The rising volume of communication, as a result of an increasing number of communications subscribers and rising demands on the volume of data to be transmitted, places greater and greater demands on switching centers, in particular on private branch exchanges, with regard to the volume of data to be transmitted for each communications link and the number of communications terminals which are to be connected to one another.
Current devices are based, by way of example, on the TDM method (Time Division Multiplexing), in which communications data on different connections are transmitted in respectively defined timeslots. A connection between different communication parties is set up by a switching matrix which assigns incoming timeslots on an incoming connection outgoing timeslots to an outgoing connection on the basis of a control information item. Such switching matrices are generally of fixed proportions and can set up only a defined number of connections, which often makes it difficult to match exchanges to requirements. Another problem with such devices is that the timeslots are able to hold only a limited amount of data.
On account of different strengths and weaknesses of networks when transporting voice and data in the local domain, various communications networks have become established for specific purposes of use.
FIG. 1 shows an example of a known private branch exchange 150 with two peripheral devices P1 and P2 to which a communications terminal KE1 and KE2 operating on a digital or analog basis is respectively connected. These peripheral devices P1 and P2 are accommodated in the same physical area as the central device ZE1. By way of example, they are in the same room or in the same cabinet as it. The terminals occupy defined timeslots in the PCM data stream (Pulse Code Modulation) with communication data. The digital or analog communications terminals KE1 and KE2 are respectively connected to subscriber line modules SLMO1 and SLMO2 which supply or take digital data, intended for the respective terminals or coming from the respective terminals, to/from the PCM data stream using timeslots stipulated by signaling. These PCM data streams are denoted by 100 and 200 in FIG. 1. In addition, signaling connections are shown which are represented by 110 and 210. It should be noted that these involve a logical representation and not a physical representation. In reality, however, the transport data and the signaling data are transmitted in the same connecting cable.
This figure also shows peripheral devices P1 and P2 and supply modules LTUC1 and LTUC2 which regulate the data traffic to the subscriber line modules of the respective peripheral devices. The peripheral device P1 is supplied with signaling data via the line 110, and the peripheral device P2 is supplied with signaling data via the signaling line 210.
As can clearly be seen here, this arrangement involves both the information to be transported and the signaling information being supplied to a central device ZE1. In this context, a messaging device DCL collects and distributes messages 2 which are interchanged between the central device ZE1 and the peripheral devices P1, P2. The call processing section CP controls the setup and clear-down of connections and, to this end, uses equipment-specific interface functions DH, inter alia, which are in the form of program modules, for example. This involves producing setting instructions 1 for the switching matrix MTS. These setting instructions essentially indicate which input of the switching matrix is to be connected to which output in order to provide a communications link. Control and connection functions are thus performed by a single physically incorporated functional unit in the communications network.
Problems arise with such configurations because the data to be transported need to be supplied to the central device ZE1. This is the case even if, by way of example, two communications terminals which are connected to the same peripheral device P1 need to communicate with one another. The wiring complexity required for such devices increases with increasing distance between the terminals and the central device ZE1, which means that this type of arrangement restricts the extent of a private branch exchange or makes installation much more expensive when covering relatively large areas.
In such devices, problems likewise arise with regard to modular extendibility both in terms of the number of connections and in terms of the volume of data to be transmitted. This type of embodiment does not allow different data rates for each individual communications link.
Alignment and/or transparent integration of different network infrastructures is likewise not possible.