Polytechnic University M. Veeraraghavan 1 Location management Prof. Malathi Veeraraghavan Elec. & Comp. Engg. Dept/CATT Polytechnic University [email protected]

1 Polytechnic UniversityM. Veeraraghavan

Location management

Prof. Malathi VeeraraghavanElec. & Comp. Engg. Dept/CATT

Polytechnic [email protected]

EL604: Wireless & Mobile Networking


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


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


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


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


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


Two approaches

• Integrated

• Overlay


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


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


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


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


Cellular network architecture

• MSC: Mobile Switching Center

• SS7: Signaling System No. 7


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


IS41 MAP

• MAP: Mobile Application Part

• Used on the interfaces between MSCs, HLRs and VLRs


IS41 location management messages

• RegistrationNotification

• RegistrationCancellation

• ServiceProfileRequest

• QualificationRequest

• LocationRequest

• RouteRequest


IS41 move operation

MSC1

VLR1VLR2

HLR

718-555

415-555

718-555-1234

air-interface/A interfaceregistration

MSC2RegistrationCancellation RegistrationNotification


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


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)


IS41 location management

• Overlay or integrated?


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)


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)


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


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


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])


Summary

• Location management– Move and find operations– Integrated and overlay methods

• Examples– IS41– Mobile IP– GSM

Documents

Polytechnic University M. Veeraraghavan 1 Location management Prof. Malathi Veeraraghavan Elec. & Comp. Engg. Dept/CATT Polytechnic University [email protected]