1. Network: Location Management Y. Richard Yang 3/21/2011

2. Admin r Assignment 3 status r Exam this Wednesday r Project meetings m Weekly meeting for 15 min. 2

3. 3 Recap: Network Layer Services r Transport packets from source to dest r Network layer protocol in host and router Basic functions: r Control plane m compute routing from sources to destinations r Data plane: forwarding m move packets from input interface to appropriate output interface(s) to reach dest B A S1S1 E D2D2 S2S2 J D1D1 C G I K M N L

4. Basic Network Layer Model 4 A ED C B F Each node is a network attachment point (e.g., router, base station), to which hosts/user equipment attaches User device identified by addressing scheme locator: identifies attachment point identifier: independent of location

5. 5 Key Problems r Location management m E.g., due to user mobility (roaming), attached point changes r Routing under mobility and wireless channels A E D CB F

6. Outline r Admin. r Location management m cellular networks 6

7. 7 BSC Radio Subsystem BSC Setting: GSM (Circuit Switching Domain) MS (mobile station) BSC (base station controller) BTS (base transceiver station) MSC (mobile switching center) GMSC (gateway MSC) fixed network MSC GMSC Network & Switching Subsystem and Operation Subsystem MS BTS

8. 8 Routing in Cellular Networks r Issues in cellular networks: m Location management: a phone # is mostly an identifier, to route a call to a phone #, how to find the current attachment point (BTS) of the phone? m Handoff: a user may move during a phone call, how to not drop the call?

9. 9 Two Primitives for Cellular Location Management r Mobile station: reports to the network of the cell it is in m called update m uses the uplink channel r Network: queries different cells to locate a mobile station m called paging m uses the downlink channel

10. 10 Performance of the Two Primitives r A city with 3M users r During busy hour (11 am - noon) r Update only m total # update messages: 25.84 millions m on average each user visited > 8 cells r Paging only m call arrival rate: 1433 calls/sec m total # paging transactions: 5.2 millions

11. Discussion r A user receives one call for ~5 cells (25M vs 5M) visited, thus may not need to update after every switching of cell r However, if no update at all, then paging cost can be high—may need to page the MS at every cell m Q: how do you page? 11

12. 12 Location Management Through Location Areas (LA) r A hybrid of paging and update r Used in the current cellular networks r Partitions the cells into location areas (LA) m e.g., around 10 cells in diameter in current systems r Each cell (BTS) periodically announces its LA id r If a mobile station arrives at a new location area, it updates the base station about its presence r When locating a MS, the network pages the cells in an LA

13. 13 How to Decide the LAs: A Simple Model r Assume the cells are given  Cell i has on average N i users in it during one unit time; each user receives calls per unit time  There are N ij users move from cell i to cell j in a unit of time Cell 1 Cell 2 N1N1 N2N2 N 12 N 21

14. 14 How to Decide the LAs: A Simple Scenario r Separate LAs for cells 1 and 2 m #update: m #paging: r Merge cells 1 and 2 into a single LA m #update: m #paging: Cell 1 Cell 2 N1N1 N2N2 N 12 N 21 N 12 + N 21 (N 1 + N 2 ) 0 2 (N 1 + N 2 )

15. Cost Comparison where C_update is relative cost of update to pgaing, assuming paging cost per cell is 1 15 At the same mobility, if call arrival rate is high, more likely separate At the same call arrival rate, if higher mobility, more likely to merge MergeSeparate

16. 16 Basic Location Management Practice in GSM r Base stations announce LA r Visiting network MSC maintains visitor location register (VLR) r If a MS moves to a new LA, it reports its location to visiting MSC r A global home location register (HLR) database for each carrier m MSC/VLR notifies HLR that it currently has MS

17. 17 BSC Radio Subsystem BSC GSM MS (mobile station) BSC (base station controller) BTS (base transceiver station) MSC (mobile switching center) GMSC (gateway MSC) fixed network MSC GMSC Network & Switching Subsystem and Operation Subsystem MS BTS VLR HLR

18. GSM Location Update: Example 18

19. GSM Location Update: Example 19

20. GSM Location Update: Example 20

21. GSM Location Update: RR Connection Setup 21

22. GSM Location Update: Update 22

23. GSM Location Update: Update 23

24. GSM Location Update: Update 24

25. GSM Location Update : Authenticate Subscriber 25

26. GSM Location Update: Enable Ciphering 26

27. GSM Location Update: RR Connection Release 27

28. Extension: From GSM to GPRS to 3G UMTS 28

29. Extension: From GSM to GPRS to 3G UMTS r Issue: it is anticipated that users will make more connections in data network m Same mobility but higher lambda => smaller location area 29

30. UMTS Location Update 30

31. 31 Summary r The LA/RA/UTRANA design considers m call pattern: when (how often) does a mobile station receive a call m mobility model: how does a mobile station move r Issues of LA based approaches m Users roaming in LA borders may generate a lot of updates

32. 32 Distributed Location Management Schemes r Timer based A MS sends an update after some given time T r Movement based A MS sends an update after it has visited N different cells r Distance based A MS sends an update after it has moved away for D distance (need ability to measure distance) r Profile based A MS predicts its mobility model and updates the network when necessary

33. 33 Timer-based Location Management  A MS sends an update after some given timer T r The network pages the MS upon a call request at all cells which the MS can potentially arrive during T m cells reachable from last update cell, e.g., within distance v max * T, where v max is the maximum speed r Question: how to determine T?

34. 34 Timer-based Location Management r Assume time between call arrivals is T call r Cell radius is d cell r Total bandwidth cost: Take derivative and set it to 0 to derive the optimal value:

35. 35 Summary: Location Management r Two primitives of location management in cellular networks m update (a proactive approach) m paging (a reactive approach) r Hybrid update/paging tradeoff m The location area (LA) approach m Distributed approaches timer based movement based distance based profile based