Mobile networks are growing rapidly. Satellite networks are used to reach subscribers around the world and are mainly used for locations where radio or cable coverage is difficult to achieve. Mobile radio networks were designed to interconnect land based vehicles to the terrestrial telephone networks. These networks mainly provide outdoor coverage, like the paneuropean digital GSM networks. Indoor mobility is achieved by extensions of cordless telephony using the digital DECT technology.
Alarm handling systems enable the network operator to run the network with minimal operating costs. The goal is to collect and interpret alarm messages and failure indications from the network elements without human intervention. The network has to adapt to most failures without additional user influence and support repair actions by supplying the relevant data to the technicians.
In large networks, like the current GSM networks, the alarm vectors supplied by the network elements tend to flood the workstations of the operators especially in critical situations like the passage of a thunderstorm front. Heavy rain affects the operation of microwave links and the electro magnetic power of lightning activates the protection switches used to safeguard the electronic equipment. Performance of the mobile network is degraded heavily in such situations and operators have difficulties interpreting the shower of important and less important messages from the network.
Mobile networks can be divided into three parts (see fig.1): the mobile station (MS), the access network with the base station transceivers (BTS) consisting of antennas, radio transceivers, cross connect systems (CC) and microwave (ML) or cable links (CL) and the base station controller (BSC), and the switched network, which is connected to the access network by the BSC's. The BSC provides the radio resource management, which serves the control and selection of appropriate radio channels to interconnect the MS and the switched network. The switched network interconnects the MS to the communication partner, which might be another MS or an ISDN subscriber.
Figure 1: Structure of the GSM network
Fig.2 show the structure of the alarm paths from the network elements (BTS, ML, CL, BSC) to the operation support system (OSS). The OSS hosts the operators and performs all data processing necessary to filter, condense and interpret the alarm messages. The logical structure of the alarm network is shown in fig.2. The physical structure is different, but not relevant for our purpose. The alarms can be transmitted via the transmission network, the microwave or cable links, or via a specialized network, the X.25 network. The X.25 network is physically separated from the transmission network. The advantage of this separation is that a failure in the mobile network does not influence the alarm propagation. The disadvantage is the additional cost. Especially in the network elements located downwards from the BSC, communication and message paths are often combined to save costs.
A mediation device, which is located either in the network element, in the BSC or the OSS adapts the proprietary interfaces of the different vendors to the standard interfaces of the OSS. This mediation device can perform filtering and condensation functions of incoming messages. As the exact specification of this function is usually not known, the interpretation of alarm messages is further complicated.
