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     

七号信令网MTP3层安全机制分析

七号信令网络由于缺乏安全机制而存在诸多安全漏洞。通过分析攻击者如何利用MTP3层的网络管理消息对七号信令网实施攻击,提出用密钥交换协议和认证头协议对MTP3层进行安全保护,从而实现了信令节点间的相互认证和对消息的完整性保护,增强了七号信令网络的安全性。     

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     

七号信令网中基于MTP3层的安全机制研究

七号信令系统作为电信网络的神经系统,其安全问题日益严重.给出了SS7网络面临的主要安全威胁,分析了攻击者利用网络缺乏认证机制,通过MTP3层的网络管理消息对七号信令网实施攻击.提出用密钥交换协议和认证头协议对MTP3层进行安全保护,增强SS7网络的安全性.     

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     

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     

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     

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     

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     

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     

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     

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     

PROMS: a PRO‐active Monitoring System for SS7 networks

In this paper, we propose a PRO‐active Monitoring System (PROMS) for SS7 networks, which actively monitors all signaling network management messages of SS7 networks, alerts operators when there is a potential network error, and provides intelligent diagnosis based on fuzzy logic and neural networks. Copyright © 2000 John Wiley & Sons, Ltd.     

The role of ISDN signaling in global networks

A historical context is provided for integrated services digital network (ISDN) to give some perspective on how the current signaling capabilities have evolved. A communications architecture is introduced and used to organize the discussion of the ISDN protocols (i.e. DSS1 and SS7) and to highlight the role of signaling in the overall architecture. The architecture defines a functional partitioning of the capabilities of ISDN, which is used to compare and contrast the DSS1 and SS7 protocols and to discuss the interfaces that support global intelligent networks. The purpose is to illustrate the similarity between the DSS1 and SS7 control protocols. The likely evolution of the ISDN protocols is discussed, showing their convergence toward a single control protocol based on the International Organization for Standardization (ISO) protocols     

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     

7号信令承载IP化组网方案探讨

本文基于IPSTP平台已在中国移动信令网中使用的前提下,研究信令网IP化承载后的组网方案,分别对本地信令网、省内长途信令网及省际长途信令网三部分进行详细论述。     

WCDMA核心网信令系统对七号信令网的影响

BICC和GCP是第三代移动网络中必不可少的信令,主要支持的承载网络是ATM和IP,许多厂商也侧重开发ATM和IP传输技术。在中国未来几年逐渐开展3G移动业务后,GSM网络的业务也可以逐渐连接到3G核心网络中,GSM也会支持分层网络,使用比STM更经济的IP作为传输,原来七号信令网络中的流量就会逐渐减少。在设计3G七号信令网络时,需要考虑3G网络信令对传输的要求,为将采用的新技术进行准备。     

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