Evolving intelligent interexchange network-an SS7 perspective

The role of common channel signaling, referred to as Signaling System No.7 (SS7), in the evolution of services in an interexchange carrier environment is discussed. The importance of SS7 in evolving the intelligent network necessary to support these services is addressed. Interworking with virtual private networks via the out-of-band ISDN messaging channel (D-channel) to extend the capabilities of SS7 network signaling to customer networks is also discussed. For ubiquitous support of ISDN, CLASS, and future services, the interworking of interexchange SS7 with domestic local exchange carriers as well as foreign administrations is critical. This service and intelligent network evolution is described. Emphasis is placed on services and the anticipated migration to those types of services which demand an intelligent interaction and close coupling of both virtual private networks and local public switched networks to the interexchange network     

Signaling System No.7 in corporate networks

Corporate network user requirements are identified. The significance of Signaling System No.7 (SS7), in corporate network as a separate backbone signaling system for implementing a robust, flexible and transparent communication network is discussed. The architecture for a corporate network utilizing enhanced signaling is described. The use of SS7 instead of the integrated services digital network primary rate interface (ISDN PRI) is explored. Some SS7 applications in corporate networks are examined     

Current role and future evolution of the ISDN Signaling system inNTT's network

The current role of the integrated services digital network (ISDN) Signaling System is examined, covering general features of the ISDN protocol, functionalities supporting ISDN services, and functionalities supporting existing services. The Signaling System No.7 (SS7) network and its operation are described. The future evolution of the ISDN signaling system is discussed     

An overview of Signaling System No.7

An overview of Signaling System No.7 (SS7) is presented. The salient features of SS7's network services part (NSP) are described. Functionally, NSP corresponds to the first three layers of the Open System Interconnection (OSI) reference model. The signaling network structures that, in conjunction with the NSP, provide integrated services digital network (ISDN) nodes with a highly reliable and efficient means of exchanging signaling messages are discussed. The nodal capabilities of call control and remote process invocation and management, part of the SS7 user parts, are described. The very stringent performance requirements of signaling systems and their reflection on the critical nature of signaling functions and their real-time exigencies are discussed. The likely evolution of network signaling in the remaining years of the 20th century is discussed     

Assuring SS7 dependability: a robustness characterization ofsignaling network elements

Current and evolving telecommunication services will rely on signaling network performance and reliability properties to build competitive call and connection control mechanisms under increasing demands on flexibility without compromising on quality. The dimensions of signaling dependability most often evaluated are the rate of call loss and end-to-end route unavailability. A third dimension of dependability that captures the concern about large or catastrophic failures can be termed network robustness. The paper is concerned with the dependability aspects of the evolving Signaling System No. 7 (SS7) networks and attempts to strike a balance between the probabilistic and deterministic measures that must be evaluated to accomplish a risk-trend assessment to drive architecture decisions. Starting with high-level network dependability objectives and field experience with SS7 in the U.S., potential areas of growing stringency in network element (NE) dependability are identified to improve against current measures of SS7 network quality, as per-call signaling interactions increase. A sensitivity analysis is presented to highlight the impact due to imperfect coverage of duplex network component or element failures (i.e., correlated failures), to assist in the setting of requirements on NE robustness. A benefit analysis, covering several dimensions of dependability, is used to generate the domain of solutions available to the network architect in terms of network and network element fault tolerance that may be specified to meet the desired signaling quality goals     

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.     

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     

Telephone challenges: a plethora of services

Technical advances and changes in the regulatory climate in US telephony since the court-ordered divestiture of AT&T Company in 1984 are examined in this second of a series of articles (for previous article, by G. Zorpette, see ibid., vol.27, no.5, p.28 (1990)). A set of services based on Custom Local Area Signaling Service (Class) technology, introduced in New Jersey in 1987, provides caller identification, call block, priority call, return call, repeat call, select forward, and call trace. Throughout the USA it is being rolled out at varying clips, depending on state regulatory climates and the pace of technology upgrades in the network. Class is usually based on Common Channel Signaling System 7 (SS7) software, but can also be implemented by the Advanced Intelligent Network, which puts the control software in a computer outside the switch so that computers more powerful than switch hardware can manipulate a call. Other major trends discussed are the growing use of cordless telephones, cellular telephony, voice mail, and computers replacing human operators     

Analysis of the link error monitoring protocols in the commonchannel 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     

Signaling System No.7 local exchange deployment

The author examines the deployment of Signaling System No.7 (SS7) from the viewpoint of the local exchange carrier. The three phases of local exchange deployment-service planning and design, local exchange network design, and interconnection design-are discussed in sequence. SS7 is a fundamental change to the infrastructure of the local exchange telecommunications network. The author describes how the backbone network, centered on the signaling transfer points (STPs), is installed first, followed by the local exchange network, and then interconnection to interchange and other networks     

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     

An Overview of Signaling System No. 7

When it was first approved by the CCITT in the 1980 Yellow Book, Signaling System No. 7 was described as "an internationally standardized general purpose Common Channel Signalling (CCS) system:bulletoptimized for operation in digital telecommunications networks in conjunction with stored program controlled exchanges;bulletthat can meet present and future requirements of information transfer (circuit and non-circuit related) for inter-processor transactions within telecommunications networks for call control, remote control, network data base access, and management and maintenance signalling;bulletthat provides a reliable means of information transfer in correct sequence, without loss or duplication." It then consisted of a three-level message transfer part (MTP-for connectionless message transfer), a telephone user part (for analog call setup and control), a data user part (for analog circuit switched data), and a four-level architectural model with a "fuzzy" relation to the OSI seven-layer model. By 1984, in the Red Book, the MTP had matured considerably (especially in the area of congestion control), a new level had been added to provide additional transport functionality (the signaling connection control part or SCCP), an ISDN user part provided call control for digital facilities, and the architectural model had been "adjusted." Future efforts are focusing on cod-to-end ISDN signaling compatibility (harmonization of SS7 andD-channel procedures), non-circuit-related transaction capabilities (e.g., for network database interactions), a complete operations and maintenance application part (OMAP), and a more formal architectural relationship with the OSI model.     

Implementation of SS7: Italtel's experience

Field results in implementing Signaling system No.7 (SS7) in preparation for the introduction of intelligent network (IN) services are reported. Besides implementing SS7 for interexchange trunk signaling, Italtel has adapted it for communications with remote units, i.e. remote switching modules and subscriber multiplexers and concentrators. IN implementation in a distributed system is discussed. The distributed architecture of the Linea UT intelligent network is described     

Routing and congestion control in common channel Signaling SystemNo.7

The routing and congestion control function of Signaling System No.7 (SS7) are described. The elements of the SS7 protocol functional division include message transfer part (MTP), signaling correction control part (SCCP), ISDN user part (ISUP), and transaction capabilities (TC). The routing function, which takes place at the MTP and SCCP, and the congestion control function, which is present in multiple layers, are discussed. This includes MTP level 2, MTP level 3 by signaling traffic flow control procedures, and flow control for connection-oriented services of SCCP. To illustrate the unique capabilities present in SS7, the routing and congestion control functions in SS7 are compared to other common connectionless network layers. Performance considerations in routing and congestion control are discussed     

Signaling System No.7: a tutorial

A tutorial overview of the salient features of SS7 is provided. Its history is briefly reviewed, and the SS7 network services part (NSP), which corresponds to the first three layers of the Open Systems Interconnection (OSI) Reference Model, is described. Signaling network structures that, in conjunction with the NSP, provide integrated services digital network (ISDN) nodes with a highly reliable and efficient means of exchanging signaling messages are discussed. The nodal capabilities of connection (call) control and remote process invocation and management and other functions of the user parts of SS7 are examined. The very stringent performance requirements of signaling systems, which reflect the critical nature of signaling functions and their real-time exigencies, are stressed. A broad outline of the likely evolution of ISDN signaling systems in the remaining years of this century is sketched     

No.7信令系统的安全威胁及其防护

No.7信令系统（SS7）是公用电话网的关键支撑系统,SS7网络最初作为封闭网络来设计的,整个网络由运营商完全控制,各实体高度信任。文章分别针对该系统的信令协议、网络节点和来自外部网络的安全威胁进行了分析,并从协议安全、边界防护和内部安全加固三个方面提出了构建信令系统防护体系的方案。     

A control mechanism to prevent correlated message arrivals fromdegrading Signaling No. 7 network performance

Signaling System No. 7 (SS7) is designed to provide a connectionless transfer of signaling messages of reasonable length. Customers having access to user signaling bearer capabilities as specified in the ANSI T1.623 and CCITT Q.931 standards can send bursts of correlated messages (e.g., by doing a file transfer that results in the segmentation of a block of data into a number of consecutive signaling messages) through SS7 networks. These message bursts with short interarrival times could have an adverse impact on the delay performance of the SS7 networks. A control mechanism, credit manager, is investigated in this paper to regulate incoming traffic to the SS7 network by imposing appropriate time separation between messages when the incoming stream is too bursty. The credit manager has a credit bank where credits accrue at a fixed rate up to a prespecified credit bank capacity. This paper presents simulation results showing delay performance of the SS7 ISUP and TCAP message traffic with a range of correlated message traffic, and control parameters of the credit manager (i.e., credit generation rate and bank capacity) are determined that ensure the traffic entering the SS7 network is acceptable. The results show that control parameters can be set so that for any incoming traffic stream there is no detrimental impact on the SS7 ISUP and TCAP message delay, and the credit manager accepts a wide range of traffic patterns without causing significant delay     

Realization of a Signaling System No. 7 Network for AT&T

Transition of the AT&T Communications Common Channel Interoffice Signaling (CCIS) Network, currently the world's largest, to a more powerful and flexible network with Common Channel Signaling System No. 7 capability has begun with the introduction of a more powerful signaling transfer point system and high-speed data links. The evolving AT&T network will be a key element in supporting an Integrated Services Digital Network (ISDN) capability. This paper describes the status of the existing AT&T CCIS network and how it will evolve toward a new network employing Signaling System No. 7 utilizing the ISDN User part (ISDN-UP). It also considers Signaling System No. 7 ISDN-UP implementation and the flexibility of the ISDNUP protocol in support of future customer needs.     

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     

Signaling System No. 7 ISDN User Part

The integrated services digital network (ISDN) user part of Signaling System No. 7 defines the signaling protocol which supports the establishment, supervision, and release of voice and nonvoice calls over circuit-switched connections between ISDN terminations of digital subscriber access lines. This paper gives an overview of the ISDN user part protocol, as defined in CCITT Recommendations Q.761-Q.766 [1], in terms of the signaling functions and procedures provided to support call and connection control in an ISDN, and in terms of the information elements and signaling messages that are used by the signaling functions in ISDN exchanges to communicate.