Analysis of Interworking Architectures for IP Multimedia Subsystem

Transcription

1 Analysis of Interworking Architectures for IP Multimedia Subsystem by Arslan Munir B.Sc., Electrical Engineering, University of Engineering and Technology, Lahore, 2004 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Applied Science in The Faculty of Graduate Studies (in Electrical and Computer Engineering) The University of British Columbia April 2007 c Arslan Munir 2007

2 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. (Signature) Electrical and Computer Engineering The University of British Columbia Vancouver, Canada Date

3 Abstract The future fourth generation wireless heterogeneous networks aim to integrate various wireless access technologies and to support the IMS (IP multimedia subsystem) sessions. In the first part of this thesis, we propose the Loosely Coupled Satellite-Cellular- WiMax-WLAN (LCSCW2) and the Tightly Coupled Satellite-Cellular-WiMax-WLAN (TCSCW2) interworking architectures. The LCSCW2 and TCSCW2 architectures use the loosely coupling and tightly coupling approach respectively and both of them integrate the satellite networks, 3rd generation (3G) wireless networks, worldwide interoperability for microwave access (WiMax), and wireless local area networks (WLANs). They can support IMS sessions and provide global coverage. The LCSCW2 architecture facilitates independent deployment and traffic engineering of various access networks. The TCSCW2 can guarantee quality of service (QoS) to a certain extent. We also propose an analytical model to determine the associate cost for the signaling and data traffic for inter-system communication in the LCSCW2 and TCSCW2 architectures. The cost analysis includes the transmission, processing, and queueing costs at various entities. Numerical results are presented for different arrival rates and session lengths. In the second part of this thesis, the signaling flows for IMS registration, IMS session establishment ii

4 Abstract and IMS session re-establishment procedure after undergoing a vertical handoff in a 4G environment are analyzed. Signaling delays are calculated for IMS signaling taking into account transmission, processing and queueing delays at network entities. The proposed analysis of the IMS signaling flows is independent of a particular access network technology and interworking architecture and can be applied to any of the access network technology and 4G interworking architecture. iii

5 Table of Contents Abstract ii Table of Contents iv List of Tables vii List of Figures viii List of Acronyms x Acknowledgements xvii 1 Introduction Motivations Contributions Structure of the Thesis Related Work Literature Survey Discussions iv

6 Table of Contents 2.3 4G Interworking Architectures Tightly Coupled (TC) Interworking Architecture Loosely Coupled (LC) Interworking Architecture Hybrid Coupled (HC) Interworking Architecture The TCDRAS Interworking Architecture The LCDRAS Interworking Architecture LCSCW2 and TCSCW2: Architectures for IP Multimedia Subsystem The LCSCW2 Architecture The TCSCW2 Architecture An Analytical Model for Cost Analysis Available Paths for Communications Transmission Cost Processing Cost Queueing Cost Numerical Results Summary Analysis of SIP-based Signaling for IMS Sessions in 4G Networks Delay Analysis of IMS Signaling Procedures Transmission Delay Processing Delay v

7 Table of Contents Queueing Delay Total Delay IMS Registration Procedure Delay IMS Session Setup Delay IMS Session Re-establishment Delay Numerical Results Summary Bibliography vi

8 List of Tables 4.1 Size of SIP messages involved in IMS signaling Values of K for signaling messages in different channel rates vii

9 List of Figures 2.1 Tightly Coupled interworking architecture Loosely Coupled interworking architecture Hybrid Coupled interworking architecture The TCDRAS interworking architecture The LCDRAS interworking architecture The LCSCW2 interworking architecture The TCSCW2 interworking architecture Signaling and data communication paths in the LCSCW2 architecture Signaling and data communication paths in the TCSCW2 architecture The breakup of system signaling cost in the LCSCW2 architecture The breakup of system signaling cost in the TCSCW2 architecture Effect of varying arrival rate on system signaling cost Effect of varying arrival rate on system data cost Effect of varying session duration on system data cost GPRS attach procedure viii

10 List of Figures 4.2 PDP context activation procedure DHCP registration process IMS registration process IMS session setup procedure IMS registration for fixed λ and p Session setup when SN is in 3G and CN is in WLAN for fixed λ and p Session setup when SN and CN are in 3G for fixed λ and p Session setup when SN and CN are in WLAN for fixed λ and p Session re-establishment when SN in 3G and CN in WLAN for fixed λ and p Session re-establishment when SN and CN are in 3G for fixed λ and p Session re-establishment when SN in WLAN and CN in 3G for fixed λ and p Session re-establishment when SN and CN are in WLAN for fixed λ and p Effect of changing λ on IMS registration delay for fixed p Effect of changing λ on IMS session setup delay for fixed p Effect of changing λ on IMS session re-establishment delay for fixed p Effect of changing p on IMS registration delay for fixed λ Effect of changing p on IMS session setup delay for fixed λ Effect of changing p on IMS session re-establishment delay for fixed λ.. 81 ix

11 List of Acronyms 3G Third Generation 3GPP 3rd Generation Partnership Project AAA Authentication, Authorization and Accounting AN Access Network AP Access Point ARG Access Router and Gateway AS Access Stratum BER Bit Error Rate BS Base Station BSC Base Station Controller CBR Constant Bit Rate CDMA Code Division Multiple Access x

12 List of Acronyms CN Correspondent Node DAD Duplicate Address Detection DHCP Dynamic Host Configuration Protocol DNS Domain Name System DS Differentiated Services DSCP Differentiated Services Code Point EAP Extensible Authentication Protocol EIR Equipment Identification Register GHSN Gateway Hotspot network Support Node GGSN Gateway GPRS Support Node GPRS General Packet Radio Service GSM Global System for Mobile Communications HARQ Hybrid Automatic Request HC Hybrid Coupled HCSCW2 Hybrid Coupled Satellite-Cellular-WiMax-WLAN HLR Home Location Register xi

13 List of Acronyms HNAC Hotspot Network Area Controller HSS Home Subscriber Server I-CSCF Interrogating-Call Session Control Function IETF Internet Engineering Task Force IM Island Manager IMS IP Multimedia Subsystem IP Internet Protocol IPSec IP Security ISDN Integrated Services Digital Network ISL Inter-Satellite Link ISUP ISDN User Part LCDRAS Loosely Coupled with Direct Radio Access System LCSCW2 Loosely Coupled Satellite-Cellular-WiMax-WLAN MAC Medium Access Control MGCF Media Gateway Control Function xii

14 List of Acronyms MGW Media Gateway MT Mobile Terminal NAS Non Access Stratum NAT Network Address Translation OBP On-board Processing PCF Packet Control Function PCS Personal Communication Services P-CSCF Proxy-Call Session Control Function PDCH Packet Data Channels PDG Packet Data Gateway PDP Packet Data Protocol PDSN Packet Data Serving Node PDU Packet Data Unit PIM-SM Protocol-Independent Multicast Sparse Mode PLMN Public Land Mobile Network PS Packet Switched xiii

15 List of Acronyms PSTN Public Switched Telephone Network QoS Quality of Service RA Routing Area RB Radio Bearer RLC-AM Radio Link Control-Acknowledged Mode RNC Radio Network Controller RTO Retransmission Time Out RTT Round Trip Time R-UIM Removable-User Identity Module S3GIF Satellite-3G Interworking Function SigComp Signaling Compression S-CSCF Serving-Call Session Control Function SFES Satellite Fixed Earth Station SGSN Serving GPRS Support Node SGW Signaling Gateway SIM Subscriber Identity Module xiv

16 List of Acronyms SIP Session Initiation Protocol SLA Service Level Agreement SMS Short Messaging Service SN Source Node SS7 Signaling System Number 7 SSB Satellite Spot Beam S-UMTS Satellite-UMTS TC Tightly Coupled TCDRAS Tightly Coupled with Direct Radio Access System TCP Transmission Control Protocol TCSCW2 Tightly Coupled Satellite-Cellular-WiMax-WLAN TE Terminal Equipment ToS Type of Service UDP User Datagram Protocol UE User Equipment xv

17 List of Acronyms UMTS Universal Mobile Telecommunications System USIM Universal Subscriber Identity Module VBR Variable Bit Rate VoIP Voice over IP WGDCT WLAN to 3G Direct Controller and Transceiver WAG Wireless Access Gateway WBSC WiMax Base Station Controller WiMax Worldwide Interoperability for Microwave Access WIF WLAN-3G Interworking Function WLAN Wireless Local Area Network WMIF WiMax-3G Interworking Function WNC WiMax Network Controller xvi

18 Acknowledgements I would like to express my sincere gratitude to my graduate supervisor Dr. Vincent Wong for his guidance and support during the course of my graduate studies. I sincerely appreciate the considerable amount of time and effort he invested in helping me with my research and thesis. I would like to thank my fellow colleagues, particularly Syed Hussain Ali, Enrique Stevens-Navarro, and Ehsan Bayaki, who have provided helpful suggestions along the way. I also acknowledge Dr. Vikram Krishnamurthy whose guidance and suggestions helped me to improve the overall horizon of my knowledge. This work is supported by Bell Canada and Natural Sciences and Engineering Research Council of Canada under project grant xvii

19 Chapter 1 Introduction The 4th generation (4G) wireless heterogeneous networks are envisioned as the integration of various wireless access technologies such as wireless local area network (WLAN), 3rd generation (3G) technologies including universal mobile telecommunications system (UMTS) and code division multiple access (CDMA) based CDMA2000 system, worldwide interoperability for microwave access (WiMax), and satellite networks. The aim behind this integration is to provide the users with global coverage and to provide the users with the capability to switch between different available access networks (ANs). The success of the 4G wireless heterogeneous networks depends on the successful integration of the currently available ANs. The IP multimedia subsystem (IMS) is standardized by the 3rd generation partnership project (3GPP) and 3GPP2 as a new core network domain [1]. The IMS enables the provision of internet protocol (IP) based multimedia applications to mobile users, guarantees quality of service (QoS) across different AN technologies and permits service providers to charge according to different policies. In addition, the IMS enables thirdparty vendors to develop new applications for operators and users. A growing number of telecommunication vendors are beginning to release devices and services based on the 1

20 Chapter 1. Introduction IMS [2]. 1.1 Motivations Although, some 4G interworking architectures have been proposed before which integrate 3G and WLAN or 3G and satellite networks or 3G and WiMax individually, to the best of our knowledge, a 4G interworking architecture that integrates satellite, WiMax, and WLAN with the 3G network has not been proposed so far. Additionally, the IMS infrastructure has not been incorporated in the previously proposed interworking architectures. The research related to performance evaluation of the interworking architectures so far either analyzes the performance or cost for signaling traffic or data traffic. Little or no work has been done before that evaluates the system performance for both signaling and data. Also a comprehensive cost analysis taking into account the transmission, processing and queueing costs of traffic in the interworking architectures has not been done before. 1.2 Contributions The main contributions of this thesis are given below: This thesis provides a comprehensive view of the 4G interworking architectures proposed so far. The pros and cons associated with each of the interworking architectures are discussed in this thesis. The previously proposed interworking architectures in the literature have been modified for the successful incorporation of 2

21 Chapter 1. Introduction IMS infrastructure. The thesis proposes two novel 4G interworking architectures namely the Loosely Coupled Satellite-Cellular-WiMax-WLAN (LCSCW2) architecture and the Tightly Coupled Satellite-Cellular-WiMax-WLAN (TCSCW2) architecture based on loosely coupled and tightly coupled paradigms respectively. The IMS has been given special consideration in the proposed interworking architectures. The proposed architectures integrate 3G, WiMax, WLAN, and satellite networks. We also propose a cost analysis model for the signaling and data traffic for intersystem communication in the proposed interworking architectures. The cost analysis includes the transmission, processing and queueing costs at various network entities. Our analysis takes into account both signaling and data traffic and describes the effect of changing traffic characteristics such as arrival rates and IMS session duration on system cost. The cost analysis will be of significance for the service providers to analyze the individual network elements as well as the proposed architectures comprehensively. This thesis analyzes the signaling flows involved in the IMS session establishment and registration considering signaling compression (SigComp) for reducing the delay. It analyzes different scenarios for IMS session re-establishment after vertical handoff in a 4G environment. 3

22 Chapter 1. Introduction 1.3 Structure of the Thesis This thesis is structured as follows. In Chapter 2, related work and the 4G interworking architectures previously proposed are described. Chapter 3 describes our proposed LCSCW2 and TCSCW2 interworking architectures. Chapter 4 presents the analysis of SIP-based signaling for IMS sessions in the 4G networks. Chapter 5 summarizes the main contributions of the thesis, and explains future trends in the area. 4

23 Chapter 2 Related Work 2.1 Literature Survey In this section, we begin by describing the previously done work in the area. Two WLAN- 3G interworking architectures have been described in [3]. One architecture can provide 3G-based access control and charging whereas the other can provide 3G-based access control and charging as well as access to 3G packet switched (PS) based services. Additionally, authentication, authorization, and accounting (AAA) signaling required for the two discussed architectures is given. An integrated UMTS IMS architecture is presented in [4] and the signaling flows for IP multimedia session control are described. The paper emphasizes the point that when multiple media types are involved in a session e.g. video and audio, synchronization is essential for simultaneous presentation of media types to the user. The IMS media gateway (MGW) is responsible for media signals translation between different formats when IMS session is established between two different ANs. The IMS media gateway is controlled by the media gateway control function (MGCF) which provides application-level signaling translation, for eg. between session initiation protocol (SIP) and integrated services digital network (ISDN) user part (ISUP) signal- 5

24 Chapter 2. Related Work ing which is the case when one AN is public switched telephone network (PSTN) and the other is UMTS. The signaling gateway (SGW) performs the transport-level signaling translation between IP-based and SS7-based transport. The performance evaluation of three UMTS-WLAN interworking strategies namely mobile IP approach, gateway approach, and emulator approach has been done in [5] and the signaling flows for UMTS to WLAN and WLAN to UMTS handover are given for the three strategies. The mobile IP approach introduces mobile IP to the two networks. Mobile IP mechanisms are implemented in the mobile nodes and on the UMTS and WLAN network devices. This approach provides IP mobility for the roaming between UMTS and WLAN. The gateway approach introduces a new logical node that connects the two wireless networks. The node exchanges necessary information between the networks, converts signals, and forwards the packets for the roaming users. Through this approach, the handoff delay and packet loss can be reduced. The emulator approach uses WLAN as an access stratum in the UMTS network. It replaces the UMTS access stratum by the WLAN layer one and layer two. A WLAN access point (AP) can be viewed as SGSN. The advantage of this approach is that mobile IP is no longer required. All packet routing and forwarding are processed by UMTS core network. The packet loss and delay can be significantly reduced by this approach. The voice over IP (VoIP) performance in 3G-WLAN interworking system with IP security (IPSec) tunnel between packet data gateway (PDG) and user equipment (UE) is evaluated in [6]. The performance metrics considered are packet inter-arrival time, 6

25 Chapter 2. Related Work data transmission rate, end-to-end delay, and packet loss. The user mobility in and out of WLAN is considered and its effect on end-to-end delay is discussed. It is observed that as the number of VoIP connections at the AP increases, the delay increases to an unacceptable level and the performance of all VoIP connections in that particular AP degrades drastically because the AP is unable to poll all the clients in the point coordination function mode. A 3GPP-WLAN interworking architecture in which subscriber identity module (SIM)-based authentication is used is described in [7]. Data routing is described for a user in WLAN accessing IP-based services in some external network. Charging infrastructure for 3GPP-WLAN interworking architecture is described. RADIUS, DIAM- ETER, and extensible authentication protocol (EAP) are discussed for authentication purposes in the interworked architecture. An interworking architecture is proposed in [8] in which the general packet radio service (GPRS) network is available all the time forming a primary network and WLANs are used as a complement when they are available. The control part never leaves the UMTS and hence there is no need for control procedures in the WLAN i.e. paging and assignment of cell or routing area identifiers. With the proposed architecture, IP sessions can be maintained in the hotspot network dark areas and short messaging service (SMS) can be accessed via WLAN. In the proposed architecture, no core network interfaces are exposed to the exterior of the core and hence ensures security. With the proposed architecture, no information is ever lost in handovers because the hotspot network area controller (HNAC) will transmit the packet again through the other interface. 7

26 Chapter 2. Related Work The loose coupling and tight coupling interworking architectures are discussed in [9]. It is discussed that the UE is made up of two disjoint entities, i.e. terminal equipment (TE) and mobile terminal (MT) according to 3GPP specifications. Different scenarios in UMTS-WLAN interworking are described. The one is that in which WLAN gateway is responsible for both the non access stratum (NAS) and access stratum (AS) signaling. The other is that in which the TE handles the NAS signaling. Another one is that in which nodes can be configured in ad-hoc mode and communicate with one another directly and the gateway is required only for accessing UMTS services. An architecture for integrating CDMA2000 and WLAN is presented in [10]. The architecture is tightly coupled since it proposes the re-use of PDSN of CDMA2000 network for WLAN traffic forwarding as well. The signaling flows when the UE is powered up in a WLAN, and CDMA2000 to WLAN handover procedure are given. The possibility of integration of satellite with terrestrial systems has been discussed in [11]. It is pointed out that satellite coverage can work alone in air and sea but the success of the satellite systems in land areas lies in their integration with terrestrial systems. On-board Processing (OBP) enables satellite systems to interconnect satellite spot beams (SSBs) and allows variable bandwidth channels. OBP allows dynamic routing between various spot beams and provides support for real-time applications such as VoIP and multiparty conference services. Satellites can be interconnected in an orbit via Inter- Satellite Link (ISL). One SSB covers many 3G cells and is suitable for high velocity users. In the satellite-3g integrated system, the number of handoffs for a fast moving user will 8

27 Chapter 2. Related Work be minimized and hence the probability of handoff call dropping. Integrated satellite-3g system can be used to offload congestion in the 3G network by handing off the users from 3G to satellite system. The footprints of SSBs cover many cellular cells and provides a pool of channels to be shared by these cells. The idea of using satellite capacity to mitigate congestion in areas served by terrestrial network has been explained in [12]. The paper evaluates the performance of the satellite-terrestrial integrated system by considering a one-dimensional analytical model of a cellular system overlaid with satellite footprints. The paper also simulates planar cellular network with satellite spot beam coverage support. It is shown that the integrated system can improve Erlang-B blocking performance. The SIP based session setup signaling for Satellite-UMTS (S-UMTS) is discussed in [13] based on the current radio link control acknowledged mode (RLC-AM). The paper proposes two schemes to reduce the inefficiency of the current RLC-AM mechanism for session setup over S-UMTS. The first scheme can recover the missing last radio segments in a single round trip time and the second scheme can reduce the redundant transmissions which occur due to multiple feedback triggers. An architecture for multiparty conferencing over satellites is described in [14]. A SIP-based conference signaling and an extension to protocol independent multicast-sparse Mode (PIM-SM) that supports QoS in DiffServ networks is proposed. A satellite emulator is used to obtain the results of user perceived QoS, signaling delay, and jitter. It is observed that the delay at 75 % background traffic is longer than that at 25 % background traffic before the activation of QoS mechanisms but it becomes the 9

28 Chapter 2. Related Work same after the activation of QoS mechanisms. An S-UMTS architecture is presented in [15] and possible signaling flows for registration, call handling and handover are given. It is discussed that for UE initiated calls, the satellite earth station allocates the resources which are one or more packet data channels (PDCH) that are shared by the users covered by a SSB. The signaling flows for conference creation over S-UMTS are described in [16] and a simulation model is presented for S-UMTS. The results show that the conference creation delay increases with the increasing block error rate and the resource reservation delay is the main contributing factor in the total delay. Also, use of packet data units (PDUs) of large size reduces the block error probability and hence the delay. An overview of WiMax/IEEE is provided in [17]. The paper mentions the achievable throughput of WiMax and suggest some enhancements to the IEEE standard that have the potential of achieving higher data rates. An architecture for UMTS-WiMax interworking is proposed in [18] and signaling flows of handover from WiMax to UMTS access network and vice versa are given. The paper describes the difference between UMTS-WLAN interworking and UMTS-WiMax interworking. The UMTS and WLAN are fully overlapped because when a UE is connected to WLAN, it can maintain simultaneous connection to the UMTS network. The UMTS and WiMax are partially overlapped because WiMax coverage area is in order of UMTS coverage area and simultaneous connection to the two ANs is not possible at all the times. In [19], an architecture is proposed for integration of WiMax and UMTS based on loosely-coupled approach. A mapping is provided between the QoS classes in UMTS and WiMax. The 10

29 Chapter 2. Related Work paper examines the throughput for constant bit rate (CBR) voice application and variable bit rate (VBR) video application via simulations. The cost analysis has been used as a means of performance evaluation in [20, 21, 22, 23, 24, 25, 26, 27, 28]. The signaling efficiency for call setup in IMS infrastructures using CDMA2000 is analyzed in [29]. Signaling flows involved in call establishment procedure are shown. It is assumed that both the SN and the CN are in CDMA2000 system. The effect of early termination due to the hybrid automatic request (HARQ) algorithm is considered in the forward link. Four call setup scenarios are considered. The first one is TCP based; the second assumes additional encoding of SIP messages apart from SigComp so that every SIP packet fits in 1 single radio frame; the third assumes that P-CSCF of caller can directly communicate with the callee P-CSCF; the fourth one uses a variation of UDP in which UDP with retransmission time out (RTO) is used, moreover RTO value is set equal to round trip time (RTT) value. The SIP session setup delay for VoIP service in 3G wireless networks is studied in [30, 31]. An adaptive retransmission timer is considered for retransmission of lost packets at the application layer. The effect of TCP, UDP, and RLP is considered on SIP session setup for VoIP. Performance of SIPbased vertical handoff is analyzed in [32]. Signaling flows are given for GPRS attach procedure, PDP context activation procedure, SIP-based mid-call terminal mobility, and DHCP registration procedure. Analytical expressions for delay of SIP-based handoff to UMTS network from another UMTS network or a WLAN as well as SIP-based handoff to WLAN network from another WLAN or a UMTS network are given. SIP-based mobility 11

30 Chapter 2. Related Work in IPv6 is described in [33]. The paper closely examines the delay incurred when a UE moves to a new link and performs the duplicate address detection (DAD) and router selection. It is shown that intelligent modifications to IPv6 Linux kernel implementation achieve a faster handoff in SIP-based terminal mobility as compared to unaltered Linux kernel. 2.2 Discussions The paper [3] is a kind of survey with no analytical model, simulation or numerical results to evaluate the proposed architectures. In the integrated UMTS IMS architecture proposed in [4], no analytical modeling is done depicting IP multimedia session establishment. Also, no consideration is given to the establishment of IMS sessions in an interworking environment. Different scenarios in the 3GPP specifications for WLAN-3G integration are discussed in [34]. Also, the tight coupling and loose coupling architecture are discussed. However, the performance evaluation of the interworking architectures is missing. The architectural details of the three discussed UMTS-WLAN interworking approaches in [5] are not very clear. In the mobile IP approach, since the user device is required to send the registration back to its home network; packet delay and loss are problems for the handover. In the gateway approach, the implementation of the newly introduced node may not be a trivial task. The emulator approach lacks the flexibility since two networks are tightly coupled. Another disadvantage of this approach is that the GGSN will be the only point to reach the Internet, and hence the GGSN be- 12

31 Chapter 2. Related Work comes bottleneck. Only handover delay for the three architectures is considered and other performance metrics are ignored. It has not been indicated which simulator is used for implementing the three interworked network architectures. Additionally, details for implementation in the used simulator are missing. A practical implementation of the system is considered in [6] but unfortunately no detail is provided about the practical implementation of the network entities. Only UEs in WLAN are considered and core UMTS network and users in UMTS environment are not considered. The signaling messages for authentication and/or charging are not discussed for the architecture proposed in [7]. Again, the core UMTS network is missing in the discussed architecture. The paper is a survey with no analytical modeling, simulation or numerical results to support the ideas presented. In the interworking architecture proposed in [8], several new components such as island manager (IM), HNAC, and gateway hotspot network support node (GHSN) are introduced and hence complexity is added to the network. GPRS radio interface always needs to be active and hence causes an increase in power consumption of the UE battery. Simulation do not model many components such as base station (BS), gateway GPRS support node (GGSN), and AAA server. Also wireless link signaling between UE and AP of WLAN and BS of UMTS network is not modeled. The paper [9] is only a survey and no analytical model, numerical or simulation results are given. The open issues in 3GPP standardization are not pointed effectively. It may be more interesting to discuss challenges involved in the execution of multimedia services in the interworking architectures. The architecture proposed in [10] is based on 13

32 Chapter 2. Related Work tightly coupled approach. The performance of the proposed architecture is not evaluated by any means. The details of the proposed integrated satellite-terrestrial architecture in [11] are missing and also the performance is not evaluated by any means. It is not outlined in the paper [12] that how satellite systems should be integrated with terrestrial systems and architectural details for the proposed architecture are missing. Similarly, the papers [13], [16] do not present details of the S-UMTS architecture for the integration of satellite and UMTS. The presented architecture in [14] is too specific for multiparty conferencing and is not applicable directly to general purpose multimedia or IMS services. An overview of physical and medium access control (MAC) layers of WiMax is provided in [17] but the paper does not propose any architecture for WiMax-3G integrated system. The proposed UMTS-WiMax interworking architecture in [18] is not evaluated. Also it may be more interesting to describe the performance of a VoIP call or a multimedia session in the proposed architecture. The traffic classes for QoS support in IEEE have been discussed and a scheduling algorithm is proposed for QoS management per connection in [35]. However, no consideration is given to the interworking of UMTS and WiMax. In [29], it may be more interesting to consider the call-establishment scenario in which one user is in WLAN and the other is in 3G system. Only SIP session setup delay is considered in [30, 31], and SIP registration and session re-establishment delay after vertical handoff is not given any consideration. In [31], it is assumed that provisional 14

33 Chapter 2. Related Work responses do not affect the session setup delay which may not be the case. The processing and queuing delays for CSCF servers in IMS are not considered in the session setup delay. The signaling between the CSCF servers of the IMS is not considered in [32] and also a number of provisional responses in the signaling flows are ignored. Additionally, AAA procedures are ignored during SIP-based vertical handoff. The paper [33] does not discuss how UE gets new IPv6 address in SIP terminal mobility. No detail is provided about the modifications made to IPv6 Linux kernel implementation. The results presented for handoff delay without kernel modification are unacceptable i.e. from 2 to 40 s. Through our proposed 4G interworking architectures and IMS signaling flow analysis, we can overcome some of the deficiencies described above in the previously done work in the literature G Interworking Architectures In this section, the 4G interworking architectures proposed so far have been discussed with their pros and cons. It is worth noting that we have drawn the interworking architectures with special reference to the IMS. We are considering the case when both 3G, satellite, WiMax, and WLAN are owned by the different service providers because this is more interesting and challenging case as compared to the case when the networks are owned by the same operator. Hence both wireless access gateway (WAG) of WLAN and GGSN of UMTS are connected to a different proxy-call session control function (P-CSCF) server of IMS. Also there are separate serving-call session control function (S-CSCF) and 15

34 Chapter 2. Related Work interrogating-call session control function (I-CSCF) servers for the two networks. For the establishment of an IMS session between the two networks, the two service providers should have service level agreements (SLAs). The IMS networks owned by different operators are connected by the IMS Backbone Network. The WAG and GGSN or packet data serving node (PDSN) will be connected to the same P-CSCF server if WLAN and 3G network are owned by the same operator Tightly Coupled (TC) Interworking Architecture Tightly Coupled (TC) WLAN-UMTS interworking architecture is shown in Figure 2.1. We use dotted lines between the two entities in our architecture to show that the two entities only share signaling messages with each other and data packets never flow through these entities. The dotted circles around access points (APs) of WLAN and base station controllers (BSCs) of 3G represent their respective coverage areas. An overlay architecture which is the main essence of 4G networks is considered in which WLAN users are also covered by BSC of 3G. The discussion has been benefited from [9, 34, 36]. The main concept behind the tightly-coupled approach is to give WLAN appearance of another UMTS access network from the perspective of UMTS core network. In other words, the WLAN is considered like another GPRS routing area (RA) in the system. The WLAN- 3G interworking function (WIF), which is connected to the SGSN of the UMTS core network, is responsible for hiding the details of the WLAN from the UMTS core network and implementation of the UMTS protocols for mobility management, authentication 16

35 Chapter 2. Related Work Figure 2.1: Tightly Coupled interworking architecture etc. essential for the UMTS radio access network. For seamless operation in the interworked architecture, UEs are required to implement the UMTS protocol stack on the top of their standard IEEE WLAN network cards. Among the disadvantages of tightly-coupled approach is the exposure of the UMTS core network interfaces directly to the WLAN network which invites security challenges. Extensive efforts are required for the implementation of WIF especially for the WLAN not owned by the UMTS operators. 17

36 Chapter 2. Related Work Figure 2.2: Loosely Coupled interworking architecture Loosely Coupled (LC) Interworking Architecture Loosely Coupled (LC) WLAN-UMTS interworking architecture is shown in Figure 2.2. The discussion has been benefited from [34, 36]. In the loosely-coupled inter-working architecture, the WLAN connects to the external packet data network (actually connects to P-CSCF in case of IMS) and does not have any direct link to 3G network elements such as SGSNs or GGSNs. Loosely-coupled architecture has distinct data paths for WLAN and UMTS traffic. The inter-operability with 3G requires the support of Mobile-IP function- 18

37 Chapter 2. Related Work alities or SIP protocol to handle mobility across networks and AAA services in the WAG of WLAN. This support is necessary to interwork with the 3G s home network AAA servers. One of the major advantages of the loosely-coupled architecture is that it permits independent deployment and traffic engineering of WLAN and 3G networks. Loose coupling utilizes standard IETF-based protocols for AAA and mobility and therefore, it does not necessitate the introduction of cellular technology into the WLAN network. WLAN uses the EAP for authentication of the MN by supplying the subscriber identity, SIM-based authentication data, and encrypted session keys. In case when WLAN is not owned by the 3G operator and SIM-based authentication is not feasible in the WLAN system, standard user name and password procedures may be deployed. The service continuity during handover to other access networks is not supported efficiently in loose-coupling and causes significant handover latency and packet loss Hybrid Coupled (HC) Interworking Architecture Hybrid Coupled (HC) WLAN-UMTS interworking architecture is shown in Figure 2.3. The basic HC interworking architecture is proposed in [37]. The HC architecture distinguishes the data paths according to the type of traffic and is capable of accommodating traffic from WLAN efficiently with guaranteed QoS and seamless mobility. The tightlycoupled network architecture is chosen for real-time traffic and the loosely-coupled architecture is selected for non-real time and bulky traffic. In HC architecture, the access router and gateway (ARG) of WLAN is responsible for forwarding packets to/from an 19

38 Chapter 2. Related Work Figure 2.3: Hybrid Coupled interworking architecture AP from/to the SGSN; supporting interfaces for signaling and data traffic to/from SGSN; management of radio resources in the WLAN and mapping them onto radio resources in the 3G network; setting data path to SGSN or external packet data network based on the type of traffic where the service types are differentiated by Type of Service (ToS) or DiffServ Code Point (DSCP) field of the IP header. The Mobile-IP or SIP protocol may be used for seamless mobility in the HC architecture. The vertical handoff procedures in HC architecture are similar to the procedures in TC architecture. In HC, the UE belongs to the UMTS network only for a user using UMTS access network. However, for 20

39 Chapter 2. Related Work Figure 2.4: The TCDRAS interworking architecture a user accessing IMS services through WLAN belongs to both the UMTS and WLAN for efficient handover purposes. Hence, when a user moves from the WLAN to the UMTS, the registration to the UMTS network is not required because it is already registered. However when moving to the WLAN from UMTS, the registration procedure with the WLAN is required. 21

40 Chapter 2. Related Work The TCDRAS Interworking Architecture Tightly Coupled with Direct Radio Access System (TCDRAS) WLAN-UMTS interworking architecture is shown in Figure 2.4. The basic TCDRAS architecture is proposed in [38]. TCDRAS is based on the tight-coupling architecture but it also creates an additional wireless link between the base station of a UMTS cell and WLAN located within the UMTS cell through WLAN to 3G Direct Controller and Transceiver (WGDCT). The signaling in TCDRAS is still routed through the original TC path for network security purposes. However, it provides the opportunity for dynamic distribution of data traffic between the original TC path and the path available due to the added wireless link. WGDCT uses IEEE air interface and a WiMax transceiver for direct wireless link established between WLAN and the UMTS base station overlaying the WLAN The LCDRAS Interworking Architecture Loosely Coupled with Direct Radio Access System (LCDRAS) WLAN-UMTS interworking architecture is shown in Figure 2.5. The basic LCDRAS architecture is proposed in [39]. LCDRAS is based on the loose-coupling architecture but it also creates an additional wireless link between the base station of a UMTS cell and WLAN located within the UMTS cell through WGDCT. The IEEE standard air interface is utilized in LCDRAS to set up direct wireless link between the base station in UMTS cellular networks and local WLAN. The LCDRAS is capable of dynamically distributing signaling and data traffic to reduce signaling cost and handoff latency via WGDCT. 22

41 Chapter 2. Related Work Figure 2.5: The LCDRAS interworking architecture 23

42 Chapter 3 LCSCW2 and TCSCW2: Architectures for IP Multimedia Subsystem In this chapter, we propose the LCSCW2 and TCSCW2 interworking architectures. The LCSCW2 and TCSCW2 architectures integrate the satellite networks, 3G wireless networks, WiMax, and WLANs, and are based on the loosely coupling and tightly coupling paradigm, respectively. They can support IMS sessions and provide global coverage. The LCSCW2 architecture facilitates independent deployment and traffic engineering of various access networks. We also propose an analytical model to determine the associate cost for the signaling and data traffic for inter-system communication in the LCSCW2 architecture. The analytical model can be easily extended to determine the associated cost for the signaling and data traffic for inter-system communication in the TCSCW2 architecture as well. The cost analysis includes the transmission, processing, and queueing costs at various entities. Numerical results are presented for different arrival rates and session lengths. 24

43 Chapter 3. LCSCW2 and TCSCW2: Architectures for IP Multimedia Subsystem Figure 3.1: The LCSCW2 interworking architecture. 3.1 The LCSCW2 Architecture Our proposed LCSCW2 interworking architecture is depicted in Figure 3.1. This interworking architecture integrates satellite networks, 3G wireless cellular networks, WiMax, and WLANs based on the loosely coupled approach. The areas covered by the SSBs, 3G base stations, WiMax base stations, and WLAN APs are shown by dotted lines in Figure 3.1. Our proposed architecture is compatible with the IMS. Different ANs (e.g., 3G networks, satellite networks, WiMax, and WLANs) can be owned by different service providers (or the same operator). The wireless access gateways (WAGs) of WLAN, WiMax, satellite and 3G networks are connected to different proxy-call session control function (P-CSCF) servers in IMS via the Internet. In general, each AN has its own sepa- 25

44 Chapter 3. LCSCW2 and TCSCW2: Architectures for IP Multimedia Subsystem rate WAG. In addition, there are separate serving-call session control function (S-CSCF) and interrogating-call session control function (I-CSCF) servers for the two networks. For the establishment of an IMS session between two access networks, the two service providers should have a SLA with each other. IMS networks which are owned by different operators are connected together through an IMS backbone network. The WAG and packet data serving node (PDSN) are connected to the same P-CSCF server if WLAN, WiMax, satellite and 3G network are owned by the same operator. The mechanisms involved in the interworking architecture along with the functionalities of various entities are explained below with reference to the 3GPP specification [40]. Access to a locally connected IP network from a WLAN directly is called WLAN direct IP access, which is provided by the loosely coupled architecture. The WAG is a gateway via which the data to/from the satellite AN, WiMax AN, or WLAN AN can be routed to/from an external IP network. In the LCSCW2 architecture, the satellite AN comprises of satellites and satellite fixed earth station (SFES). Satellites convey data and signaling messages between UE and SFES. The SFES performs power control, link control, radio bearer control and paging functions. The SFES is connected to WAG for accessing 3GPP packet switched (PS) and IMS services. The SFES determines whether or not a given UE can receive the requested services based on the user subscription. The SFES also determines the UE s location via looking at the UE s entry in the database and its associated SSB ID. The UE s database entry is created when the UE first registers with the satellite network and is updated when the UE moves from coverage area of 26

45 Chapter 3. LCSCW2 and TCSCW2: Architectures for IP Multimedia Subsystem one SSB to another. The SFES sends a page request to the UE including its identifier. During a pre-defined time, if the SFES gets the response from the UE, it then instructs the UE to go through radio bearer (RB) establishment procedure. If the UE is unable to respond to the page message within the pre-defined time, the SFES concludes that the UE is unreachable [15]. The WiMax AN consists of WiMax base stations, which are controlled by the WiMax base station controller (WBSC). Several WBSCs are controlled by one WiMax network controller (WNC). The WNC is connected to WAG to provide WiMax users with 3GPP PS and IMS services. The LCSCW2 interworking architecture integrates satellite networks, 3G wireless networks, WiMax, and WLANs based on the loose coupling approach since these ANs connect to the Internet or Intranet via WAG. Then, through the Internet or Intranet, the UE can access CSCF servers of the IMS network. In the LCSCW2 architecture, the satellite network, WiMax and WLAN do not have any direct link to 3G network elements such as serving GPRS support nodes (SGSNs) or gateway GPRS support nodes (GGSNs). The LCSCW2 architecture has distinct signaling and data paths for different ANs. The inter-operability with 3G requires the support of mobile-ip functionalities and Session Initiation Protocol (SIP) to handle mobility across networks, and authentication, authorization, and accounting (AAA) services in the WAG of the AN. This support is necessary to interwork with the 3G s home network AAA servers. The authentication in the ANs is provided through the 3GPP system [40]. The main advantage of the LCSCW2 architecture is that it allows independent deploy- 27

46 Chapter 3. LCSCW2 and TCSCW2: Architectures for IP Multimedia Subsystem ment and traffic engineering of satellite networks, WiMax, WLANs, and 3G networks. In addition, this architecture utilizes standard IETF (Internet Engineering Task Force) based protocols for AAA and mobility in the WiMax, WLANs, and satellite networks. Our discussion and the cost analysis is equally valid whether the 3G technology being used is UMTS or CDMA2000 because there are corresponding network entities in CDMA2000 for the entities in UMTS. Packet data serving node (PDSN) in CDMA2000 performs the same functions as GGSN in UMTS. Packet control function (PCF) in CDMA2000 performs the same function as SGSN in UMTS. PCF connects to the PDSN in CDMA2000 as SGSN connects to GGSN in UMTS. 3.2 The TCSCW2 Architecture Our proposed TCSCW2 interworking architecture is depicted in Figure 3.2. This interworking architecture integrates satellite networks, 3G wireless cellular networks, WiMax, and WLANs based on the loosely coupled approach. The areas covered by the satellite spot beams SSBs, 3G base stations, WiMax base stations, and WLAN access points APs are shown by dotted lines in Figure 3.2. Our proposed architecture is compatible with the IMS. Different ANs (e.g., 3G networks, satellite networks, WiMax, and WLANs) can be owned by different service providers (or the same operator). The packet data gateways (PDGs) of WLAN, WiMax, satellite and 3G networks are connected to different P-CSCF servers in IMS. In general, each AN has its own separate WAG. In addition, there are separate S-CSCF and I-CSCF servers for the two networks. For the establishment of an 28

47 Chapter 3. LCSCW2 and TCSCW2: Architectures for IP Multimedia Subsystem Figure 3.2: The TCSCW2 interworking architecture IMS session between two access networks, the two service providers should have a SLA with each other. IMS networks which are owned by different operators are connected together through an IMS backbone network. The PDG and PDSN are connected to the same P-CSCF server if WLAN, WiMax, satellite and 3G network are owned by the same operator. The mechanisms involved in the interworking architecture along with the functionalities of the important entities are explained below with reference to the 3GPP Specification [40]. Access to external IP networks such as IMS, 3G operators network corporate Intranets or the Internet through the 3GPP system is called WLAN 3GPP IP Access. The PDG provides WLAN 3GPP IP Access to external IP networks. The WAG is a gate- 29