Multiplex communications – Wide area network – Packet switching
Patent
1983-12-29
1985-12-17
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 58, 370 67, H04Q 1100, H04Q 1104
Patent
active
045596247
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a digital concentrator for time-division-multiplex (TDM) channel set-ups from incoming subscriber lines to outgoing PCM links, the concentrator including line circuit modules, each one connected to a group of subscriber lines, the total number of channels in the links being less than the total number of subscriber lines and the number of links being less than the number of line circuit modules.
BACKGROUND ART
For channel set-ups from a single group of subscriber lines, constituting a single incoming TDM line, to a single outgoing PCM link, a single time stage for switching in time is sufficient for providing a set-up between an arbitrary subscriber line and an arbitrary link channel. However, a large digital concentrator including a plurality of subscriber line groups and a plurality of PCM links going to a central transit exchange needs, in principle, both a time stage for switching in time and a space stage for switching from an arbitrary incoming TDM line to an arbitrary outgoing PCM link.
It is known, e.g. from the U.S. Pat. No. 4,167,652 that the space stage can be avoided if a TDM bus system is provided, to the input modules of which are connected all TDM lines for transferring of information coming from the subscribers. PCM links for transferring information intended for the central exchange, as well as outgoing TDM lines for transferring internal information from one to the other of the subscribers without loading the PCM links, may be connected to the output modules of the bus system.
A so-called time-time system is obtained, which carries out a first time switch from an incoming subscriber channel to a bus channel and a second time switch from this bus channel, either to an outgoing link channel or to an outgoing subscriber channel. The time-time system is congestion-free if the number of bus channels is just as great as the total number of subscriber lines, the concentrator effect then occurring between the bus and the outgoing PCM links. Known TDM buses in large time-time systems are very high-speed and include very complicated input and output modules. Designs with two-way traffic on the bus and loop bus designs for one-way traffic are also known.
DISCLOSURE OF THE INVENTION
One object of the present invention is to provide a digital concentrator for a plurality of subscriber line groups and a plurality of PCM links without a space stage, and a TDM bus which is low-speed and uncomplicated as far as possible, by not dimensioning the bus so that it is free from congestion. If a bus, which has been connected in accordance with the above to the subscriber line groups and to the PCM links, has a number of TDM channels lying between the total number of PCM link channels and the total number of subscriber lines, there is obtained a two-stage concentration from the incoming subscriber lines to the outgoing PCM links and a one-stage concentration from the incoming to the outgoing subscriber lines. If there is congestion on the bus due to intensive internal traffic between the subscribers, congestion is also obtained to the central exchange even if there are idle channels on the PCM links. If the number of channels on the bus is less than the total number of channels on the links, the concentration is entirely disposed between the subscriber lines and the bus, and the risk for bus congestion will then be particularly large.
A further object of the invention is the avoidance as far as possible of congestion to the central exchange due to congestion on the simplified bus, this being effected by connecting the subscriber line groups in a novel manner to the bus and to the PCM links. Apart from the time stage for time-time switching from the subscriber lines via the bus to the link channels, time stages are also arranged for switching from a subscriber line group directly to an assigned PCM link. The inventive concentrator is controlled so that time-time switching is carried out only if a direct set-up from subscriber to PCM link is impossible because
REFERENCES:
patent: 3787631 (1974-01-01), Lewis
patent: 4354264 (1982-10-01), Wurst
patent: 4366566 (1982-12-01), Cochennec
Fagerstedt Nils U. H.
Pehrson Jens E.
Roos Sture G.
Chin Wellington
Olms Douglas W.
Telefonaktiebolaget LM Ericsson
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