Analytical Study of a Dual Pointer Based Strategy for Location Update Using Node B Sojourn Time in UMTS Networks

Analytical Study of a Dual Pointer Based Strategy for Location Update Using Node B Sojourn Time in UMTS Networks

Samir K. Sadhukhan (Indian Institute of Management Calcutta, Calcutta, India), Chayanika Bose (Jadavpur University, Calcutta, India), Debashis Saha (Indian Institute of Management Calcutta, Calcutta, India) and Asis Chattopadhyay (Calcutta University, Calcutta, India)
DOI: 10.4018/IJBDCN.2018070104
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This article describes how Universal Mobile Telecommunications System (UMTS) is a 3G cellular network standard that uses location update (LU) and location search (LS) for mobility management. LU requires update in two location registers (LRs) - home LR (HLR) and visiting LR (VLR) - where one HLR controls multiple VLRs. HLR updates (HLRUs) are costlier, and hence should be less frequent. To achieve it, VLRs maintain a forward pointer chain among themselves, instead of updating HLR. But a lengthy chain increases LS cost considerably. So, we propose to restrict the chain length to unity by introducing an additional backward pointer, and using the concept of root-VLR similar to the home agent concept of mobile IP. We derive a closed form solution to approximate the average HLRUs per call, and substantiate it by simulation in cases of both random and diurnal mobilities. Results reveal substantial reduction in HLRUs per call, even when call-to-mobility ratio is high. UMTS operators will find the analysis worth considering, while managing their 3G networks.
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1. Introduction

Though fourth generation (4G) mobile services are emerging fast as the customers’ preferred choice, Universal Mobile Telecommunications System (UMTS) (aka third generation (3G) mobile cellular network standard) is still the prevalent mode of mobile communication in most of the countries today. UMTS supports both voice calls and data services in mobile terminals (MTs) (EIA/TIA, 1991). Topologically speaking, in a typical UMTS network, the large service area is divided into several location areas (LAs) (Figure 1). Usually, each LA is quite big in area, covered by a single mobile switching centre (MSC) (Lin, Reducing Location Update Cost in a PCS Networks, 1997). But an LA can be smaller in size too, say the area under one radio network controller (RNC) as shown in Figure 1, provided the subscriber density be high in that region. In order to manage voice calls effectively, UMTS networks maintain two types of location registers (LRs), namely home LR (HLR) and visitor LR (VLR) (Lu, Shyn, & Wang, 2016), (Popal & Sharma, 2017), (Zhao, Liew, Zhang, & Yu, 2016). Typically, each MSC has an associated VLR (Figure 1) so that there are many VLRs normally in a UMTS network. However, usually, one HLR is maintained for each service area, and consequently, each HLR controls multiple VLRs.

To track MTs, the UMTS network performs two well-known operations, viz. location search (LS) and location update (LU), utilizing the information already stored in HLR and VLR(s). Conventionally, the network follows the standard IS-41 protocol (EIA/TIA, 1991) to carry out location management in the following manner. Let us consider an MT (say MT1) on the move. If it changes its LA without changing its MSC, only a VLR update (VLRU) happens for MT1. However, if it changes MSC too, a VLR update happens as usual plus an additional HLR update (HLRU) happens i.e., its current LA address is updated in the VLR and its current VLR address is updated in the HLR. Telecom operators prefer to delay HLRU as late as possible because HLRU is much costlier than VLRU (Popal & Sharma, 2017), (Zhao, Liew, Zhang, & Yu, 2016), (Sadhukhan, Moitra, Venkateswaran, & Saha, December 2014), (Wang, Lei, Fan, & Hu, 2014) (Wang, Jiang, Yuan, & Ferng, 2014). So, every LU protocol must keep this mind, while planning location management.

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