Mobility Management Schemes for Support of UPT in Mobile Networks

Mobility Management Schemes for Support of UPT in Mobile Networks Dept. of EE & CS, Korea Advanced Institute of Science and Technology, Korea Switching & Transmission Technology Laboratory, ETRI, Korea sjkwon@kaist.ac.kr, mychung@etri.re.kr, and dksung@ee.kaist.ac.kr Sun Jong Kwon, Min Young Chung, and Dan Keun Sung Abstract When a universal personal telecommunications (UPT) user visits a mobile network, both terminal mobility and personal mobility are involved and it may take a long time for UPT call delivery to the UPT user because it is required to retrieve both the terminal mobility related data in mobile network and the UPT user related data in UPT database. If the UPT database also manages location and status information of the on which the UPT user has registered, incoming call delivery to the UPT user can be improved in a situation. Mobility management schemes for UPT users roaming in a mobile network are analyzed. The performance is evaluated in terms of signaling cost and the number of node accesses during an InCall registration. Keywords personal mobility, universal personal telecommunications (UPT), intelligent network (IN), incoming UPT call, terminal mobility, mobile network, attachment/detachment of mobile terminal, location update, InCall registration. I. INTRODUCTION Terminal mobility (TM) allows users to move their wireless terminals from one location to another while accessing telecommunications services. Location management for support of the TM in mobile networks is based on a two-level hierarchy of databases, the home location register (HLR) and the visitor location register (VLR). Recently, concept of intelligent network (IN) in existing mobile networks has been introduced in order to increase service creation capability of the networks and reduce the time-to-market of new service features [][]. Personal mobility (PM) allows users to access their personal services independent of their attachment points or terminals. Universal personal telecommunication (UPT) provides personal mobility on wireless as well as wireline networks and is implemented utilizing IN capabilities [3]-[4]. Since UPT can be a very important value added telecommunication service in the future, mobile networks should be enhanced to support UPT based on IN. I- network requirements include the support of UPT. When a UPT user has access to UPT services via a mobile network, both PM and TM are involved. During a UPT InCall registration the association between the universal personal telecommunication number (UPTN) and the mobile subscriber/terminal number (MSISDN) is stored in home UPT database. Call delivery of an incoming call to the UPT user requires queries of the UPT database, HLR, and VLR, which may result in a long setup delay, especially when the mobile terminal () is roaming. Furthermore, the UPT user can switch the off or on in order to be unreachable or reachable from the This study is supported in part by the BK program of the Ministry of Education. network. When the is unreachable and the UPT user has a subscription on a call forwarding on terminal not reachable (CFNRc) supplementary service, incoming UPT calls should be forwarded to another terminal. It may be efficient to store some of TM related data in UPT database, and some of the UPT user related data in mobile network database. If the UPT service control point () knows current location of the on which a UPT user has registered, i.e., /VLR identity, the UPT call can be directly routed to the visited network without passing through the home network of the when the is visiting a network. Moreover, if UPT retains status information of the, incoming UPT calls can be forwarded without querying location register when the is in the unreachable state. In this paper, two mobility management schemes for UPT users roaming in a mobile network are introduced and the performance of the schemes is evaluated in terms of signaling cost and the number of node accesses. II. RELATED WORK Studies on support of UPT in mobile networks have been carried out [5]-[8]. Yabusaki and Nakajima[6] provided the concept of universal mobility (UM) that integrates TM and PM, and presented a network technique for UM. Morris and Nelson[7] dealt with interworking and integration aspects of UPT and US at a service control level. Chen[8] described the concept of TM and PM, and analyzed the relationship in a qualitative way. For support of UPT service to UPT users roaming in a mobile network, interworking between the mobile network and home UPT network is required, and there can exist several possible interworking scenarios. We consider an inter-networking architecture shown in Fig.. There is a link for interworking between in the mobile network and in the home UPT network. It is assumed that the mobile network is a UPT capable network and an consists of service control function (SCF) and service data function (SDF). IN capability set- (CS-) for interworking between two networks is assumed to be supported. It is also assumed that each mobile switching center () has its own VLR and the VLR is deployed internal to the. VLRs and s are enhanced with IN functional entities in order to interact with IN nodes. The first phase UPT environment supports four essential features: UPT user identity authentication, InCall registration, outgoing UPT call, and InCall delivery. There is no correlation

Home UPT network well as in HLR/VLR. IP h SSP v Gateway HLR VLR Fig.. Inter-networking architecture for support of UPT in mobile network. between InCall registration and outgoing UPT call. Outgoing UPT call feature enables that UPT users make calls from any terminal and is not considered in performance analysis. We first consider a basic scheme for mobility management for UPT users roaming in a mobile network: When an In- Call registration request occurs, the request is transferred to the via the. Following the UPT InCall registration procedure, the MSISDN of the is stored in the. Location registers in the mobile network manage location and status information of the on which the UPT user has registered and the information is not informed to any service control point. Service profile of the UPT user is not copied to the mobile network. When an incoming call to the UPT user is detected by an in mobile networks or a service switching point (SSP) in wireline networks, the or the SSP asks about the directory number of the terminal on which the UPT user has registered, then the call is processed as a normal mobile terminated call. As PM and TM are separately managed, PM management is relieved of any terminal tracking function and can be overlaid on mobile networks already providing TM management. It can be implemented with few changes in existing networks, but incoming calls may not optimally routed. If UPT database also manages location and status information of the, routing of the incoming UPT call can be improved. III. MOBILITY MANAGEMENT SCHEMES FOR SUPPORT OF UPT IN MOBILE NETWORKS Two mobility management schemes are considered as follows: : When an InCall registration request occurs, the request is transferred to via. The UPT user s identity is stored in VLR. During the InCall registration, the VLR triggers the based on /VLR change, attachment, and detachment of the, and the forwards the information to the. The manages the location (identity of the /VLR) and status information of the. : When an InCall registration request occurs, the request is transferred to the via the. The address of the visited network is stored in the, and then the service profile of the UPT user is downloaded to the, and the UPT user s identity is stored in VLR. During the InCall registration, the VLR triggers the based on /VLR area change, attachment, and detachment of the, and the location and status information of the is stored in as A. Signaling Message Procedures It is assumed that a UPT user roaming in a mobile network requests an InCall registration using call unrelated signaling. Personal identification number (PIN) is locally used to authenticate the UPT user to the UPT device, and challenge-response type authentication is assumed to be used to authenticate the UPT user to UPT service provider. Fig. (a) shows signaling message flow for the InCall registration request in when the UPT user has not registered for incoming calls on an : receives an InCall registration request via /VLR and (Steps through 3), and sends an authentication request to personal identity module (PIM) in the through and /VLR (Steps 4 through 6). The authentication algorithm in PIM calculates a variable authentication code, and then sends it to through /VLR and (Steps 7 through 9). The UPT user is authenticated and the stores the visited network identity. The service profile of the UPT user is replicated from the to (Steps and ). Additionally, the stores the identity of the /VLR and the number, and then forwards a registration acknowledgment to the /VLR (Step 3). When the /VLR receives the acknowledgment from the, the VLR stores the identity of the UPT user and forwards the acknowledgment to the (Step 4). In case of, signaling message flow for the InCall registration request is the same as for except for Steps and shown in Fig. (a). Fig. (b) shows the InCall registration procedure in Scheme when the UPT user has been already registered for incoming calls on another in the mobile network. Since the retains the replicated service profile for the UPT user, the In- Call registration request is processed within the network. The authenticates the UPT user, orders old VLR to delete the identity of the user, stores new /VLR identity and the number, and sends a registration acknowledgment to the. When the terminal is switched off, a detach message is sent to the network. When it is switched on again, an attach message is sent to the network, provided that the is still in the same location area (LA). If the LA is changed, a normal location update occurs[9]. If the new LA belongs to the coverage area of a new VLR, the new VLR informs of its identity after location update in the mobile network is performed. Information on the registered UPT user is assumed to be obtained by the new VLR from either the old VLR or the location update message from the. Fig. 3 shows the procedure for Scheme when the sends an attach message. The mobile network performs an attach operation, and then the state change is reported to by the VLR that receives the attach message from the. The in forwards the message to the and the updates the state the. In Scheme, the updates the state of the without forwarding the message to. Message flow for each scheme in case of location update or detach request by the is the same as

s 3 () InCall Reg. Req. (6) Auth. Req. /VLR v h () InCall Reg. Req. (5) Auth. Req. (7) Auth. Resp. (8) Auth. Resp. (4) InCall Reg. Resp. () InCall Reg. Req. (4) Auth. Req. (5) Auth. Resp. () InCall Reg. Resp. /VLR (3) InCall Reg. Resp. (a) () InCall Reg. Req. (3) Auth. Req. (6) Auth. Resp. (9) InCall Reg. Resp. (b) v (3) InCall Reg. Req. (4) Auth. Req. (9) Auth. Resp. () ProfileCopy () ProfileCopyResp. () InCallReg. Resp. (7) Delete Req. (8) Delete Resp. old /VLR Fig.. InCall registration procedures for. (a) new InCall registration, (b) overridden InCall Registration. /VLR HLR v h Attach Req. Attach Resp. state update InitialMMDP ContinueMM Modify Entry Fig. 3. Attach procedure for. Modify Entry Resp. the attach message flow of the corresponding scheme. Fig. 4 shows the incoming call delivery procedure for when an incoming call is originated from the called UPT user s home network and the is in the attached state. The which receives a call setup request from a calling user triggers the. The returns an address of the network visited by the UPT user to the (Steps and ). The call is then routed to the visited network (Step 3). The gateway interrogates and obtains a roaming number assigned by the serving /VLR of the called UPT user by Steps 4 through 7. Finally, the call is routed to the serving /VLR (Step 8). When the call is originated from the visited mobile network and the is in the attached state, the incoming call to the UPT user in can be handled in the network without querying the. When the is in the detached state, a detachment cause is delivered to the SSP or where the service was triggered, and the SSP or forwards the incoming UPT call by CFNRc service after obtaining a forwarding address from. IV. PERFORMANCE ANALYSIS In order to evaluate the performance of mobility management schemes, the following assumptions are made: A UPT user switches an on at time and immediately Home UPT network IP () h () SSP o (3) (4) v (7) Gateway (5) (8) HLR (6) VLR Fig. 4. Incoming call delivery procedure for when the is in the attached state and the call is originated from home UPT network. requests an InCall registration. The InCall registration is deregistered by an explicit request by the UPT user, by a timer/counter expiry, or by a new InCall registration, and the fractions of the three InCall deregistration types are denoted by,, and, respectively. The InCall registration duration follows an exponential distribution with mean. Incoming calls to the UPT user follow a Poisson process with rate!". The state of an can be modeled as an alternating renewal process. The expected value $#&%(' of sum of detachment durations during an InCall registration, mean numbers of transitions from the attached to the detached state and from the detached to the attached state during the InCall registration, and)+#&%('.- * ',' )+* ','.-/#&%(' are derived from the alternating renewal process. Fig. 5 represents a timing diagram of the state change of an, InCall registration time, and LA residence time. Expo- and3, respectively, are assumed. A VLR control area is assumed to consist of an LA. Let LA residence time 45/687:9<;>= nential time distributions with parameters and for be an independent and identically distributed random variable with mean?>@, a density function A BC6D4 5 =, and the Laplace transform A$E B 6GFH=. The Erlang type distribution with a shape parameter of I and a scale parameter of JLKMIN! B is assumed for 4 5. The probability that there are O LA boundary crossings during an InCall registration duration is expressed as []: P R 6.OQ= K ;TS<U&VXW?>@ @[Z Y D\^]?>@ b;tsca$e B 6Dd$e(=(f ba$e _ B 6Dd$e(=(f,g Vh _ Ò Ojikml Ka () Let4$% be the time when the LAOQn. prqts 4t s 4h scuvuvuws 4hnHVh Then,4$%oK. The Laplace transform A$E n 6xFH= of the distribution of 4 % is as follows: A ne 6GFH=K!yB F b;tsza BE 6GFH=rfbA BE 6GFH=(f n>vh l () The probability that an is in the attached state at time{ is expressed as 6D{= K s s y} VX~ r _ {:9jml (3)

L Z Y Z Y Z 3 state t T T T T 3 k- L incall registration request attachment request location update L L 3 L 4 incall deregistration request detachment request L k- L k t i time LA residence time Fig. 5. Timing diagram for state change of the, InCall registration time, and LA residence time. The probabilityn that the is in the attached state at the time when the O n is expressed as follows: n Kƒ q 6.{=mA n 6D{X= ˆ{ _ (4) where A nm6 p = represents the inverse Laplace transform of A$E n 6GFH=. LetŠ #&%(',Št* ',', andšh 8Œ be the expected numbers of detach messages, attach messages and location updates transmitted during the InCall registration, respectively. Then, Št#&%(', Š * ',', andš Œ are given as follows: Št#&%('KŽ) * ','.-/#&%(' (5) Š Œ K P 6DŠt= n 6 Xn s 6 ;os Xn = = (6) Št* ',' KŽ) #&%r'.- * ',' S P 6.Št= n 6 ;os n = _ (7) where is the probability that an, which was in the detached state when the entered an LA, will transfer to the attached state before leaving out of the LA, and it is given by K ;TScA BE 6. =K ;TSj6 Ĩ s!yb Ĩ! B = B l (8) Incoming calls are assumed to be originated from either the home UPT network or the visited network, and the fractions of the calls are denoted by 6w; Sjš= andš, respectively. Let be the probability that the visits a network other than the home mobile network. Let [œ "., [œ œg, B œ ", and [ be the costs for handling a message at the, SSP, /VLR, and HLR, respectively. Qe 'D * and e '.%r represent the costs for transferring a signaling message between two nodes in a network, and between a node in a network and another node in the other network, respectively. Cost parameters for the attach(ž ), detach(ÿ ), location update( ), InCall registration( ), In- Call Deregistration(Ÿ ), new InCall } registration(): ), and locating( ) costs of the two schemes are given as follows: KaŸ } KM QB œ " s e 'D * s œ ". s ) KM ˆ QB œ " s` e 'D * s` œw". s e '.%r e '.%r ž ªKMŸ«TK TKa B œ " s Qe 'D * s` [œ ". s ˆ Qe '.%r #&%r'd K ˆ B œ " s ˆ Qe 'D * s [œ ". s * e '.%r ','.± Ka QœwœG s ˆ B œ " s Qe 'D * s [œ ". s` * Qe '.% ','D KM QB œ " s ˆ e 'D * s œ ". s e '.%r #&%r'.± KŽ QœwœG s ˆ Qe 'D * s Kk B œ " s Qe 'D * s`² [œ ". ;> [œ ". s ) Ka B œ " s` Qe 'D * s` [œ ". Qe '.%r (9) Ÿ } KŽ QB œw" s e 'D * s œ ". s ˆ žo KaŸLoKa okm #&%('.³ Ka ˆ B œ " s e e '.%r 'D * s * [œ ". ','.³± Ka QœwœG s B œ " s ˆ Qe 'D * s ˆ [œ ". s * ','³ K B œ " s Qe 'D * s [œ ". Qe '.%r #&%r'³± Ka œwœg s ˆ QB œ " s e 'D * s ˆ œ ". s e '.%r _ where subscripts and represent Schemes and, respectively. Consequently, the total cost for Scheme7 (7kḰ ; _ ) during InCall registration for a UPT user, who visits a mobile network and subscribes a CFNRc service, is given by 5 K 6 ;os µ =w 5 s ) 5 s & Ÿ } 5 s Š #&%('Ÿ 5 s Š Œ5 s Š * ','ržt5 s!" t#&%(' 6 ;TScšX= #&%('. ± s s š #&%('!" 6 d$e ; Sc $#&%('w= 6 ;TScšX= * ',' ± s š * ',' l () A. Numerical Examples We choose the basic scheme as a reference for performance comparison, and define the relative cost of each scheme as the ratio of cost of each scheme to that of the basic scheme. It is here assumed that the probabilities,, and are set at.,.5, and.3, respectively. We consider an extreme situation that the signaling cost or node access cost is dominant in the total cost. When ck [/hour], ok [/hour],! B K ¹ [/hour], d$etk w [/hour], Í K,š Kºml», and ¼Kºyl8;, Fig. 6 shows the relative signaling and node access costs for different values of e '.%r as the value of call-to-mobility ratio!"&½! B varies from.5 to 3. The signaling of each scheme is calculated by setting the node access costs B œ ", [œ œg, [œ "., and Q at s in the total cost. As the inter-network signaling cost increases, the relative signaling cost in increases, whereas the cost in decreases. When!"&½ˆ! B is low, the signaling costs of Schemes and are high, compared to the cost of the basic scheme because the cost for delivering the location and status information of is given much weight in the signaling cost. As!"&½! B increases the signaling costs of Schemes and decrease below the cost of the basic scheme because the call delivery cost is given much weight in the signaling cost as! " ½ˆ!yB increases, and Schemes and have the improved routing of incoming calls compared with the basic scheme. Fig. 6(b) shows the relative number of node accesses. The relative number of node accesses decreases as!"¾½! B increases. It is observed from Fig. 6 that in order to reduce the network costs of Schemes and, the call-to-mobility ratio of the UPT user should be high. In addition, is 4

5.5. C inter = C intra Relative signaling cost.5 C inter= C intra Relative signaling i cost.8 α = /3 α = / C inter = C intra.5.5.5 3 Call to mobility ratio λ c / λ m (a).6...3.4.5 Fraction of incoming calls originated from a visited mobile network φ Fig. 7. Relative signaling cost for different values of ÃmÄ. Relative number of node accesses.5.5.5 3 Call to mobility ratio (b) Fig. 6. Relative costs for varying the call to mobility ratio. (a) Signaling cost, (b) Number of node accesses. preferable in the situation that the inter-network signaling cost is higher than the intra-network signaling cost. Fig. 7 shows the relative signaling cost versus the fraction of incoming calls originated from a visited mobile network š for varying values of when K [/hour],d e K [/hour],! " K ; [/hour],!bàk ¹ [/hour],í K, and ¼KÁmlÂ;. The relative signaling cost in decreases as š increases and is below for high values of š because the visited network can handle the incoming UPT calls originated from the visited network without any query to the home UPT network. The relative signaling costs of Schemes and decrease as the average detach time ~ ³ increases because an increase in the average detach time for a given InCall registration duration reduces the number of state transitions of the. λ c / λ m V. CONCLUSIONS When a UPT user has access to UPT services via a mobile network, both PM and TM are involved and an incoming call delivery to the UPT user may take a long time. The location of mobile users can be changed at any time within the visited network as well as the home network. Mobile networks have distinctive features including attachment and detachment of terminals, compared to fixed network. In addition, CFNRc service, which is a supplementary service for UPT users having registered on mobile terminals, is defined in an ITU-T recommendation. The mobility management for UPT users roaming in the mobile network should reflect these features. Two mobility management schemes for UPT users roaming in mobile networks are considered. Performance of the schemes is compared in terms of the signaling cost and the number of node accesses during an InCall registration duration. The results show that the incoming call delivery cost can be reduced at the expense of management of location and attach/detach status information of s in UPT. Performance of two schemes depends on the attach/detach characteristic of s, the roaming probability of s, the fraction of incoming calls generated in the visited network, and the traffic and various mobility parameters including LA residence time and incoming call arrival rate. outperforms both and the basic scheme when the call-to-mobility ratio is high, the fraction of incoming calls originated from a mobile network is high, and the inter-network signaling cost is higher than the intra-network signaling cost. REFERENCES [] I, Faynberg, L. R. Gabuzda, T. Jacobson, and H.-L. Lu, The development of the wireless intelligent network (WIN) and its relation to the international intelligent network standards, Bell Labs Technical Journal, Summer 997, pp. 57-8. [] ETSI TS 85 v6.., Digital cellular telecommunications system (phase +); customized applications for mobile network enhanced logic (CAMEL); service definition - stage (GSM.78 version 6.. Release 997), 998. [3] ITU-T Recommendation F.85, Universal personal telecommunication(upt) - service description (service set ), February 995. [4] ITU-T Recommendation F.853, Supplementary services in the universal personal telecommunication (UPT) environment, November 998. [5] M. Zaid, Personal mobility in PCS, IEEE Personal Communications, vol., no. 4, pp. -6, Fourth Quarter 994. [6] M. Yabusaki and A. Nakajima, Network issues for universal mobility, IEICE Trans. Fundamentals, vol. E78-A, no. 7, pp. 764-77, July 995. [7] C. Morris and J. Nelson, Architectures and control issues for the support of UPT in US, in Proc. IEEE Globecom 96, pp. 63-67. [8] L.-S. Chen, Apply personal mobility in PCS environment for universal personal communications, in Proc. ICUPC 96, pp. 53-57. [9] ITU-T Recommendation Q.3, Location registration procedures, 988. [] Y. B. Lin, Reducing location update cost in a PCS network, IEEE/ACM Transactions on Networking, vol. 5, no., pp. 5-33, 997.