Common Channel Signaling Network Research Articles

Analyzing Telephone Network Data

As our reliance on computer networks grows, it becomes increasingly important that we understand the behavior of the traffic that they carry. Because of the speeds and sizes involved, working with traffic collected from a computer network usually means working with large datasets. This article describes our experience with traffic collected from the common channel signaling (CCS) network. I will briefly describe the data and how they are collected and discuss similarities with and differences from other large datasets. Next, I will describe our analysis tools and outline the reasons that they have been found useful. Finally, I will discuss the challenges facing us as we strive for a better understanding of more data from faster networks. Although my emphasis in this article is on the CCS network, it has been my experience that both the problems and the solutions generalize to data from other networks.

Performability analysis of common-channel signaling networks, based on signaling system 7

Within integrated services digital networks (ISDN), all inter-change signaling messages for ISDN and intelligent network (IN) call controls are carried through a common channel signaling network (CCSN) as a backbone signaling network. Since CCSN usually have very strict reliability requirements as well as good performance objectives, performance and reliability of CCSN need to be jointly analyzed. This paper evaluates the mean end-to-end delay of a single-mated pair (SMP) CCSN for various call-arrival rates in a normal state and several failure states, as a performance index. As a performability index, this paper also analyzes the mean time to unreliable operation (MTUO) of a given network for various call-arrival rates at each signaling end point (SEP) and the failure rate of each signaling transfer point (STP). These results can be used in the design of common-channel signaling networks. This performability evaluation can be further studied for varying the failure rates of SEP and linksets, and the various threshold values of the unreliable operation.

Design and performance evaluation of intelligent multimedia services

Telecommunications networks are evolving globally to keep pace with rapid technological, regulatory and market changes. This is particularly evident in the introduction of intelligent network (IN) capabilities by network providers around the world. These IN capabilities will augment the network “intelligence” via the common channel signaling network and distributed service control points allowing users to gain access to advanced communications services. In this paper, we present the results of our research in the area of intelligent multimedia services. One of the main results has been the design of novel multimedia services operating over different network platforms. One of the new services being designed is an intelligent multimedia gateway, providing interconnectivity between the public service telephone network and the Internet. The design of this service has proved useful in gaining insight into the way novel intelligent multimedia services across network platforms will benefit from the use of IN technology. A performance evaluation of the service has also proved valuable to identify the major system and traffic parameters to consider when designing and deploying IN multimedia services across multiple networks.

A comparison of CCS tandem overload controls

In this paper we analyse issues associated with overloads in tandem switching systems in Common Channel Signalling (CCS) networks. In particular, we examine the need for, and effectiveness of, Automatic Congestion Control (ACC), a CCS mechanism which allows a congested switching system to inform adjacent CCS nodes of its level of overload, and subsequently controls the rate at which traffic is sent to the congested node. We demonstrate the critical need for end-offices and tandem switching systems to implement some form of ACC if network performance is to be maintained during congestion, especially in tandem exchanges. In addition, we find that the presently defined ACC should be expanded to allow more levels of congestion to be reported to adjacent nodes, so that a more effective, finer grained control is produced.

Traffic aspect of personal telecommunications in intelligent networks

Abstract This paper evaluates the traffic load for Intelligent Networks nodes and Common Channel Signaling networks (CCS), and it clarifies the impact of traffic on these resources. The main results are that: (i) CCS load is sensitive to the calling rate of personal telecommunications but largely insensitive to the proportion of radio users, the radius of the location registration zone, the distance between calling and called parties, and the size of NSPs. (ii) Large NSPs are cost-effective. Large STPs are also cost-effective except when the number of subscribers is small and the circuit cost proportional to length is more important than the node cost. (iii) The transfer delay in the CCS and in the transport network is the most important factor determining maximum end-to-end delay.

Alternatives to achieve software diversity in common channel signaling networks

With the increasing amount of software deployed in the common channel signaling networks (CCSNs) and its increasing complexity, software and its failure effects on the CCSNs have become a major concern. The software error contributing to the 1991 CCSN outages, which affected a large number of customer lines, has underscored the vulnerability of the CCSNs to software failures. The current mated pair signaling transfer point (STP) implementations in the CCSNs, with both STPs from the same supplier having the same software, make this architecture susceptible to common-cause software failure modes that might result in failures of both STPs simultaneously. To address these concerns, ways have been considered to achieve software diversity in the CCSNs by ensuring software failure mode independence among network nodes. Four potential alternatives are identified here: (i) multiple software developments in STPs; (ii) different software generics for backup; (iii) mixed-supplier STP pairs; and (iv) E-link sets to different supplier STPs. The advantages and disadvantages of these alternatives to ensure software diversity are examined in this paper and should be weighed by individual telecommunications network providers. concerns expressed in this paper are not exhaustive listings, but rather catalysts for further studies and discussions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Issues on the design of survivable common channel signaling networks

Common channel signaling networks (CCSNs) play a central role in the delivery of a wide range of telecommunications services. In designing such networks, it is of paramount importance to have redundancy in CCS network elements (signaling points and signaling linksets) and to achieve architectural diversity in the transport network that provides bandwidth, transmission equipment, transport media, and physical structures to the CCSN. Such design considerations can help reduce the probability of occurrence or limit the scope of network outages due to traffic congestion and/or transmission equipment or transport facility failures. This paper contains a high-level discussion of issues relevant to the design of survivable CCSN architectures, provides a framework for CCSN survivability analysis, and presents novel heuristics that can be used to compute paths across the transport network on which to route signaling linksets, subject to diversity constraints that include combinations of "two-way diversity" and "three-way diversity." This first attempt at formally defining the topology design problem and formulating architectural diversity constraints for CCSNs can provide the technical basis for further CCSN survivability studies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the efficacy of using the transfer-controlled procedure during periods of STP processor overload in SS7 networks

The author examines call completion performance, rather than message throughput, in a common channel signaling network in which the processing resources, and not transmission resources, of a signaling transfer point (STP) are overloaded. Specifically, he performs a transient analysis, via simulation, of a network consisting of a single central processor-based STP connecting many local exchanges. He considers the efficacy of using the transfer controlled (TFC) procedure when the network call attempt rate exceeds the processing capability of the STP. He finds the following: (1) the success of the control depends critically on the rate at which TFCs are sent; and (2) use of the TFC procedure in the event of processor overload can provide reasonable call completion rates.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Deployment issues of CCS links on self-healing rings

Fiber-based self-healing rings (SHRs) are being deployed for trunking purposes for voice/data/video services because of their high reliability and survivability. To reduce deployment and maintenance costs of provisioning different facilities for these services and common channel signaling (CCS) networks, network planners have begun to deploy CCS network signaling links on SHRs. This paper examines some issues of deploying A/B/C/D link sets on SHRs. >

Performance analysis of SS7 congestion controls under sustained overload

Congestion controls are a key factor in achieving the robust performance required of common channel signaling (CCS) networks in the face of partial network failures and extreme traffic loads, especially as networks become large and carry high traffic volume. The CCITT recommendations define a number of types of congestion control, and the parameters of the controls must be well set in order to ensure their efficacy under transient and sustained signalling network overload. The objective of this paper is to present a modeling approach to the determination of the network parameters that govern the performance of the SS7 congestion controls under sustained overload. Results of the investigation by simulation are presented and discussed. >

Capacity and performance analysis of signaling networks in multivendor environments

The load of common channel signaling networks is being increased through the introduction of new services such as supplementary services or mobile communication services. This may lead to a performance degradation of the signaling network, which affects both the quality of the new services and of the services already offered by the network. In the paper, a generic modeling methodology for the signaling load and the signaling network performance as a result of the various communication services is extended in order to include certain implementation-dependent particularities. The models are obtained by considering the protocol functions of Signaling System No. 7 as specified by the CCITT, as well as the information flows through these functions. With this approach, virtual processor models are derived which can be mapped onto particular implementations. This allows the analysis of signaling networks in a multivendor environment. Using these principles, a signaling network planning tool concept has been developed which provides the distinct loading of hardware and software signaling network resources, and on which hierarchical performance analysis and planning procedures are based. This allows to support the planning of signaling networks according to given service, load, and grade-of-service figures. A simple case study outlines the application of the tool concept to a network supporting Freephone, Credit Card, and ISDN voice services.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

Analysis of the link error monitoring protocols in the common channel signaling network

Motivated by the excessive link status changes observed in some field operations of the common channel signaling (CCS) network, the authors provide a detailed analysis of the signaling link error monitoring algorithms in the Signaling System No. 7 (SS7) protocol. These algorithms determine when to fail a link due to excessive error rates and when to put a failed link back into service. The analysis shows that, under current SS7 specifications of the error monitoring algorithms, the probability of a signaling link oscillating in and out of service could be high, depending on the traffic load, signal unit size, and the statistical nature of errors (bursty or random). The link oscillation phenomenon could become worse as longer Transaction Capability Application Part (TCAP) messages for transaction-based services (e.g., 800 Service) are carried in the CCS networks. While the risk to the existing network may not be high due to the light loads carried at present, there is still a need to study the error monitoring issues thoroughly.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of common‐channel signaling network congestion in the presence of considering various kinds of delay

AbstractCommon channel signaling networks play an important role in providing advanced switching services. With the increase in the degree of the reliability of such switching services on common channel signaling networks, the common channel signaling networks are easily congested, and controlling congestion on these networks has become increasingly important. On the other hand, the network scale has been increasing with the development of the information society. With the increase in the network scale, signal transmission delay and control signal delay have increased, giving adverse effects on congestion control. In this article, the congestion control on common channel signaling networks recommended by CCITT has been analyzed considering the above‐said transmission delay and control signal delay. As a result of this analysis, the above‐said adverse effects could be evaluated quantitatively. A rigorous solution of this model could not be obtained. Thus, a method of analysis by fluid approximation is proposed. In addition, this approximating analytical method is shown to have sufficient practical accuracy in comparison with simulation results. By this analytical method, the rates of blocking of congested resources (signal links, circuits), mean delays, etc., can be easily obtained. As a result of the analysis, it is shown that these delays greatly influence the efficiency of congestion control. Especially, it is shown that the call loss rate shows a great effect; and control parameters must be determined considering these delays in order to satisfy certain standard values by congestion control.

An analytical model for adaptive routing networks

Real-time network routing (RTNR) is a new adaptive routing method. With RTNR, switches have a simple way of exchanging link status bit map information, thereby determining the availability and load conditions of the direct and all two-link paths to the destination. Link busy-idle status is exchanged between the network nodes using a bit map data exchange through the common channel signaling (CCS) network, and calls are set up where there is the most available capacity in the network. To date the analysis of RTNR networks has been limited to simulation models. The present authors develop an analytical model for the AT&T network under RTNR, which is shown to provide good agreement with simulation models. The analytical model for RTNR networks uses an Erlang fixed point method to solve the nonlinear equations describing dynamical network behavior. The equations include the link state probability, network flows, link arrival rates, adaptive trunk reservation level, and adaptive path selection depth. The link state model provides the aggregate link state probabilities through solution of the birth-death equations, and models the adaptive nature of trunk reservation. The network flow model provides a method to calculate the traffic flow using the least busy concept employed in RTNR, and also models the adaptive nature of the path selection depth. The analytical model addresses asymmetrical networks, and computational examples show the differences from the simulation model to be small. The authors also use the analytical model to examine key RTNR parameters over a range of values.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Integrated methodology for supporting packet network performance management and planning

This paper describes an integrated approach for supporting packet network performance management and planning. As more and more packet networks — such as the public packet switched networks, common channel signalling networks and metropolitan area networks — are being deployed in the Regional Bell Operating Companies, new network operations systems are required for planning the evolution and engineering the service performance of these traffic-sensitive packet networks. This paper describes some of the synthesis and analysis algorithms that we have designed for supporting the traffic engineering of a public packet switched network. The synthesis algorithms include network element sizing, processor load balancing, network layer window size adjustment and traffic rerouting. The analysis algorithms include network element utilization and delay estimation as well as network end-to-end delay estimation.

Common channel signaling: the nexus of an advanced communications network

An overview of BellSouth's current and future common channel signaling (CCS) network is presented. The current network and its architecture are described. Network element testing and network interconnection in a multivendor, multinetwork environment are discussed. Services offered by BellSouth via the existing network are summarized. Future plans for the CSS network are outlined. These include the establishment of a target architecture that will permit the rapid introduction of a wide range of communications services in a manner consistent with the probable evolution of the market and the regulatory environment. The introduction of two BellSouth programmable nodes-the local service control point (SCP) and the ISDN service node-is described. Advanced services are highlighted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>