Functionality and Testing of Policy Control in IP Multimedia Subsystem Skander Chaichee

1. Functionality and Testing of Policy Control in IP Multimedia Subsystem Skander Chaichee HUT/Nokia Networks 17.8. 2004 Supervisor: Professor Raimo Kantola Instructor: Mikko Kiiski, M. Sc.

2. Objectives and Purpose of the Thesis • Thesis tries to answer the problem of how to test the IMS Policy Control functionality in GGSN. • This requires designing and building a test network and methods how to use it properly. • It also requires planning a comprehensive set of the test cases, writing them to test scripts and finding a way to execute them. • The second objective is to explain the reader the functionality of the IMS Policy Control and the interfaces and network elements taking part of it. • The Go interface is a new interface and this is the first time it is implemented in Nokia GGSN. Thus, the functionality of it deserves to be analyzed and tested.

3. GPRS & 3G Network • GPRS comes as an upgrade to the existing GSM networks. It offers packet-switched data service and possible connection to the external networks e.g. Internet. Universal Mobile Telecommunication System (UMTS) is a 3G wireless system that provides higher data rates and enhanced services to subscribers compared to the 2.5G mobile networks.

4. SGSN & GGSN • The Serving GPRS Support Node (SGSN) provides the interface between the GPRS core network and the mobile radio networks. SGSN handles several functions, such as packet routing and transfer, mobile attach and detach procedure, location management, assigning channels and time slots, and authentication. • The Gateway GPRS Support Node (GGSN) is the place in the network, which allows the mobile operators to control the service access and to perform differentiated charging based on the services and applications that are used. • GPRS Tunneling Protocol between SGSN and GGSN in the Gn interface • A PDP Context can be understood as a ‘call’ in a packet switched network. A PDP context is a logical connection between a mobile and an external data network, with pre-defined and dynamic parameters. • Secondary PDP contexts

5. The Go Interface towards IP Multimedia Subsystem (IMS) • The IMS can be understood to be an evolution of 2.5G and 3G mobile technologies that brings the ability to deliver IP-based person-to-person real-time multimedia communications.

6. Protocol Stack in the Go Interface • The Policy Decision Function (PDF) is a logical policy decision element that uses standard IP mechanisms to implement policy in the IP media layer. The PDF makes decisions in regard to network based IP policy using policy rules and communicates these decisions to the PEP in the GGSN. • The Common Open Policy Service for Policy Provisioning (COPS-PR) over TCP. PDF = PDP, GGSN = PEP. • For the purpose of exchanging the required specific Go information, a 3GPP Go COPS-PR PIB is defined. The Go PIB defines all objects to carry the information specific to the Go interface. COPS/COPS-PR/Go PIB. • The Go interface allows service-based local policy information to be "pushed" to or requested by the Policy Enforcement Point (PEP) in the GGSN from a Policy Decision Function (PDF).

7. IMS Policy Control/Go Interface Functionality • IMS PDP Context Activation and Modification/ Media Authorization • IMS PDP Context Modification • Gating Functionality • Indication of PDP Context Release / Revoke Authorization for GPRS and IP resources • IMS PDP Context QoS Modification to/from 0 kbps • Charging correlation

8. Binding Information and Authorized QoS • The binding information is used by the GGSN to identify the correct PDF and subsequently request service-based local policy information from the PDF. • The Authorized QoS specifies the maximum QoS that is authorized for a PDP context for that specific binding information.

9. The Flow Specific Policy • The flow specific policy is supplied by a PDF for each direction of an IP flow. There can be one or more IP flows to be carried in the one PDP context.

10. IMS PDP Context Procedures • IMS PDP Context Activation • IMS PDP Context Modification • IMS PDP Context Deactivation IMS PDP Context Activation Procedure

11. Unsolicited (PDF initiated) PDP Context Modification

12. IMS Policy Control Test Tools • TTCN COPS Tester emulating PDF in the Go interface • GTPtool: emulates the SGSN. It can be used to send, receive and process GTP-C/GTP-U messages in the Gn interface. • Netcat: provides a tool to send downlink user data packets in Gi interface from any source IP address and port to a wanted UE IP address and port via GGSN. • Ethereal protocol analyzer is used in the emulated Gn, Go and Gi interfaces for verifying the correctness of messages. • GGSN Internal Tools. There are some tools implemented to help the testing to verify the status of PDP contexts and processes running in the GGSN.

13. IMS Policy Control Testing Environment

14. Further Development – Testing Automation • Policy Control functionality found many faults in the code already in the early phase of the testing. This caused much re-testing and regression testing. • The GGSN build contains also other subsystems. Changes to another subsystem requires regression testing also for IMS Policy Control feature • HIT (Holistic Integration Testing). HIT is widely used for automation of testing scripts and macros. It can also run scripts in TTCN Testers.

15. IMS Policy Control Test Automation Network

16. Conclusions (1/3) • The study showed that the Go interface is an interface addition to the GPRS/3G network causing more signaling via the PDF for the PDP context activation, modification and deactivation procedures. • The test planning covered successfully tests for the IMS Policy Control features to achieve functioning code • Studies and testing proved that the COPS/COPS-PR/Go PIB is a functioning protocol stack to provide the IMS Policy Control functionality for the GGSN. • The Go PIB/COPS-PR/COPS protocol stack has also its drawbacks. The stack is over TCP and therefore quite heavy for real-time PDP context signaling. The Go PIB/COPS-PR/COPS structure contains three different layers for handling one PIB. • The Intel COPS Client is more optimal for COPS Differentiated Services (DiffServ) PIB usage. In this case PDP pushes to PEP heavy Decisions seldom and real-time factor is not important.

17. Conclusions (2/3) • The tester proved to be efficient tool for the Go interface testing. Especially, regression and automation testing shows the usefulness of the TTCN COPS Tester. On the other hand, the user must make sure that the structure of the Go COPS message is correct in PRI level. • A lot of faults were found in the COPS and COPS-PR layer for the code based on the open source Intel COPS Client SDK. • As criticism towards the IMS Policy Control we can ask what is the purpose of controlling in detail what the users can do with an open network with intelligent terminals. • GGSN performance problem: The implementation of the Go interface adds the amount of rules the GGSN has to process for every IMS PDP context user data packet. ->ASIC based packet processing?

18. Conclusions (3/3) • Deficiencies in the Specifications: Go interface is a new interface meaning that the standard [29207] is not yet mature and there can be faults in it. This can cause misunderstandings in development and testing process.