Common channel signaling for international service applications

The message transfer, telephone user, and integrated services digital network (ISDN) user parts of CCITT Signaling System No.7 (SS7) are described. The introduction of SS7 to provide control of international circuits is described. The intent is to provide a perspective on the advantages of using common channel signaling for ISDN     

Common channel signaling networks: past, present, future

The authors wish to provide a unification of this issue's papers by providing a clear context for them. Common channel signaling can be defined as the system that enables stored program control exchanges, network databases, and other nodes of a network to exchange messages related to call setup, supervision, and take down (call and connection control information); information needed for distributed application processing (interprocess query and response or user-to-user data); and network management information     

Common channel signaling in the AT&T US 5ESS switch

A brief history of the evolution that has led to the development of Signaling System No.7 (SS7) capabilities on the 5ESS switch is presented, and the hardware and software components that provide the SS7 functionality for the 5ESS switch are described. Specifically, the functionality provided by the Common Network Interface (CNI) ring, which has been used on several AT&T SS7 products is discussed. The 5ESS switch-specific common channel signaling (CCS) transport software (which is responsible for the transport of SS7 messages among 5ESS switch processing elements), the user interfaces (which provide customer administration of switch data, color display of status information, reports on the state of the SS7 network, and the tests to verify message routing through the network), and message routing itself are discussed. The SS7 ISDN user part (ISUP) and transaction capabilities application (TCAP) functionalities implemented in 5ESS switch software are described in terms of how they fit into the 5ESS switch architecture. SS7 call handling capacities and the ways in which reliability challenges are met are described     

Common channel signaling interface for local exchange carrier tointerexchange carrier interconnection

Issues associated with the interconnection of common channel signaling (CCS) networks are identified. Protocol additions to support exchange access services are discussed. Possible extensions for circuit-switched services beyond basic exchange access, as well as further extensions of Signaling System No.7 to support non-circuit-associated signaling between carriers, are described     

Guest editorial. Common channel signaling networks: performance,engineering protocols, and capacity management

An introductory article covers SS7 protocol, services, reliability, performance, and congestion control. Following the introductory article, the papers are arranged in three sections. The largest section is on performance analysis and congestion control. The papers in the second section address several issues relevant to the network level, including the impact of new services. The last section of this issue contains papers that highlight technical issues for future studies. This section carries a dual purpose: to introduce the preliminary results achieved by the authors and to suggest directions for additional work in this area     

Bounds on the information rate of intertransition-time-restrictedbinary signaling over an AWGN channel

Upper and lower bounds on the capacity of a continuous-time additive white Gaussian noise (AWGN) channel with bilevel (±√P) input signals subjected to a minimum inter-transition time (T_min) constraint are derived. The channel model and input constraints reflect basic features of certain magnetic recording systems. The upper bounds are based on Duncan's relation between the average mutual information in an AWGN regime and the mean-square error (MSE) of an optimal causal estimator. Evaluation or upper-bounding the MSE of suboptimal causal estimators yields the desired upper bounds. The lower bound is found by invoking the extended “Mrs. Gerber's” lemma and asymptotic properties of the entropy of max-entropic bipolar (d, k) codes. Asymptotic results indicate that at low SNR=PT_min/N₀, with N₀ designating the noise one-sided power spectral density, the capacity tends to P/N ₀ nats per second (nats/s), i.e., it equals the capacity in the simplest average power limited case. At high SNR, the capacity in the simplest average power limited case. At high SNR, the capacity behaves asymptotically as T_min^-1ln(SNR/ln(SNR)) (nats/s), demonstrating the degradation relatively to T_avg ^-1 lnSNR, which is the asymptotic known behavior of the capacity with a bilevel average intertransition-time (T_avg) restricted channel input. Additional lower bounds are obtained by considering specific signaling formats such as pulsewidth modulation. The effect of mild channel filtering on the lower bounds on capacity is also addressed, and novel techniques to lower-bound the capacity in this case are introduced     

Nonequiprobable signaling on the Gaussian channel

Signaling schemes for the Gaussian channel based on finite-dimensional lattices are considered. The signal constellation consists of all lattice points within a region R, and the shape of this region determines the average signal power. Spherical signal constellations minimize average signal power, and in the limit as N →∞, the shape gain of the N-sphere over the N-cube approaches πe/6≈1.53 dB. A nonequiprobable signaling scheme is described that approaches this full asymptotic shape gain in any fixed dimension. A signal constellation, Ω is partitioned into T subconstellations Ω₀ , . . ., Ω_τ-1 of equal size by scaling a basic region R. Signal points in the same subconstellation are used equiprobably, and a shaping code selects the subconstellation Ω_i with frequency f_i. Shaping codes make it possible to achieve any desired fractional bit rate. The schemes presented are compared with equiprobable signaling schemes based on Voronoi regions of multidimensional lattices. For comparable shape gain and constellation expansion ratio, the peak to average power ratio of the schemes presented is superior. Furthermore, a simple table lookup is all that is required to address points in the constellations. It is also shown that it is possible to integrate coding and nonequiprobable signaling within a common multilevel framework     

Back channel etch chemistry of advanced a-Si:H TFTs

We report on the effects of back channel etch depth and etchant chemistry on the electrical characteristics of inverted staggered advanced amorphous silicon thin-film transistors. We found that the optimum amorphous silicon film thickness in the channel is about 800-1100 Å. Three dry etch, HBr + Cl₂, C₂F₆, and CCl₂F₂ + O₂, and one wet etch, KOH, chemistries are used for the back channel etch processing. We established that dry etch can be used for the back channel etch of amorphous silicon transistor without degrading its electrical characteristics.     

An advanced multiple channel cochlear implant

An advanced multiple channel cochlear implant hearing prosthesis is described. Stimulation is presented through an array of 20 electrodes located in the scala tympani. Any two electrodes can be configured as a bipolar pair to conduct a symmetrical, biphasic, constant-current pulsatile stimulus. Up to three stimuli can be presented in rapid succession or effectively simultaneously. For simultaneous stimulation, a novel time-division current multiplexing technique has been developed to obviate electrode interactions that may compromise safety. The stimuli are independently controllable in current amplitude, duration, and onset time. Groups of three stimuli can be generated at a rate of typically 500 Hz. Stimulus control data and power are conveyed to the implant through a single transcutaneous inductive link. The device also incorporates a telemetry system that enables electrode voltage waveforms to be monitored externally in real time. The electronics of the implant are contained almost entirely on a custom designed integrated circuit. Preliminary results obtained with the first patient to receive the advanced implant are included.     

Repetitive signaling using a noisy feedback channel

Several feedback coding schemes considered recently are repetitive signaling schemes. The sender retransmits the message, if necessary, on the basis of information received over the feedback channel. This paper considers a repetitive signaling scheme in which the user's estimate of the transmitted message is sent over the feedback channel to the sender with high energy if the user is uncertain of the estimate and with lower energy if otherwise. The sender retransmits the message with high energy if it decides the user's estimate is incorrect. This scheme is applied to a wide-band, additive-white-Gaussian-noise, average-power-constrained feedback communication system. Orthogonal signals are used for transmission over both forward and feedback channels. A lower bound is obtained for the probability of error when arbitrary decision rules are used. This lower bound is achieved asymptotically for long block duration by using decision rules implemented with correlation receivers. The resulting asymptotic error performance is superior to that of any feedback coding scheme previously considered for use in a wide-band additive-white-Gaussian-noise system for any values of the forward and feedback channel capacities.     

Error monitoring issues for common channel signaling

Motivated by field data which showed a large number of link changeovers and incidences of link oscillations between in-service and out-of-service states in common channel signalling (CCS) networks, a number of analyses of the link error monitoring procedures in the SS7 protocol were performed by the authors. This paper summarizes the results obtained thus far and include the following: (a) results of an exact analysis of the performance of the error monitoring procedures under both random and bursty errors; (b) a demonstration that there exists a range of error rates within which the error monitoring procedures of SS7 may induce frequent changeovers and changebacks; (c) an analysis of the performance of the SS7 level-2 transmission protocol to determine the tolerable error rates within which the delay requirements can be met; (d) a demonstration that the tolerable error rate depends strongly on various link and traffic characteristics, thereby implying that a single set of error monitor parameters will not work well in all situations; and (e) some recommendations on a customizable/adaptable scheme of error monitoring with a discussion on their implementability. These issues may be particularly relevant in the presence of anticipated increases in SS7 traffic due to widespread deployment of advanced intelligent network (AIN) and personal communications service (PCS) as well as for developing procedures for high-speed SS7 links currently under consideration by standards bodies     

Computing the capacity of a MIMO fading channel under PSK signaling

We study the constrained capacity of a multiple-input multiple-output (MIMO) fading channel with a phase-shift keying (PSK) input alphabet and show a uniform prior distribution is capacity achieving. An expression for the capacity is derived which requires a single expectation and can be evaluated easily through simulation. The simulations are facilitated by analytical expressions for the eigenvalues and eigenvectors of a required covariance matrix. The derived expression is used to provide good approximations to the capacity at low signal-to-noise ratios (SNRs) as well as to compare the input-constrained MIMO capacity to the unconstrained MIMO capacity.     

Selective reject ALOHA/FCFS: An advanced VSAT channel access protocol

This paper proposes and evaluates selective reject (SREJ) ALOHA/FCFS, a highly efficient, flexible and robust multiaccess protocol for very small aperture terminal (VSAT) applications. SREJ-ALOHA with locally synchronous FCFS retransmission scheduling is a ‘semi-compatible’ enhancement of asynchronous SREJ-ALOHA, which has earlier been shown to be an attractive satellite channel sharing protocol for low volume bursty terminals with variable length messages. The FCFS retransmission scheduling policy proposed here broadens the applicability of SREJ-ALOHA by providing higher maximum throughput, particularly in the important source traffic scenario with bimodal message length distributions. Improved channel-sharing efficiency and delay are achieved by exploiting time-of-arrival feedback naturally embedded in an unslotted SREJ-ALOHA channel to develop an implicit time-of-arrival based (FCFS) ordering for conflict-free, locally synchronous retransmission of most contending messages. An analytical procedure for evaluation of stability, throughput and delay for a general finite source, variable message length traffic model is described. The model is used to demonstrate that random access SREJ-ALOHA/FCFS typically achieves a maximum throughput in the region of 0·4–0·45 along with excellent stability and delay properties. In addition, a natural extension of the protocol which supports implicit reservation for long messages is described and shown to offer a high maximum throughput (>0·6), comparable to that achieved by highly co-ordinated slotted systems, for example mixed interactive/file-transfer traffic scenarios.     

Aspects on single symbol signaling on the frequency flat Rayleighfading channel

The optimal single symbol detector on the Rayleigh fading channel computes a functional quadratic form in the time continuous received signal. A drawback is that closed-form solutions of integral equations based on the channel statistics are required. This makes simplified discrete receivers attractive. A class of suboptimal receivers that transforms the received random process to a set of discrete observables is derived. The set of observables constitutes a random vector in a finite dimensional receiver signal space. Given this vector, the maximum likelihood detector computes a quadratic form in the received vector. The discretization implies a loss of information, therefore such a detector is not, in general, optimal given the received time continuous signal. The purpose is, however, to achieve close to optimal performance when the number of observables becomes large. This class of detectors is analyzed using exact error probability calculations, which reveal several interesting properties. The length of the observation interval and the number of discrete observables have significant influences on the error probability when the time variations of the fading process are rapid compared with the symbol duration. By increasing the number of observables, the error floor is lowered, and the implicit diversity order is increased. This implicit diversity arises as soon as more than one observable per symbol interval is used and is a consequence of the information bearing signal being a random process. Matched filter receivers use few discrete observables per symbol interval, and thus suffer from high error floors and low implicit diversity orders on fast fading channels. The error probability is highly dependent on the shapes and durations of the modulator waveforms. For instance, pulses of long duration give lower error probabilities than shorter pulses, and for a certain type of orthogonal waveforms there is no error floor     

Traffic routing and link dimensioning in the common channel signaling networks

Signaling can be defined as the exchange of information specifically concerned with the establishment and control of connections, and with network management, in a telecommunications network. It constitutes the command/control infrastructure of the modern telecommunications networks. The Common Channel Signaling (CCS) network not only forms the foundation for control and management in the modern telecommunications environments but also provides database transaction processing capability for special services such as the 800 Service and Alternate Billing Service (ABS). The CCS network is the backbone for providing the Integrated Services Digital Network (ISDN) signaling, the Advanced Intelligent Network (AIN) services, and the Personal Communications Service (PCS). It is therefore critical to provide adequate switching and transmission (link) capacities so that performance of CCS networks can be ensured. This paper describes a flexible link set dimensioning algorithm for supporting CCS network and traffic engineering. We first show that increasing a link set by one or more links may not always increase the link set capacity accordingly because of the current routing procedure defined in the Signaling System No. 7 (SS7) protocol. We then demonstrate a theorem that enables us to construct the number of all possible meaningful links in a CCS link set. Based on the theorem, an efficient and flexible procedure for implementing the link dimensioning algorithm in software is devised to support the mechanization of the CCS network planning traffic engineering functions. Finally, we show an approach to improve the CCS link utilization efficiency and its sufficient and necessary conditions.     

Eavesdropping in the synchronous CDMA channel: an EM-based approach

The problem of blind detection in a synchronous code division multiple access (CDMA) system when there is no knowledge of the users' spreading sequences is considered. An expectation maximization (EM)-based algorithm that exploits the finite alphabet (FA) property of the digital communications source is proposed. Simulations indicate that this approach, which makes use of knowledge of the subspace spanned by the signaling multiplex, achieves the Cramer-Rao lower bound (CRB). The issues of subspace estimation and timing acquisition are also considered     

TELPACK: an advanced teletraffic analysis package

The performance evaluation of computer and communication networks gives rise to teletraffic problems of potentially large dimensionality. We summarize a unifying system theoretic approach to efficient solution of a diversity of such problems, and introduce TELPACK, a publicly available software that implements this approach     

Optimization for faster-than-Nyquist signaling based combining under multi-path channel

We propose a faster-than-Nyquist (FTN) signaling based combining scheme to increase the achievable rate for the single-input-single-output (SISO) system and the single-carrier system under the multi-path channel, where the combining scheme aims to combine the signals received at all symbol periods during the channel length for each transmitted symbol. An important feature of the FTN signaling based combining scheme is that the transmitter ceases the transmission for b symbol periods after transmitting each symbol. By proposing the optimization algorithm for finding the optimum b that maximizes the achievable (information) rate, we propose in this paper the optimal FTN signaling based combining scheme. We first establish the optimization problem and then present a theorem for proving the existence of the optimum b that maximizes the lower bound of the average achievable (information) rate. On the basis of this theorem, we present the steps of the proposed optimization algorithm. Numerical results are provided, and they confirm that the proposed optimization algorithm can find the optimum b.