Design Article
Interworking between WLANs and 3G - Part 2: Tight coupling approach
Vijay Garg
11/5/2010 11:56 AM EDT
The MS supports two radio subsystems (or interfaces) for transporting GPRS signaling and user data (see Figure 22.8).
The first interface is implemented with the GPRS-specific radio link control (RLC)/MAC and physical layers, whereas the second interface is implemented with 802.11-specific MAC and physical layers. These two interfaces provide two alternative means for transporting LLC packet data units (PDUs).
Typically, when the MS is outside a WLAN area, LLC PDUs are transmitted over the GPRS interface (Um). However, when the mobile enters a WLAN area, LLC PDUs are transmitted over the WLAN interface. This switching is performed with the help of WAF and could be completely transparent to the user and to the upper GPRS layers.
The WAF operates in both MS and GIF. It provides an adaptation function for interworking between LLC and 802.11 MAC (in the mobile) and between 802.3 MAC and BSSGP (in GIF). The GIF also implements the GPRS protocols specified on Gb interface, frame relay (FR), network service (NS), and base station subsystem GPRS protocol (BSSGP). The AP implements the 802.11 and 802.3 protocols and a simple interworking function that provides bridging between them.
Next: WLAN Adaptation Function
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