Congestion and flow control in Signaling System No. 7-impacts ofintelligent networks and new services

Focuses on the transient performance analysis of the congestion and flow control mechanisms in CCITT Signaling System No. 7 (SS7). Special attention is directed to the impacts of the introduction of intelligent services and new applications, e.g., Freephone, credit card services, user-to-user signaling, etc. In particular, the authors show that signaling traffic characteristics like signaling scenarios or signaling message length as well as end-to-end signaling capabilities have a significant influence on the congestion and flow control and, therefore, on the real-time signaling performance. One important result of the performance studies is that if, e.g., intelligent services are introduced, the SS7 congestion and flow control does not work correctly. To solve this problem, some reinvestigations into these mechanisms would be necessary. Therefore, some approaches, e.g., modification of the signaling connection control part (SCCP) congestion control, usage of the SCCP relay function, or a redesign of the message transfer part (MTP) flow control procedures are discussed in order to guarantee the efficacy of the congestion and flow control mechanisms also in the future     

Performance modeling of Signaling System No.7

The layered performance modeling approach is refined and extended to cover the latest CCITT Blue Book specifications. Specific submodels for the higher-level functional blocks, such as the message transfer part (MTP) level 3, the signaling connection control part (SCCP), the ISDN user part (ISDN-UP), and the transaction capabilities application part (TCAP), are given in a generic way, explicitly. With these submodels, generic models for signaling points and signaling transfer points are constructed. The major functional parts of the layered protocol architecture of SS7 are modeled in a generic way by extended queuing network elements such as full duplex flow controlled links, priority processors, multiple-chain multiple-class traffic streams, or elements for segmenting and reassembling of messages. The analysis of the whole network starts from a global traffic flow analysis, which takes all the different signaling message types, their paths through the network, and the load into account. The overall performance measures, such as end-to-end transfer times, are found from all the component delays. The analytical results have been validated by simulation, revealing a high degree of accuracy     

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.     

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     

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: 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.     

A Comparison of the Triggering Behavior of SS7 Congestion Control Options

This paper focuses on the transient performance analysis ofthe User Part (UP) congestion and flow control mechanisms in ITU-T Signaling System No.7 (SS7). In particular, we developed an analytic model that we use to study the steady-state performance of the UP congestion control scheme. Numerical results of the investigation are presented and 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。     

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     

Performance analysis of SS7 congestion controls under sustainedoverload

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     

基于MPC8260MCC的MTP2协议的实现

在E1收发器MT9075实现信令数据链路级功能的基础上,按照MPC8260的MCC的7号信令模式处理E1信令,实现MTP2协议。重点说明了初始化MCC信道为7号信令信道的流程和实现的功能。将此信令处理方案应用于E1接口板,实验证明可以实现MTP2协议,同时为7号信令信令网级和用户级功能的实现提供了信令处理平台。     

Threshold-based congestion control for the SS7 signaling network inthe GSM digital cellular network

This paper considers the congestion control scheme for the SS7 signaling network in the group special mobile (GSM) digital cellular network. This congestion control scheme is based on monitoring the SS7 link buffer occupancy. In this scheme, a congestion onset message is sent to the user parts of the SS7 network when the buffer occupancy exceeds a certain threshold, and, subsequently, a congestion abatement message is sent when the buffer occupancy goes below another threshold. Upon receipt of the congestion onset message, the user parts are expected to “intelligently” throttle the user traffic (reduce the traffic rate) so as to yield speedy recovery from congestion. Subsequently, on receipt of the abatement message, the user traffic is restored to precongestion levels. This paper primarily proposes appropriate choice of throttles and an algorithmic procedure to size the thresholds so as to yield good performance during congestion. The paper also addresses some implementation issues related to the throttles. Finally, it considers the effects of delays for the onset and abatement messages in reaching the user parts on the performance and parameters of the congestion control scheme     

数字移动通信信令网SCCP寻址

在ＧＳＭ网中，交换局间的非电路相关的呼叫控制停产旧局间信领必不可少的的部分，信号连接控制部分（ＳＣＣＰ）则为信领的传递提供了可能。文章通过一个基本的ＳＣＣＰ寻址的实例，对移动网移动应用部分（ＭＡＰ）消息的传送流程进行了基本描述，同时也对目前ＧＳＭ网上实际的ＳＣＣ 址过程中消息通过各网络节点时相关中由参数的变化格了较斩解释。     

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 signalling system number 7 for ISDN and intelligentnetworks

Various functional parts of signalling system number 7 and the underlying concepts are described. The unique attributes of the lower and higher functional layers are discussed. Applications of signaling system number 7 for call control and for transaction services are presented. The signaling transfer point makes signalling networks possible. Using the lower layers of the protocol, it provides routing capability for signaling messages between the exchange offices and access of these exchange offices to the network databases. The author discusses the performance parameters associated with the signalling transfer point and examines its implementations     

七号信令中SCCP面向连接业务实现的关键问题

信令连接控制部分(SCCP)面向连接业务的最主要特点是在传递数据之前的连接建立阶段就完成了路由选择,因而如何解决路由控制和多用户识别问题是实现该业务的关键。通过对协议的深入分析及实际应用的考虑,设计出路由控制流程和多用户连接段表,从而很好地解决了上述问题,并由测试结果对SCCP面向连接业务进行了性能评估。     

A comparison of SS7 congestion control options during mass call-insituations

The ITU-T (International Telecommunications Union, Telecommunications Standardization Sector, formerly known as CCITT), in its specification of the SS7 protocol, describes a number of alternatives for congestion control. In this paper we provide a direct comparison of the effectiveness of some of these methods in dealing with a mass call-in situation. We find that the international option provides better call throughput and is more robust to threshold settings and delays in feeding back congestion information than the national option with congestion priorities and a combination of the two options. The results can provide guidance to those attempting to define application level overload procedures, to those studying internetworking issues for connection between countries employing different SS7 congestion control options, and to those preparing to formulate B-ISDN overload strategies     

End-to-end congestion control schemes: utility functions, random losses and ECN marks

We present a framework for designing end-to-end congestion control schemes in a network where each user may have a different utility function and may experience noncongestion-related losses. We first show that there exists an additive-increase-multiplicative-decrease scheme using only end-to-end measurable losses such that a socially optimal solution can be reached. We incorporate round-trip delay in this model, and show that one can generalize observations regarding TCP-type congestion avoidance to more general window flow control schemes. We then consider explicit congestion notification (ECN) as an alternate mechanism (instead of losses) for signaling congestion and show that ECN marking levels can be designed to nearly eliminate losses in the network by choosing the marking level independently for each node in the network. While the ECN marking level at each node may depend on the number of flows through the node, the appropriate marking level can be estimated using only aggregate flow measurements, i.e., per-flow measurements are not required.