Download - Location management
1 Polytechnic UniversityM. Veeraraghavan
Location management
Prof. Malathi VeeraraghavanElec. & Comp. Engg. Dept/CATT
Polytechnic [email protected]
EL604: Wireless & Mobile Networking
2 Polytechnic UniversityM. Veeraraghavan
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 UniversityM. Veeraraghavan
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
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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
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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
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Routing protocol + routing table precomputation + “move” update
Host A I
IV
III
II
Routing protocol
Routing protocol
Dest. Next hop
III-* IIDest. 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
Mobile III-5
III-5 IV
III-5 Local
IV
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Two approaches
• Integrated
• Overlay
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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
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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
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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
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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
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Cellular network architecture
• MSC: Mobile Switching Center
• SS7: Signaling System No. 7
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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
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IS41 MAP
• MAP: Mobile Application Part
• Used on the interfaces between MSCs, HLRs and VLRs
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IS41 location management messages
• RegistrationNotification
• RegistrationCancellation
• ServiceProfileRequest
• QualificationRequest
• LocationRequest
• RouteRequest
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IS41 move operation
MSC1
VLR1VLR2
HLR
718-555
415-555
718-555-1234
air-interface/A interfaceregistration
MSC2RegistrationCancellation RegistrationNotification
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IS41 find operation
MSC1
VLR1VLR2
HLR
718-555
415-555
718-555-1234TLDN: Temporary Local Directory Number
MSC2
RouteRequest
PSTNSwitch
LocationQuery
PSTNSwitch
Setup (718-555-1234)
RouteRequest
Reply (TLDN = 415-555-5643)
PSTNSwitch
Setup (415-555-5643)
Page
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IS41 find operation – if originating switch does not support mobility
VLR1
VLR2HLR
718-555
415-555
718-555-1234TLDN: Temporary Local Directory Number
MSC2
RouteRequest
PSTNSwitch
LocationQuery
PSTNSwitch
Setup (718-555-1234)
RouteRequest
Reply (TLDN = 415-555-5643)
PSTNSwitch
Page
PSTNSwitch
Setup (718-555-1234)
MSC1 Setup(415-555-5643)
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IS41 location management
• Overlay or integrated?
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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)
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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)
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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
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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
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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., [email protected])
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Summary
• Location management– Move and find operations– Integrated and overlay methods
• Examples– IS41– Mobile IP– GSM