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GPRS Auto-Configuration in Wireless Wide Area Networks

Updated: May 5, 2003

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Introduction
Overview of GPRS and Configuration Services
GPRS Miniport Driver Communication
GPRS Auto-Configuration Service Architecture
Benefits of the GPRS Auto-Configuration Service
Call to Action and Resources

Introduction

Microsoft is investigating wireless wide area network (WWAN) services that rely on General Packet Radio Services (GPRS) technology. GPRS is a packet-based wireless data communication service that promises continuous connection to the Internet for mobile phone and computer users.

Microsoft and the hardware industry have long shared a goal to design Microsoft Windows operating systems and edge devices (mobile phones, network adapters, wireless access points, and so on) that require little or no intervention on the part of end users. The idea, known as auto-configuration, is that the devices “just work” without complex manual configuration. Auto-configuration is being extended from todays enterprise data networks to WWANs. By supporting the proposed GPRS Auto-Configuration Service in Windows Vista, vendors can achieve Ethernet-style connectivity between PCs, phones, and the WWAN networks.

GPRS Auto-Configuration benefits independent hardware vendors (IHVs) and original equipment manufacturers (OEMs) who create GPRS devices and interfaces that interoperate with Windows operating systems. Through this service, vendors can streamline a configuration task that today is overly complicated for operators and users alike. The approach outlined in this white paper offers several advantages:

Ease of use. IHVs and OEMs can provide a simplified experience for their users similar to the existing 802.11 auto configuration experience and enable simple IP configuration as well.
Access and data transport. Compliant devices and interfaces can provide simultaneous access to control and status information, as well as data transport.
Downloadable profiles. Operators can download profiles to customers. For example, an operator can provide a profile of credentials to a mobile phone, enabling a laptop to copy the profile from the phone.
Profile management. Users who have multiple accounts and services can manage their connection to those services through customized preferences and roaming intelligence

The benefits of GPRS Auto-Configuration are available for the following:

Phones connected through Bluetooth and other interfaces
Personal computer network adapters
Laptops with an embedded radio

This document provides preliminary information to IHVs and OEMs about how to design devices and interfaces that take advantage of the GPRS Auto-Configuration Service in future Windows operating systems.

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Overview of GPRS and Configuration Services

The proposed GRPS Auto-Configuration Service is an extension to the next generation of the Wireless Zero Configuration (WZC) service in Windows XP for wireless local area networks (WLAN). The WZC service dynamically selects a wireless network with which to attempt connection, based either on a users preferences or on default settings. This process includes automatically selecting and connecting to a more preferred wireless network when it becomes available. If none of the preferred wireless networks are found nearby, the WZC service configures the wireless adapter so that there is no accidental connection until the wireless client roams within the range of a preferred network.

In the same way that the WZC service automatically locates all available access points, the GPRS Auto-Configuration Service automates wireless configuration and authentication between a PC and a phone. The interface can use the Bluetooth wireless technology specification.

WWANs and GPRS

WWAN technologies enable users to establish wireless connections over remote public or private networks. Some of the current WWAN technologies based on second-generation (2G) systems have limited roaming capabilities and are incompatible with each other. Still in development are the third-generation (3G) technologies that will follow a global standard to provide worldwide roaming capabilities.

GPRS bridges the gap between 2G and 3G systems by providing a continuous connection to the Internet for mobile phone and computer users. Through the GPRS Auto-Configuration Service, future Windows operating systems can gain access to a GPRS network as a connectionless network. The GPRS Auto-Configuration Service connects a local GPRS network adapter or a remote GPRS phone to a GPRS network. The service then activates the required packet data protocol (PDP) contexts.

The GPRS Auto-Configuration Service is designed for any 2.5G Global System for Mobile Communications (GSM) and later technologies, such as handsets based on the Universal Mobile Telecommunications System (UMTS), a popular 3G mobile technology.

Connections by RADIUS Servers

If the APN requests a connection to a private network, that network is likely to handle authentication, in which case the credentials are taken from the active context request and passed to a RADIUS client. The NAI from the username is then used by the RADIUS client to send a request to the correct corporate RADIUS server. The server can specify the IP configuration, which is passed to the phone by means of the active context response. This IP configuration information does not include the DNS servers IP address.

IP Configuration

The active context request is routed to a Gateway GPRS Support Node (GGSN). After the GGSN accepts the PDP context, it routes IP packets from the phone to the selected network. When the phone receives the IP configuration, it passes this information to the computer. Then IP packets can be sent over the phone, which forwards them to the GGSN, which in turn routes them to the correct network.

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GPRS Miniport Driver Communication

To use the WZC services, a wireless network adapter and its Network Driver Interface Specification (NDIS) driver must support the NDIS object identifiers (OIDs) that are used to query and set device and driver behavior.

To use the GPRS Auto-Configuration Services, vendors must also support the following:

GPRS network adapter driver/firmware. A GPRS miniport driver must support and implement the GPRS OIDs on the top edge as Figure 1 shows.
Bluetooth PAN miniport driver. Remote GPRS phone connectivity is available through UPnP using a personal area network (PAN) profile for Bluetooth.

Figure 1. GPRS Network Adapter Miniport Driver

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GPRS Auto-Configuration Service Architecture

The following sections describe the basic components of the GPRS Auto-Configuration Service and their interfaces. Figure 2 illustrates the overall architecture.

Figure 2. Top-level Architecture of the GPRS Auto-Configuration Services

Any interaction with a local miniport driver or remote phone is through the media-specific layer, which does the following:

Takes commands from the state machine and other components of the configuration service and converts them to the appropriate calls for the underlying GPRS device.
Receives indications from the local miniport driver or phone, including notifications for device arrival and departure, and then informs the controller.
Receives GPRS indications from the underlying devices, and then uses the interface manager to inform the state machine by using the appropriate user mode functions.
Sets IP address configuration for the interface. When the service has been activated successfully, the IP configuration is set into the stack using Dynamic Host Configuration Protocol (DHCP).
Media layer for local GPRS miniport driver. This layer uses Windows Management Instrumentation (WMI) to perform set and query actions and receive indications from the OIDs.
Media layer for Bluetooth-enabled remote phone. The Bluetooth PAN miniport driver communicates with the media-specific layer through WMI.

The media layer for Bluetooth-enabled phones uses UPnP to exchange control and status information over Internet Protocol version 6 (IPv6). The phone, in effect, serves as an IPv6 router that provides a Bluetooth interface on one side and a GPRS interface on the other. However, if a cellular network is not IPv6-enabled, the phone will use both v6 and v4. IPv6 nodes on the same link use the neighbor discovery protocol to discover each other's presence, determine each other's link-layer addresses, find routers, and maintain reachability information about the paths to active neighbors.

The IP configuration is sent differently depending on the version used:

IPv4. DHCP or GSM options are used to send the IP configuration.
IPv6. The IP configuration is prefixed with the IPv6 network and sent through the GSM network to configure the phone.

Media-Independent Layer and Controller

The media-independent layer provides a set of functions as a single interface to the upper layers of the architecture. The media-independent layer receives GPRS indications from the media-specific layers and passes them to the interface manager, which uses the interface to issue commands to the local or remote GPRS devices.

The media-independent layer also provides an interface for the controller, notifying it of new GPRS device arrivals and departures. The controller controls the overall behavior of the service for each GPRS device by tracking the currently available interfaces, keeping them connected and appropriately configured. The controller receives and responds to interface events from the media-specific layer as well as the interface manager.

Data Configuration and Control

The interface manager is central to the GPRS Auto-Configuration. For each of the configured GPRS interfaces (local and remote), the interface manager maintains all the configuration data and control mechanisms in a single structure. The interface manager provides some notifications to the controller, including bad interface behavior and changes in interface characteristics. However, for the most part its management is passive, driven by a client or the controller and also by indications from the media layers.

The interface manager initializes the auto-configuration state machine, which attaches a GPRS device to a GPRS. Through the interface manager, the state machine receives events from the media as well as from internally generated events, and it issues commands to the media layers to request that the GPRS devices perform certain actions.

In addition, the interface manager drives the registry persistence component, which handles the persistence of all configuration data associated with a GPRS interface in the registry.

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Benefits of the GPRS Auto-Configuration Service

Support in future versions of Windows for the GPRS Auto-Configuration Service will provide IHVs and OEMsand end userswith the following benefits:

Automatic operator and APN selection. Clients are attached automatically to the most preferred operator (public land mobile network, or PLMN) that is visible. After successfully attaching to an operator, the service activates the most preferred PDP context.
Device and interruption handling. The service handles the arrival and removal of GPRS devices and also handles multiple GPRS devices. In addition, when a voice call interrupts the GPRS connection, the service smoothly handles the interruption.
On-demand connection. A user can initiate a connection to GPRS networks and disconnect from them. Users can even be shown a list of the cellular operators for which the phone is provisioned and a list of cellular operators currently available to the phone.
Data persistence. The GPRS configuration data is persistent. However, for a manual connection, the persisted data can be bypassed using a one-time configuration setup.
Smart card operability. A Subscriber Identity Module (SIM) can be used to store configuration data. When a user can insert a SIM into a device, a GPRS connection is made.
Error detection. The service detects device errors and provides a graceful interface.

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Call to Action and Resources

Call to Action:

For WWAN terminal device manufacturers: Implement the UPnP for remote phones.
For driver/firmware engineers: Create a GPRS miniport driver to directly manage the network adapter and provides an interface to higher-level drivers. The miniport driver must implement the WWAN OIDs for GPRS.

Resources:

Microsoft Hardware and Driver Developer Information
http://www.microsoft.com/whdc/default.mspx

Microsoft Platform Software Development Kit (SDK)
http://msdn.microsoft.com/downloads/

Microsoft Windows Driver Development Kit (DDK)
http://www.microsoft.com/whdc/devtools/ddk/default.mspx

Microsoft Windows Logo Program System and Device Requirements
http://msdn.microsoft.com/en-us/windows/hardware/gg463010.aspx

Windows XP Application Compatibility Toolkit
http://msdn.microsoft.com/compatibility/

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