1. Polytechnic University  M. Veeraraghavan 1 Location management Prof. Malathi Veeraraghavan Elec. & Comp. Engg. Dept/CATT Polytechnic University mv@poly.edu EL604: Wireless & Mobile Networking

2. Polytechnic University  M. Veeraraghavan 2 What is the problem? How does a network deliver a packet or a call to a destination that may not be located at the physical location indicated by its address? –e.g., a 212 telephone user located in SF

3. Polytechnic University  M. Veeraraghavan 3 Location management Solutions to the problem combine mobile location with limited mobile tracking in order to decrease the “find” operation cost Thus, location management is the set of procedures to –track a mobile user –find a mobile user to deliver it calls or packets

4. Polytechnic University  M. Veeraraghavan 4 Extreme solution: an overlay approach Don’t track the mobile user at all When a call/packet is to be delivered, page at all base stations in all networks Cost –huge “find” cost –zero “move” cost

5. Polytechnic University  M. Veeraraghavan 5 Another extreme solution an integrated approach Every time a mobile moves, send a routing update with its reachability to all switches in all networks When a call/packet arrives at a switch, it immediately knows where mobile is Cost –huge “move” cost –zero “find” cost

6. Polytechnic University  M. Veeraraghavan 6 Routing protocol + routing table precomputation + “move” update Host A I IV III II Routing protocol Dest.Next hop III-*II Dest.Next hop III-*III Dest.Next hop III-5 Local Routing tables Routing protocols exchange topology/loading/reachability information Summarized routes precomputed Mobile III-5’s move causes a route update Mobile III-5 III-5 IV III-5Local IV

7. Polytechnic University  M. Veeraraghavan 7 Two approaches Integrated Overlay

8. Polytechnic University  M. Veeraraghavan 8 Completely integrated approach Move operation –Send updates via routing protocol as mobile user moves Find operation –Route packets or calls trusting routing information Second “extreme” case solution

9. Polytechnic University  M. Veeraraghavan 9 Overlay approach Move operation –Send updates via a separate registration message to one “home” server Find operation –Send a query message to find location of mobile before routing calls/packets Solution somewhere between extremes

10. Polytechnic University  M. Veeraraghavan 10 Hybrid integrated/overlay Move –Limit region to which routing updates sent (integrated) Say just CA if NY mobile is visiting in SF Create a “neighborhood” around mobile –Register current neighborhood with home switch (overlay) –Cancel information at old neighborhood Find (integrated) –If calls/packets originate at some other switch within CA, call/packet will be routed directly –If calls/packets originate in other neighborhoods, they will be routed to home switch and will then be forwarded to mobile’s current neighborhood may need route optimization

11. Polytechnic University  M. Veeraraghavan 11 e.g. Location management in cellular networks Move operation –a mobile’s location is registered at a Home Location Register (HLR) or a Visitor Location Register (VLR) – 2-level database hierarchy Find operation –location query message is sent to HLR to find mobile’s location when a call arrives

12. Polytechnic University  M. Veeraraghavan 12 Cellular network architecture MSC: Mobile Switching Center SS7: Signaling System No. 7

13. Polytechnic University  M. Veeraraghavan 13 Signaling associated with location management On air interface: –Registration: a mobile sends a registration (called association in 802.11) to the network when it changes location area Group of cells form a registration area or location area; BSs send ID of location area in their beacons allowing a mobile to recognize an area change as it moves –Page: to find mobile to deliver it a call Between base-stations and MSCs: A interface Between network elements: IS-41

14. Polytechnic University  M. Veeraraghavan 14 IS41 MAP MAP: Mobile Application Part Used on the interfaces between MSCs, HLRs and VLRs

15. Polytechnic University  M. Veeraraghavan 15 IS41 location management messages RegistrationNotification RegistrationCancellation ServiceProfileRequest QualificationRequest LocationRequest RouteRequest

16. Polytechnic University  M. Veeraraghavan 16 IS41 move operation MSC1 VLR1VLR2HLR 718-555 415-555 718-555-1234 air-interface/ A interface registration MSC2 RegistrationCancellation RegistrationNotification

17. Polytechnic University  M. Veeraraghavan 17 IS41 find operation MSC1 VLR1 VLR2 HLR 718-555 415-555 718-555-1234 TLDN: Temporary Local Directory Number MSC2 RouteRequest PSTN Switch LocationQuery PSTN Switch Setup (718-555-1234) RouteRequest Reply (TLDN = 415-555-5643) PSTN Switch Setup (415-555-5643) Page

18. Polytechnic University  M. Veeraraghavan 18 IS41 find operation – if originating switch does not support mobility VLR1 VLR2 HLR 718-555 415-555 718-555-1234 TLDN: Temporary Local Directory Number MSC2 RouteRequest PSTN Switch LocationQuery PSTN Switch Setup (718-555-1234) RouteRequest Reply (TLDN = 415-555-5643) PSTN Switch Page PSTN Switch Setup (718-555-1234) MSC1 Setup(415-555-5643)

19. Polytechnic University  M. Veeraraghavan 19 IS41 location management Overlay or integrated?

20. Polytechnic University  M. Veeraraghavan 20 IS41 questions How are the IS41 signaling messages transported? How does the originating switch know the address HLR of the called party? –Type of address: point codes (SS7 network)

21. Polytechnic University  M. Veeraraghavan 21 Transport of IS41 signaling messages in cellular networks Telephony networks are circuit switched Signaling messages to set up circuits could potentially be sent on direct links between switches Mobility management related signaling messages (i.e., IS41 messages) are sent between “non-neighboring” nodes (location registers, switches)

22. Polytechnic University  M. Veeraraghavan 22 Best choice: CL network Best choice for such messaging: CL network Don’t want to waste time setting up a connection from VLR to HLR before sending a Register message The network used for this purpose: SS7

23. Polytechnic University  M. Veeraraghavan 23 GTT – Global Title Translation Solution for the second problem: –How does the originating switch know the address HLR of the called party? GTT is used to determine point code address of HLR corresponding to a mobile’s MIN Mappings are stored in STPs Analogy: STP is comparable to a combined IP router/DNS server

24. Polytechnic University  M. Veeraraghavan 24 Analogous to DNS for email service DNS typically used to translate domain name to IP address of host Also used to find the server of a specific host for applications such as the Simple Mail Transfer Protocol (SMTP) DNS type field: MX MX DNS queries ask for IP address of SMTP server that serves a given email user given the user’s email address (e.g., xxx@yahoo.com)

25. Polytechnic University  M. Veeraraghavan 25 Summary Location management –Move and find operations –Integrated and overlay methods Examples –IS41 –Mobile IP –GSM