WLAN – Cellular Interworking

November 2003

Stephen McCann, Siemens Roke Manor

Slide 1

IEEE P802 Handoff ECSG

Submission

WLAN – Cellular Interworking

Stephen McCann, Siemens Roke [email protected]

November 2003


Slide 2


Submission

Who am I?

• I work for Siemens in the UK.• I don’t represent ETSI, MMAC or any

working group within it, nor does this presentation

• However, this is an attempt to be a non-partisan overview of previous interworking activities in ETSI, MMAC and IEEE 802.11

November 2003


Slide 3


Submission

Coupling Approaches• Loosely, classify against two extremes:

– Re-use WLAN radio layer within existing public network– Deploy public network services on WLAN network

• The ‘tight’ approaches are more specific, complex, functional– (and disruptive to existing standards)

• The ‘loose’ approaches don’t rule out operators falling into the more specific categories

Also, alternative directions for other mobile standards (CDMA etc.)

tighter

R'99 UMTS UMTS 3G 2/3G Any operatorwith an HLR

Anyoperator

looser

November 2003


Slide 4


Submission

Previous work

November 2003


Slide 5


Submission

WLAN Standardisation

} WIG

November 2003


Slide 6


Submission

IEEE 802.11 & WIG

• Plenary Motion Approved in 2002Plenary Motion Approved in 2002

– Move that the WNG Standing Committee Move that the WNG Standing Committee requests the 802.11 WG to accept the requests the 802.11 WG to accept the invitation from ETSI-BRAN and MMAC invitation from ETSI-BRAN and MMAC to participate in the “to participate in the “WLAN – 3G and WLAN – 3G and other Public Access networks other Public Access networks “interworking” (WIG) project.“interworking” (WIG) project.

November 2003


Slide 7


Submission

What was WIG all about ?

• To establish a joint-effort between 802.11 and ETSI BRAN/MMAC HSWA for the interworking of WLANs to 3G Cellular systems.

• 802.11 should be represented by its own interworking group.

November 2003


Slide 8


Submission

Previous work• At engineering level, TGi already has

similar approach to external authentication (EAPoL) to that of other WLAN standards (e.g. Hiperlan & HiSWAN)

• Previous interworking activities done by ETSI BRAN and MMAC HSWA have similar approach to that of 802.1x

November 2003


Slide 9


Submission

WIG Intended Output ?

• WIG Baseline Document• Common text, which will then be passed

based to recognised WLAN standards bodies (ETSI, IEEE & MMAC) for their regulatory approval.

• WIG cannot NOT approve final output

November 2003


Slide 10


Submission

Why bother ?

• To create a world wide standard for WLAN interworking with Cellular and Public Access networks.

• To encourage the proliferation of world wide WLAN hotspots, regardless of local regulatory constraints.

November 2003


Slide 11


Submission

IEEE 802.11 activities

• Necessity to align interworking work from TGe, TGi, WNG and 802.1

• Procedural requirement to establish some kind of interworking group within 802.11 to address these issues.

November 2003


Slide 12


Submission

IEEE 802.11 Interworking

• No specific group in IEEE802.11 dedicated to interworking issues

• Many external activities in this area, 3GPP, 3GPP2, GSMA, WiFi Alliance all addressing interworking issues.

• Bits of interworking done in WNG, TGi, TGe, 802.1 (802.1x and 802.1aa)

November 2003


Slide 13


Submission

IEEE 802.11Interworking Study Group

Proposed Scope The scope of the study group is to consider whether there is a requirement

to enhance the IEEE 802.11 standard (and amendments), to add interworking capability to both cellular and external IP based networks.

The intention is to re-use the output of existing Task Groups to form a complete interworking solution, and to fill in any gaps.

November 2003


Slide 14


Submission

Coupling

November 2003


Slide 15


Submission

Traditional Coupling Models• Loose Coupling

– Avoids use of core network gateways (e.g. SSGN)

– Applicable to many 2.5G, 3G systems

• Tight Coupling– WLAN is an alternative UTRAN– Specific to particular network technology

• Hybrid – bit of both

November 2003


Slide 16


Submission

Control Plane Interworking

• Defines a ‘control plane only’ convergence layer

• Handles primarily AAA issues– Can authenticate using SIM or other identifier– Focus is on security and roaming support– Intra-network mobility and QoS are handled in

‘user plane’

November 2003


Slide 17


Submission

Architecture

WLAN

AP Router

AAAL

Authentication Information Service Provider

Network

AAAH

Diameter/RADIUS is used to communicate with the

AAAH /HSS

User traffic

MT

Internet

3GPP System IWU

IETF IWU

IETF (Wireless ISP) flavour MT does not have (U)SIM card functionality therefore the IWU is used to inter-operate with the AAAH/HLR/HSS UMTS-HSS flavour MT has (U)SIM card functionality therefore the IW U will be used to inter-operate with the AAAH/HLR/HSS

User traffic

MAP

In the simplest case the IETF IWU may not exist.

Diameter/RAD HLR

HSS

November 2003


Slide 18


Submission

Control & User Plane Interworking

• WLAN becomes a ‘peer’ RAN to UTRAN– Similar status to GERAN for GSM/GPRS– Re-use many UMTS functions as is (e.g. idle mode?)

• Covers the complete security/mobility/QoS problem, using UTRA-like internal model

• Retains 3GPP Iu interface, mainly unmodified• Whole family of new WLAN related interfaces

– IurWLAN, IubWLAN – network internal– UuWLAN – extensions or changes to air interface

protocols (mainly in RLC layer)

November 2003


Slide 19


Submission

Architecture

• Similar interface methodology to UTRAN

• Can extend to very seamless UTRA-WLAN handover (dual mode terminals)

IWU RNC IWU

GGSN

SGSN SGSN SGSN

dual mode mobile

AP AP AP AP NODE B

NODE B

Iu Iu* Iur*/utr Iur*

Iub Iub* Iub*

Uu Uu*

November 2003


Slide 20


Submission

Implications• Strong dependencies on what mobile network

considered– Even on UMTS release number (R5, R6)

• Strong dependencies on WLAN technology• Simpler AN functionality – Core does much more

of the work• Significantly greater impact on WLAN and non-

WLAN standards (apparently)– Re-engineering of one to fit into the assumptions of the

other

November 2003


Slide 21


Submission

Architecture detail

November 2003


Slide 22


Submission

Interworking architecture

W2 W3AI

WLAN Functions

EaLa

Epa

EsLs

Lp

Attendant

ResourceMonitor

AuthoriserEp

WLAN

User CredentialStorage

MT

AccountingFunction

AuthenticationFunction

User Data Flow

Interface

Application

AuthorisationFunction

User DataForwarding Function

Authenticator

Ms

WLAN Technology

Standard Network Protocols

WLAN Technology

Standard Network Protocols

November 2003


Slide 23


Submission

802.11 Phy

802.11 MAC

802.1x/EAPoL

EAP

EAP Method

802.11 Phy

802.11 MAC

802.1x/EAPoL

EAP

Radius

IETF Transport

EAP

EAP Method

Radius

IETF Transport

Service providers netAPMT

WLAN AN

HL

2/H

iSW

AN

a80

2.11

i

GST/EAPoH

EAP

EAP Method

GST/EAPoH

EAP

Diameter

IETF Transport

EAP

EAP Method

Diameter

IETF Transport

Phy

DLC/RLC DLC/RLC

Phy

November 2003


Slide 24


Submission

Security Issues

• Working assumption to use EAP• Method for transport of EAP over air is defined• Support for SIM/USIM authentication required by

2G/3G operators– But also required that this is not the only mechanism– AKA extension (i-d) for mapping 2G/3G messages to

EAP

November 2003


Slide 25


Submission

Accounting and Charging• System level requirements :

– Basic access/session (pay by subscription)– Access/session duration– Credit card access/session/ Not real time pre paid– Calendar and time related charging – Duration dependent charging– Flat rate– Volume of transferred packet traffic – Multiple rate charge

• Useful features– Rate of transferred packet traffic (Vol/sec). – Toll free (like a 0800 call)– Premium rate access/session – Real time Pre-paid

November 2003


Slide 26


Submission

Inter-System Handover Issues• Inter-system handover is a very hard problem

– Weakly supported in loose coupling case• Basically network reselection by terminal• Terminal has to accept that it will get a new IP address with

implications for session continuity

– Possible in tight coupling case but very hard• IurWLAN very complex and interacts strongly with existing

equipment• Main gain comes from joint management of the radio resource

(but main pain also)

– MobileIP is always a fall-back (and near-transparent)– Affects only multi-mode terminals anyway– Need in public environment needs to be examined

November 2003


Slide 27


Submission

Quality of Service• If anything, can be even more complex than

security and mobility• Loose coupling approach leaves most options

open (TGe etc)• Tight coupling leverages UMTS QoS architecture • Need to distinguish carefully:

– What the operator wants to do– What the user wants to do– What the user’s applications are capable of doing

November 2003


Slide 28


Submission

Way Forward• 802 Handoff produces generic solution to

homogeneous and heterogeneous interworking.

• 802.11 Interworking group (?) studies specific problems related to Cellular interworking.

November 2003


Slide 29


Submission

Documents

WLAN – Cellular Interworking