RNC3810—Ericsson’s first WCDMA radio network controller

As the cellular industry has evolved from first-generation to third-generation cellular systems, system architects have refined the role of nodes in the network. In hindsight, one can say that the architects of firstgeneration cellular systems, such as AMPS and NMT, had quite modest expectations regarding the scope of future traffic volumes. Accordingly, a simple architecture could meet these modest needs: all control resided within a single node—the mobile switching center (MSC)—which managed the call, the subscriber, mobility, and the base transceiver station (BTS). When the system architects defined the architecture for GSM, they drew on experiences of first-generation networks, revising expectations for growth, improving multivendor capabilities, operations, and so on. New demands pointed to the need to separate subscriber aspects from radio aspects. As a consequence, the MSC, BSC and BTS were designed as separate nodes. This architecture has served the industry well and allowed GSM networks to grow far beyond early expectations. As the name implies, the base station controller (BSC) is responsible for controlling base stations (BTS), including most handover tasks. All subscriberrelated and most call-related tasks have been retained in the MSC. Later, when work was begun on the architecture for third-generation systems (WCDMA), significant experience had been gained from second-generation systems. Numerous services that had not even been envisioned at the inception had been introduced successfully. However, the radio technology had shown itself to be more noticeable to the core network nodes than was desirable. Given the multitude of services envisioned in the Mobile Internet, the architects understood that they would need to better isolate the radio resources from the core network. They selected GSM as the base for the new architecture, but saw the shift in generations as a window of opportunity for making certain desirable adjustments (Figure 2). In the third-generation specification, the successor to the BSC has a modified role and a new name: radio network controller (RNC). The key external interfaces of the radio network are • the air interface to the terminal or handset, designated Uu; and • the interface to the core network, designated Iu. The Iu interface corresponds to the A and Gb interfaces in GSM and GPRS. The internal interfaces of the radio access network are as follows: • Iub—which corresponds to the Abis interface in GSM; and • Iur—this is a new interface. It is required for performance in CDMA networks and to make mobility transparent to the core network.