Design Architectures for 3G and IEEE 802.11 WLAN Integration

7/28/2019 Design Architectures for 3G and IEEE 802.11 WLAN Integration

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P. Lorenz and P. Dini (Eds.): ICN 2005, LNCS 3421, pp. 10471054, 2005.

Springer-Verlag Berlin Heidelberg 2005

Design Architectures for 3G and IEEE 802.11

WLAN Integration

F. Siddiqui1, S. Zeadally 1, and E. Yaprak2

1 High Speed Networking Laboratory, Department of Computer Science,

Wayne State University, Detroit, MI 48202, USA{Farhan, Zeadally}@cs.wayne.edu

2 Division of Engineering Technology,

Wayne State University, Detroit, MI 48202, [email protected]

Abstract. Wireless LAN access networks show a strong potential in providing

a broadband complement to Third Generation cellular systems. 3G networks

provide a wider service area, and ubiquitous connectivity with low-speed data

rates. WLAN networks offer higher data rate but cover smaller areas. Integrat-

ing 3G and WLAN networks can offer subscribers high-speed wireless data ser-

vices as well as ubiquitous connectivity. The key issue involved in achieving

these objectives is the development of integration architectures of WLAN and

3G technologies. The choice of the integration point depends on a number offactors including handoff latency, mobility support, cost-performance benefit,

security, authentication, accounting and billing mechanisms. We review 3G-

WLAN integration architectures and investigate two such architectures in the

case when the UMTS network is connected to a WLAN network at different in-

tegration points, namely the SGSN and the GGSN. The evaluation of these in-

tegration architectures were conducted through experimental simulation tests

using OPNET.

1 Introduction

Mobile communications and wireless networks are developing at a rapid pace. Ad-

vanced techniques are emerging in both these disciplines. There exists a strong need

for integrating WLANs with 3G networks to develop hybrid mobile data networks

capable of ubiquitous data services and very high data rates in strategic locations

called hotspots. 3G wireless systems such as Universal Mobile Telecommunication

Systems (UMTS) can provide mobility over a large coverage area, but with relatively

low speeds of about 144 Kbits/sec. On the other hand, WLANs provide high speeddata services (up to 11 Mbits/sec with 802.11b) over a geographically smaller area.

The rest of this paper is organized as follows. Section 2 provides a brief background

on 3G and WLAN networks. Section 3 describes the related research and contribu-

tions of this work. Section 4 presents a comparison of the various internetworking ar-

chitectures. In section 5 we compare two integration architectures connecting UMTS


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1048 F. Siddiqui, S. Zeadally, and E. Yaprak

and 802.11 networks. Section 6 presents our simulation results. Finally in section 7

we present some concluding remarks and future works.

2 Background

802.11b [3] WLAN has been widely deployed in offices, homes and public hotspots

such as airports and hotels given its low cost, reasonable bandwidth (11Mbits/s), and

ease of deployment. However, a serious disadvantage of 802.11 is the small coverage

area (up to 100 meters) [5]. Other 802.11 standards include 802.11a and 802.11g

which allow bit rates of up to 54 Mbits/sec.

3G devices can transfer data at up to 384 Kbps. A 3G network (figure 1) consists

of three interacting domains- a Core Network (CN), Radio Access Network (RAN)

and the User Equipment (UE). 3G operation utilizes two standard suites: UMTS andCode Division Multiple Access (CDMA2000). The main function of the 3G core net-

work is to provide switching, routing for user traffic. The core network is divided into

Circuit-switched (CS) and Packet-switched (PS) domains. Circuit switched elements

include Mobile Services Switching Center (MSC), Visitor Location Register (VLR),

and gateway MSC. These circuit switched entities are common to both the UMTS as

well as the CDMA2000 standards. The differences in the CN with respect to the two

standards lie in the PS domain.

SGSN

PDSN

IP Network

Circuit switched

network

GGSN

3G Radio Access Network 3G Core Network

UE

UTRAN

cdma2000 RANBS

BS

BS

BS

RNC

PCF

MSC GMSC

HLR

Packet switched domain

Circuit switched domai n

UMTS

cdma2000

BS: Base station; UE: User equipment; RNC: Radio network controller

SGSN: Serving GPRS support node; GGSN: Gateway GPRS support node

PDSN: Packet data serving node; MSC: Mobile switching center

GMSC: Gateway mobile switching center; HLR: Home location register

RA N: Radi o A cces s N et wo rk U TRA N: U MTS Terres tri al RA Numts and

cdma2000

Fig. 1. Components of a 3G Network

GGSN is the gateway to external data networks and provides authentication and

IP-address allocation. SGSN provides session management. It also supports inter-

system handoff between mobile networks. PDSN incorporates numerous functions


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Design Architectures for 3G and IEEE 802.11 WLAN Integration 1049

within one node such as routing packets to the IP network, assignment of dynamic IP-

addresses and maintaining point-to-point protocol (PPP) sessions. The radio access

network provides the air interface access method for the UE. A CDMA2000 RAN

consists of a base station and 2 logical components- the Packet Control Function

(PCF) and the Radio Resources Control (RRC). The primary function of the PCF is toestablish, maintain and terminate connections to the PDSN.

3 Related Work and Contributions

A lot of recent works have focused on the design and evaluation of architectures to in-

tegrate 3G and WLAN networks. Buddhikot et al. [6] described the implementation of

a loosely coupled integrated network that provides roaming between 3G and WLAN

networks. Tsao et al. [7] presented another method to support roaming between 3Gand WLANs by introducing a new node called the virtual GPRS support node in be-

tween the WLAN and the UMTS networks. Tsao et al. [8] evaluated three different

internetworking strategies: the mobile IP approach, the gateway approach and the

emulator approach with respect to their handoff latencies. Bing et al. [9] discussed

mobile IP based vertical handoff management and its performance with respect to

signaling cost and handoff latency. All of the above works have focused on evaluating

integration architectures in terms of the handoff latency experienced by the users

when trying to move across 3G and WLAN networks while accessing a public net-

work such as the Internet. In contrast to the above related efforts, our work mainly fo-

cuses on the end-to-end delay experienced when users located in two different net-works, namely the IEEE 802.11b and the UMTS communicate with each other

directly. We describe two basic integration architectures that are used to connect these

networks. Through simulations, the end-to-end packet latencies experienced by users

when data is exchanged between these networks through the SGSN and the GGSN

nodes are recorded and verified using various types of applications. The results dem-

onstrate the feasibility of these integration architectures.

4 WLAN and 3G Cellular Data Network IntegrationArchitectures A Review

Table 1 reviews the various 3G-WLAN internetworking strategies and their features.

The Mobile IP [8] internetworking architecture allows easy deployment but suffers

from long handoff latency and might not be able to support real-time services and ap-

plications. The gateway approach [7] permits independent operation of the two net-

works and provides seamless roaming facility between them. The emulator approach

[8] is difficult to deploy since it requires combined ownership of the two networks but

does yield low handoff latency. Tight coupling [6] deploys WLAN as an alternativeradio access network and offers faster handoffs and high security but requires com-

bined ownership. Loose coupling [6] has low investment costs and permits independ-

ent deployment. However it suffers from high handoff delays. The choice of the inte-

gration architecture is important since multiple integration points exist with different

cost-performance benefits for different scenarios.


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Table 1. Comparison of various 3G-WLAN Internetworking Strategies

Internetworking

Approach

Deployment Network

ownership

Handoff

delay

Mobility

scheme

Mobile-IP Easy Separate High Mobile IP

Gateway Moderate Separate Low Roaming

agreement

Emulator Very diffi-

cult

Combined Low UMTS and

GPRS mobility

Tight Moderate Combined Low GPRS mobility

Loose Difficult Separate High Mobile-IP

5 Simulated Architectures

We evaluated via simulations using OPNET two internetworking architectures to

interoperate the 3G (UMTS) and WLAN networks by connecting them at two strate-

gic points- the SGSN node and the GGSN node as shown in figure 2.

RNC

BSUE

Internet

UMTSCore Network

UMTS RAN

UE: User Equipment

AP: Access Point

MN: Mobile Node

BS: Base station

SGSN: Serving GPRS support nodeGGSN: Gateway GPRS support node

VGSN: Virtual GPRS support node

RNC: Radio network controller

GW: Gateway

Wireless LAN

AP

MN

SGSN GGSN

Data flow via

SGSN

Data flow via

GGSN

Fig. 2. 3G-WLAN Integration a) SGSN b) GGSN

5.1 UMTS-WLAN Integration at the SGSN NodeWhen the UMTS and WLAN networks are connected through the SGSN node, the

WLAN network does not appear to the UMTS core network as an external packet

data network. Instead, it simply appears as another radio access network. The WLAN

AP in this case needs to have the capability of processing UMTS messages. Thus,

whenever a Mobile Node (MN) in the WLAN network wants to exchange data with


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the UMTS UE, it first needs to undergo the GMM attach procedure to notify the

SGSN of the location on the communicating node and also to establish a packet-

switched signaling connection. The WLAN AP is responsible for sending these re-

quest messages to the SGSN on behalf of the WLAN MN. The GMM attach proce-

dure is a three-way handshake between the MN, RNC and the SGSN. Upon comple-tion of this procedure, the WLAN MN is authenticated into the UMTS network.

5.2 UMTS-WLAN Integration at the GGSN Node

In this type of integration, whenever a MN in a WLAN network wants to communi-

cate with a UE in the UMTS network, it does so through the GGSN node. The UE in

the UMTS network first activates the Packet Data Protocol (PDP) context that it

wants to use. This operation makes the UE known to its GGSN and to the external

data networks, in this case, the WLAN network. User data is transferred transparentlybetween the UE and the WLAN network with a method known as encapsulation and

tunneling. The protocol that takes care of this is the GPRS Tunneling Protocol (GTP).

For this kind of internetworking configuration, the WLAN AP is a simple 802.11b ac-

cess point and does not need to process UMTS messages.

5.3 Simulation Testbed

A network simulation model was constructed using OPNET 10.0.A [10]. OPNET is a

discrete event simulator with a sophisticated software package capable of supporting

simulation and performance evaluation of communication networks and distributedsystems.

Table 2. Descriptions of various applications tested

Application QoS Class Measurement

(seconds)

Size Proocol

FTP Background File download

time

100-1000 Ki-

lobytes

TCP

FTP Background File upload time 100-1000 Ki-lobytes

TCP

GSM encoded

voice

Conversa-

tional

End-to-end delay 33 Bytes UDP

GSM encoded

voice

Conversa-

tional

Jitter 33 Bytes UDP

HTTP Web

browsing

Interactive Page response

time

3000 Bytes TCP

The simulation environment we used had a UMTS network connected to a WLANnetwork. The UMTS network was composed of the RAN and a packet-based CN with

SGSN and GGSN nodes The WLAN network is composed of 802.11b wireless MNs

configured in Infrastructure Basic Service Set mode. In the GGSN integration case, a

simple WLAN access point was used, while in the SGSN integration case, a different

access point with additional capability of processing UMTS messages was employed.


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The goal of the simulations was to compare the delays involved when user data is ex-

changed between the UMTS and WLAN networks connected via two methods,

namely GGSN and SGSN. Different types of traffic was generated using four differ-

ent applications including Voice over IP (VoIP) t, FTP, and HTTP (web browsing) as

shown in table 2. These applications correspond to the various UMTS QoS classes-Conversational class for real time flows such as VoIP, interactive and background

classes for FTP and HTTP respectively. Packet delay, jitter, upload, and download re-

sponse times were measured. Other parameters associated with each application are

summarized in table 2.

6 Simulation Results and Discussion

Simulations performed for both UDP and TCP flows are presented. For the UDP flow(VoIP traffic), end-to-end packet delays and jitter were measured. For TCP flows

(FTP, HTTP) the upload/download response times were measured.

FTP: File upload Response Time

0

1

2

3

4

5

6

7

8

100 200 300 400 500 600 700 800 900 1000

File Size (KB)

Upload

Tim

e

(seconds)

GGSN

SGSN

Voice Packet End-to-end delay

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

100

700

1300

1900

2500

3100

3700

Simulation Run-Time (se conds)

En

d-to-end

delay

(s

econd

s) GGSN

SGSN

Fig. 3. Application Response Times: a) FTP Upload b) VoIP delay

Figure 3a shows the simulation run-times corresponding to the average file uploadtimes experienced when transferring files of various sizes between the UE and the

WLAN MN under two different integration scenarios. In figures 3b and 4a the aver-

age delay and jitter for voice is presented. It is observed that both, delay and jitter

values are much lower in the GGSN case. Similarly, figure 4b shows the response

time to access a web page of size 3000 bytes. As figure 4b illustrates, the page re-sponse time is initially high and then decreases as the simulation progresses. We

speculate that this reduction in the page response time may be because the web

servers cache is initially empty and the first few page requests will cause the page to

be fetched from the disk resulting in a high response time. As the more requests are

generated with time, the cache is being filled and there is an increasing probability


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that one or more requests can be satisfied by the cache thereby reducing the overall

page response time.

Voice Jitter

0

0.05

0.1

0.15

0.2

0.25

0.3

100

700

1300

1900

2500

3100

3700

Sim ulation Run-Time (se conds)

Jitter(seconds)

GGSN

SGSN

HTTP Page Response Time

0

5

10

15

20

25

30

35

100

700

1300

1900

2500

3100

3700

Simulation Run-Time (se conds)

P

ageresponsetim

e

(seconds)

GGSN

SGSN

Fig. 4. Application Response Times: a) VoIP Jitter b) HTTP Page Response time

The simulation results reveal that the application response time (delay) is consis-

tently higher in the case where the UMTS and WLAN networks are connectedthrough the SGSN node, as compared to the case where the two networks are con-

nected at the GGSN. This higher response time can be attributed to the additional

processing time required at the WLAN access point in the first case. When the two

networks are connected at the SGSN node. The WLAN access point performs the

functions of a RNC on as well as a WLAN AP. Therefore, it has to perform the addi-

tional initialization steps to authenticate the WLAN MN to the UMTS network

(GMM Attach procedure and PDP context activations). When integration is done at

the GGSN node, the WLAN AP is a simple 802.11b access point and does not require

any special capabilities to process UMTS messages. Data packets are transferred be-tween the UE and the WLAN network using encapsulation by the GPRS tunneling

protocol. This reduces the packet latency as there is no additional delay due UMTS

initialization procedures or packet conversions.

The advantages, however, of using SGSN integration scheme include the reuse of

UMTS authentication, authorization, accounting (AAA) mechanisms, usage of com-

mon subscriber databases and billing systems, increased security features (since the

UMTS security mechanisms are reused), as well as possibility of having continuous

sessions as users move across the two networks, since the handoff in this case is very

similar to an intra-UMTS handoff as the WLAN AP appears as another RNC to theSGSN node. In the case of GGSN integration, since the WLAN is considered to be an

external network, different billing and security mechanisms are needed. Service dis-

ruption is also possible during a handoff from one network to another.


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7 Conclusions

In this paper we discussed the architecture and performance of a 3G-WLAN inte-

grated system connected at two different points namely the SGSN and GGSN. The

architectures were evaluated with respect to the end-to-end latency, jitter and upload

times obtained when data is exchanged between nodes located in the UMTS and

WLAN networks respectively. Our simulation results show that the overall delays are

much lower when the data exchange is done through the GGSN node as compared to

when the networks are connected through the SGSN node. Traffic passage through

the GGSN is faster due to simple encapsulation procedure employed by the GPRS

tunneling protocol. However, SGSN integration has its own advantages of providing

strong security, common billing, authentication, etc. Our future work focuses on

evaluating these integration schemes with respect to the handoff latency and the de-

velopment of an architecture that provides seamless session mobility when MNsmove across the 3G and WLAN networks.

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Design Architectures for 3G and IEEE 802.11 WLAN Integration