Chapter 1. Introduction

By simulating the Foreign Agent and Home Agent required for a Mobile IP connection, the Mobile IP Simulator (MOB-IP-SIM) provides the tools needed for complete developmental testing of wireless devices using Mobile IP as the high-speed data interconnectivity protocol. The wireless device can access web content supplied by the MOB-IP-SIM for testing specific features or can access the Internet by means of the simulator. Two models are available: The MIP-5800 provides the minimum set of configuration parameters needed to support Mobile IP connectivity under standard network conditions, while the MIP-5850 provides additional configuration parameters to allow network error simulation and system configuration control. The MIP-5850 is designed for Mobile IP protocol development and supports test features required to verify compliance with the IS-835 standard. Refer to Figure 1-1 for an conceptual overview of the system.

The previous figure shows the complete Mobile IP network test system. The Agilent E5515C communications test set provides the required cdma2000 or 1xEV-DO radio network emulation and control, containing the radio link, call setup, and Inter-Working Function (IWF) needed for packet data communications. A second E5515C may be connected for hybrid cdma2000/1xEV-DO testing of a single mobile station. The MOB-IP-SIM supports only a single mobile station; therefore, this configuration is useful only for hybrid-mode testing. The MOB-IP-SIM provides the additional IP network elements needed to complete the Mobile IP network simulation environment, namely the simulated PDSN, Foreign Agent (FA), and Home Agent (HA).

The combination of the E5515C and the MOB-IP-SIM therefore provides a complete solution for Mobile IP connectivity and testing, allowing you to choose levels of features that range from basic connectivity to semi-automated conformance testing.

The simulator is contained in a small enclosure with serial port and LAN connectors. PPP data running over the LAN interfaces the Mobile IP simulator to a cdma2000 or 1xEV-DO communication test set and supports Mobile IP for a single device. The LAN connection provides a web-based user interface to configure the simulator as well as a text-based command port. Configuration requires setting the MOB-IP-SIM to match your specific LAN connection, setting the PPP links for Simple IP and Mobile IP provisioning and operation, and setting up the NAT router. The user interface also provides access to system and data logs and online documentation.

The relationship of the various components required to set up an end-to-end data call is indicated in Figure 1-2.

The mobile station makes a data call or session to the Agilent E5515C, which forwards the data to the MOB-IP-SIM's internal PDSN. If the mobile supports hybrid mode, it can maintain a registration on a cdma2000 network and a data session on a 1xEV-DO network simultaneously; to test this behavior, two E5515C sets are required. The PDSN handles the PPP frames and forwards registration and user data messages between the home agent and the radio network. In hybrid mode, this includes keeping track of which radio network the mobile is using.

The home agent processes registration requests, consulting the AAA to decide how to handle them. It also forwards the user data to the IP network. The MIP-5850 supports simulation of three home agents; the MIP-5800 supports only one.

The AAA examines each incoming registration request and decides, based on the authenticator and timestamp, whether to accept or reject it. In addition, the AAA can perform dynamic mobile-IP key update (DMU), which uses public-key cryptography to set up the shared MN-HA, MN-AAA, and CHAP keys securely.

The MOB-IP-SIM includes a router with optional network address translation (NAT). NAT mapping allows the mobile station to share the MOB-IP-SIM's address when contacting external servers, so the MOB-IP-SIM and mobile need only one IP address on your LAN. The drawback to this mode is that servers on the LAN cannot initiate connections to the mobile, as the MOB-IP-SIM would receive the connection attempts. NAT redirection allows you to redirect the mobile's connection requests to the server of your choice. This can be useful when testing mobiles or applications with hard-coded IP addresses.

The MOB-IP-SIM includes an FTP server and an HTTP server, into which you can upload your own content for testing. See Appendix A for details. In addition, the HTTP server is used to configure everything. See Chapter 3.

The HTTP proxy allows mobiles with HTTP mini-browsers (also known as WAP 2) to communicate with HTTP origin servers. It translates GIF images to PNG as required. The proxy can modify the requested URL before sending the request. This allows testing mobiles or applications with hard-coded URLs. The URL rewriting mechanism is described in detail in the Section called HTTP Proxy Configuration in Chapter 3. The proxy can communicate directly with an origin server, or it can use another proxy if required by local network policy.

If you need functionality beyond basic HTTP and FTP service, you can connect the MOB-IP-SIM to external servers, either on your local network or elsewhere on the Internet.

The MOB-IP-SIM provides three types of access to network packets. PPP frames in transit between the mobile station and the PDSN are captured in a file for inspection with any network analyzer that supports tcpdump format. All Ethernet frames between the MOB-IP-SIM and the Ethernet are repeated out a second network port for capture and analysis (see Appendix D. In addition, the MIP-5850 has AT commands to capture and analyze PPP frames.

The MOB-IP-SIM must be configured to work within the bounds of your local area network. This configuration, covered in Chapter 3, sets up access to the external Internet and provides routing connections to other entities that you may plan to use as part of your wireless IP test environment. Setup is accessed through any standard Internet browser connected to the LAN where the simulator is installed. The MIP-Manager, a simulator setup utility, is included on the accompanying CD to assist with the initial installation.

The MIP-5800 simulator provides web-based user access to the basic parameters needed to provision the mobile device for Simple IP and Mobile IP operation.

The MIP-5850 simulator provides dynamic control of many additional test parameters that can be modified prior to a data connection attempt or during the data connection in some cases. The most common setup parameters can be set using the web-based interface, while more complex controls must be changed using "AT" commands sent from a terminal or conformance test script.

The following table indicates the features supported by the two models of the Mobile IP Simulator.