Given the increasing penetration of Internet Protocol (IP) technologies and the tremendous growth in wireless data traffic, the telecom industry is evolving towards All-IP based Next Generation Networks (NGN). The Third Generation Partnership Project (3GPP) has specified an IP Multimedia Subsystem (IMS) in 3GPP Release 5 to support converged multimedia applications across both wireless and wireline devices. IMS provides full packet call control capabilities by using the Session Initiation Protocol (SIP). SIP has been chosen by 3GPP as the signaling protocol to handle user registrations and multimedia session management in the IMS. Using IP protocols defined by the Internet Engineering Task Force (IETF), IMS will merge cellular networks and the internet, offering new service capabilities for rapid service creation and deployment of integrated IP multimedia applications.
This diploma thesis provides an insight into the IP Multimedia Core Network, specifically focusing on its key element, the Call Session Control Function (CSCF). The CSCF serves as control point to manage all IMS sessions in the network, whether they are voice, video, data, messaging, gaming, or any other service. Moreover, this paper discusses the requirements identified by 3GPP to support SIP in cellular networks, and the extensions to the SIP protocol suite in order to fulfill them.
The practical part of the thesis evaluates the Open Source IMS Core platform of the Fraunhofer Institute FOKUS with respect to the CSCF which is based on the SIP Express Router (SER). The analysis describes the new modules and advanced functions of SER, required to cope with the extended version of SIP and to act as a CSCF for IMS purposes.
At a glance
- Grade: 1.0 (1.0 is the best grade)
- Practical testbed built on Open IMS Core Revision 199
- Single-machine IMS testbed with multiple virtual network interfaces
- 73 sources in the bibliography
- 88 figures and 7 tables
Contents
Abstract
1. Purpose of this Thesis
2. Introduction
I UNDERSTANDING IMS
3. Principles of the IP Multimedia Subsystem
3.1. What is the IP Multimedia Subsystem?
3.2. IMS Specification Bodies: 3GPP and IETF
3.3. High Level Requirements
3.3.1. Differences to RFC 3261 SIP
3.3.2. Registration
3.3.3. Session Setup & Control
3.4. Private Header Extensions to SIP for 3GPP
3.4.1. P-Access-Network-Info Header
3.4.2. P-Asserted-Identity Header
3.4.3. P-Associated-URI Header
3.4.4. P-Called-Party-ID Header
3.4.5. P-Charging-Function-Addresses Header
3.4.6. P-Charging-Vector Header
3.4.7. P-Media-Authorization Header
3.4.8. P-Preferred-Identity Header
3.4.9. P-Visited-Network-ID Header
3.4.10. Path Header
3.4.11. Security-Client Header
3.4.12. Security-Server Header
3.4.13. Security-Verify Header
3.4.14. Service-Route Header
4. The IP Multimedia Subsystem Architecture
4.1. Home Subscriber Server
4.1.1. Private User Identity
4.1.2. Public User Identity
4.2. Subscription Locator Function
4.3. Application Server
4.4. Media Gateway Control Function
4.5. IP Multimedia Subsystem Media Gateway
4.6. Signaling Gateway
4.7. Multimedia Resource Function
4.7.1. Multimedia Resource Function Controller
4.7.2. Multimedia Resource Function Processor
4.8. Breakout Gateway Control Function
4.9. IMS Application Layer Gateway
4.10. Transition Gateway
5. The Call Session Control Function
5.1. Proxy Call Session Control Function
5.1.1. P-CSCF Discovery
5.1.2. Discovery of I-CSCF in Home Network Domain
5.1.3. Confidentiality and Integrity Protection of SIP Signaling
5.1.4. Signaling Compression
5.1.5. Treatment for SIP Dialogs and Transactions
5.1.6. Bearer Authorization & Quality of Service Management
5.1.7. Subscription to reg event state at the S-CSCF
5.1.8. Charging
5.1.9. Emergency Services
5.2. Interrogating Call Session Control Function
5.2.1. User Location Query Procedure
5.2.2. User Registration Status Query
5.2.3. S-CSCF Assignment during IMS Registration
5.2.4. Topology Hiding Inter-network Gateway
5.2.5. Network Domain Security
5.2.6. IMS-Application Layer Gateway
5.2.7. Charging
5.3. Service Call Session Control Function
5.3.1. Subscriber Authentication
5.3.2. S-CSCF Registration Notification
5.3.3. Notification Server for “reg”-event
5.3.4. Treatment for SIP Dialogs and Transactions
5.3.5. Charging
5.3.6. Timer Supervision
II IMPLEMENTATION
6. Testbed Specification
6.1. Introduction
6.2. Architecture
6.3. Hardware and Software Components
6.4. Open Source IMS Core
7. Open IMS Core Installation
7.1. Prerequisites
7.2. SIP Express Router
7.3. Fraunhofer HSS
8. Open IMS Core Configuration
8.1. Domain Name Service
8.2. Proxy Call Session Control Function
8.3. Interrogating Call Session Control Function
8.4. Serving Call Session Control Function
8.5. Home Subscriber Server
8.6. User Endpoints
8.6.1. Snom Phone
8.6.2. eyeBeam Software Client
8.6.3. SIPp performance testing tool
9. The Open IMS Core CSCF Modules
9.1. The Proxy CSCF Module
9.1.1. REGISTER Request
9.1.2. REGISTER Response
9.1.3. NOTIFY Request
9.1.4. Mobile-Originating Request
9.1.5. Mobile-Terminating Request
9.2. The Interrogating CSCF Module
9.2.1. REGISTER Request
9.2.2. Initial Request
9.3. The Serving CSCF Module
9.3.1. REGISTER Request
9.3.2. SUBSCRIBE reg event Request
9.3.3. Mobile-Originating Request
9.3.4. Mobile-Terminating Request
III DISCUSSION
10. Conclusions
11. Future Work
Objectives and Topics
This thesis evaluates the Fraunhofer FOKUS Open Source IMS Core and asks how IMS-specific SIP Express Router modules and functions enable the platform to operate as a Call Session Control Function. It combines an examination of IMS standards and signaling with a practical testbed implementation and analysis of the platform’s routing logic.
- IMS architecture and 3GPP requirements
- SIP extensions for registration and session control
- Proxy, interrogating and serving CSCF roles
- Testbed installation, configuration and endpoints
- IMS-specific router modules and signaling flows
- Security, charging and quality of service
Excerpt from the Book
5.1.3. Confidentiality and Integrity Protection of SIP Signaling
As part of the IMS access security the P-CSCF is responsible to protect traffic between the IMS terminal and the network. This functionality includes the confidentiality protection to SIP signaling messages between the UE and the P-CSCF but also integrity protection which means the ability for the receiver of a message to verify that the SIP message has not been modified in transit.
IMS security mechanisms are based on the Authentication and Key Agreement (AKA). The UE shall always offer encryption algorithms for the P-CSCF to be used for the session. The P-CSCF shall decide whether the IMS specific encryption mechanism is used. If used, UE and P-CSCF shall agree on Security Associations (SAs), which include the encryption key for confidentiality protection and the integrity key for integrity protection.
The UE and the P-CSCF shall both verify that the data received originates from a node, which has the agreed integrity key. Integrity protection relates to the calculation of a secure hash value known as the Integrity Check Value (ICV) and the amendment of this hash value to the original SIP-message. This verification is also used to detect if the data has been tampered. 3GPP TS 33.203 [21]
Two pairs of (unilateral) Security Associations are established between the UE and the P-CSCF. The subscriber may have several IMPUs associated with one IMPI. These may belong to the same or different service profiles. Only two pairs of SAs shall be active between the UE and the P-CSCF. These two pairs of SAs shall be updated when a new successful authentication of the subscriber has occurred.
With each pair of security associations established in an authenticated registration two ports are associated at the UE and the P-CSCF (⇨ Fig. 31). port_pc and port_ps are the protected client and protected server ports at the P-CSCF. port_uc and port_us are the protected client and protected server ports at the UE. These ports are different from the standard SIP ports 5060 and 5061 and should not be used for the transmission of unprotected messages.
Chapter Summaries
1. Purpose of this Thesis: The author places IMS in the context of next-generation networks and sets out the evaluation of the Fraunhofer platform and its SER-based CSCF.
2. Introduction: The introduction explains the organization of the thesis and the relationship between its standards-based discussion and practical implementation.
3. Principles of the IP Multimedia Subsystem: This chapter introduces IMS requirements, specification bodies and SIP extensions for cellular multimedia services.
4. The IP Multimedia Subsystem Architecture: The chapter describes the network’s functional entities, subscriber information, application servers and gateways.
5. The Call Session Control Function: The author examines the proxy, interrogating and serving CSCFs, including registration, authentication, routing, security and charging.
6. Testbed Specification: This chapter describes the test environment, its architecture, hardware, software and the Open IMS Core revision used.
7. Open IMS Core Installation: The installation chapter covers prerequisites and the setup of the SIP Express Router and Fraunhofer Home Subscriber Server.
8. Open IMS Core Configuration: The author explains configuration of DNS, CSCF components, subscriber data and user endpoints, including SIPp.
9. The Open IMS Core CSCF Modules: This chapter analyzes the routing logic of the proxy, interrogating and serving modules for registration and session requests.
10. Conclusions: The author discusses the evaluation and its implications for the prototype’s relationship to IMS specifications.
11. Future Work: The final chapter considers the role of an open IMS platform in research, interoperability testing and service development.
Keywords
IP Multimedia Subsystem, Open IMS Core, Fraunhofer FOKUS, Call Session Control Function, SIP Express Router, Session Initiation Protocol, 3GPP, IMS testbed, SIP extensions, subscriber authentication, signaling security, session routing, Home Subscriber Server, SIPp
Frequently Asked Questions
What is the thesis about?
It evaluates the Fraunhofer FOKUS Open Source IMS Core, with particular attention to its call session control functions.
What are the main topics?
The thesis covers IMS architecture, SIP extensions, CSCF roles, signaling security, testbed configuration and implementation logic.
What is the primary objective?
The author aims to evaluate the platform and analyze how IMS-specific SIP Express Router modules and functions support CSCF operation.
What method does the author use?
The work combines analysis of technical specifications with implementation and evaluation of an Open IMS Core testbed and examination of its routing modules.
What does the main body cover?
It explains IMS network functions and signaling procedures before presenting the testbed, installation, configuration and CSCF module analysis.
Which keywords characterize the work?
Key terms include IMS, CSCF, SIP, SIP Express Router, 3GPP, subscriber authentication and Open IMS Core.
How are the three CSCF roles distinguished?
The proxy CSCF provides the endpoint’s signaling entry point, the interrogating CSCF locates or selects a serving CSCF, and the serving CSCF manages session control and subscriber-related services.
What platform version does the testbed use?
The implementation is based on Open IMS Core Revision 199 and runs its network entities on one machine using multiple virtual network interfaces.
How is SIPp used in the testbed?
SIPp is configured as a user endpoint, with an XML scenario for IMS registration and deregistration and an external file for authentication data.
- Quote paper
- DI(FH) Mag. Rainer Hallwachs (Author), 2007, Evaluation of the Fraunhofer Open Source IMS Core platform with special focus on the Call Session Control Function (CSCF), Munich, GRIN Verlag, https://www.hausarbeiten.de/document/134743
