| 摘要 |
A switching architecture interconnecting remote switches to a central processor via standard links which may be set up through any number of intervening switching systems utilizing standard switching procedures. The standard links are ISDN links that may be set up dynamically via switching networks within the switching system or via the public switching network. The fact that an ISDN linkgoes through a portion of the switching system or the public switching network is transparent to both the central processor and remote switch. Upon detecting that a primary central processor is no longer in control, each remote switch attempts to obtain an alternate path to the primary central processor. If a remote switch isunable to obtain an alternate path to the primary central processor, the remote switch switches to an alternate central processor on the assumption that the primary central processor has failed. Because the paths can be made on directly connected ISDN links, through the switching system, or through the public switching network to either the primary central processor or the alternate central processor, there is a high probability of a remote switch being able to obtain such a path. To place calls switched by the remote switch under control of the central processor, the remoteswitch and the central processor each execute a plurality of hierarchical call control functions. Utilizing the ISDN protocol, these call control functions initiate and maintain a call through the switching system via the ISDN links. After initiating the call, the remote switch and the central processor establish a transport path on the call. Upon establishment of the transport path, low level call control functions in the remote switch transmit (via the transport path) all signaling and control information for other calls switched by the remote switch to high level call control functions in the central processor. However, the call that is communicating the transport path remains entirely under the control of the call control functions in the remote switch. The high level control functions in the central processor process the information and generate new signaling and control information. In order to control the other calls, this new information is transmitted to the low level call control functions in the remote switch via the transport path. Each ISDN link has a plurality of B channels and a D channel having a number of logical links. The transport path may be established on packetized B channels of the ISDN links communicating the call, on logical links of D channels of the ISDN links communicating the call, or by utilizing user communication facilities associated with the call.
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