Cost Analysis of Integrated Terminal Mobility and Personal Mobility Managements in Mobile Communication Networks

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1 Cost Analysis of Integrated Terminal Mobility and Personal Mobility Managements in Mobile Communication Networks Yun Won Chung, Min Young Chung, and Dan Keun Sung ywchung@ieee.org Dept. of EECS KAIST, 7- Kusong-dong Yusong-gu, Taejon 0-70, KOREA Switching & Transmission Techno. Lab. ETRI, 6 Kajong-dong Yusong-gu, Taejon 0-0, KOREA Abstract Personal mobility (PM) is one of key issues in realizing emerging third generation mobile communication systems such as International Mobile Telecommunication 000 (IMT- 000) and it can be realized through universal personal telecommunication (UPT) service. A PM management scheme is considered in order to manage PM information related to UPT users for incall registration/deregistration, incall registration reset by mobile terminal (MT) owner, and incall delivery to UPT user in mobile communication networks. The relative cost, i.e., the ratio of cost per unit time for supporting both terminal mobility (TM) and PM managements to that of TM management is derived and the effect of PM management is analyzed. I. INTRODUCTION The ultimate vision for mobile communication systems is to enable users to communicate with a person at any time, at any place, and in any form. Thus, third generation mobile communication systems such as International Mobile Telecommunication (IMT-000) require terminal mobility (TM) provided by wireless access, personal mobility (PM) based on the use of a unique personal identity, and service mobility (SM) through management of user profiles []. TM has been covered by many international standard bodies in the context of first generation analog cellular systems (Advanced Mobile Phone System (AMPS)), second generation digital cellular systems (Interim Standard (IS-) and Global System for Mobile Communications (GSM)), and third generation mobile communication systems (IMT-000) which are currently under development. The location management of MTs is essential to implement TM and extensive studies have been carried out in this area. On the contrary, most studies on PM management were applied to fixed communication networks. ITU- T has recommended the principles of UPT [], network capabilities to support UPT services [], service procedures for UPT [], and service descriptions and operational provisions for UPT Service Sets (SS-) [] based on fixed communication networks. Studies on the UPT functional architectures, information flow, and performance evaluations have been carried out. Various aspects of PM to mobile communication networks were studied [6] - [7]. Yabusaki et al. [6] provided the concept of universal mobility (UM) that integrates TM and PM, described the identity and This study is supported in part by the BK program of the Ministry of Education. number configurations for UM, and presented network techniques for UM, i.e., the network architecture and UM management procedures. Chen [7] presented the concept of mobility which encompasses TM provided by mobile systems and PM defined by UPT services and their relationships with respect to definition and service applications, numbering and identity, and mobility management and call handling. He also discussed technical challenges in supporting UPT service in a PCS environment. In IMT-000 the networks should support both TM and PM management as core network capabilities of capability set (CS-) to provide enhanced mobility services compared to the conventional first and second generation mobile communication networks [8]. Unfortunately, additional signaling load is added to manage PM in mobile communication networks which have suffered from signaling load due to TM management. Therefore, it is required to analyze the effect of PM management in order to effectively design the emerging third generation mobile communication networks. In this paper a PM management scheme is considered in order to manage PM information related to UPT users for incall registration/deregistration, incall registration reset by MT owner, and incall delivery to UPT users in mobile communication networks. The relative cost, i.e., the ratio of cost per unit time for supporting both TM and PM management to that of TM management is derived and the effect of PM management is analyzed. The organization of this paper is as follows: Section introduces an architecture of mobile communication network supporting PM and describes TM and PM managements; Section derives the relative cost of PM management to that of TM management and shows numerical examples; finally, Section presents conclusions. II. NETWORK ARCHITECTURE AND MOBILITY A. Network Architecture MANAGEMENTS Fig. shows a mobile communication network architecture which supports PM. The whole service area is divided into cells and cells are grouped into location areas (LAs). Every LA has a pair of visited location

2 registers (VLRs) for mobile users (VLR(T)) and UPT users (VLR(P)), and a single mobile service switching point (M-SSP). Each M-SSP is connected to VLR(T) and VLR(P) through direct links and the M-SSP is connected to service control point (SCP) and home location register for mobile users (HLR(T)) through signaling networks. The M-SSP can also access home location register for UPT users (HLR(P)) for UPT users through the SCP. The SCP contains UPT service logic to provide PM to UPT users. The M-SSP has a function of both mobile switching center (MSC) and service switching point (SSP). It provides the processing of calls to/from mobile users as a function of MSC and detects UPT service requests and delivers them to SCP as a function of SSP. The location registers (LRs) such as HLR(T)/VLR(T) and the HLR(P)/VLR(P) keep track of the location information of mobile and UPT users, respectively. The HLR(T) stores the service profiles of mobile users. These service profiles contain information such as the type of services subscribed, the billing information and the current location of MTs. The location information in the HLR(T) includes the relationship between the identity of MT such as mobile identification number (MIN) and the identity of VLR(T) serving the area at which the MT is currently located. The VLR(T) stores the information of MTs currently residing in its associated area such as the relationship between the MIN and the UPT numbers (UPTNs) of UPT users who currently have registered for incoming calls on the MTs. The HLR(P) stores the service profiles of UPT users. These service profiles contain information such as the type of UPT services subscribed, the billing information and the current location of UPT users. The location information in the HLR(P) includes the relationship between the identity of UPT user such as UPTN and the identity of VLR(P) serving the MT at which the UPT user has registered for incoming call. The VLR(P) stores the information of the UPT users currently residing in its associated area such as the relationship between the UPTN and MIN of an MT at which the UPT user has registered for incoming call. These relationships between identities in LRs are summarized in Table I. B. TM and PM Managements In conventional mobile communication networks, wireless access technique and location management are required to support TM to mobile users in the radio interface and networks aspects, respectively. The wireless access technique is out of scope of this paper and only location management is considered. The location management includes location registration (or location update) and call delivery. In the location registration process, MTs notify network of their new access points, allowing the network to keep track of the current location of them. The call delivery process is required to deliver incoming calls to the MTs. We follow conventional location management protocols such as IS- [9] and GSM MAP [0] in order to support TM to mobile users and omit the detailed procedures. ITU-T has recommended a number of essential and optional features of UPT service in order to support PM to UPT users [] - []. Among them, we consider incall registration/deregistration to enable the UPT user to register/deregister for incoming call to be presented at an MT and incall delivery to UPT user in order to provide the incoming call to UPT user. Also, incall registration reset by MT owner is considered in order to protect the right of MT owner. These UPT features which are based on fixed communication network environments are modified appropriately to be compatible with mobile communication network environments. Fig. shows an explicit incall registration procedure when a UPT user has not registered for incoming call at an MT. When the UPT user initiates incall registration attempt, the request is sent from the UPT user to serving VLR(P). Then, the VLR(P) stores the relationship between UPTN and MIN, and transfers the request to HLR(P). The HLR(P) stores the relationship between the UPTN and the identity of VLR(P), and sends an incall registration completion message with the UPT user service profile to the VLR(P). The VLR(P) initiates an incall registration request message to VLR(T) in order to update the relationship between the MIN and the registered UPTN. After completing this procedure, the VLR(T) returns an incall registration completion message to VLR(P). Finally, the VLR(P) informs the UPT user that the incall registration request is completed. The explicit incall deregistration procedure is similar to the explicit incall registration procedure except that incall deregistration request and completion messages are used instead of incall registration request and completion messages, respectively and all the information on the relationships are deleted from the associated LRs. Other PM management procedures can be obtained by modifying UPT procedures of fixed networks and they are omitted due to limited space. III. PERFORMANCE ANALYSIS In order to evaluate the effect of PM management in mobile communication networks, the following assumptions are made: Incall registration is deregistered by one of the following requests: explicit request of UPT users, implicit request by incall registration request of UPT users at a new MT, explicit request by incall registration reset request of MT owners, or implicit request by location update request of MTs;

3 () () Incall registration requests for an MT occur according to a Poisson process with parameter ; Incoming call requests for an MT owner and a UPT user occur according to a Poisson process with parameter and, respectively; An MT owner resets all incall registrations for the MT at time ; There is no incall registration reset request during, where is the time instant of reset for incall registration; The incoming call arrival process, the incall registration/deregistration request process, the incall registration reset request process, and the location update request process of an MT are mutually independent. In order to construct a cost function which is associated with updating data profiles, message handling, and message delivery, the unit cost parameters are introduced, as summarized in Table II. We also introduce cost expressions for TM and PM management procedures and they are summarized in Table III It is assumed that the incall registration duration for a UPT user, the interarrival time between two successive incall registration reset requests by MT owner, and the LA residence duration for an MT follow exponential distributions with parameters,, and, respectively. We also assume that the distribution of the first LA residence duration is the same as the remaining ones. Using the above assumptions, the cost per unit time is derived as Eqns. and for TM and PM managements, respectively, where, and are the probabilities that a registration (deregistration) request corresponds to ( ), ( ), and (, respectively. A hint for detailed derivation can be found in []. The cost expressions in Eqns. and can be obtained based on the TM and PM management procedures as described in Section II. For example, the cost for an explicit incall registration request at an MT when a UPT user has not registered for incoming calls is derived from Fig. and is given by () We define as the ratio of the cost per unit time for supporting both TM and PM management to that of TM management in order to analyze the effect of PM management in mobile communication networks and it is given by () According to the values of,,,,, and, the relative cost can represent various performance measures. For example, for parameter values,,,,, and, the relative cost means the ratio of mean number of LR queries or updates for supporting both TM and PM management to that of TM management. We focus here on those cost parameter values in terms of the delay experienced by a particular network node or through the signaling network due to processing/transferring of signaling messages. The mean delays experienced for processing a message at each node, transferring a signaling message through a signaling network, and setting up a connection between two M-SSPs are listed in Table IV. These values are referred from []. It is also assumed that the probabilities, and are set at 0.6, 0., and 0., respectively. Fig. shows the relative cost for varying the mean interarrival time between incall registration reset requests, when and [/hour]. To demonstrate the effect of varying the mean incall registration duration,, five different values are considered. In this parameter set the cost for TM management is constant. The relative cost decreases for a small values of. This is because that the effect of incall registration reset is more dominant than other events in the cost for PM management for small values of. For large values of, the relative cost increases for small and decreases for large and the effect of is more dominant for large values of. In all values of, the relative cost for small is higher than for large.

4 Fig. shows the relative cost for varying the value of when and [/hour]. To demonstrate the effect of varying the LA residence duration,, five different values are considered. The relative cost rapidly decreases for small and decreases in a small amount for large values of in all values of. The rapid decrease reflects the fact that the effect of incall registration reset is more dominant than other events in the cost for PM management for small values of. The relative cost is higher for small than for large for all values of. However, the difference in the relative cost becomes small with the and this shows that the effect of is negligible for large values of. Fig. shows the relative cost for varying the value of when and [/hour]. The relative cost rapidly decreases for small values of and decreases in a small amount for large values of in all values of. The relative cost becomes higher when the value of increases. IV. CONCLUSIONS A PM management scheme is considered in order to manage PM information related to UPT users for incall registration/deregistration, incall registration reset by MT owner, and incall delivery to UPT users in mobile communication networks. The relative cost of PM management, i.e., the ratio of cost per unit time for supporting both TM and PM management to that of TM management is derived and the effect of PM management is analyzed. The results show that the relative cost is high for large values of incall registration duration and LA residence duration for an MT. The effect of incall registration reset is more dominant than other events in the relative cost for small values of and the relative cost becomes high when the value of increases. These results can be utilized in the implementation of PM management and the design of emerging third generation mobile communication networks such as IMT-000 which support both TM and PM. REFERENCES [] R. Pandya, Emerging Mobile and Personal Communication Systems, IEEE Communications Magazine, pp. -, June [] ITU-T Recommendation F.80, Principles of universal personal telecommunication (UPT), Mar. 99. [] ITU-T Recommendation I.7, Network capabilities to support universal personal telecommunication (UPT), Mar. 99. [] ITU-T Recommendation Q.76, Service procedures for universal universal personal telecommunication. Functional modeling and information flows, Feb. [] ITU-T Recommendation F.8, Universal personal telecommunication (UPT) - service description (service set ), Feb. [6] M. Yabusaki and A. Nakajima, Network Issues for Universal Mobility, IEICE Trans. Fundamentals, vol. E78-A, no.7, July [7] L. S. Chen, Apply Personal Mobility in PCS environment for Universal Personal Communications, Proc. of ICUPC, pp. 0-07, 996. [8] ITU-T Recommendation Q.70, Version., Framework for IMT-000 Networks, May 998. [9] M. D. Gallagher and R. A. Snyder, Mobile Telecommunication Networking With IS-, McGraw-Hill, 997. [0] S. M. Redl, M. K. Weber, and M. W. Oliphant, GSM and Personal Communication Handbook, Artech House Publishers, 998. [] M. Y. Chung, and D. K. Sung, Performance Analysis of a Profile Management Scheme for Incall Registration/Deregistration in Wireline UPT Networks Part I: Request-Based Scheme, IEICE Trans. Commun., vol. E8-B, no., pp , May 999. VLR(T) VLR(P) HLR(T) M-SSP LA SCP Signaling network LA M-SSP HLR(P) VLR(T) VLR(P) Fig.. Mobile communication network architecture supporting PM. MT VLR(P) VLR(T) HLR(P) Fig.. Explicit incall registration procedure. = / (/hour) = / (/hour) = / (/hour) = / (/hour) = /8 (/hour) Fig.. for varying the mean interarrival time between and [/hour]).

5 TABLE I RELATIONSHIPS BETWEEN IDENTITIES IN LRS HLR(T) HLR(P) VLR(T) VLR(P) MIN - VLR(T) ID UPTN - VLR(P) ID MIN - UPTNs UPTN - MIN TABLE II UNIT COST PARAMETERS cost for a query or update of a UPT user service profile in VLR(P) and HLR(P) cost for a query or update of an MT service profile in VLR(T) and HLR(T) cost for handling a message at the SCP cost for handling a message at the M-SSP cost for transferring a signaling message between the M-SSP and the HLR or the SCP through a signaling network cost for transferring a signaling message related to a connection setup between two M-SSPs through the signaling and transport networks TABLE III COST EXPRESSIONS FOR TM AND PM MANAGEMENT PROCEDURES cost for transferring a signaling message related to a call setup between two M-SSPs through the signaling and transport networks cost for an explicit incall registration request at an MT when a UPT user has not registered for incoming call cost for an explicit incall registration request at a new MT in the same LA cost for an explicit incall registration request at an MT in the new LA cost for an explicit incall deregistration request at an MT at which a UPT user has registered for incoming call when the incall registration has not been reset by the MT owner cost for an implicit incall deregistration request due to an explicit incall registration request at a new MT in the same LA cost for an implicit incall deregistration request due to an explicit incall registration request at an MT in the new LA cost for an explicit incall deregistration request at an MT at which a UPT user has registered for incoming call when the incall registration has been reset by the MT owner cost for a location update/cancellation for an MT cost for an implicit incall registration/deregistration for a UPT user when the MT at which UPT users have registered for incoming call moves between two LAs cost for an incall registration reset request by the MT owner cost for an implicit incall deregistration for a UPT user for an incall registration reset request by the MT owner cost for an incoming call delivery for an MT owner cost for an incoming call delivery for a UPT user when its associated incall registration has not been reset cost for an incoming call delivery for a UPT user when its associated incall registration has been reset TABLE IV UNIT COST PARAMETER VALUES Mean delay 0 msec 0 msec 0 msec 0 msec 0 msec 0 msec Cost. = / (/hour) = / (/hour) = / (/hour) = / (/hour) = /8 (/hour) 6. = 0. (/hour) = 0. (/hour) = 0.6 (/hour) = 0.8 (/hour) =.0 (/hour) Fig.. for varying the mean interarrival time between and [/hour]) Fig.. for varying the mean interarrival time between and [/hour]).

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