Advanced Cross-Layer Mobility Mechanisms in a Heterogeneous WLAN Scenario
Authors
Abstract
The IEEE 802.11 standard [1, 2] has become very popular as access technology in multiple scenarios, such as schools, commercial public areas, and homes. Originally, this Wireless Local Area Network (WLAN) standard was conceived to provision devices with wireless network connectivity and did not provide mechanisms for Quality of Service (QoS) support. As multimedia applications such as Voice over IP (VoIP),Video Streaming and Video Conferencing have become widely used, IEEE 802.11 has been extended to support QoS provisioning mechanisms.The combination of WLAN as end-user access network with broadband-wired access technolo- gies, such as Digital Subscriber Line (DSL), as a backhaul connection, is a common deployment scenario, which is able to fulfill the major requirements of almost all typical Internet applications. Recently broad- band wired access technologies are being complemented with broadband wireless access technologies to support end-user mobility and to enable faster deployment in remote areas. However, the integration of IEEE 802.11 access with backhaul connections using broadband wireless technology creates new challenges concerning the innate resource reservation and mobility mechanisms of these technologies that must be addressed to successfully fulfill user requirements.
Worldwide Interoperability for Microwave Access (WiMAX) [3] is one of the technologies fac- ing the challenges of 3G and beyond broadband wireless access technologies. As frequency licensing is becoming commercially available throughout the world, it is still unclear whether WiMAX will be better positioned than its main competitors, such as High Speed Packet Access (HSPA) and Long
Term Evolution (LTE). All these technologies can be used in diverse network scenarios, namely as a real end-user access technology or in the backhaul using, for instance, IEEE 802.11 as access tech- nology. Concerning the later scenario, it is critical to evaluate the behavior of both IEEE 802.11 and WiMAX technologies within the foreseen all-IP communications world and taking into ac- count the management of a seamless mobility scenario between different IEEE 802.11 access net- works.
In the challenging environment described above two types of mobility can be considered, namely micro and macro mobility. Micro mobility is usually handled by the technology. However, when there is mobility between different networks, there is a need to perform mechanism at the IP layer, which is known as macro-mobility. One of the possibilities to enable the macro-mobility support is to use a technique named make-before-break, where the future connection and possible resource reservations are handled before the current connection is broken. The mobile version of WiMAX has native support for micro mobility. However it does not support, by itself, Internet Protocol (IP) Layer-3 mobility mechanisms, which need to be included in order to handle macro mobility.
Even though WiMAX is a natural candidate for the last mile wireless broadband access due to the innate quality of service capabilities and the higher bandwidth supported when compared with the third generation of mobile telecommunications standards (3G) competitors, there are a few problems regarding the technology deployment and costs. WiMAX systems have the potential to offer a good tradeoff cost/benefit solution to cover inaccessible and isolated areas within an all-IP network. However, in many cases end-users equipments are not yet able to supportWiMAX,which increases the deployment cost. To accomplish a better cost/benefit tradeoff, a possible solution is to use WiMAX as a backhaul solution and IEEE 802.11 as access technology for the end-users. The challenge is how to achieve an EEE 802.11 seamless handover support within a WiMAX backhaul network using the information gathered within the WLAN.
To overcome this challenge, this work proposes a seamless mobility schema between different IEEE 802.11 networks, when WiMAX is used as the backhaul technology. The proposal includes the configuration of the QoS mechanisms, mobility management and resource reservation modules as well as the cross-layer approach employed. Moreover, the Media Independent Handover (MIH) [4] and an extension to the Next Steps in Signalling Framework (NSIS) [5] for mobility management support was designed and integrated in the mentioned scenario.
The chapter is organized as follows: Section 14.2 describes the WiFi and WiMAX technologies, as well as the mobility handover assistance mechanisms, within the cross-layer design principle. Section 14.3 presents a detailed description of the proposed seamless mobility approach. The results of the experimental validation of the proposal on a testbed are discussed in Section14.4. Finally, Section14.5 presents the main conclusions of the work.