NASA and the challenge of ISDN: The role of satellites in an ISDN world

To understand what role satellites may play in Integrated Services Digital Network (ISDN), it is necessary to understand the concept of ISDN, including key organizations involved, the current status of key standards recommendations, and domestic and international progress implementation of ISDN. Each of these areas are explained. A summary of the technical performance criteria for ISDN, current standards for satellites in ISDN, key players in the ISDN environment, and what steps can be taken to encourage application of satellites in ISDN are also covered

Scenarios and performance measures for advanced ISDN satellite design and experiments

Described here are the contemplated input and expected output for the Interim Service Integrated Services Digital Network (ISDN) Satellite (ISIS) and Full Service ISDN Satellite (FSIS) Models. The discrete event simulations of these models are presented with specific scenarios that stress ISDN satellite parameters. Performance measure criteria are presented for evaluating the advanced ISDN communication satellite designs of the NASA Satellite Communications Research (SCAR) Program

Nitric oxide donation lowers blood pressure in adrenocorticotrophic hormone-induced hypertensive rats.

Adrenocorticotrophic hormone (ACTH) elevates systolic blood pressure (SBP) and lowers plasma reactive nitrogen intermediates in rats. We assessed the ability of NO donation from isosorbide dinitrate (ISDN) to prevent or reverse the hypertension caused by ACTH. In the prevention study, male Sprague Dawley rats were treated with ACTH (0.2 mg/kg/day) or saline control for 8 days, with either concurrent ISDN (100 mg/kg/day) via the drinking water or water alone. Animals receiving ISDN via the drinking water were provided with nitrate-free water for 8 hours every day. In the reversal study ISDN (100 mg/kg) or vehicle was given as a single oral dose on day 8. SBP was measured daily by the indirect tail-cuff method in conscious, restrained rats. ACTH caused a significant increase in SBP compared with saline (P < 0.0015). In the prevention study, chronic administration of ISDN (100 mg/kg/day) did not affect the SBP in either group. In the reversal study, ISDN significantly lowered SBP in ACTH-treated rats at 1 and 2.5 hours (132 +/- 3 mmHg (1 h) and 131 +/- 2 mmHg (2.5 h) versus 143 +/- 3 mmHg (0 h), P < 0.002), but not to control levels. It had no effect in control (saline treated) rats. In conclusion, the lowering of SBP by NO donation is consistent with the notion that ACTH-induced hypertension involves an impaired bioavailability or action of NO in vivo

Isosorbide dinitrate, with or without hydralazine, does not reduce wave reflections, left ventricular hypertrophy, or myocardial fibrosis in patients with heart failure with preserved ejection fraction

Background-Wave reflections, which are increased in patients with heart failure with preserved ejection fraction, impair diastolic function and promote pathologic myocardial remodeling. Organic nitrates reduce wave reflections acutely, but whether this is sustained chronically or affected by hydralazine coadministration is unknown. Methods and Results-We randomized 44 patients with heart failure with preserved ejection fraction in a double-blinded fashion to isosorbide dinitrate (ISDN; n=13), ISDN+hydralazine (ISDN+hydral; n=15), or placebo (n=16) for 6months. The primary end point was the change in reflection magnitude (RM; assessed with arterial tonometry and Doppler echocardiography). Secondary end points included change in left ventricular mass and fibrosis, measured with cardiac magnetic resonance imaging, and the 6-minute walk distance. ISDN reduced aortic characteristic impedance (mean baseline=0.15 [95% CI, 0.14-0.17], 3 months=0.11 [95% CI, 0.10-0.13], 6 months=0.10 [95% CI, 0.08-0.12] mmHg/mL per second; P=0.003) and forward wave amplitude (P-f, mean baseline=54.8 [95% CI, 47.6-62.0], 3 months=42.2 [95% CI, 33.2-51.3]; 6 months=37.0 [95% CI, 27.2-46.8] mmHg, P=0.04), but had no effect on RM (P=0.64), left ventricular mass (P=0.33), or fibrosis (P=0.63). ISDN+hydral increased RM (mean baseline=0.39 [95% CI, 0.35-0.43]; 3 months=0.31 [95% CI, 0.25-0.36]; 6 months=0.44 [95% CI, 0.37-0.51], P=0.03), reduced 6-minute walk distance (mean baseline=343.3 [95% CI, 319.2-367.4]; 6 months=277.0 [95% CI, 242.7-311.4] meters, P=0.022), and increased native myocardial T1 (mean baseline=1016.2 [95% CI, 1002.7-1029.7]; 6 months=1054.5 [95% CI, 1036.5-1072.3], P=0.021). A high proportion of patients experienced adverse events with active therapy (ISDN=61.5%, ISDN+hydral=60.0%; placebo=12.5%; P=0.007). Conclusions-ISDN, with or without hydralazine, does not exert beneficial effects on RM, left ventricular remodeling, or submaximal exercise and is poorly tolerated. ISDN+hydral appears to have deleterious effects on RM, myocardial remodeling, and submaximal exercise. Our findings do not support the routine use of these vasodilators in patients with heart failure with preserved ejection fraction

Introduction of a pseudo-6th order ISDN splitter with bandstop topology

A newly developed ‘integrated services digital network’ (ISDN) splitter with bandstop (BS) topology is presented and compared to an actual ISDN splitter with a traditional lowpass (LP) topology. The LP-to-BS topology change reduced the amount of filter stages: a LP ISDN splitter requires an 8th order elliptic-like filter in order to be compliant to the standard ‘TS 101 952-1-4 V1.1.1’ [1] of the European Telecommunications Standards Institute (ETSI), whereas the BS ISDN splitter only needs a pseudo-6th order elliptic-like filter. The design of the new BS ISDN filter is discussed in the light of the enforced ETSI specifications. Furthermore, both the ISDN splitters are compared in the field of their specific stopband performance and their physical implementation. The area reduction that comes together with the introduction of the new ISDN splitter with BS topology is more than 25%

Traffic model for advanced satellite designs and experiments for ISDN services

The data base structure and fields for categorizing and storing Integrated Services Digital Network (ISDN) user characteristics is outlined. This traffic model data base will be used to exercise models of the ISDN Advanced Communication Satellite to determine design parameters and performance for the NASA Satellite Communications Applications Research (SCAR) Program

Interim Service ISDN Satellite (ISIS) network model for advanced satellite designs and experiments

The Interim Service Integrated Services Digital Network (ISDN) Satellite (ISIS) Network Model for Advanced Satellite Designs and Experiments describes a model suitable for discrete event simulations. A top-down model design uses the Advanced Communications Technology Satellite (ACTS) as its basis. The ISDN modeling abstractions are added to permit the determination and performance for the NASA Satellite Communications Research (SCAR) Program

Full Service ISDN Satellite (FSIS) network model for advanced ISDN satellite design and experiments

The Full Service Integrated Services Digital Network (FSIS) network model for advanced satellite designs describes a model suitable for discrete event simulations. A top down model design uses the Advanced Communications Technology Satellite (ACTS) as its basis. The ACTS and the Interim Service ISDN Satellite (ISIS) perform ISDN protocol analyses and switching decisions in the terrestrial domain, whereas FSIS makes all its analyses and decisions on-board the ISDN satellite

Connectionless communications using the Asynchronous Transfer Mode

For a large number of applications, there is a strong need for the provision of a connectionless service by the B-ISDN. However, the cell-based ATM, which is used for switching and multiplexing in this public telecommunication network, is a connection-oriented technique. The B-ISDN should therefore be extended with functionality to allow for connectionless communications. This dissertation addresses the design and analysis of such an extension. An architectural framework is presented, which places the protocols to be used in perspective. Two possible network architectures result from the functional decomposition of the connectionless service into cooperating protocol entities \ud and the underlying ATM service. In the first one, end-systems of the B-ISDN are interconnected by means of end-to-end ATM connections. In the second one, endsystems are connected to special entities in the B-ISDN, called Connectionless Servers (CLSs). The CLSs are interconnected by ATM connections, thus constituting a connectionless overlay network on top of ATM.\ud A number of different implementation architectures for a CLS are proposed, and analysed with respect to effectiveness, availability, scalability, and in particular, performance. The major distinction between these implementation architectures is the distribution of functionality over modules. Furthermore, two different modes of operation are identified for a CLS. In the message mode of operation, a packet is reassembled from the incoming cells before it is processed and forwarded. In streaming mode of operation, the first cell of a packet is immediately processed and forwarded upon arrival, while state information is maintained for the processing and forwarding of subsequent cells of the packet. A number of performance models are developed in this dissertation. An approximate model of a CLS is analysed to allow for comparison of the delay which is experienced by cells for different implementation architectures and modes of operation. If the bandwidth assigned to ATM connections between CLSs is relatively high, message mode of operation yields the lowest delay, otherwise streaming mode performs best. In order to support the dimensioning of a reassembly buffer in a CLS operating in message mode, another, more detailed model is developed and analysed. It allows the computation of the packet loss probability of a buffer, as a function of its size. An essential function for the provision of a connectionless service using ATM is connection management. This function instructs the signalling system of the B-ISDN to establish and release ATM connections as needed for the transfer of packets. A new mechanism is proposed that exploits the expected correlation\ud between subsequent packet arrivals to reduce the average bandwidth that needs to be reserved by the ATM network. A performance model is developed and analysed to determine the optimal control parameters of the new mechanism, and to evaluate its behaviour. It is shown that bandwidth reductions of up to 95% can be obtained, compared to conventional mechanisms, without affecting the \ud average delay experienced by packets