| 摘要 |
1351717 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 6 July 1972 [9 July 1971] 31664/72 Heading H4K In a private branch exchange catering for telephone subscribers and for data subscribers who may set up calls of differing format, e.g. in speed, modulation or error checking method, every call is initially set up to a telephone junctor and then, if necessary, this is replaced by a data junctor and a so-called data link circuit that provides the necessary interface for the data format involved. A junctor (see Fig. 5) provides line power feed supply SP for both ends of a connection, an a.c. speech path, a unit DU for connecting it to data links DUe, and, optionally, supplies for dial tone WT, and ringing RU as well as dialled digit reception WA and register connecting RA facilities. In Fig. 2 a calling PBX subscriber Tln1 is normally connected to a telephone junctor IVS via switching network NStAnl but in response to digits indicating a data call this connection is replaced by one to data junctor DVS which returns a second dial tone. A register Reg armed with the identity of the wanted party and knowing the caller's identity selects an appropriate pair of data links such as to allow compatible communications between the two parties. In the case of a call to a computer DVA only one link DUe1 or DUe2 is required, these links being operable at different speeds, e.g. 200 and 1200 baud respectively. For an external call a pair, e.g. DUe5, DUe6, are chosen as also is an outgoing relay at AVS of the main network. The link pair may be permanently associated (Fig. 1, not shown), selectively connectible by a switching network KF2 as shown, or interconnectible by a communications computer (Fig. 3, not shown). The latter may incorporate computer DVA and may be remotely located in which case switching network KF1, which gives access to the links, is also remotely located thereby restricting the conductor runs to simply the data message pairs and the control data bus extending from the register via a common control circuit to all the individual control circuits of the switching networks and the computer. Once the connection has been set up and checked by a speech message, the subscribers switch from their telephone sets to their data sets DEE1. Data may be sent using frequency modulation. |
