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WLAN-GPRS Integration for Next-Generation Mobile Data Network

報告人 :李偉晟

18 / 6 / 2003

Apostolis K. Salkintzis, Chad Fors, and Rajesh Pazhyannur Motorola

IEEE Wireless Communications Magazine October 2002

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Outline

• Motivation• The general aspects of integrated

WLAN-cellular network• Interworking architecture

Tight Couple Architecture Loose Couple Architecture

• Conclusion

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Motivation• The operator has the large

investments made for new spectrum in which to offer 3G services, but 3G data technology is not available

• And 2.5G(GPRS) cellular data technology is available in large coverage, but can't meet business and multimedia application requirement

• The recent evolution and successful deployment of WLAN systems worldwide, and its high data rate

• An integrated network combines the strenghths of each, provides users with ubiquitous data service.

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The general aspects of integrated WLAN-cellular network

• Who owns the WLAN? Cellular operator Wireless Internet Service

Provider(WISP)• Session Mobility

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Interworking Architecture

• The Tight Couple Architecture• The Loose Couple Architecture

External Packet datanetwork

Gi

Loose coupling point

HLR

SGSN

SGSN

Gb

Gr

Gn/p

Gn/p

Iu-ps

UTRAN

GRPSRAN

Tight coupling point

MS

MS

Mobielstation

Um

Uu

GGSN

Gc

HLR:Home location registerSGSN:Serving GPRS support nodeGGSN:Gateway GPRS support node

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The Tight Couple Architecture

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Benefits

• Seamless service continuation across WLAN and GPRS

• Reuse of GPRS AAA Authentication, Authorization, and

Accouting• Reuse of GPRS infrastructure• Access to core GPRS services

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WLAN System Description• A WLAN network is deployed with one

or more off-the-shelf access ponts(APs)• APs are connected by means of a

distribution system(DS)• In the system, DS is a LAN (IEEE 802.3)• APs behave like base stations• The service area of a AP

is a basic service set (BSS)• Each WLAN composes many BSSs,

all form an ESS• The WLAN is considered like any other

GPRS routing area (RA:group of cells) in the system

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GIF:GPRS Interworking functionCG:Charging gatewayHLR:Home location registerAuC:Authentication centerSGSN:Serving GPRS support nodeGGSN:Gateway GPRS support nodeBSS:Basic service setAP:Access point

Firewall

Operator's IP network

802.11 standar service set(ESS)

Beacon (SSID) Beacon (SSID) Beacon (SSID)

BSS-1 BSS-2 BSS-3

FeatureServers

Internet

WLAN network

Distribution system

Dual mode MS

GIF

48-bit802 MACaddress

(AuC)

HLR

CG

GPRS core

Billing mediator

Billing system

RadioAccessNetwork(UTRAN/GPRSRAN)

SGSN GGSN

AP

Gb

All mobile terminals and the GIF use MAC address

All mobile terminals and the GIF use MAC address

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New Component

• GPRS interworking function (GIF) Is connected to a DS and to a serving

GPRS support node (SGSN) Provide a standardized interface to the

GPRS core network Hides the WLAN particularities

• WLAN adaptation function (WAF) Identifies when the MS associates with a

valid AP Informs the LLC layer , which

subsequently redirects signaling and data traffic to the WLAN

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LLC

WLANAdaptation Function (WAF)

WLAN radio subsystem

GPRS radio subsystem

Um

Gb

Gb WLAN access network

GPRS access network

GPRS corenetwork

GPRSInterworking Function (GIF)

Dual-mode MS

WLAN access network

Defined by 802.11

New interworking componets

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Protocol Architecture

802.11 MAC 802.11 MAC

802.11 X PHY802.11 X PHY

User data

GMM/SM SNDCP

LLC

WAF

RLC/MAC

GPRS PHY

Um

Dual-mode MS Access point GPRS interworkingFunction (GIF)

802.3 MAC

10Base-Tor other

10Base-Tor other

802.3 MAC

PHY(e.g. G.703/704)

FR

NS

BSSGP

WAF

Gb

SGSN

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WLAN Adaptation Function

• Functions： Signals the activation of WLAN

interface when the mobile enters a WLAN area

Supports the paging procedures (SGSN pages the MS)

Transfers PDUs (Packet Data Unit) between mobiles and GIF

Supports QoS (transmission scheduling in GIF and the MS)

Transfers the TLLI and QoS information in the WAF header

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WLAN Adaptation Function (cont.)

• TLLI ( Temporary Logical Link Identifier ) Is used by GIF to update an internal

mapping table that correlates TLLI and MS's MAC addresses

The SGSN uses TLLI as MS address informatioin, whereas the WLAN utilizes MAC addresses

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WLAN Adaptation Function (cont.)

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GIF/RAI Discovery Procedure

1. MS’s WAF send

Discovery Request ,SA=MS

,DA=Broadcast,IMSI

Start

2. Data is directed to

the AP with BSSID

3. The AP broadcast

this messageto the DS

4. The GIF receive

this message,associate the IMSI

with the MS'sMAC address

5. Then the GIF's WAFResponds DiscoveryResponse

,GIF's MAC Address,

WLAN's RAI

6. The MS receives this response

, stores the GIFaddress and

the RAI

7. The MS notifiesthe GMMlayer that the currentGPRS RA

has changed

8. The GMM layer notifies

the SGSN thatthe MS has change RA

End

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The Loose Couple Architecture

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System Description

• The WLAN network is coupled with the GPRS network in the operator’s IP network

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CAG:Cellular acess gatewayCG:Charging gatewayHLR:Home location registerAuC:Authentication centerSGSN:Serving GPRS support nodeGGSN:Gateway GPRS support nodeAAA:Authentication, authorization, accountingFA:Foreign agentHA:Home agent

Dual mode MS

Internet

Operator's IP network

Billing system

FA

WLAN network

GPRS core

(AuC)

HLR

CG

HA

AAA

FA

CAG

Billing mediator

FeatureServersRadio

AccessNetwork(UTRAN/GPRSRAN)

SGSN GGSNFirewall

Firewall

AP

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Authentication• The Extensible Authentication

Protocol(EAP)： Performs authentication of the MS Passing the subscriber identity Passing SIM-based authentication

data Encrypted session key

• The cellular accesss gateway(CAG) acts as an authenticator for WLAN users

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MS AP CAG HLR

5. Send authentication info

2. EAPOW-request/identity

7. RADIUS access-challenge

10. RADIUS access-request

1. EAPOW-start

12. EAP-sucess

13. EAP-key

8. EAP-request(RAND)

9. EAP-response(SRES)

3. EAPOW -response/identity

(IMSI) 4. RADIUS access-request

(IMSI)

6. Send authentication info ack

RANDXRES

11. RADIUS access-accept if XRES == SRES

(AAA server)

[Signed Result]

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Encryption

• Weakness of the 802.11 WLAN standard in its encryption technology

• Wired Equivalent Privacy(WEP) is a relatively inefficient encryption

scheme• With the use of EAP, WEP may be

enhaced by the use of a unique session key (EAPOW-Key) for each user of the WLAN

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Billing

• Integrated billing is achieved via the billing mediator function

• The billing mediator convert accounting statistics from

both the GPRS and WLAN access networks into a format of the particular billing system used by the operator

• The AP in the WLAN will report accounting statistics to the CAG

• The GPRS core will report accounting statistics (via CG) pertaining to GPRS usage

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Sesson Mobility

• Mobile IP (MIP) can be used to provide seeion mobility across GPRS and WLAN domain

• The MIP framework contains： A MIP client (MS) A foreign agent (FA) A home agent (HA)

• The FA in the GPRS resides in the GGSN; in the WLAN can reside in an access router

• The HA is located in the operator's network

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Sesson Mobility (cont.)

When the MS move from one system to another system

When the MS move from one system to another system

The MS performs a MIP registeration via the FA

The MS performs a MIP registeration via the FA

The FA provides a care-of address to the HA to completes the registeration

The FA provides a care-of address to the HA to completes the registeration

The FA acts as the proxy on behalf of the MS for the life of the registeration

The FA acts as the proxy on behalf of the MS for the life of the registeration

The FA then associates the care-of address with that of the MS

The FA then associates the care-of address with that of the MS

Start

End

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Conclusion• The recent evolution and successful

deployment of WLAN sustems worldwide has fueled the need for interworking mechanisms between WLANs and cellar data networks such as GPRS

• Tight coupling is fit for the cellular operator having WLAN

• Loose coupling is fit for the wireless network composed of a large number of WLAN operators and cellular operators

• WLAN technology will play an important role in supplementing wide-area cellular network

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The End !