SS7 Network Management Using Link Monitors

The disruption and loss of SS7 signalling networks during the summer of 1991 in North America by the “brown outs” and the resultant loss of services, revenue and customers, has focused the minds of many Telcos to put management systems in place to ensure network robustness. Their primary purpose being to identify problem trends earlier and speed up restoration of failed signalling components. We consider the role of SS7 link monitors in the management of a Common Channel Signalling (CCS) network. Several applications were prototyped as a proof of principle, demonstrating the suitability of the Inet GeoProbe System as a platform for service and network management applications. Introduction As the world’s major Telcos strive to gain market share and provide global networks to multi-national corporations, they perceive the ownership of an Intelligent Network (IN) to be of key importance in achieving their ambitions. The IN should enable them to provide new services, in a flexible manner and a shorter time frame, to customers with diverse needs, whilst reducing the need for overlay networks. Central to the IN is the SS7 Signalling network [1], [2], [3], this carries the database queries and responses between the Service Switching Point (SSP) and the Service Control Point (SCP), in addition to the messages which set-up and cleardown the circuit switched part of the IN call. Without the SS7 network the IN and the ISDN would be unable to offer any services to its users, because as Manterfield states, “Signalling is the life-blood of telecommunications networks.” [3]. During the summer of 1991 a series of major network outages occurred in the USA, several of which resulted from problems associated with SS7 signalling networks, including those of Bell Atlantic and Pacific Bell [4]. The American Federal Communications Commission was very concerned by these events and set up a Network Reliability Council to investigate and report how to improve the reliability of the networks [5]. 1 A more recent example of a major network outage occurred in Israel during 1995. In 1992 BT decided to implement a new IN platform and a strategic study was commissioned to investigate the possible options. It identified signalling traffic management as being crucial to those who wish to offer IN services whose signalling traffic may be volatile in nature; because it is not constrained by the availability of free traffic circuits. One of its major recommendations was that SS7 link monitors should be deployed to give network managers visibility of the SS7 noncircuit related network. A similar requirement for an independent entity to provide surveillance capabilities is also identified by Hoang, et al [4]. The primary focus of signalling network management is to identify problem trends earlier and speed up restoration of failed signalling components. SS7 link monitors are seen as being central to this function because unlike the nodes they can give visibility of the CCS network under all circumstances. A subsequent world-wide invitation to tender under European Commission regulations was conducted in 1994 and BT selected the GeoProbe system from Inet Inc., Texas, USA [13]. This paper describes the functionality provided by the GeoProbe system and identifies how a network operator can gain additional benefits by building additional applications onto this platform. We investigate applications which can be implemented by extending the GeoProbe’s Oracle database. SS7 Network Management A recent study by the authors has revealed that very few papers have been published in the area of SS7 network management. This could be for several reasons, the most likely being its commercial importance and sensitivity to Telcos. Also it is a fairly new area, since major outages due to SS7 signalling networks did not occur until relatively recently. Of the papers reviewed the main focus was on TMN solutions to SS7 management [6], [7]. Other papers looked at an implementation of an SS7 management system based on TMN using the Ericsson Telecommunications Management Operations Support System (TMOS) platform [8], [9]. The North American long distance carrier MCI has recently published a paper which describes a functional software architecture for its system called SS7 Data Manager (SS7DM) [10]. France Telecom has extended its traffic management system to monitor the signalling network [11]. No papers have been found on the management of SS7 networks using SS7 link monitors although Schmid, et al [9] states that, “The actual measurements may be done in the network elements themselves or in an external system, where probes are directly attached to the signalling links. Additionally, derived measurements may be obtained from collected raw measurements.” The remainder of this paper will focus on the management of SS7 networks using link monitors. SS7 Link Monitors Link monitors are available commercially from several vendors. The GeoProbe system comprises four major components: an SS7 probe (SpIprobe), a central UNIX server (SpIserver), a UNIX Workstation (SpIstation), and a transport network (see Fig. 1). The SpIprobe is situated with the network elements to be monitored, for example at a Signalling Transfer Point (STP) site and is connected to the 2Mb/s transmission bearers which carry the signalling channels via a high impedance ‘T’ connector; usually at the 2Mb/s Digital Distribution Frame (DDF). Thus enabling the SpIprobe to monitor the SS7 links which are carried within the 64Kb/s timeslots. The SS7 raw data is converted by the SpIprobe into the measurement types which are defined in the ITU-T Rec. Q.752 Monitoring and Measurements for SS7 networks [12]. The real-time applications reside on SpIprobe to avoid incurring the delay of transporting data to the server for processing. It is possible to collect both real-time and historical statistics, the former are displayed on the SpIstation in realtime, whilst the latter are collected by the SpIserver and stored in a database. The server can be situated at a network management centre remote from the probes and holds the configuration data for the probes and non-real-time applications. The workstation provides a graphical user interface (GUI) and display function for the system, consisting of network maps which indicate the status of the network elements “nodes and linksets” and data query forms, to help the user select the statistics which are to be collected. The transport network connects the probes, server, workstations and any external management systems together using the TCP/IP protocol. The GeoProbe can provide continuous real-time monitoring of the entire network, if all the links are being monitored. It is able to detect and report abnormal network events through the analysis of SS7 traffic patterns. The collected statistics can be correlated by link, linkset and node and displayed in graphical or tabular formats for easy analysis by the user. Three major functions are provided by the system these are network surveillance, protocol analysis and user call trace. Several options are available for building additional applications either by using the supplied application programming interfaces (APIs) or by extending the Oracle database; which stores the historical statistics on the SpIserver [13]. We selected the latter option. New Management Applications It is possible to classify management applications in many ways, one of the more common approaches is by functional domains, for example network planning , performance management or service management. Each new application developed by the authors is categorised into one or more management domains and a brief functional description given. SEP STP SEP Transport Network SpIstation SpIserver Printer