Advanced SIP Series: SIP and 3GPP

Advanced SIP Series: SIP and 3GPP, Award Solutions, Inc Abstract The Session Initiation Protocol has been selected as the main signaling protocol of the Third Generation Partnership Projects IP Multimedia Subsystem. This paper will show the architecture of the IP Multimedia Subsystem and how the Session Initiation Protocol has been used to achieve the goals of the Third Generation Partnership Projects. This paper will include a discussion of the architecture, the motivation for the evolution to this architecture and some examples of how this architecture can be used to provide advanced services. Introduction Universal Mobile Telecommunication System (UMTS) is expected to become a dominant network for 3 rd generation wireless systems. Standardized by 3GPP, UMTS is built to offer next generation services. In this paper, we will discuss the role of SIP in UMTS networks. We will begin with a brief overview of the history of UMTS followed by the discussion of existing UMTS architecture. Following this, we will have a section on the motivation for converged networks and options available in UMTS for convergence. The next section focuses on the new IP Multimedia Subsystem architecture to be used in the next release of UMTS. It details the new components in the IP Multimedia Subsystem and their functions. The focus of the following section is the SIP signaling within UMTS Once we have introduced the basic signaling architecture, the services architecture of the IP Multimedia Subsystem is introduced. The technologies available for services in UMTS network such as SIP Servlets and intelligent networking are discussed. Some examples of enhanced services are presented as well. Finally, we conclude the paper detailing benefits of using SIP based technologies in UMTS History of UMTS Universal Mobile Telecommunication System (UMTS) is a third generation wireless system designed to provide higher data rates and enhanced services to subscribers. In a short span of 20 years, wireless networks have undergone three generations of evolution. The first generation networks in the early 1980s supported traditional voice services. The second generation networks in the early 1990s supported voice services as well as low rate (14.4 kbps 28.8 kbps) data services. One of the dominant second generation networks is Global System for Mobile Communication (GSM). The GSM networks are widely deployed throughout the world and garners more than 60% of the wireless market. Since, GSM networks are designed for circuit switched voice services and offer low data rates, it is not well suited to support packet switched Internet services. In the interim, the General Packet Radio Service (GPRS) network is added to the GSM networks to efficiently support packet switched services. GSM/GPRS networks are referred to as 2.5 Generation (2.5G) networks. However, the available data rates on GPRS networks is limited to around 64 kbps per subscriber. Moreover, it supports only nonreal time packet switched services. UMTS represents the next step in the evolution of GSM/GPRS networks. UMTS can offer data rates in the range of 2 Mb/s and supports enhanced services such as streaming video/audio and location based services. UMTS is standardized by 3 rd Generation Partnership Project (3GPP) which is a conglomeration of regional standards bodies such as European Telecommunication Standards Institute (ETSI), Association of Radio Industry Businesses (ARIB) and others. The standardization of UMTS has progressed in 3 phases. The first phase is known as Release 99. The Release 99 specifications define the basic architecture that consists of UMTS Terrestrial Radio Access Network (UTRAN), Circuit Switched Core Network (CS-CN) and Packet Switched Core Network (PS-CN). The release 99 offers traditional circuit as well as packet switched services. The next phase in the standardization is Release 4. Release 4 adds new services to the release 99 architecture, but it does not change the release 99 architecture. Release 5 represents a major shift in the UMTS architecture. Release 5 proposes to offer both traditional telephony as well as packet switched www.awardsolutions.com 1

services over a single converged packet based 3GPP has chosen SIP as the protocol for the release 5 UMTS networks to offer traditional telephony and enhanced multimedia services. Release 99 Architecture Before we present the Release 5 architecture, it is important to understand the Release 99 architecture. The Release 99 architecture is shown in Fig. 1. As mentioned earlier, it consists of three important components: UTRAN, CS-CN and PS-CN. In addition, UMTS defines the W-CDMA air interface that supports the link between the UE and the UTRAN. The UTRAN is responsible for handling complete radio functionality. In fact, UMTS mandates that the core networks are complete insulated from radio functionality so that they can work with different types of radio networks such as UTRAN and Wireless LANs. The UTRAN uses Asynchronous Transfer Mode (ATM) as the transport network option. The future releases of UMTS are expected to provide IP as an option for transport The UMTS core networks have evolved from GSM/GPRS networks, i.e. the UMTS CS-CN has evolved from SS7 based GSM core networks and the PS-CN has evolved from IP based GPRS core networks. The CS-CN supports connectivity to the Public Switched Telephony Network (PSTN) and the Integrated Digital Services Network (ISDN) for circuit switched services. The PS-CN supports connectivity to the Internet for packet switched services. The PSTN, ISDN and Internet can be regarded as services networks. UE W-CDMA RNC Node B UTRAN 3G MSC/VLR 3G SGSN SCP Service Layer HLR/AC CS-CN SS7 network Private IP network PS PS-CN GGSN G-MSC PSTN/ ISDN IP Network Optional Fig. 1. UMTS Release 99 Architecture The CS-CN provides traditional telephony services such as voice and fax. The CS-CN also supports enhanced services such as Short Message Service (SMS) and circuit switched data services. The important components of the CS-CN are the Mobile Switching Center (MSC), Visitor Location Register (VLR), Home Location Register (HLR) and Authentication Center (AC). The HLR maintains the subscriber profile for both circuit and packet services. The AC supports authentication functions for both domains. Therefore, these components belong to both domains. The PS-CN supports connectivity to the packet data networks such as the Internet. In fact, the PS-CN supports only the Internet option unlike in the GPRS networks, which supported both Internet and X.25 networks. The PS-CN supports services such as Internet access, Virtual Private Networks (VPN) and SMS. The important components of PS-CN are the Service GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN). The SGSN is responsible for mobility management, security and authorization functions. The GGSN is responsible for IP address management, QoS management and external gateway functions. Converged Network The Release 99 architecture allows GSM/GPRS operators to gracefully evolve their networks to the UMTS architecture. However, deploying two separate networks for telephony and data services introduces severe limitations in terms of multimedia services and management of these networks. This section discusses these limitations, rationale for converged network and options for convergence. Motivation for Convergence The wireless industry has clearly realized the benefits of a converged Some of the reasons and benefits of a converged wireless network are discussed in this section. Lower infrastructure cost: The converged network means the Circuit Switched Core Network (CS-CN) is no longer necessary. Therefore, this results in lower capital expenditure for operators. One may argue that the new converged network will have to deploy new components to support CS-CN functionality; however, these components are based on IP technologies. Traditionally IP network components cost less compared to telephony components due to competition and open standards. Moreover, operators can remove redundant components that perform the same functions in both networks. For example, a single integrated network www.awardsolutions.com 2

management platform can now manage the whole network instead of two separate platforms for the CS- CN and the PS-CN Lower maintenance cost: A single converged network based on IP results in reduced maintenance and operations costs. Again the management of the IP networking components is easier compared to telephony components due to open standard management platforms. The operators can manage the converged network with a smaller operational staff. Moreover, the operators need not invest in developing expertise in multiple technologies since the converged network will be based on one signaling and bearer Enhanced Services: The integration of voice and data networks offers opportunities for deploying enhanced multimedia services. Almost every service other than telephony services is available on the Internet today. The combination of Internet and telephony services opens a world of new revenue opportunities for service providers. We will explore some of these innovative services in the services section. Rapid Service Deployment: Development of a converged network based on a single standard allows for rapid deployment of new services. The configuration and co-ordination required to introduce new services is reduced due to the integrated management of wireless networks. Architecture of the converged network We have made a strong case for convergence in the previous section. What are the options available for convergence? There are two choices for convergence in UMTS networks. The packet switched services, such as Internet access and VPN, may be provided over the CS-CN and remove the PS-CN completely. However, this represents a backward step in evolution since the CS-CN was never designed to support packet switched services. The obvious choice is to deploy the traditional telephony services over the PS-CN. Some of the rationale for this approach has been explained in the previous section (Motivation for Convergence). These reasons are the flexibility of IP networks, lower deployment cost for IP networks, open standards and a wide spread support for Internet throughout the world. The UMTS Release 5 architecture proposes the addition of a new subsystem known as the IP Multimedia Subsystem (IMS) to the PS-CN for supporting traditional telephony as well as new multimedia services. Fig. 2 shows a high level view of the UMTS Release 5 architecture. The components within the IMS will be explored in the next section. UE Voice over IP/ Multimedia services UTRAN PS-CN IMS Telephony services Internet services Voice over IP/ Multimedia services PSTN/ ISDN Internet Fig. 2. High level Release 5 Architecture The IMS supports an IP based network to support traditional telephony as well as multimedia services. The UE supports voice over IP technologies to setup voice and multimedia services. The IMS connects to both PSTN/ISDN as well as Internet. It may terminate voice and multi-media calls on both PSTN/ISDN and Internet. The 3GPP has chosen the Session Initiation Protocol (SIP) for signaling between the UE and the IMS as well as between the components within the IMS. The IMS uses SIP also to complete voice and multimedia calls in the Internet. The 3GPP has chosen SIP for its simplicity, extensibility 1 and its wide availability. While we have made the case for converging the network based on the PS-CN and the IMS, it is important to realize some of the challenges in providing telephony services over packet based networks. One of the challenges is the required reliability of telephony services. The telephony services are required to have high reliability (99.999 or five 9s reliability) due to regulatory requirements. The packet switched networks of today are not as reliable as circuit switched network components. It will be a challenge to meet these reliability requirements while maintaining cost benefits. The other key challenge to is related to Quality of Service (QoS). In a traditional telephony network QoS was not an issues since resources where dedicated for the call. It will be a challenge for the packet network to meet these same QoS requirements and continue to provide the above stated benefits of the packet www.awardsolutions.com 3

Release 5 Architecture This section will present the UMTS Release 5 architecture 2. The specification for this release of UMTS has not been completed. Everything that is presented in this paper is based on the latest specifications that are available. The components that will be presented are the Call Session Control Function (CSCF) components and the Media Gateway (MGW)/Media Gateway Control Function (MGCF) network components. UMTS Release 5 allows mobiles operating in packet mode to establish voice calls using SIP as the signaling protocol. These SIP messages are sent to communicate the request to the Call Session Control Function (CSCF) in the IMS. In this case, the voice data is transmitted as packets throughout the UMTS SGSN P - CSCF I - CSCF IP Multimedia Subsystem MGCF User data Signaling Fig. 3. GGSN Internet S - CSCF MGW HSS T - SGW IP Multimedia Subsystem PSTN Call Session Control Functions As alluded to previously, the UMTS core network is evolving from the current separated network into a consolidated Now let s introduce the components of the IP Multimedia Subsystem. The first key elements are the Call Session Control Functions (CSCF) and the Home Subscriber Server. The CSCF has taken the majority of the MSC functionality in the IMS architecture. The CSCF is analogous to the SIP server in the IETF architecture 3. Call Session Control Functions (CSCF) The first component that needs to be discussed is the Call Session Control Function (CSCF.) Its function is to process signaling messages for controlling the user s multimedia session. The existing packet switched core network is used to support the bearer path for the multimedia session and the CSCFs are used to establish the sessions and perform features. The service control protocols are compliant with the Internet Engineering Task Force (IETF) based protocols. The protocol that is used for the majority of the signaling is SIP. The CSCFs perform a number of functions. The first is the multimedia session control function. This is an evolution of the MSC call control function. Next is the address translation function (i.e. evolution of the digit translation function.) The CSCF must also perform services switching for services and vocoder negotiation. The CSCF must perform the handling of the subscriber profile (i.e. the VLR.) The CSCF can play three roles; the Proxy CSCF (P- CSCF) role, the Interrogating CSCF (I-CSCF) role and the Serving CSCF (S-CSCF) role. The P-CSCF it is the mobiles first point of contact in the IMS The I-CSCF s function is to determine the S-CSCF based on load or capability. The S-CSCF is responsible for the mobile s session management. All three of these roles can support the firewall capability. Each role will now be presented. Proxy - CSCF As stated before, the Proxy Call Session Control Function (P-CSCF) is the mobiles first point of contact in the visited IMS The others only exist in the home The P-CSCF has two main functions. Its primary function is to be the Quality of Service Policy Enforcement Point within the visited IMS Its second responsibility is to provide the local control for emergency services. It also performs the local numbering plans directory assistance under the direction of the Serving CSCF. The P-CSCF forwards the SIP registration messages and session establishment messages to the home The Proxy-CSCF is analogous to the Proxy Server in the SIP architecture. Interrogating - CSCF The Interrogating Call Session Control Function (I- CSCF) is the first point of contract within the home network from a visited It main job is to query the HSS and find the location of the Serving CSCF. This is an optional node in the IMS architecture. It could be configured so that the P- CSCF could contact the S-CSCF directly. The I-CSCF has a number of functions. It performs load balancing between the S-CSCFs with the support of the HSS. The I-CSCF hides the specific www.awardsolutions.com 4

configuration of the home network form other network operators by providing the single point of entry into the The I-CSCF can also perform some forms of billing. If the I-CSCF is the gateway into the home network, it must support the firewall function. Serving CSCF (S-CSCF) The Serving Call Session Control Function (S-CSCF) is the node that performs the session management for the IMS There can be several S-CSCFs in the They can be added as needed based on the capabilities of the nodes or the capacity requirements of the The S-CSCF in the home network is responsible for all session control, but it could forward the specific request to a P-CSCF in the visited network based on the requirements of the request. For example, the visited network will be in a better position to support the local dialing plan or some other local service that the user may be interested in (i.e. where is the closest coffee shop.) The S-CSCF may be chosen differently based on the services requested or the capabilities of the mobile. One key advantage of this architecture is that the home network provides the service features. This means that the mobile is not restricted to the capabilities of the visited network as is seen in the current wireless network (i.e. if an MSC does not support a feature that you have subscribed to, you will not be able to use that feature.) This ability to allow the user to always be able to get access to their subscribed to features is referred to as Virtual Home Environment (VHE.) Home Subscriber Server As in the legacy mobile network, there is still a need for a centralized subscriber database. The Home Location Register (HLR) has evolved into the Home Subscriber Server (HSS.) The HSS interfaces with the I-CSCF and the S-CSCF to provide information about the location of the subscriber and the subscriber s subscription information. The HSS uses the only protocol that is not IETF based, the Cx interface 4. The HSS and the CSCF communicate via the new Cx interface. The protocol on the Cx interface is not an IETF protocol, but it is IP based. Media Gateway and Media Gateway Control Function In an environment where all of the sessions are between IP capable end user devices, there would be no need for anything other than the CSCF s and the HSS. In reality, there will be a very long transition period to completely eliminate the legacy PSTN and mobile networks. The IMS supports several nodes for interworking with legacy networks. These are the Media Gateway (MGW), the Media Gateway Control Function (MGCF), and the Transport Signaling Gateway (T- SGW.) The concept of a switching matrix has been divided into two parts. Simply these can be considered the brains and the brawn of the The brain is the MGCF and the brawn is the MGW itself. Media Gateway Control Function The MGCF controls one or more MGW s, which allows for more scalability in the The MGCF manages the connection between the PSTN bearer (the trunk) and the IP stream. For simplicity the MGCF could be collocated with the MGW. The MGCF converts SIP messages into either Megaco or ISUP messages. The MGCF receives a SIP message from the CSCF and it determines what to establish within the MGW. It also creates the appropriate ISUP message and sends it, via IP, to the Transport Signaling Gateway (T-SGW.) The MGCF is a software or a server function. This means it must run on a highly available computing platform versus on a real-time hardware processing environment. Media Gateway If the MGCF is the brains of the operation then the Media Gateway (MGW) is the brawn. It is the workhorse that does the processing of the media bits between end users. Its primary function is to convert media from one format to another. In UMTS this will predominantly be between Pulse Code Modulation (PCM) in the PSTN and an IP based vocoder format. The MGW is likely to be a real-time hardware based platform. It is critical that it processes the bits as quickly as possible so that delay is not added to the transmission of the information. Transport Signaling Gateway A key characteristic of the IP Multimedia Subsystem is that most of the communication between components is IP based. There are only two interfaces that are not IP based. Both of these are used during interactions with a legacy network (either www.awardsolutions.com 5

the PSTN or a mobile ) These two interfaces are the bearer path and the signaling path to the legacy The only other interface that needs to be discussed is the signaling interface to the PSTN. The PSTN currently only understands SS7 and there is no incentive for it to provide support for anything other than SS7. SS7 has limitations and is not as flexible as IP. To prevent the need for the MGCF to support SS7 the Transport Signaling Gateway (T-SGW) was created. Its job is to convert SS7 to IP. The T-SGW converts the lower layers of SS7 into IP. The application layer protocols shall not be affected. One example of an application layer protocol is ISDN User Part (ISUP,) that is used for establishing call with the PSTN. It is important to note that it is always an option to have the MGCF support SS7 and then the T-SGW would not be required. Distribution of CS functionality Now that we have presented the components that make up the UMTS IP Multimedia Subsystem, it would be good to look at the essential functions of processing a call in the circuit switched world and see where these functions have moved to in the IMS Call Control and Feature Processing: In the circuit switched network the MSC did the call control to process a call. This function has been moved into the CSCF. Specifically this function is performed in the S-CSCF unless it is for a local function, then it is performed in the P-CSCF. Billing: At the end of the call the MSC must perform the billing function by generating a billing record. This function has been moved to the S-CSCF and the P-CSCF. The reason it is in both is so that the home network can bill the subscriber and the visited network can bill the home network for the subscriber s use of their resources. Switching Matrix: There are two answers to where the switching matrix has moved. In a scenario where both terminations of the call are IP capable (i.e. both are SIP capable phones) then the IP network itself takes on the role of the switching matrix. In the case where one of the terminations is in a legacy network, then the switching matrix is distributed between the MGW and the MGCF. Subscriber Profile Management: The MSC was responsible for keeping a local copy of the subscriber s profile that would be used to assist in processing a call. The profile data included the mobiles identity, phone number, and the subscribed feature set. This function is now in the S-CSCF. It will need this information to process the requests from the mobile. A simple example is for the international call barring restriction. If the mobile has this restriction and dials an international call, the S- CSCF will not allow the call from being completed. Mobility Management and Authentication: The MSC performed mobility management to know the location of the mobile as it moves around the Since the mobile is communicating over an air interface, which cannot be protected, the MSC must also authenticate the identity of the user to ensure that it is not fraudulent. In previous releases of UMTS these functions were performed in the circuit switched network and in the packet switched network (i.e. this was performed in the MSC and SGSN separately.) It is redundant for both of these functions to be in both networks. In the IMS it will only be performed in the packet switched network (i.e. the SGSN.) There is no change to these procedures within the SGSN. Call Flows Fig. 4 shows the flow of signaling messages and the flow of the user data (i.e. the digitized voice packets.) Let s take a look at each of these in turn. First let s look at the signaling messages. As you can see from the figure, the signaling messages will go from the mobile through the UTRAN, to the SGSN/GGSN, out to the CSCF s and out to the destination network (either to another Release 5 IMS network, to the MGCF/MGW network, or just out to the IP ) It is important to note which of these components are processing the message versus the components that are routing the message. At the time the mobile is sending a request to establish a service, this request is sent to S-CSCF (via the Proxy and the Interrogating) to request the service. The SGSN and the GGSN will only perform the function of routers. They do not look at the contents of the message, they only look at the destination IP address and route the message accordingly. Now that we have looked at the singling path, let s take a look at the flow of the user data. As you can see from the figure the user information will flow from the mobile, through the SGSN and the GGSN out to the destination network (again either to the GGSN of another Release 5 network, to the MGW out to the PSTN, or out to the Internet.) It will bypass the CSCF network all together. This is important to note that the IMS still follows the philosophy that the www.awardsolutions.com 6

signaling and user information will take different paths through the PSTN Mobile Rel. 5 Network IP MGCF/ MGW Destinations UTRAN Fig. 4. 3G-SGSN S-CSCF Visited Network GGSN Key: Signaling Home Network P-CSCF User Traffic Signaling and Traffic Paths I-CSCF Fig. 5 shows an example of a mobile initiating a multimedia session. It shows the Session Description Protocol negotiation and the resource reservation steps. Any of the standard IP QoS mechanisms can be used to perform the resource reservation. UE P-CSCF I-CSCF S-CSCF Destination INVITE SDP Negotiation Resource Reservation Session Setup Confirmation (OK & ACK) Fig. 5. Session in Progress Mobile Originated Multimedia Session IP Multimedia Subsystem Services Architecture As we discussed earlier, the converged network carrying voice and data bearers offers opportunities for introduction of innovative services. Combining the flexibility of IP networks and extensibility of SIP, the IMS Services architecture provides support for legacy as well as new services. The IMS services architecture is shown in Fig. 6. HSS Native SIP Services SIP Servlets CPL Scripts SIP CGI JAIN SIP Application Server Cx MAP ISC S - CSCF ISC ISC OSA Service Capability Server (SCS) IM - SSF Legacy IN Services CAP CAMEL Service Environment 3 rd Party Services OSA API OSA Application Server Fig. 6. IMS Services Architecture The IMS services architecture allows deployment of new services by operators and 3 rd party service providers. This provides subscribes a wide choice of services. The S-CSCF is the anchor point for delivering new services since it manages the SIP sessions. However, services can be developed and deployed in a distributed architecture. Multiple service platforms may be used to deploy wide variety of services. The IMS defines three different was of delivering services. These are explained below: Native SIP Services: In the last few years, a wide variety of technologies have been developed by various organizations for developing SIP services. They include SIP servlets, Call Processing Language (CPL) script 5, SIP Common Gateway Interface (CGI) and Java APIs for Integrated Networks (JAIN) 6. One or more SIP application servers may be used to deploy services using these technologies Legacy IN services: While new and innovative services are required, the legacy telephony services cannot be ignored. The release 99 networks use CAMEL (Customized Applications for Mobile Enhanced Logic) Service Environment for deploying intelligent networking services such as pre-paid service and 1-800 service. 3 rd party services: UMTS has defined Open Services Access (OSA) 7 to allow 3 rd party service providers to offer services through UMTS The OSA offers a secure API for 3 rd party service providers to access UMTS networks. Therefore, subscribes are not restricted to the services offered by the operators. The S-CSCF uses the Cx interface to retrieve subscriber profile from the HSS. The S-CSCF interacts with different service platforms through IMS Services Control (ISC) interface that is based on www.awardsolutions.com 7

SIP and its extensions. However, the OSA and CAMEL environments do not support ISC interface. The OSA Service Capability Server (SCS) performs mediation between the ISC and the OSA API. The IM-SSF performs mediation between the ISC and CAMEL Application Protocol (CAP). Enhanced Services As way of example, lets discuss some of the types of enhanced services that are made possible with the IMS architecture that are not possible with the traditional PSTN architecture. The simplest example that can be provided is where data is combined with voice. For example, a user receives a voice call and included with that voice call is public information on the user. This could be business related (position, company, title, etc.) or it could be personal information (birthday, spouses name, children s names, hobbies, etc.) Could you image being in a phone conversation, checking the personal information on the other party, finding that that person had a birthday last week and then being able to tell them happy birthday. The next example is where the characteristics of the communication can change based on the information that needs to be sent. Again we will start with our typical voice conversation, but during the call one party wants to show a video of Tiger Woods making that putt to win the golf tournament or to play an MP3 of the latest Meat Loaf song (no, there has not been a new album out for a few years.) The characteristics of the connection will be modified to allow for the additional data requirements of these new applications. These two services are very easy to implement using SIP since the SDP can include the appropriate information for both types of service (the basic voice call and the data stream.) This data stream could be a simple as additional text information that needs to be displayed or as complicated as streaming audio or video. The last example that will be presented again starts with a voice call. The difference is that this call is a conference call with four people (Bob, Carol, Ted, and Alice.) During the duration of the call Bob and Alice get into a very technical discussion. Now Ted and Carol are not interested in the details of this discussion, but they understand that it needs to be resolved. To not waste time, they spawn a private conference room that will allow them to have a conversation while they continue to have Bob and Alice s conversation in the background (so they can hear when Bob and Alice have completed their discussion and the meeting can continue.) When Bob and Alice are done, Ted and Carol rejoin the main conference call to complete there meeting. 8 SIP is used in this example to start the original conference call with some form of a conferencing bridge. SIP will then by used by Ted or Carol to interact with the conferencing bridge to setup the private conference bridge. Conclusion In conclusion, 3GPP has decided to develop an architecture that is based on SIP to solve a number of architectural requirements. These requirements include a disturbed architecture, services architecture flexible enough to provide enhanced services, and the requirement of a Virtual Home Environment. 1 Advanced SIP Series: Extending SIP, Gary Cote, www.sipcenter.com 2 3GPP TS 23.228: IP Multimedia (IM) Subsystem - Stage 2 3 RFC 2543 Session Initiation Protocol (SIP) 4 3GPP TS 29.228: IP Multimedia (IM) Subsystem Cx Interface; Signaling Flows and Message Content 5 Information on CPL - draft-ietf-iptel-cpl-04.txt, www.oasis-open.com/cover/cpl.html 6 Information on JAIN and SIP Servlet APIs - java.sun.com/products/jain 7 3GPP TS 29.198: Open Services Access (OSA) Application Programming Interface (API) 8 3GPP TS 22.228: IP Multimedia (IM) Subsystem - Stage 2 www.awardsolutions.com 8

About the Authors: As a Director of Product Management for Award Solutions, Narayan Parameshwar provides consulting and training in areas of cdma2000, UMTS, MPLS and Internet Telephony. As a Senior Consultant for Award Solutions, Chris Reece provides consulting and training in UMTS, Wireless Network Planning, Internet Telephony and Next Generation Networks. About Award Solutions: Award Solutions, Inc. is a premier provider of training, consulting, and development solutions. We are a "knowledge based" company rooted in the areas of advanced wireless and Internet technologies. Visit us at www.awardsolutions.com. www.awardsolutions.com 9