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1 Mobility Management
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Mobility Management
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Introduction
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A Common PCS NetworkArchitecture
MSC
VLR Cloud
Cloud
Cloud
HLR
MSC
VLR
PSTN
BS
HLR: Home Location Register
MSC: Mobile Switching CenterPSTN: Public Switched Telephone Network
VLR: Visitor Location Register
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Two Aspects of Mobility in a PCSNetwork
Handoff• Link transfer, or Handover
• A mobile user moves from one coverage area of anold BS to the coverage area of a new BS during the
conversation.• The radio link to the old BS is disconnected and aradio link to the new BS should be established tocontinue the conversation.
Roaming• When a mobile user moves from one system to
another, the location of the user should tell the PCSsystem.
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Roaming Management
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Location Tracking and Update
When a mobile usermoves from one PCSsystem to another, the
current location of theuser should be updated.
How to get the current
location of the user ?Where to store the
current location of the
user ?
Database
MSC
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Two-level Hierarchical Strategy
In IS-41 and GSM MAP, the two-levelstrategies are proposed.
A two-tier system of home and visited
databases• Home Location Register (HLR)
• Visited Location Register (VLR) HLR
VLRVLR
VLR
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Home Location Register (HLR)
HLR is a network database that stores andmanages all subscriptions of a specific operator.
The information in HLR:
• MS Identity, directory number, profile information,current location, validation period .
HLR
MS 1. location,...
MS 2. location,...
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Visitor Location Register (VLR)
The VLR has temporary information for thevisiting mobile users.
The information in VLR:
• MS Identity, directory number, current location.
VLR
Visiting MS 1...
Visiting MS 2...
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Basic Operations
Two basic operations in roamingmanagement.
• Registration: an MS informs the system of its
current location• Location Tracking: the system locates the MS
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MS Registration Process
Cloud
HLR
New
VLROld
VLR
1 3
2
4
Taichung
Taipei
Tainan
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Call Origination Procedure
VLR
MSC
PSTN
PCS
Network
Central
Office
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Call Delivery
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Roaming Management under
SS7
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Signaling in Core Network
How is the mobile roaming managed by thesignaling?
Signaling System No. 7 (SS7) is used forcore network of the cellular systems.
Protocols to support mobility management:
• EIA/TIA Interim Standard 41 (IS-41 or ANSI-41)
• GSM Mobile Application Part (MAP)• IS-41and GSM MAP are based on SS7.
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Signaling between a PCS network and thePSTN are typically achieved by the SS7network.
Roaming Management under SS7
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Registration
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Traffic Cost
The traffic in the SS7 network is heavy.Approach to reduce the deregistration
traffic：
• Implicit deregistration + Periodic re-registrationApproach to reduce the registration traffic：
• Point forwarding scheme
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Implicit deregistration
MSC 1
SCP
VLR1MSC 2
STPSTP2
PSTN
CloudPSTN
CloudPSTNSTP
STP3
CloudPSTN
STPSTP4
SCPVLR2
SCPHLR4
1
2
2 Registration
Global
Title
Translation
3
4
5 deregistration
registration ack.
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The MS periodically re-registers to the VLR.
Periodic re-registration
Visiting MS 1...
Visiting MS 2...
123
456
789
*0#
VLRMSC
VLR
MSC123
456
789
*0#
MS 1
MS 2
Period
registration
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SCP(HLR)
MSC
SCP
(VLR1) MSC
SCP
(VLR2) MSC
SCP
(VLR3)
(a) Move Operation
SCP(HLR)
MSC
SCP
(VLR1) MSC
SCP
(VLR2) MSC
SCP
(VLR3)
(b) Find Operation
Pointer Forwarding Scheme
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Call Delivery
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Call Delivery through SS7
STPSTP1
SSP
STPSTP3
Cloud
PSTNCloud
PSTN
Cloud
PSTN
STPSTP2
STP
STP4
MSC
SCP
(VLR)
SCP (HLR)
Global Title
Translation
1 1
3
2
3
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Traffic Cost for Call Deliverythrough SS7
Cache scheme was proposed to reduce thecall delivery traffic.
Two possible positions for the cache:
• Method 1. In the originating SSPs• Method 2. In the STP that performs GTTs
Two two fields in cache:
• MIN of an MS• Current visited VLR of the MS
The cache contains entries for MSs recentlyaccessed from the SSP (MSC).
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Cache Scheme
STPSTP1
SSP
STPSTP3
Cloud
PSTN
Cloud
PSTN
Cloud
PSTN
STPSTP2
STPSTP4
MSC
SCP
(VLRA)
SCP (HLR)
Mobile Phone 1
VLRA
Global Title
Translation
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Summary
Roaming Management
Roaming Management through SS7
• Reducing the traffic cost of deregistration
Implicit Deregistration
Periodic Re-registration
• Reducing the traffic cost of registration
Pointer Forwarding Scheme
• Reducing the traffic cost of call deliveryCache Scheme
