An Improved Profile-Based Location Caching with Fixed Local Anchor Based on Group Deregistration for Wireless Networks

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1 An Improved Prole-Based Locaton Cachng wth Fxed Local Anchor Based on Group Deregstraton or Wreless Networks Md. Kowsar Hossan, Mousume Bhowmck, Tumpa Ran Roy 3 Department o Computer Scence and Engneerng, Khulna Unversty o Engneerng and Technology (KUET) Khulna, Bangladesh auvkuet@yahoo.com mousumcsekuet@yahoo.com 3 tumparoy_st@yahoo.com Abstract Prole-Based Locaton Cachng wth Fxed Local Anchor (PCFLA) Strategy helps to reduce the total locaton management cost by reducng the requent access at HLR n wreless moble network. The HLR s normed each tme, whenever an moves rom one LSTP regon to another LSTP regon. The old FLA and old VLR know about that by regstraton cancellaton message rom HLR. Then the old FLA and old VLR delete the s prole and old FLA sends a regstraton cancellaton acknowledgement message to HLR. These cancellaton messages or each LSTP movement create load on the HLR as well as on the network. In ths paper, Group Deregstraton (GD) s used n PCFLA to reduce these loads by mnmzng the sgnalng cost and locaton management cost. The analytcal modelng and expermental results demonstrate that our proposed method reduces the overall cost than PCFLA. Keyword- call delvery, locaton management, locaton regstraton, Group Deregstraton, Prole- Based Locaton Cachng wth Fxed Local Anchor I. INTRODUCTION Locaton management s an mportant ssue n wreless moble networks. It s concerned wth the locatng and ndng an n the network coverage area. Bascally, two types o standards are used n all types o wreless communcatons or locaton management o an such as IS-4 [] and GSM []. Both IS-4 and GSM use two-level database herarchy archtecture. Fg. [0] shows the basc archtecture o the wreless moble networks under ths two-level database herarchy. Ths archtecture contans two types o databases such as Home Locaton Regster (HLR) and Vstor Locator Regsters (VLRs). The locaton normaton and permanent user prole or each s stored and mantaned by HLR. VLRs are dstrbuted throughout the network. VLRs store locaton normaton o each currently resdng n the Regstraton Area (RA). The task o Moble Swtchng Centers (MSCs) s to provde swtchng unctons or the s n ther assocated RAs. In addton, the MSCs o derent RAs are connected to a two-level herarchy o Sgnalng Transer Pont (STP). Ths STP s comprsed o a Regonal STP (RSTP) and Local STPs (LSTP). An LSTP regon conssts o some VLRs and the RSTP regon contans the LSTP regons. Wrelnks are used to connect these network elements. Two basc operatons must be perormed ecently n Locaton management strategy: () locaton regstraton and () call delvery. The locaton regstraton s the process o normng the network about the s current locaton normaton, and the call delvery means the process o determnng the servng VLR and the cell locaton o the called pror to connecton establshment between the caller and called s. ISSN : Dec 0- Jan 0 49

2 c h HLR Cra Remote A-lnk D-lnk RSTP local A-lnk LSTP C d LSTP C v C la VLR MSC Fg.. Network cost model. As the numbers o the s wthn the network are explodng rapdly and ther servce requrements are also ncreasng day-by-day, The IS-4 standard cannot support these ncreasng amount o s. As a result, these s make the network congested and creates heavy load at HLR. Derent types o strateges have been proposed to overcome ths problem under the IS-4 [3]-[0]. Among those strateges PCFLA strategy s one o the modern exstng strateges [0]. In PCFLA, user proles are eectvely utlzed to determne at whch stes throughout the networks user s locaton normaton should be cached. In ths approach, these ste lsts are prepared based on the long-term call related statstcs mantaned by the HLR rom the callee s user prole. These lsts are used to store the callees locaton normaton to some o the most requently callng VLR caches o the correspondng callees. In IS-4 standard, whenever an changes ts Regstraton Area (RA), the HLR gets a locaton regstraton message rom VLR assocated wth the new RA and updates the s servce prole to pont to new RA and sends the servce prole to that new VLR. The HLR also sends a regstraton cancellaton message to the old VLR. The old VLR then removes the s servce prole and sends a cancellaton acknowledgement message to the HLR. Ths s known as deregstraton o. Ths deregstraton method produce huge sgnalng trac n network. The HLR s also accessed every tme whenever an goes rom one RA to another. As a result the load at HLR s ncreased. Wth ncreasng number o s and ther servce requrements, these may create serous bottleneck n the network. A deregstraton method known as Group Deregstraton s proposed n [] to reduce the sgnalng trac n the network. In ths method, the HLR does not send the locaton cancellaton message to the old VLR mmedately ater recevng the cancellaton message to the new VLR o the. It keeps the normaton nto a lst or the old RA. When a locaton regstraton message comes rom the old RA, the HLR sends the move-out s lst to the old VLR together wth the locaton regstraton acknowledge message or the newly entered. Accordng to [], ths strategy sgncantly reduces the sgnalng trac and database access load wthout ncreasng the database sze o the VLRs and replacng vald user regstraton records n the VLRs. In ths paper, the Group Deregstraton method s ncluded nto the PCFLA strategy. In PCFLA, a locaton update message s sent to HLR when an changes ts LSTP regon. Ater recevng a regstraton cancellaton message rom HLR, the old FLA and old VLR remove the s normaton. The HLR then gets a cancellaton acknowledgement message rom old FLA. These produce sgnalng trac and load on the network. We use the Group deregstraton method n PCFLA to reduce the trac and load. The rest o the paper s organzed as ollows. Secton II gves an overvew o the exstng related research work. Our proposed approach s descrbed n secton III. Secton IV provdes the analytcal modelng. In secton V, Numercal results and comparson among derent approaches based on some expermental results are descrbed. Fnally, a concludng remark s provded n secton VI. II. EXISTING RELATED WORK A consderable amount o work has been done on locaton management to reduce the overall locaton management cost n terms o locaton regstraton cost and call delvery cost [3]-[0]. Some manage the locaton rrespectve o all the wreless networks. The user locaton normaton obtaned durng the prevous call to the user s reused by some others. These approaches reduce the call delvery cost. Whle, some others are used to manage the local hando locally wthout normng the centralzed HLR. In ths way, the locaton regstraton cost s reduced. There are also some methods whch use the s callng statstcs rom the HLR and replcate ts locaton normaton to these callng VLR cache to manage the local hando locally nstead o accessng the heavly congested HLR. As a result, the locaton regstraton and call delvery cost are reduced. Fg Fg 5 shows some exstng locaton management strateges. Table I descrbes the symbols used n Fg Fg 5 and the ISSN : Dec 0- Jan 0 430

3 sgnalng and database access costs or the cost analyss s descrbed n Table II. The ollowng subsectons gve some descrptons o locaton management procedures o these strateges. Symbol TABLE I Descrpton o symbols Descrpton () Correspondng message number [] Cost or the partcular sgnalng exchange {} Cost or accessng the partcular database Exchange o the partcular sgnalng message Acknowledgement o the sgnalng message Parameter C la C d C ra C v C C h TABLE II Descrpton o cost parameters Descrpton Cost or sendng a sgnalng message through the local A-lnk Cost or sendng a sgnalng message through D-lnk Cost or sendng a sgnalng message through the remote A-lnk Cost or a query or an update o the VLR Cost or a query or an update o the FLA Cost or a query or an update o the HLR A. IS-4 Standard In basc IS-4 standard [], each norms ts locaton normaton to the HLR durng all type o hando procedures. When a call s ntated, the called s locaton normaton s searched n the HLR. New HLR Old () [C la +C d +C ra ] () [C la +C d +C ra ] (3) [C la +C d +C ra ] (4) [C la +C d +C ra ] (5) [C la +C d +C ra ] {C v } {C h } {C v } Fg.. Locaton regstraton under the IS-4 standard. The locaton regstraton procedure o ths strategy can be descrbed usng the ollowng steps (see Fg. ). () An enters nto a new RA and norms ts new locaton to the new MSC through the nearby BTS. () The MSC updates ts assocated VLR about ths newly entered. Ater that, t sends a locaton regstraton message to the HLR. (3) Ater recevng the locaton regstraton message, the HLR updates the s record and sends back a regstraton acknowledgement message to the new VLR. (4) It also sends a regstraton cancellaton message to the old VLR. (5) The old VLR removes the record o the mmedately and sends back a cancellaton acknowledgement message to the HLR. Callng HLR Called () [C la +C d +C ra ] () [C la +C d +C ra ] (3) [C la +C d +C ra ] (4) [C la +C d +C ra ] (5) [C la +C d +C ra ] (6) Call Setup {C v } {C h } {C v } Fg. 3. Call delvery under the IS-4 standard. ISSN : Dec 0- Jan 0 43

4 On the other hand, the call delvery procedure under ths strategy s descrbed as ollows (see Fg. 3). () The callng ntates a call and sends a sgnal to ts servng MSC through a nearby base staton. () The callng MSC sends a request message to the HLR or the called s locaton normaton. (3) The HLR determnes the called s current servng MSC and sends a locaton request message to that MSC. (4) The MSC allocates a Temporary Local Drectory Number (TLDN) [0] to the and sends back a reply to the HLR together wth the TLDN. (5) The HLR propagates ths normaton to the callng MSC. (6) The MSC sends a call setup request message to the called MSC through the network shown n Fg.. B. PCFLA Strategy PCFLA strategy [0] s a combnaton o LC (Locaton Cachng) strategy and FLA (Fxed Local Anchor) strategy. It takes the advantages o both LC strategy and FLA strategy. In PCFLA strategy, each LSTP has a FLA (Fxed Local Anchor) whch s actually a specc VLR. The FLA has a table whch keeps the current servng VLR or all s n ts LSTP regon. When an enters nto a new RA then the MSC o the new RA regsters the s locaton at the FLA. The HLR then gets the normaton about the new FLA. The FLA may be the current servng VLR or the other VLR wthn that RA. However, all the user proles are stored and manage n the current HLR n the PCS systems whch contans the user normaton such as a user s locaton, authentcate normaton, and callng actvty log, etc. New FLA/MSC Old () () [C la ] (3) [C la ] (4) [C la ] (5) [C la ] {C v } {C } {C v } (a) Intra- LSTP movement () New New FLA/MSC () [C la ] ( 6.) [C la +C d +C ra ] HLR Cachng MSC Old Old FLA/MSC (6.3) [C la ] ( 6.) [C la +C d +C ra ] ( 6.4) [C la +C d +C ra ] ( 6.5) [C la +C d +C ra ] ( 6.6) [C la +C d +C ra ] (6.7) [C la ] (6.8) [C la ] {C v } {C } {C h } {0} {C } {C v } (b) Inter- LSTP movement Fg. 4. Locaton regstraton under the PCFLA strategy. The locaton regstraton procedure under the PCFLA strategy s descrbed n the ollowng steps (see Fg. 4 (a)). () An sends a locaton update regstraton sgnal to the new MSC through the nearby BS ater enterng to the new RA. () The MSC sends a locaton regstraton message to ts desgnated FLA n ts LSTP regon to check whether t has the s prole. (3) I the has just moved nto a new LSTP regon then s record wll not be ound n the FLA. In that case, go to step (6). On the other hand, the FLA contans the s record then, t updates the s prevous ISSN : Dec 0- Jan 0 43

5 record wth the new one whch ndcates the assocated new VLR. The FLA then sends a regstraton acknowledge message to the new MSC together wth a copy o the s current record. (4) Ater that, The FLA sends a message to the old MSC to remove the s record. (5) The old MSC removes the move- out s normaton rom ts assocated VLR and sends an acknowledge message to the FLA to norm that the deleton s complete. (Locaton regstraton by ntra-lstp movement s complete. Do not contnue to the next step). (6) I there s no s record n FLA then the ollowng steps are perormed (see Fg. 4 (b)). 6.) The MSC assocated wth the s new FLA sends a message to the HLR or locaton regstraton. 6.) As the moves to a new FLA, the HLR updates the s record wth that normaton and sends a copy o the s updated prole to the new FLA. 6.3) The FLA updates ts table by the s record to ndcate that the assocated new VLR and sends a copy o the s prole wth a regstraton acknowledgment message. 6.4) All the MSCs those have locaton cache or the should be updated. For ths reason, the HLR sends locaton cache update messages to those MSCs. 6.5) The HLR sends a message to the s old FLA to cancel the regstraton o the, whch then removes the s record. 6.6) In response o the regstraton cancellaton message rom the HLR, the old FLA sends a regstraton cancellaton acknowledgment message back to the HLR. 6.7) The old FLA sends a regstraton cancellaton message to the s old VLR n order to remove the s obsolete record. 6.8) Ater removng the s record, the old VLR sends a regstraton cancellaton acknowledgment message back to the old FLA (Locaton regstraton by nter-lstp movement s complete). Callng Called FLA/MSC () () [C la ] or [C la +C d ] (3) [C la ] Called (4) [C la ] or [C la +C d ] (5) Call setup {C v } {C } {C v } (a) When callng MSC has locaton cache or the called FLA Callng HLR Called FLA/MSC Called () ( 6.) [C la +C d +C ra ] ( 6.) [Cla +C d +C ra ] (6.3) [C la ] ( 6.5) [C la +C d +C ra ] (6.6) Call setup ( 6.4) [C la +C d +C ra ] {C v } {C h } {C } {C v } (b) When callng MSC does not have locaton cache or the called FLA Fg. 5. Call delvery under the PCFLA strategy. The call delvery procedure under the PCFLA strategy s descrbed as ollows (see Fg. 5 (a)). () The callng ntates a call and sends a sgnal to ts servng MSC through the nearby base staton. () The callng MSC checks ts cache or the locaton o the called s FLA. I the locaton s ound then t sends a locaton request message to the called FLA. Otherwse, go to the step (6). (3) The called FLA then orwards the locaton request message to the called MSC or the called. (4) The called MSC allocates TLDN to the and sends a reply back to the callng MSC together wth the TLDN. (5) The callng MSC sends a message or call setup to the called MSC through the network show n Fg. (Call delvery s complete. Do not contnue to the next step). (6) I the callng MSC s cache does not contan the locaton o the called FLA, the ollowng occurs (see Fg. 5 (b)). 6.) The callng MSC sends a request message to the HLR or the locaton o called. ISSN : Dec 0- Jan 0 433

6 6.) The HLR sends a locaton request message to the called FLA. 6.3) The called FLA then orwards ths message to called MSC. 6.4) The called MSC allocates TLDN to the and reply back to the HLR together wth the TLDN. 6.5) Ater recevng ths normaton, the HLR orwards t to the callng MSC. 6.6) The callng MSC send a message or call setup to the called MSC through the network shown n Fg. (Call delvery s complete). C. Group Deregstraton Ths method s used to mnmze the messages exchange between HLR and VLRs. As a result, the HLR s accessed ewer tmes than beore. The procedure o Group Deregstraton strategy [] can be descrbed as ollows. () When an moves a new RA, the HLR gets a regstraton message rom the VLR assocated wth the new RA. () The HLR updates the s servce prole to ndcate that t s now n new RA. The HLR does not send a regstraton cancellaton message to the old VLR mmedately; rather t keeps the dentcaton o the n a lst mantaned or the old RA. The lst s called old lst (OML). (3) The HLR sends a regstraton acknowledgment message to the new VLR o the along wth a copy o the s servce prole and all s dentcatons kept n the OML o the new RA, and emptes ths OML. (4) The new VLR assocated wth the new RA receves the regstraton acknowledgement message and takes the move-out s dentcatons rom the message. Ater that, the VLR removes these s servce proles. Thus, whenever a new enters nto a new RA, the obsolete s records o that RA are removed rom the assocated VLR. In that case, a new s dentcaton may be n the new RA s OML, the RA has perormed no regstratons snce the s last departure rom the same RA. In ths case, the new s record n the new VLR would be deleted. To avod ths, the new s allocated a record n the new VLR only ater the has regstered tsel at the HLR and the VLR has deleted the obsolete user records. So, the HLR contans OML or every RA. Assume, the sze o an OML s K. An eager deregstraton s needed the number o entres o an OML exceeds K snce the last regstraton. In that case, the HLR sends all dentcatons that are currently n the OML together wth the dentcaton o the leavng the RA most recently and emptes the OML. Ater recevng the dentcatons rom the HLR, the VLR assocated wth the RA deregsters the correspondng s. III. PROPOSED STRATEGY In the PCFLA strategy, whenever an perorms nter-lstp movement the new MSC assocated wth the new FLA sends a locaton regstraton message to HLR. The HLR updates the s prole and sends ths prole to the new FLA. The HLR also sends a regstraton cancellaton message to old FLA. The old FLA removes the s record and also tells the old VLR to remove the s normaton. The old VLA then sends a regstraton cancellaton acknowledgement message to HLR. So, two sgnalng messages are exchanged between HLR and old FLA and two are exchanged between old FLA and old VLR or each LSTP movement o whch ncreases the sgnalng trac and creates load on HLR. To mnmze these extra messages Group Deregstraton method s used n PCFLA n our proposed strategy whch s known as PCFLA wth Group Deregstraton (). () New () [C la ] FLA/MSC Old (3) [C la ] (4) [C la ] (5) [C la ] {C v } {C } {C v } (a) Intra- LSTP ISSN : Dec 0- Jan 0 434

7 New () () [C la ] (6.3) [C la ] New FLA/MSC HLR (6.) [C la +C d +C ra ] (6.) Cachng MSCs [C la +C d +C ra ] (6.4) [C la +C d +C ra ] {C v } {C } {C h } {0} (b) Inter- LSTP movement Fg. 6. Locaton regstraton under The locaton regstraton procedure under s done usng the ollowng steps (see Fg. 6 (a)). () An sends a locaton update regstraton sgnal to the new MSC through the nearby BS ater enterng to the new RA. () The MSC sends a locaton regstraton message to ts desgnated FLA n ts LSTP regon to check whether t has the s prole. (3) I the has just moved nto a new LSTP regon then s record wll not be ound n the FLA. In that case, go to step (6). On the other hand, the FLA contans the s record then t updates the s prevous record wth the new one whch ndcates the assocated new VLR. The FLA then sends a regstraton acknowledge message to the new MSC together wth a copy o the s current record. (4) Ater that, The FLA sends a message to the old MSC to remove the s record. (5) The old MSC removes the move- out s normaton rom ts assocated VLR and sends an acknowledge message to the FLA to norm that the deleton s complete. (Locaton regstraton by ntra-lstp movement s complete. Do not contnue to the next step). (6) I there s no s record n FLA then the ollowng steps are perormed (see Fg. 6 (b)). 6.) The MSC assocated wth the s new FLA sends a message to the HLR or locaton regstraton. As the moves to a new FLA, the HLR updates the s record wth that normaton. But the HLR does not send a regstraton cancellaton message to the old FLA mmedately lke PCFLA strategy; rather t keeps the dentcaton o the n a lst mantaned or the old LSTP. The lst s called old lst (OML). The HLR also sends a copy o the s updated prole to the new FLA. The HLR also sends all s dentcatons kept n the OML o the FLA s assocated LSTP, and emptes ths OML. 6.) The new FLA updates ts table by the s record to ndcate that the assocated new VLR. It also deletes all the s record rom ts table whch s ound rom HLR 6.3) Ater that t sends a copy o the s prole to the new VLR together wth the obsolete s dentcatons. 6.4) All the MSCs those have locaton cache or the should be updated. For ths reason, the HLR sends locaton cache update messages to those MSCs. (Locaton regstraton by nter-lstp movement s complete). The call delvery procedure under the s same as the PCFLA strategy. IV. ANALYTICAL MODEL To evaluate the perormance o our proposed strategy and PCFLA strategy a lud low moblty model [] s used. In ths model, there needs some assumptons such that s are movng at an average speed o v n unormly dstrbuted drecton over [0, π] wth a vew to crossng the LSTP regon composed o N equal rectangular-shaped and szed RAs [0]. The ollowng parameters used or the s movement rates analyss. : the s movement rate out o an RA : the s movement rate out o an LSTP regon : the s movement rate to an adjacent RA wthn a gven LSTP regon Accordng to [3], these parameters are calculated as ollows. 4v () S 4v () NS ISSN : Dec 0- Jan 0 435

8 N Where v s the average movng speed o an, S s the sze o the RA, and N s the number o RAs wthn a LSTP regon. A contnuous-tme Markov Chan state transton dagram s used to show an s RA movement. It s shown n Fg. 7 whch represents the lud low moblty model. Each state ( 0) denes as the RA number o a gven LSTP regon where an can stay and state 0 means the stays outsde o ths regon. The state transton a, j ( ) represents an s movement rate to an adjacent RA wthn a gven LSTP regon, and a0, represents an s movement rate to an RA o that regon rom another one. On the other hand, b, 0( ) represents an s nter-lstp regon movement rate and t s assumed that there are maxmum K number o such movements. Thereore, rom Fg. 7, t s obtaned that respectvely. a, j ) a 0, a, a k-,k K ( b 0 and 0,,, a (3) b,0 b,0 b k,0 Fg.7. State transton dagram o an s RA movement On the other hand, assumng that s the equlbrum probablty o state, the ollowng equatons can be obtaned rom a contnuous-tme Markov Chan gven n Fgure 7. K 0, 0, K, K (4) (5) (6) (7) Accordng to the law o the total probablty, the sum o the probabltes o all states s. So, K 0 K 0 By substtutng (8) nto (4), t can be obtaned the equlbrum probablty o state 0, 0.So, 0 Fnally, rom (5), (6), (7) and (9), s obtaned as ollows. 0 K K (8) (9) (0) In ths secton, based on the user moblty model, we derve the locaton regstraton costs, the call delvery costs and the total locaton management costs o the strategy. Table III shows the varous parameters used or the cost analyss o strategy. ISSN : Dec 0- Jan 0 436

9 P l P n P o P P c q m TABLE III Parameters used or the cost analyss. Probablty (caller and callee are located wthn the same LSTP regon) Probablty (new VLR s the FLA) Probablty (old VLR s the FLA) Probablty (callee s located n the FLA area) Probablty (callng MSC has locaton cache or the called FLA under the strategy) The s CMR (call-to-moblty rato) The number o the MSCs whch have locaton caches or the called FLA under the strategy (= the number o the most requently callng VLRs to the specy) Table II and III descrbe derent parameters that are used n order to calculate locaton management cost, sgnalng cost. The ollowng notatons are also used to represent the cost o each strategy [0]. U X : The average locaton regstraton cost o the X strategy or an stayng n an LSTP regon. S X : The average call delvery cost o the X strategy or an stayng n an LSTP regon. T X : The average total locaton management cost o the X strategy or an stayng n an LSTP regon. Y U X : the average locaton regstraton cost o the X strategy generated by movement type Y or an stayng n an LSTP regon From Fg. 7, the average number o unque RAs that an vsts wthn a gven LSTP or K movements whch can be represented by the ollowng equaton. ( K) K 3 The average locaton regstraton cost under the strategy can be expressed as [0]: U = nt 0 *U er nt + ( (K )-) *U ra nt nt and U ra can be expressed as ollows: U er nt U ra nt U er p p0 M p p M p p M p p M p p M p p M p p M = n 0 n n 0 4 = n 0 n n 0 3 n K K 0 Where M x (x ε {,, 3, 4}) = locaton regstraton costs or ntra-lstp movement n case o (x) gven n Table IV. M (x ε {,, 3, 4}) = locaton regstraton costs or nter-lstp movement under strategy n case x o (x) gven n Table IV. These costs can be expressed as ollows (see Fg. 6(a) and 6(b)): M = M = Cla Cv C M 4C C C 4 la v 3 C C C mc C C C C M = la d ra la d ra h M = 3 ClaCd CramC lacd CraC Ch ClaCv The HLR should update m locaton caches or the throughout the networks whch occurs or the nter- LSTP movement. In ths case, the sgnalng cost or sendng cache update messages s taken under consderaton, but the cache access cost s gnored because t s relatvely too small as compared to the database access cost [3]. () () (3) (4) (5) (6) (7) (8) TABLE IV Four possble cases or locaton regstraton under strategy. Case Descrpton () New VLR s the FLA, and old VLR s not the FLA. () Old VLR s the FLA, and new VLR s not the FLA. (3) Both new VLR and old VLR are the FLAs. (4) Both new VLR and old VLR are not the FLAs. ISSN : Dec 0- Jan 0 437

10 On the other hand, the average call delvery cost under the strategy s expressed as ollows [0]: S = P c * C cache + ( - P c) *C nocache cache Where C = the call delvery costs under the strategy when the callng MSC has locaton cache or the called FLA. nocache And C = the call delvery costs when the callng MSC does not have locaton cache or the called FLA. TABLE V Four possble cases or call delvery when the callng MSC has locaton cache or the called FLA under the strategy Case Descrpton () The caller and called are located wthn the same LSTP regon, and the called s ound n the FLA area. () The caller and the called are located wthn the same LSTP regon, and the called s ound n the other VLR area, not the FLA area. (3) The caller and the called are located n the derent LSTP regons, and the called s ound n the FLA area. (4) The caller and the called are located n the derent LSTP regons, and the called s ound n the other VLR area, not the FLA area. Accordng to the our possble cases gven n Table V, these costs are as ollows (see Fg. 5(a) and Fg. 5(b)): = p P N P * N Pl * P * N3 P C cache * N * where N x (x ε {,, 3, 4}) ndcates the call delvery costs when the callng MSC has locaton cache or the called FLA under the strategy n case o case (x) gven n Table V. These costs can be expressed as ollows (see Fg. 5(a)): N C C C la v N 3 Cla Cv C N3 C la C d Cv C N C C C C C la d v la 4 C nocache = P * D P * D Where D = the call delvery costs when the called s ound n ts FLA area. And D = the call delvery cost when called s ound n the other VLR area. These costs are as ollows (see Fg. 5(b)): D 4C la Cd Cra C v C Ch D 4C la Cd Cra C v C Ch Cla Fnally, the average total cost o the strategy can be expressed as T = U + q * S 4 (9) (0) () () (3) (4) (5) (6) (7) (8) V. NUMERICAL RESULTS AND COMPARISONS In ths secton, strategy compared wth PCFLA strategy based on sgnalng cost, database access cost and total cost. For analyss purpose, N s set to 55. The number o the RA s per LSTP regon s 55 [3], [4], [6]. So, we set P n = P o = P = /55 = 0.08 and the number o the LSTPs per regon s 60/7 = 3 so the value o P l s /3= For smplcty we assume P c = 0.7 and m = 5 [0]. The value o v and S s consdered as 5.6 km/h and 0 km [].The comparsons are shown graphcally n the ollowng subsecton by takng values rom Table VI and Table VII. TABLE VI Sgnalng costs parameter set. Set C la C d C ra 3 6 ISSN : Dec 0- Jan 0 438

11 TABLE VII Database access costs parameter set. Set C v C C h A. Sgnalng cost (a) Set () (b) Set () Fg. 8. Sgnalng Costs Sgnalng cost o PCFLA and s determned by settng the database access cost parameters, C h, C v, C and to be 0. Table VI s used to calculate sgnalng costs or both and PCFLA. Fg. 8 shows the comparson o Sgnalng costs between and PCFLA. B. Database access cost For calculatng database access cost we assume sgnalng cost s zero. Table VII s used to calculate Database access cost by settng C la, C d, C ra to zero. As the old VLR and old FLA database are not accessed durng nter- LSTP movement o n but these databases are accessed n PCFLA strategy. So our proposed strategy perorms better than PCFLA strategy n case o database access cost and the comparson s shown n Fg. 9. (a) Set (3) ISSN : Dec 0- Jan 0 439

12 (b) Set (4) Fg. 9. Database Access Costs C. Total cost We calculate the total cost by consderng set () and set (3) n Fg. 0(a) and set () and set (4) n Fg. 0(b). In both cases, shows better result than PCFLA. (a) Set () and Set (3) (b) Set () and Set (4) Fg. 0. Total Costs Accordng to [], a small amount o storage s needed n HLR or the OML or each LSTP and the length o exstng regstraton acknowledgement message does not ncrease so much to nclude the old moble lst. So, cosderng the above comparsons and the amount o extra storage needed n HLR t can be concluded that has better perormance than PCFLA strategy. VI. CONCLUSION Locaton management n wreless moble networks s a major concern n today s world. To reduce locaton management cost an eectve strategy called s proposed n ths paper. The proposed strategy uses Group Deregstraton method wth PCFLA strategy. It reduces the sgnalng messages and database access cost when an perorms an nter-lstp movement. As a result, the total cost s reduced n terms o locaton regstraton cost and call delvery cost regardless o the CMR. The numercal results and comparsons between ISSN : Dec 0- Jan 0 440

13 and PCFLA show that proposed strategy outperorms the PCFLA strategy rrespectve o the s callng and moblty pattern. REFERENCES [] Akyldz, J. McNar, J. Ho, H. Uzunaloglu, and W. Wenye, Moblty management n next-generaton wreless systems, Proc. IEEE, vol.87, no.8, pp , Aug [] M. Mouly and M.B. Pautet, The GSM system or moble communcatons, 49 rue Louse Bruneau, Palaseau, France, Telecom Publshng, January 99. [3] R. Jan, Y.B. Ln, and S. Mohan, A cachng strategy to reduce network mpacts o PCS, IEEE J. Sel. Areas Commun., vol., no.8, pp , Oct [4] J. Ho and I. Akyldz, Local anchor scheme or reducng sgnallng costs n personal communcatons networks, IEEE/ACM Trans. Netw., vol.4, no.5, pp , Oct [5] E. Bae, M. Chung, and D. Sung, Perormance analyss o xed local anchor scheme or supportng UPT servces n wrelne networks, Comput. Commun., vol.3, pp , 000. [6] R. Jan and Y.B. Ln, An auxlary user locaton strategy employng orwardng ponters to reduce network mpacts o PCS, ACMBaltzer J. Wreless Networks, vol., no., pp.97 0, July 995. [7] G. Varsamopoulos and S. Gupta, Dynamcally adaptng regstraton areas to user moblty and call patterns or ecent locaton management n PCS networks, IEEE/ACM Trans. Netw., vol., no.5,pp , Oct [8] W. Ma and Y. Fang, A ponter orwardng based local anchorng (POFLA) scheme or wreless networks, IEEE Trans. Veh. Technol., vol.54, no.3, pp.35 46, May 005. [9] J. L and Y. Pan, A dynamc HLR locaton management scheme or PCS networks, Proc. INFOCOM 004, vol., pp.66 76, March 004. [0] K. Kong. Perormance analyss o prole-based locaton cachng wth xed local anchor or next-generaton wreless networks. IEICE transactons on communcatons, E9-B(): , November 008. [] Zuj Mao,, Chrstos Doulgers, "Group Deregstraton Strategy or PCS Networks," IEEE COMMUNICATIONS LETTERS, VOL. 6, NO. 4, APRIL 00. [] F. Baumann and I. Nemegeers. An evaluaton o locaton management procedures. In Proceedngs o the Thrd Annual Internatonal Conerence on Unversal Personal Communcatons, USA, pp , September 994. [3] K. Kong, M. Song, K. Park, and C. Hwang. A comparatve analyss on the sgnalng load o Moble IPv6 and Herarchcal Moble IPv6: Analytcal approach. IEICE Transactons on Inormaton and Systems, E89-D():39 49, Japan, January 006. ISSN : Dec 0- Jan 0 44