A Novel Monitoring and Network Control System for increased Resource Management S. Kyriazakos, V. Gkroustiotis, C. Karambalis, C. Kechagias, N. Papaoulakis, D. Nikitopoulos and G. Karetsos Telecommunications Laboratory National Technical University of Athens Heroon Polytechniou 9, 15773 Athens, Greece Tel: +30 10 7722558, email:
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ABSTRACT Traffic overload in wireless systems is one of the major network shortcomings which has a direct influence on the user satisfaction. In this paper we briefly describe the problem of traffic congestion and we propose an architecture that can be integrated in any cellular system of present generation and considering a set of modifications can also be applied in future generation systems. The motivation for this work is mainly the huge problems encountered in the past in cellular systems.
I. INTRODUCTION In the light of the deployment of 3G systems and introduction of new services mainly based on high speed communication, several problems of existing systems are analyzed, so that they can encountered in next generation networks. A novel management system is proposed and described in the following sections. This paper is organized as follows. Chapter 2 is describing the traffic overload situations in cellular systems. Chapter 3 presents the CAUTION system, which promises real-time network reconfigurability, in order to results in a stable system that can encounter traffic congestion. In chapter 4, we present the trial plan that is foreseen to validate the CAUTION system. Chapter 5 describes the expected results of the trials and the future work. Finally, in chapter 6 we sum up the studies that are performed and we end with the conclusions.
these cases, the offered traffic is rapidly increasing up to the maximum, which represents the maximum traffic that can be handled from the network. Unfortunately, the maximum sustainable traffic overload is much lower, since it has been proved that after reaching a specific threshold the blocking- and drop call-rate are increasing dramatically.
Figure 1: Network performance In the above figure, the gray area represents the additional revenues, due to the increased traffic during traffic congestion. On the other hand the Blocking- / Drop Call-rate represented by the dashed line, represents the unsatisfied subscribers and part of the revenue loss due to the calls that could not be handled. Therefore, the operator should calculate the investment to shift the maximum capacity line and this should be lower than the difference of the two areas – the gray one and the other defined by the dashed line. On the other hand there is much concern, that cellular systems are not optimized and the systems are underutilized. In the following sections, a novel monitoring and management system is proposed, so that both users and operators will be satisfied.
II. TRAFFIC CONGESTION IN CELLULAR SYSTEMS III. CAUTION SYSTEM Network shortcomings are not just predictable situations that are encountered every day. Revenues are lost, every time traffic overload occurs and huge investments are needed to overcome these situations. In Figure 1 a characteristic problem is presented. The daily offered traffic is presented. We assume that no congestion takes place, something that is very optimistic, since congestion can also be predicted at a daily basis. This study mainly concerns enormous congestion situations mainly caused in large scale events, catastrophes, etc. In
Traffic congestion is a situation that is hardly managed in cellular networks. Traffic overload arises every day during rush hours and quite often in non-predictable events, and cellular networks are not built with a redundancy similar to the one of fixed networks; therefore, they are more sensitive to congestion situations than fixed network. The need of high-speed data technologies, in combination with the development of several data services, results in network
shortcomings. CAUTION system tackles the problem of traffic congestion in cellular networks and the main goals are to monitor cellular networks, to predict and/or detect congestion situations, to apply management techniques to avoid traffic overload and finally to ensure stable transition from the congested state to the normal one. For the above-mentioned objectives a suitable architecture should be designed. A very important network element is the one, responsible for real-time system monitoring. Unfortunately, real-time monitoring is a very difficult task in existing networks. Monitoring tools, cannot respond in real-time and additionally they cannot automatically enable mechanisms to overcome congestion problems. The idea of Interface Traffic Monitoring Unit (ITMU) is to exploit all available reporting mechanisms and collect those that can give an idea of the traffic overload. In this way redundant procedures will be avoided, and with no additional overhead the system can be monitored in terms of utilization and channel blocking. Therefore, ITMU will guarantee the accurate detection of problems and will manage the reporting to the Resource Management Unit (RMU). On the other hand and despite the implementation difficulties of the distributed monitoring solution, ITMU will not have knowledge management mechanisms implemented, in order to ensure safe system rollout. The system element, which has to be very carefully designed, following intelligent algorithms and knowledge-based management, is the RMU. The reported alarms, originated from ITMU, will have to be mapped and processed in a way to match the appropriate traffic-load scenario. In a further stage, a management technique should be selected and applied after adjusting several parameters. This is also related with on-the-fly adjustments that will lead to the wanted result. CAUTION system is composed by four new elements interconnected by means of dedicated wired lines or IP backbone network as illustrated in Figure 2. The new CAUTION network elements are the following ones: • ITMU (Interface Traffic Monitoring Unit) • RMU (Resource Management Unit) • ECS (Emergency Call Server) • PCS (Priority Call Server) The ITMU collects, from several concentrators, information about the radio resource utilization in each cell. It will also constructs a matrix for all BTSs with the purpose of compacting several data coming from several concentrators. Each column contains the BTS’ identifier and information about the utilization of all the logical channels of a given cell. A sliding window aggregates and averages the data, estimating the realtime resource utilization. The ITMU internally stores the matrixes and when congestion is detected in the radio interface of a given cell, the ITMU will forward alarm messages to the RMU. The RMU is the core element of the CAUTION system by which resource management techniques are decided as well as executed through the OMC after a detection of network congestion. The RMU is a centralized element. It manages the alarms generated by several
ITMUs and depending on the type of data, the RMU reacts properly by sending messages to the OMC. The messages contain radio resource management information used to change the radio resource allocation of the overloaded cells. In some cases the RMU can respond to an ITMU message with a request for additional information about traffic-load in adjacent cells, in order to execute the most appropriate Resource Management Technique (RMT). For example if a RMT has an effect on the alarmed cell as well as on its adjacent cells, the RMU may decide to control the status of the radio resources of the adjacent cells in order to verify that the candidate RMT will not influence negatively the neighboring cells. The RMU may also decide to apply a RMT even before alarms are generated by the ITMUs, when some predicted congestion event is going to happen. In this case the RMU knows beforehand that a particular traffic condition will occur at a given time and at specific cells, and it can decide to prevent the probable cell overload by applying, in advance, the proper RMT. After a radio resource modification, the RMU monitors the radio resource utilization in order to check if the applied RMT has gained the desiderate effects.
Figure 2: CAUTION system architecture In addition, a PCS and an ECS are connected to the RMU and ITMU elements. Priority call server will be an additional element of the CAUTION architecture that will enable the prioritized assignment of bandwidth, according to the user’s class. ETSI and 3GPP have specified user’s prioritization classes for priority calls, preemption and queuing. In CAUTION project, it will be important to avoid prioritization of users according to their contract with the cellular operator, since several legal issues should be considered. The priority call server will be an element that can be “on the fly” reconfigured in such a way to assign priorities according to the traffic-load situations. The users will be classified to several classes, such as ambulances, authorities, police, fire department, etc. In this way after the monitoring of the system, that will take place in ITMU, the priority server will provide the RMU information related to the priority classes of the subscribers.
The emergency call center will be a CAUTION element that should guarantee a full-time availability of the network, especially in emergency situations. In GSM networks, these elements already exist but they are not operational in extreme congestion situations. Emergency call centers will be attached to each ITMU in the CAUTION architecture. Their functionality is to monitor the traffic load in all cells and alarm reporting from ITMU. The emergency call centers will be distributed to each ITMU and also connected to the centralized RMU. Whenever ITMU reports congestion alarms to the emergency call center, the emergency call center will take the decision about the required bandwidth needed. This would be adjustable and reconfigurable from external places, in a way to require on-demand bandwidth or QoS. For instance, if a catastrophe has taken place the QoS grade will be definitely increased in such a way that all emergency calls will be served, even if they are performed from the operator. For the optimal usage of the emergency call centers, operators should in the future monitor the reserved resources. The connection with the RMU, might change the selected management technique, therefore, it will be the dominant element in cases of emergency that in spite of the RMU decisions, might require the execution of a mechanism, which will enable the handling of emergency calls.
switched off. Subsequently, the system will start and the network improvement will be measured in a set of traffic load scenarios. HSCSD trials are also foreseen as well as GPRS. For the latter there is a limitation, due to the need of connecting the monitoring system-ITMU with the SGSN that is not available at the trial site. Therefore, the external GPRS segment will be applied.
V. EXPECTED RESULTS AND FUTURE WORK The system’s performance is already predicted by means of simulations. Most of the management techniques that are selected for RMU are studied with simulators. The increased network performance in combination with the decreased blocking and drop call rate are expected. The system is scalable, thus modular, so that it can be easily modified and applied in next generation wireless systems. The main goal after validating the system is to extend it for next generation wireless systems including UMTS, WLAN, etc. For that purpose, standardized interfaces for monitoring and command execution should be defined apart from the additional network management techniques.
IV. CAUTION TRIAL In the previous sections the CAUTION system was presented. The system is specified and designed at a low-level. Currently the system modules are under implementation and it is expected that in short time from now the system integration and verification will take place. Several trials and validation procedures are foreseen for the system. A GSM 1800 testbedenvironment is already constructed as shown in the following figure:
VI. CONCLUSION The problem of traffic congestion in cellular systems was presented. In addition the strong impact on the user satisfaction and the operator’s revenues was also described. The authors propose a novel system platform that can support network decisions in cases of congestion, so that wireless systems will become more stable. The architecture and functionalities of the system are presented, as well as the trials that are foreseen to validate the system.
ACKNOWLEDGMENT This work has been performed in the framework of the project IST CAUTION, which is partly funded by the European Community. The Authors would like to acknowledge the contributions of their colleagues from National Technical University of Athens, VTT Information Technology, Cosmote Mobile Telecommunications S. A., Telia Mobile and Motorola S.p.A.
Figure 3: CAUTION trial system For thee purposes of the trial, all equipment needed for the trials are placed, namely BSCs, MSC, BTSs, HLR, etc. In addition, a traffic generator is constructed, so that congestion scenarios can be constructed. Initially, a set of measurements will take place, when the RMU is
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