Network:Location Management

Y. Richard Yang

3/21/2011

Admin

Assignment 3 status

Exam this Wednesday

Project meetings Weekly meeting for 15 min.

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3

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

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

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

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)

Cost Comparison

where C_update is relative cost of update to pgaing, assuming paging cost per cell is 1

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)(?)( 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

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 )(

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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

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2

max2 paging

updatecall

b

b

v

dTT cell

pagingcell

bd

Tv2

max