外文翻譯---理論研究通用分組無線業(yè)務-在線瀏覽
2025-07-31 09:06本頁面
【正文】 subscriber to initiate or receive a voice call without interrupting a data transmission or reception activity. This type of terminal probably will not be available when GPRS is initially deployed due to its plexity and high cost. An MS of classB is able to connect to both GSM and GPRS at the same time but an ining voice call requires GPRS data transactions in progress to be suspended for the duration of the call. GPRS data transactions can then resume at the end of the voice call. Finally, a classC MS allows subscribers to access one service type only at a given time in an exclusive manner. The GPRS MS has two ponents: a MT (Mobile Terminal) which is typically a handset used to access the radio interface as a radio modem, and a TE (Terminal Equipment) which is typically a laptop or a PDA (Personal Digital Assistant). GPRS MSs will also e as one unit bining the functionalities of an MT and a TE. Base Station Subsystem GPRS has minor impact on the existing GSM BSS making it easy to reuse existing ponent and links without major modifications. This is possible because GPRS uses the same frequency bands and hopping techniques, the same TDMA frame structure, the same radio modulation and burst structure as GSM. A new functional ponent called PCU (packet control unit) was added to the BSS in the GPRS standard to support the handling of data packets. The PCU is placed logically between the BSS and the GPRS NSS. Unlike the voice circuit connections however, connections in GPRS have to be established and released between the BSS and the MS only when data need to be transported over the air interface. Therefore, ETSI has defined new procedures to adapt such connections. Network Switching Subsystem The GPRS NSS can be viewed as an overlay work ensuring the link between mobile users and data works. GPRS introduces a new functional element to the GSM infrastructure: GSN (GPRS Support Node) which can be either a SGSN (ServingGSN) or a GGSN (GatewayGSN). This addition is necessary for the GSM work in order to support packet data services. The work is generally divided into several service areas controlled by separate SGSNs. Only one SGSN serves an MS at a given time provided it is located in its service area. The SGSN is primarily responsible for keeping track of the MSs it serves, and for access control to data services. The GGSN on the other hand provides the interface to external PDN (Packet Data Networks). The SGSN is connected to the BSS by frame relay and to possibly several GGSNs via a GPRS backbone work. The HLR database is updated to contain GPRSsubscriber information. Adaptations to an existing MSC/VLR are not required but the GPRS standard suggests some enhancements to coordinate between the SGSN and the MSC/VLR if the optional interface between the two is to be supported. Several interfaces have been introduced in GPRS to define entitytoentity interactions. For instance, the Gb interface is required between the BSC and the SGSN. Two GSNs municate through a Gn interface, and the SGSN sends queries and receives subscriber information to/from the HLR through the Gr interface. The Gs interface between the SGSN and the MSC/VLR was left optional while the Gi interface which connects a GGSN to a PDN was not specified in the standard to allow implementation preferences. As mentioned, GPRS standard activities focused mainly on PTP connections to IP PDNs at the Gi interface. An example of such IP PDN can be a corporate Intra where access is restricted to authenticated corporate employees allowing them to access for instance the corporate web and mail servers. Another example is connectivity to an ISP (Inter service provider) offering In
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