| 摘要 |
This invention relates to a method of establishing connections over a public switched telephone network to a customer whose telephone number is in a block associated, for routing purposes, with a first telephone switching system, but who is actually served by a second telephone switching system. The facility for carrying out this method is desirable in order to serve customers who need the advanced functions of a digital switching system, who are currently served by ananalog switching system, and do not wish to have their telephone number changed when they switch to being served by the digital switching system. In accordance with the invention, a common channel signaling initial address message is sent to the first system. The first system translates the telephone number of that initial address message and finds that the customer for that telephone number is now served by asecond switch. The first switch then sends a release message containing the identification of the second switch back to the source of the initial address message. The source of the first initial address message then sends a second initial address message to the identified second switch and the call connection can now be established to the customer served by the second switch. During the time the customer is being moved from the first switch to the second switch, one of the two returns a "temporarily out of service" type of announcement.
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