電子類畢業(yè)設(shè)計(jì)中英文翻譯-其他專業(yè)(參考版)
2025-01-23 03:11本頁面
【正文】 . The transport packet and the PES packet are pletely defined in the MPEG2 System specification [1]. . TSI upper layers Apart from the Packetised Elementary Stream, any layering or structure of the MPEG2 data above the Transport Stream layer is not relevant to this specification. However the specification does assume that the module will find and extract certain data required for its operation, such as ECM and EMM messages, directly from the Transport Stream. 。. If scrambling is performed at Packetised Elementary Stream (PES) level, then the module reacts in the same way and under the same conditions as above, and returns the corresponding descrambled PES with the PES_scrambling_control flag set to 39。s Transport Stream path. It is acceptable that some Transport Stream data is lost during this process. At the same time a Transport Layer connection shall be established on the Command Interface to allow Application Layer initialization to take place and normal Application Layer munications to proceed. If the Physical Layer is used in other applications than as a DVBconformant module connection, and if a nonconformant module is connected to the host, no damage shall be caused to the module or the host, and the host shall not attempt to plete initialization as though it were a DVBconformant module. Optionally, the host may signal to the user that an unrecognized module has been connected. On disconnection of the module, the host shall remove the module from the Transport Stream data path. It is acceptable that some Transport Stream data is lost during this process. Also, the Command Interface connection shall be terminated by the host. . Multiple Modules The Application Layer places no limit on the number of modules that may be connected to the host at any time. However, particular Physical Layers and particular host design choices may do so. The Physical Layer specification must allow there to be several modules connected simultaneously to the host, even though a minimum host design may only provide for one connection. Ideally the Physical Layer specification should place no hard limit on the number of modules, but if a limit is imposed, then it shall be set at no less than 15 modules. Where there is provision for more than one module to be connected, the Transport Stream Interface connection shall be daisychained through each module in turn, as illustrated in figure below. The host shall maintain separate and simultaneous Command Interface connections to each module, so that transactions between host and module are treated independently for each module. When a module is unplugged the Command Interface transport layer connection to any other module shall not be disturbed or terminated. When several modules are connected to a host, the host should be able to select the module(s) relevant for the descrambling of the selected service(s). . Operational Example To illustrate some of the features described above consider this example of the processes that occur when a PC Card module is plugged into a host. The PC Card initialization mences with sensing of the module being plugged in by sense pins on the interface. The host then reads the Card information Structure residing in the Attribute Memory of the module. This contains lowlevel configuration information for the module, such as PC Card read and writes addresses used by the module, and indicates to the host that it is a DVBconformant module. The host now turns off the Transport Stream Interface bypass link and allows the transport packets to flow through the module. This introduces a delay, and consequently a short gap in the Transport Stream data, but this is unavoidable. At the same time the physical layer interface initialization process takes place to negotiate the buffer size to be used for munication. At this point the physical layer initialization process is plete and the upperlayer initialization process, mon to all physical implementations, mences with the host creating a Transport Layer connection to the module. This process and the rest of the upperlayer initialization process are described elsewhere in this document. The i
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