Base Station Subsystem

The base station controller (BSC; German base station control means) is a network element of the digital GSM mobile radio network.

General

At the Base Station Controller ( " Base Transceiver Station " BTS, English) are more base stations connected. The connection between a base station and the higher-level base station controller is called the A-bis link. This usually 2 Mbit PCM lines can be realized. Base station controller, base stations and transcoder ( TRC) together form the Base Station Subsystem (BSS).

A plurality of base station subsystem are connected via so-called A- links to a mobile services switching center (MSC). About the MSC telephony and circuit-switched data traffic are handled. For packet-switched data services ( GPRS), however, the base station controller are connected via a Gb connection to a serving GPRS support node (SGSN).

Tasks of the Base Station Controller

The Base Station Controller monitors the wireless connections in GSM network and initiates any necessary power control ( power control) and cell change (handover). If the old and new base station on the same base station controllers are connected during a handover, the controller performs the handover by independent, otherwise the parent MSC is involved.

To obtain a basis for decisions Power Control and Handover, level and quality measurements from mobile station and base station is performed and communicated to the measurement results to the base station controller.

Interfaces

A- bis interface

The A- bis interface between the base station and base station controller tells 64-kbit/s-Kanäle into multiple sub-channels as the voice information is encoded in the mobile network with a lower bit rate. The signaling is performed in accordance with the LAPD protocol to the ISDN DSS1 signaling. In general, the manufacturer also use proprietary protocols for Operation and Maintenance (O & M), so that the A - bis interface is at least partially proprietary. See also: Operation and Maintenance Center

A- ter interface

About the A- ter interface between the base station controller and transcoders of the Base Station Controller requests the encoding of a 64-kbit/s-Kanals for a specific codec. The standard range of the GSM codec for Phase 1 FR ( Full Rate ), FR Phase 2 ( Enhanced Full Rate ), FR Phase 3 (AMR full-rate ) and HR Phase 1 ( half-rate ) and HR Phase 3 (AMR Half Rate ). In the event that the transcoder of the preferred codec is not available, the base station controller is here a list of possible codecs. The A- ter interface is usually proprietary, so it is not usually possible to connect base station controller and transcoders different manufacturers.

A- interface

The A interface to the MSC corresponding to a 2-Mbit/s-Übertragungssystem PCM30 30 bearer channels and a signaling channel. To reduce the need for multiplexers, however, is SDH ( 155 Mbit / s STM- 1). The signaling protocol is part of the Signaling System 7 The A- interface is very well standardized, so that Mobile Switching Center and Base Station Controller from different manufacturers can work together. The A- ter interface is logically direct connection to the MSC, but physically usually runs through the transcoder, in turn, has no logical connection to the MSC.

The Gb interface connects the base station controller to the serving GPRS support node (SGSN) and used for IP -based services. The Base Station Controller serves the Packet Control Unit ( PCU). As transmission technology either Ethernet or Frame Relay is used over 2-Mbit/s-PCM-Leitungen.

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