Transcript WLAN-GPRS Integration for Next-Generation Mobile Data Network

WLAN-GPRS Integration
for Next-Generation
Mobile Data Network
Apostolis K. Salkintzis, Chad Fors, and Rajesh Pazhyannur
Motorola
IEEE Wireless Communications Magazine
October 2002
報告人:李偉晟
18 / 6 / 2003
1
Outline
• Motivation
• The general aspects of integrated
WLAN-cellular network
• Interworking architecture
 Tight Couple Architecture
 Loose Couple Architecture
• Conclusion
2
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.
3
The general aspects of integrated
WLAN-cellular network
• Who owns the WLAN?
 Cellular operator
 Wireless Internet Service Provider(WISP)
• Session Mobility
4
Interworking Architecture
• The Tight Couple Architecture
• The Loose Couple Architecture
HLR
Loose coupling
point
Gr
Gc
Mobiel
station
MS
Iu-ps
UTRAN
Gi
SGSN
Uu
MS
Um
GRPS
RAN
Gb
Gn/p
GGSN
External
Packet data
network
Gn/p
SGSN
Tight coupling
point
HLR:Home location register
SGSN:Serving GPRS support node
GGSN: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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Radio
Access
Network
(UTRAN/
GPRS
RAN)
Feature
Servers
HLR
(AuC)
Operator's IP
network
GPRS core
SGSN
Internet
GGSN
Firewall
CG
Billing mediator
Gb
48-bit
802 MAC GIF
address
Billing system
WLAN network
Distribution system
AP
Dual mode
MS
All mobile
terminals
and the GIF
use MAC
address
Beacon (SSID)
BSS-1
Beacon (SSID)
BSS-2
Beacon (SSID)
BSS-3
GIF:GPRS Interworking function
CG:Charging gateway
HLR:Home location register
AuC:Authentication center
SGSN:Serving GPRS support node
GGSN:Gateway GPRS support node
BSS:Basic service set
AP:Access point
802.11 standar service set(ESS)
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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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WLAN access network
Defined by 802.11
Dual-mode MS
WLAN
Adaptation
Function
(WAF)
LLC
WLAN
access
network
WLAN
radio
subsystem
GPRS
radio
subsystem
GPRS
Interworking
Function
(GIF)
Um
GPRS
access
network
Gb
GPRS
core
network
Gb
New interworking componets
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Protocol Architecture
User data
GMM/SM
SNDCP
SGSN
LLC
WAF
WAF
BSSGP
NS
RLC/MAC
802.11 MAC
802.11 MAC
GPRS PHY
802.11 X PHY
802.11 X PHY
802.3 MAC
10Base-T
or other
802.3 MAC
FR
10Base-T
or other
PHY
(e.g. G.703/704)
Um
Dual-mode MS
Gb
Access point
GPRS interworking
Function (GIF)
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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 5.Discovery
Procedure
Then the
Start
1. MS’s WAF
send
Discovery
Request
,SA=MS
,DA=Broadcast
,IMSI
2. Data is
directed to
the AP
with BSSID
GIF's WAF
Responds
Discovery
Response
,GIF's MAC
Address,
WLAN's RAI
6. The
MS receives
this response
, stores the GIF
address and
the RAI
7. The
4. The GIF
receive
this message
,associate
the IMSI
with the MS's
MAC address
MS notifies
the GMM
layer that
the current
GPRS RA
has changed
8. The GMM
3. The AP
broadcast
this message
to the DS
layer notifies
the SGSN that
the 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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Radio
Access
Network
(UTRAN/
GPRS
RAN)
CAG
HLR
(AuC)
GPRS core
FA
Operator's IP
network
Internet
Firewall
GGSN
SGSN
Feature
Servers
HA
CG
Billing mediator
Billing system
WLAN network
FA
Firewall
AAA
Dual mode
MS
AP
CAG:Cellular acess gateway
CG:Charging gateway
HLR:Home location register
AuC:Authentication center
SGSN:Serving GPRS support node
GGSN:Gateway GPRS support node
AAA:Authentication, authorization, accounting
FA:Foreign agent
HA:Home agent
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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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AP
MS
CAG
(AAA server)
HLR
1. EAPOW-start
2. EAPOW-request/identity
3. EAPOW -response/identity
(IMSI)
4. RADIUS access-request
(IMSI)
5. Send authentication info
6. Send authentication info ack
7. RADIUS access-challenge
8. EAP-request(RAND)
RAND
XRES
9. EAP-response(SRES)
[Signed Result]
10. RADIUS access-request
11. RADIUS access-accept
if XRES == SRES
12. EAP-sucess
13. EAP-key
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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.)
Start
When the MS
move from one
system to another
system
The MS performs
a MIP
registeration via
the FA
The FA then
associates the
care-of address
with that of the
MS
The FA acts as
the proxy on
behalf of the MS
for the life of the
registeration
The FA provides
a care-of address
to the HA to
completes the
registeration
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 !
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