account and that the X.805 standard can be used to identify the security threats. Finally, the model shows themitigation in downtime by including intrusion-tolerance features in the product and network design. Consideration of security-caused downtimewill lead to increased focus on preventing security vulnerabilities that can lead to service outages and also allow service providers to save on maintenance costs. © 2006 Lucent Technologies Inc. [source] VoIP network architectures and QoS strategyBELL LABS TECHNICAL JOURNAL, Issue 4 2003Bharat T. Doshi Voice over IP (VoIP) has received much attention in recent years with the promise of lower costs, as well as new revenue-generating services. Cost and services advantages of carrying voice over IP compared to over the current circuit network are made possible by a common high-capacity packet infrastructure for voice, data, and multimedia services. An important requirement of such a packet infrastructure is the ability to provide public-switched telephone network (PSTN) grade quality without excessive over-provisioning. In this paper, we describe an approach to offer AbsoluteQoSÔ to voice and other demanding applications over a general-purpose packet network. AbsoluteQoS is defined as the ability to provide an engineered bound on call-blocking and quantitative QoS guarantee that calls-in-progress will receive. The proposed strategy is based on key innovations in architectures and protocols, as well as business models of PSTN and packet networks. © 2003 Lucent Technologies Inc. [source] Web communication services and the PacketIN® application hosting environmentBELL LABS TECHNICAL JOURNAL, Issue 1 2002Yang Chen Large telecommunication customers are migrating their network infrastructure to support new converged services, while containing their operating costs. Deploying converged services on the networks today represents great opportunities to network service providers for new revenue generation. It brings big challenges as well, due to the requirements for a service platform with high capability to deal with the complexity of the network infrastructure, the difficulty of interoperability between different service platforms, and the diversity of signaling protocols and application programming interfaces (APIs). The Lucent PacketIN® application hosting environment (AHE) provides a solution that empowers network service providers to deliver a wide variety of enhanced services over the converged (packet and circuit, wireline and wireless) networks. It enables the creation and deployment of enhanced services on converged networks via the open service platform with interoperability, programmability, scalability, and wide protocol compliance. In particular, a new class of services is presented to demonstrate the transformation of telecommunication services that is enabled through Web presence. This article gives an overview of the PacketIN AHE with the focus on the customer values, the architecture, and enabling capability to deploy advanced applications and services. A new service portal, enterprise communication, is presented as an example of the innovation and implementation enabled by the service enabling environment. The enterprise communication provides Web access to presence information, instant messaging, third-party call management, and location. This convergence of features is enabled by the PacketIN AHE integration of the public switched telephone network (PSTN), session initiation protocol (SIP), and H.323 protocols through standard open APIs. The voice communication protocols are combined with a Web access interface to establish a new Internet presence, while leveraging existing switching products and reusing deployed communication networks and services. © 2002 Lucent Technologies Inc. [source] Performance of soft phones and advances in associated technologyBELL LABS TECHNICAL JOURNAL, Issue 1 2002Christopher Chrin Soft-phone technology for Internet protocol (IP) voice is growing in importance. However, soft phones exhibit poorer quality than public switched telephone network (PSTN) phones. A goal is to improve that quality, perhaps even to the point that the communication experience is better than with PSTN phones. This letter presents an analysis of soft-phone performance and describes acoustic echo cancellation and other technologies that improve soft-phone performance. © 2002 Lucent Technologies Inc. [source] Middleboxes: Controllable media firewallsBELL LABS TECHNICAL JOURNAL, Issue 1 2002Paul Sijben Internet technology is promised for the broadband multi-service future. However, it is unclear how this technology can bring service providers the needed revenue, since today this technology cannot provide basic quality guarantees for the services rendered. Generally, over-provisioning of the bandwidth is used to get the services to an acceptable level, but this is costly and cannot work in areas where high aggregation rates are necessary (such as the local loop). Today IP (router) technology lacks mechanisms for high-granularity access control, per-user accounting, and quality of service (QoS) policing. We believe that, for a service provider to deploy billable services, these issues need to be resolved. Only if access to the service is controlled and only when the network provides information about the usage of the network elements can next-generation services in the telecommunication industry, like voice over IP (VoIP) and multimedia conferencing, be rolled out profitably. In this paper, we present a technology that can address these needs. We employ controllable firewalls that have the ability to prevent unwanted IP traffic from entering a network. Creating pinholes that allow individual calls (voice or real-time multimedia streams) in controllable firewalls can be done very fast and efficiently. Traditional firewalls have no such provisioning. Multiple application servers should be able to request pinholes to one or more controllable firewalls. This approach, while familiar from the public switched telephone network (PSTN), is a new paradigm for IP networks. © 2002 Lucent Technologies Inc. [source] Multiple geographies of the Arab InternetAREA, Issue 1 2007Barney Warf The Arab world plays a relatively minor role in the rapidly changing geographies of global cyberspace. This paper explores the multiple geographies of the Arab Internet. First, it addresses Internet penetration rates, which averaged 7.8 per cent in 2006, although these varied widely among and within the region's countries. Between 2000 and 2006, the number of users jumped by 830 per cent, indicating these geographies are in rapid flux. It then examines the telecommunications infrastructure of the Middle East and North Africa, including fixed and mobile telephone networks and Internet cafes. Third, it turns to the reasons why the Internet has experienced relatively late adoption among Arab countries, including the dominance of the Latin alphabet, high access costs reflecting state-owned telecommunications monopolies, low Arab literacy rates, and restrictive gender relations that keep the proportion of female users low. The paper pays special attention both to government censorship of the Arab Internet as well as resistance to such controls and attempts to utilize the Internet counter-hegemonically. Finally, it explores the impacts of the Internet on some Arab societies, including the opening of discursive communities of politics, the Palestinian,Israeli conflict, Iraq and electronic commerce. [source] | ||||||||||||||||