A Comparative Cost Analysis of Degradable Location Management Algorithms in Wireless Networks

1. A Comparative Cost Analysis of Degradable Location Management Algorithms in Wireless Networks Ing-Ray Chen and Baoshan Gu Presented by: Hongqiang Yang , Jianghui Ying Northern Virginia Center, Virginia Tech

2. Agenda • Architecture of Paper: • Introduction • Notion of Degradable Location Management Algorithm • Examples of Degradable Location Management Algorithm • Two-tier Hierarchical Framework • Comparison • Application in the analysis of service handoffs • Summary

3. Introduction • Problem • A class of degradable location management algorithms in Personal Communication Service network for tracking mobile user in two-tier HLR-VLR structure • IS-41, FRA, PLA, LAA • Which is better?

4. Introduction • Objective • Develop a uniform framework to provide a cost analysis of location update and search operations for a class of degradable location management algorithms in personal communication service (PCS) networks

5. Introduction • Method--Two level hierarchical modeling framework • High-level model Calculate the costs incurred to the PCS network: • Location-update operations • Call-delivery operations • Low-level model A stochastic model to estimate the values of high-level model parameters

6. Introduction • Location Management Scheme • Aimed to minimize the total cost • Location Update Occurs when a mobile user moves to a new location • Call delivery Occurs when there is a call for mobile user and the network must deliver the call.

7. Introduction • Workload condition is indicated by Call-to-Mobility ratio (CMR) • CMR is high: Location Cache Scheme is effective • CMR is low: FRA, PLA, LAA are effective

8. Degradable Location Management • No assumption regarding the structure of the PCS network • Conceptually, HLR is in high level and VLR is in low level. • Maybe some network switches connecting the HLR to VLRs in the mobile network

9. Degradable Location Management • IS41: • Service area divided into registration areas each corresponding to a VLR User moves to a new registration area Send the registration information to the new VLR Update information

10. Home Location Register Public Switched Telephone Network Regional Signaling Transfer Point Local Signaling Transfer Point Visitor Location Register HLR • A hierarchical PCS network PSTN RSTP LSTP LSTP LSTP … … … VLR VLR VLR VLR VLR VLR

11. Degradable Location Management • The state of a location management algorithm: depends on the extent to which the location information has been degraded since the last location update operation was performed to the HLR • Strong • Weak

12. Degradable Location Management • Strong State: • means the HLR store the current information of the mobile user in its own database • HLR can find the mobile user directly • Weak State: • means the current information of the mobile user is not in the HLR • HLR must consult location database stored elsewhere to find the mobile user

13. Degradable Location Management • The spectrum of degradable location algorithms • encompasses all existing location management algorithm • differ on how fast and in what way the system’s state degrades over time as the user moves across VLR boundaries

14. Degradable Location Management The spectrum of degradable location algorithm IS-41 LAA(2) FRA(2) PLA(2) LAA(3) FRA(4) PLA(3) Paging

15. Degradable Location Management • IS-41 User moves across VLR boundary Send information to new VLR Update information in HLR

16. Degradable Location Management • FRA(K) • User moves across VLR boundary • Length of link of pointers < K: Set up a pointer to the two involved VLRs • Length of link of pointers = K: Update information in HLR • Degrades over time as more and more moves

17. Degradable Location Management • PLA(n) • HLR records a VLR as the agent • The agent covers all VLRs within a distance n from the agent( local region) • No update at all with local moving • Update when across local region boundary • Paging starts from the agent • Degrades over time since the location of the mobile user becomes fuzzier to the HLR as more and more time has elapsed since the last update performed

18. Degradable Location Management • LAA(n) • HLR records a VLR as the local anchor(LA) • The LA covers all VLRs within a distance n from the LA • Update in LA with local moving • Update in HLR when across a regional switch boundary • Three steps researching: • HLR -> LA -> VLR

19. Degradable Location Management • Performance metric: • The network cost due to location update between two successive calls to a mobile user • Paper contribution: • Provides method to quantifying the location update cost for a given location management algorithm with respect to the basic scheme • Classify the algorithm

20. The ratio of the average communication cost between two VLRs to the average communication cost between the HLR and a VLR is 0.3

21. Degradable Location Management • Classify mobile users into priority classes based on their quality of service(QoS) requirements • Separate QoS classes are being served by separate location management schemes • Simplify the per-user-based location management to the per-class-based location management

22. Modeling Degradable Location Management Algorithm • Description of two-level model • Examples of Degradable location management algorithm • Description of algorithm • Low-level model

23. Modeling Degradable Location Management Algorithm • Two-level model • High-level model: cost model • Update cost Xupdate • Query cost Xsearch • Xcost = Xupdate *  / + Xsearch • Low-level model • Aimed to provide the parameters for high-level model • Low-level model • Parameterize equation in high-level model • Define parameters in our model

25. Basic HLR/VLR • A mobile user is permanently registered under a location register(HLR) • Mobile user enters a new VLR area • Reports to VLR • VLR inform HLR • HLR update location information Location Update Cost = 1

26. Paging and Location Algorithm(PLA) • Agent: the VLR performs the last update operation to the HLR • HLR update location information only when the distance between the agent and the current VLR is great than or equal to a predefined distance value n

27. R2 R2 R2 R2 R1 R2 R1 R1 R2 R0 R2 R1 R1 R2 R1 R2 R2 R2 R2 SDF partitioning under the hexagonal model

28. PLA Algorithm HLR PSTN Regional Movement: Outside of 2-Distance Region Action: Update the HLR F E D A C B Local Movement: within the 2-Distance region Update Action: None

29. Paging and Location Algorithm(PLA) • Modeling parameters • n: specify the (n-1)-distance region within a user causes no update cost • i : the mobility rate of the mobile user moving from ring i to ring i + 1 • i : the mobility rate of the mobile user moving from ring i + 1 to ring i •  r : the execution rate to perform a location update to the HLR •  I : the execution rate to locate the mobile user currently located in ring I • P(i,j):The probability that the system is in a particular state in equilibrium

30. Paging and Location Algorithm(PLA) • Assuming random move • The probability of the mobile user moving from ring i to i + 1, i >= 0 (2i + 1) / 6i , if i >= 1, 1, if i = 0. • The probability of the mobile user moving from ring i + 1 to i, i >= 0 (2 (i + 1) - 1 )/ (6(i +1)), if i >= 0,

31. Paging and Location Algorithm(PLA) • The mobility rate of the mobile user moving from ring i to ring i + 1 (2i + 1)  / 6i , if i >= 1, i = , if i = 0. • The mobility rate of the mobile user moving from ring i + 1 to ring i i = (2i +1) /( 6* (i + 1)) , i >= 0

32. Paging and Location Algorithm(PLA) • The execution rate to perform a location update from a new VLR agent to the HLR r = 1 / T

33. Paging and Location Algorithm(PLA) • The time to locate the mobile user in ring i • From HLR to agent • From the agent to the current VLR(in ring i) • From the current VLR back to the HLR • The execution rate to locate the mobile user in ring i i = 1/(T + 0.5*(3i2 + 3i) * ) Query one-half of the VLRs in the i-distance region

34. Paging and Location Algorithm(PLA) • Low-level Makov model • State represented by (a, b) • a: 0, IDLE 1, CALLED • b: the current distance between the mobile user and the local agent

35. Markov Model for PLA r 0 1 2 n-1 0,0 0,1 0,2 0,n-1 0,n-1* 0 1 2    0   1 2 0 n-1 1,0 1,1 1,n-1* 1,2 1,n-1 0 1 2 1 2 n-1 r

36. Paging and Location Algorithm(PLA) • Average cost for location update operation • Average cost for location search operation • Average total cost:

37. Forwarding and Resetting Algorithm(FRA) • HLR only points to the VLR at the beginning of the forwarding chain • User moves across VLR boundary • Length of link of pointers < K: Set up a pointer to the two involved VLRs • Length of link of pointers = K: Update information in HLR

38. FRA Algorithm: K=5 HLR PSTN Regional Movement: Chain Length = 5 Action: Update the HLR F E D A C B Local Movement: length of the forwarding chain is less than 5 Update Action: update the Forwarding Pointer between Two involved VLRs

39. Forwarding and Resetting Algorithm(FRA) • Two additional behaviors in modified Markov Model under FRA • The forwarding chain will be reset after a location query operation is performed • When the mobile user moves back to the previously visited VLR in the chain, the length of the forwarding chain is reduced by 1 and no pointer deletion operation is required between • Obsolete pointers will be purged automatically after a period of time much greater than the average reset period

40. Forwarding and Resetting Algorithm(FRA) • Looping behavior is accounted in Markov model • Assume : when the mobile user moves across a VLR, the forwarding pointer information will be updated before it crosses another VLR • Imply that the dwell time of mobile user in a VLR is much greater than the forwarding pointer update operation time

41. Forwarding and Resetting Algorithm(FRA) • Model Parameters • k : the length of the forwarding chain at which a reset operation is performed • n : the mobility rate of the mobile user moving to a new VLR. • b : the mobility rate of the mobile user moving to the previous VLR • r : the execution rate to reset a forwarding chain, i.e. to update the HLR • f : the execution rate to set-up or travel a pointer between two VLRs • i : 0<= i <=k-1, the execution rate to locate the mobile when the length of forwarding pointer is i.

42. Forwarding and Resetting Algorithm(FRA) • The mobility rate of the mobile user moving to a new VLR n= (5/6) *  • The mobility rate of the mobile user moving to the previous VLR b= (1/6) * 

43. Forwarding and Resetting Algorithm(FRA) • The execution rate to reset a forwarding chain, i.e. to update the HLR r = 1/T • The execution rate to set-up a forwarding chain, i.e. to update the HLR f = 1/ • The execution rate to locate the mobile when the length of forwarding pointer is i( 0<= i <= k-1) i = 1/(T + i *)

44. Forwarding and Resetting Algorithm(FRA) • Low-level Markov Model • States represented by (s1, s2) • s1= 0 , standing for IDLE 1 , standing for Called • s2 indicates the current length of the forwarding chain • States followed by symbol ‘*’ means the mobile user just enters a new VLR but the forwarding pointer operation is not yet performed

45. Markov model for the PCS network under FRA r b b f  n n f 0,0 0,1* 0,1 0,2* 0,k-1 0,k-1* 0 f  n f       n 1,0 1,1* 1,1 1,2* 1,k-1 1,k-1* b b 1 k-1 r

46. Forwarding and Resetting Algorithm(FRA) • P(i , j) : represent the probability that the system is in state (i , j) • fraupdate: average cost to perform a location update operation

47. Forwarding and Resetting Algorithm(FRA) • frasearch: average cost to perform a location search operation • fracost: the average total cost

48. Local Anchor Algorithm(LAA) • Basic idea • Location Registration operations should be as localized as possible so as to reduce the number of registration messages to the HLR. • Local Anchor (LA) • The VLR which performs the last registration operation with the HLR is called the LA of the mobile user.

49. Local Anchor Algorithm(LAA) • LA’s Coverage

50. Local Anchor Algorithm(LAA) • Algorithm • Movement: Cross a VLR boundary but within the local region Operation: New VLR informs the LA without informing the HLR • Movement: regional move Operation: New VLR informs the HLR and also becomes the new LA of the mobile user.