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Location management

Location management. Prof. Malathi Veeraraghavan Elec. & Comp. Engg. Dept/CATT Polytechnic University mv@poly.edu. EL604: Wireless & Mobile Networking. What is the problem?.

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Location management

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

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

  7. Two approaches • Integrated • Overlay

  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. 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. 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. 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. Cellular network architecture • MSC: Mobile Switching Center • SS7: Signaling System No. 7

  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. IS41 MAP • MAP: Mobile Application Part • Used on the interfaces between MSCs, HLRs and VLRs

  15. IS41 location management messages • RegistrationNotification • RegistrationCancellation • ServiceProfileRequest • QualificationRequest • LocationRequest • RouteRequest

  16. RegistrationCancellation RegistrationNotification VLR1 VLR2 HLR air-interface/ A interface registration 718-555-1234 IS41 move operation MSC2 415-555 MSC1 718-555

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

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

  19. IS41 location management • Overlay or integrated?

  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. 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. 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. 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. 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. Summary • Location management • Move and find operations • Integrated and overlay methods • Examples • IS41 • Mobile IP • GSM

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