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Network:Location Management
Y. Richard Yang
3/21/2011
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Admin
Assignment 3 status
Exam this Wednesday
Project meetings Weekly meeting for 15 min.
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Recap: Network Layer Services Transport packets from source to dest Network layer protocol in host and
router
Basic functions: Control plane
compute routing from sources to destinations
Data plane: forwarding move packets from input interface to
appropriate output interface(s) to reach dest
B
A
S1 ED2
S2
JD1
CG
IK
M
N
L
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Basic Network Layer Model
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A
ED
CB
F
Each node is a network attachment point (e.g., router, base station), to
which hosts/user equipment attaches
User device identified by addressing scheme• locator: identifies attachment point• identifier: independent of location
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Key Problems
Location managementE.g., due to user mobility (roaming),
attached point changes
Routing under mobility and wireless channels
A
ED
CB
F
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Outline
Admin. Location management
cellular networks
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BSC
Radio Subsystem
BSC
Setting: GSM (Circuit Switching Domain)
MS (mobile station)BSC (base station controller)BTS (base transceiver station)MSC (mobile switching center)GMSC (gateway MSC)
fixed network
MSC MSC
GMSC
Network &Switching Subsystemand OperationSubsystem
MS
MS
MS
MS
MS
MS
BTS
BTS
BTS
BTS
BTS
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Routing in Cellular Networks
Issues in cellular networks:Location management: a phone # is
mostly an identifier, to route a call to a phone #, how to find the current attachment point (BTS) of the phone?
Handoff: a user may move during a phone call, how to not drop the call?
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Two Primitives for Cellular Location Management
Mobile station: reports to the network of the cell it is in called update uses the uplink channel
Network: queries different cells to locate a mobile station called paging uses the downlink channel
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Performance of the Two Primitives
A city with 3M users During busy hour (11 am - noon)
Update only total # update messages: 25.84 millions on average each user visited > 8 cells
Paging only call arrival rate: 1433 calls/sec total # paging transactions: 5.2 millions
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Discussion
A user receives one call for ~5 cells (25M vs 5M) visited, thus may not need to update after every switching of cell
However, if no update at all, then paging cost can be high—may need to page the MS at every cell Q: how do you page?
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Location Management Through Location Areas (LA)
A hybrid of paging and update Used in the current cellular
networks Partitions the cells into
location areas (LA) e.g., around 10 cells in diameter
in current systems Each cell (BTS) periodically
announces its LA id If a mobile station arrives
at a new location area, it updates the base station about its presence
When locating a MS, the network pages the cells in an LA
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How to Decide the LAs: A Simple Model
Assume the cells are given Cell i has on average Ni users in it
during one unit time; each user receives calls per unit time
There are Nij users move from cell i to cell j in a unit of time
Cell 1 Cell 2
N1N2
N12
N21
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How to Decide the LAs: A Simple Scenario
Separate LAs for cells 1 and 2 #update: #paging:
Merge cells 1 and 2 into a single LA #update: #paging:
Cell 1 Cell 2
N1N2
N12
N21
N12 + N21
(N1 + N2)
0
2 (N1 + N2)
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Cost Comparison
where C_update is relative cost of update to pgaing, assuming paging cost per cell is 1
15
)(?)( 212112 NNNNCupdate
• At the same mobility, if call arrival rate is high, more likely separate
• At the same call arrival rate, if higher mobility, more likely to merge
Merge Separate
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Basic Location Management Practice in GSM
Base stations announce LA Visiting network MSC maintains visitor
location register (VLR) If a MS moves to a new LA, it reports its
location to visiting MSC A global home location register (HLR)
database for each carrier MSC/VLR notifies HLR that it currently has
MS
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BSC
Radio Subsystem
BSC
GSM
MS (mobile station)BSC (base station controller)BTS (base transceiver station)MSC (mobile switching center)GMSC (gateway MSC)
fixed network
MSC MSC
GMSC
Network &Switching Subsystemand OperationSubsystem
MS
MS
MS
MS
MS
MS
BTS
BTS
BTS
BTS
BTS
VLRVLR
HLR
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GSM Location Update: Example
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GSM Location Update: Example
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GSM Location Update: Example
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GSM Location Update: RR Connection Setup
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GSM Location Update: Update
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GSM Location Update: Update
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GSM Location Update: Update
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GSM Location Update : Authenticate Subscriber
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GSM Location Update: Enable Ciphering
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GSM Location Update: RR Connection Release
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Extension: From GSM to GPRS to 3G UMTS
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Extension: From GSM to GPRS to 3G UMTS Issue: it is anticipated that users will
make more connections in data network Same mobility but higher lambda =>
smaller location area
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UMTS Location Update
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Summary
The LA/RA/UTRANA design considers call pattern: when (how often) does a
mobile station receive a call mobility model: how does a mobile station
move
Issues of LA based approaches Users roaming in LA borders
may generate a lot of updates
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Distributed Location Management Schemes
Timer based• A MS sends an update after some given time T
Movement based• A MS sends an update after it has visited N
different cells
Distance based• A MS sends an update after it has moved away for
D distance (need ability to measure distance)
Profile based• A MS predicts its mobility model and updates the
network when necessary
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Timer-based Location Management
A MS sends an update after some given timer T
The network pages the MS upon a call request at all cells which the MS can potentially arrive during T cells reachable from last update cell, e.g.,
within distance vmax * T, where vmax is the maximum speed
Question: how to determine T?
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Timer-based Location Management
Assume time between call arrivals is Tcall
Cell radius is dcell
Total bandwidth cost:
pagingcell
updatecall b
d
Tvb
T
T2
2max )(
32
2
max2
1
paging
updatecall b
bT
v
dT cell
Take derivative and set it to 0 to derive the optimal value:
updatecall bT
Tpaging
cell
bd
Tv2
max
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Summary: Location ManagementTwo primitives of location management
in cellular networks update (a proactive approach) paging (a reactive approach)
Hybrid update/paging tradeoff The location area (LA) approach Distributed approaches
• timer based• movement based• distance based• profile based
updatecall bT
T
32
2
max2 paging
updatecall
b
b
v
dTT cell
pagingcell
bd
Tv2
max