Advanced Methods in GPRS Network Analysis P´alVarga,P´ eter Tatai Abstract — Network operators need up to date infor- mation about the status of their network in order to im- prove customer satisfaction. Usual status- and alarm- messages generated by GPRS network nodes are not being analyzed fully, unless a network node or link be- comes unusable and fast recovery actions are needed to take place. Correlating signaling procedures and key signaling message parameters captured on signaling links leads to better understanding of network performance. The aim of this paper is to suggest passive monitoring-based methods for extracting network characteristics infor- mation from data collected mainly on the G b and A bis interfaces. The methodology described in this paper is based on the expertise gathered during analyzing early results of measurements taken by the SGA-GPRS (Sig- naling Generator and Analyzer for GPRS) Monitoring System. SGA-GPRS had been developed in BUTE, Department of Telecommunications and Media Infor- matics in cooperation with Aitia Inc. Keywords — passive monitoring, performance evalua- tion, event-correlation, GPRS. I. Introduction S EVERAL implementations exist for public mobile data-services. The one we focus on is GPRS (Gen- eral Packet Radio Service) [1], [2], often referred to as 2.5G, since it is based on the established GSM architecture (2nd Generation Mobile), and provides fast data-transmission services, which is the feature of the 3G (i.e., UMTS, Universal Mobile Telecommuni- cations System). The basic architecture of a GPRS network is shown in Figure 1. The acronyms of Figure 1 are listed below. • MS - Mobile Station • BTS - Base Transceiver Station • BSC - Base Station Controller • SGSN - Serving GPRS Support Node • GGSN - Gateway GPRS Support Node • EIR - Equipment Identity Register • MSC/VLR - Mobile Switching Center/ Visitor Location Register • SMS-GMSC - Short Message Service - Gateway Mobile Switching Center • HLR - Home Location Register • U m , A bis , G ... - interfaces between elements Covering all the listed interfaces with monitoring units is expensive and provides redundant informa- P´al Varga is proceeding with his Ph.D. studies at the Depart- ment of Telecommunications and Media Informatics, Budapest University of Technology and Economics (DTMI-BUTE), Hun- gary. P´ eter Tatai is the Head of Telecommunications Signal Pro- cessing Laboratory (TSPLab) of DTMI-BUTE, Hungary. Address:Magyartud´osokk¨or´ utja 2., Budapest, Hungary, H- 1117. Phone: +36-1-463-3424. E-mail: {pvarga,tatai}@tmit.bme.hu tion. An engineering tradeoff must be made to find the most appropriate interfaces for monitoring. Subscriber satisfaction is very important for net- work operators. Regarding this, the most useful data appears on the U m (air) interface: radio resource prop- erties can be extracted as well as mobility manage- ment and application-level characteristics. Neverthe- less, the task of collecting information from this in- terface is complicated, moreover, covering all ”U m in- terfaces” is not feasible. This almost applies to the A bis interface, between BTSs and BSCs. Many moni- toring units should have been placed physically beside each BSC to gather data continuously from the whole network. This is hardly feasible either. The most plausible solution is to cover all G b in- terfaces, which lay between BSCs and SGSNs, as all GPRS application data transfers cross them. More- over, complete data regarding mobility- and session- management as well as some radio resource status in- formation can be collected here, too. By continuous monitoring of these interfaces abnormal network be- havior can be captured and corrective actions can be initiated before a major or critical fault happens. BTS SGSN GGSN HLR EIR MSC/VLR SMS-GMSC BSC MS Packet Data Network Other PLMN G f G s G d G r G c G b G n G i G p A bis U m Fig. 1. GPRS network architecture Analysis results of processing G b -data can indicate suspicious behavior in a Location Area managed by a designated BSC. Under such conditions (eg. no suc- cessful GPRS Attach procedures have been completed for a given time-period at a Location Area), more ex- haustive radio resources information can be gathered by temporarily monitoring the corresponding A bis in- terfaces, too.