Interoperability services in a GSM – WiMax network

Introduction

This document will describe the various aspects involved in providing and using interoperability services in a GSM – WiMax network. This includes network detection, network selection, log-in, log-out, presentation of billing information, etc., from the points of view of both the user and the operator. The idea is to make the implementation of GSM – WiMax integrated networks user-friendly and operationally efficient.

The document is organized as follows: first a description of the present situation of GSM and WiMax technology and of systems that support interoperability between the two; then a series of considerations that must be supported, such as the various scenarios, processes for assessing the user’s experience; then some technical considerations, architecture descriptions, and the details of a standard solution; and lastly a brief description of future developments being implemented.

Scope

We intend to cover the various aspects of GSM – WiMax network service use, from the perspective of both the user and the operator. We have drawn upon a number of documents of both the GSMA WLAN Task Force and the 3GPP Technical Standards Group.  These determine the guidelines to be followed in WLAN-Cellular networks, considering the user’s experience at the various stages of service use and in the transition between them; they also specify the various interoperability scenarios to be considered.

The document is intended as an introductory guide to the interoperability services and implementations defined in the standards for wireless and cellular networks.

The present situation

The WiMax standard (IEEE 802.16) is emerging globally as the form of broadband wireless access capable of delivering multiples megabits of shared data yield, supporting fixed, portable, and mobile operations. The standard offers great flexibility of design, including support for licensed and non-licensed frequency bands, with channel bandwidths from 1.25 to 20 MHz, establishment of quality of service (QoS) by connection, strong security primitives, multicast support, and low latency and package loss during handovers.

Initially, the deployment of networks based on the 802.16 standard was intended for fixed connectivity access.  Today, the solutions proposed under this standard have evolved to include a phase known as “portability with simple mobility,” providing the user with basic mobility during a session, and future implementation (802.16e) in the phase known as “complete mobility,” in which changes are introduced in the network to support low latency and real-time handovers between APs at speeds of 120 Km./h, or even higher, both within a single network and among various networks.

While the WiMax technology evolves to support portable and mobile services, it means that radio interface requirements call for interoperability and support among networks such as WiFi, GSM, and 3G, to allow transparent access to services, regardless of the radio interface used.

The mere fact of allowing such access to various networks discharges the need for various improvements at the network level.

We will base this analysis on the recommendations of the 3GPP and the GSM Association.

Interoperability considerations

User experience with WiMax – Cellular systems depends on a set of parameters inherent not only to the user but also to the system.

System scenarios

The following scenarios will be considered:

Assuming that the WLAN1 belongs to and possesses interoperability with the home network (HPLMN), the WLAN2 belongs to and possesses interoperability and a roaming agreement with the cellular network (VPLMN) and the WLAN3 is independent, does not belong to any cellular network, but possesses interoperability with one or more cellular networks.

WLAN – cellular interoperability scenarios

Under the 3GPP standards, the following interoperability scenarios should be considered:

• Shared billing and customer service

The customer receives a single invoice for the use of both networks. Integration of customer service simplifies the provision of services.

• The cellular system provides control of access and rates

Authentication, authorization, and accounting are handled by the cellular operator, also aligning security functions.

• Access to the cellular operator’s package switching system

This scenario allows the operator to guarantee access to some or all package switching services through the WiMax network. However, service continuity and handovers are not available.

• Service continuity

This scenario assumes that the cellular network’s package switching service sessions will remain active even when the user is in motion under WiMax network coverage. However, quality could be degraded and package loss could occur during handover.

• Transparent services

This scenario assumes that the cellular network’s package switching service sessions will remain active when the user is in motion under WiMax network coverage, but in a way that minimizes phenomena such as data loss and interruption during handover.

• Access to circuit switching services

This scenario allows access to services provided by the network’s circuit switching entities over the wireless network. It does not involve the inclusion of any type of circuit switching in the wireless network.

It should be possible to provide a technical solution allowing:

• Access to circuit switching services over the wireless interface.
• Transparent switching between access technologies for connections carrying services provided by the network circuit switching entities.

Ruben Kustra
Technological Institute of Buenos Aires (ITBA)