Multiplex communications – Wide area network – Packet switching
Patent
1991-11-05
1994-02-01
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
370 857, 370 951, H04J 110, H04J 308
Patent
active
052837858
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improvement in add-drop multiplexes, known also as add-drop multiplexer, also known in Europe as drop-and-insert multiplexes. Such multiplexes are a particular form of combined multiplexer/demultiplexer for digital signals, optimised for the low cost insertion or extraction of a proportion of the "through" traffic capacity of the multiplex.
2. Description of the Related Art
A digital multiplex combines multiple digital signals streams into a composite stream of digits, each of the digits in the original streams conventionally being allocated to a unique timeslot in the frame structure of the composite stream. Following recognition of the inserted frame start signal at the demultiplexer, the demultiplexer separates the multiple signals so as to restore them to their original form.
In a terminal digital multiplex, all of the capacity of the composite stream is accessible in the form of multiple individual streams; by contrast, in an add-drop multiplex this is commonly not the case, and there are other differences which are outlined below.
It is gradually becoming a common feature of add-drop multiplexes that they incorporate a matrix switch. This switch has the ability to control the routing of traffic in small increments, each of which is a small fraction of the total traffic passing through the multiplex.
Where this fraction is particularly small, the switch has a correspondingly high complexity, because of the large number of such increments to be manipulated, and this invention relates to a proposed simplification of the switch.
SUMMARY OF THE INVENTION
Accordingly the present invention provides an add-drop multiplex comprising a matrix switch, a pair of time slot assignment function circuits connected to the drop-side of the matrix switch, and one or more data buses interconnecting the timeslot assignment function circuits.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the present invention may be more readily understood an embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which;
FIG. 1 a block diagram showing the basic functions of an add-drop multiplex;
FIG. 2 shows conventional add-drop multiplexes,
FIG. 3 shows a network incorporating add-drop multiplexes, and
FIG. 4 is a block diagram of an add-drop multiplex according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1 of the drawings, FIG. 1 shows how an add-drop multiplex is conventionally arranged.
FIG. 1 shows the basic function of an add-drop Multiplex. In the embodiment shown in this figure the traffic is multiplexed demultiplexed at the terminal multiplexes 1 and 2 and sent between the multiplexes via wire links 3. In accordance with requirements the traffic can pass between the multiplexes untouched or can be routed so that it is added to or dropped. Tributaries for adding or dropping traffic are shown at 4. This arrangement has the restriction that it involves the expense of two full terminal multiplexes and requires manual arrangement of the cables each time there is to be a change in routing of any component of the traffic.
Referring now to FIG. 2 of the drawings this shows a conventional add-drop multiplex system where routing flexibility is given by an interchange or matrix switch 5. Optical fibre lines are shown at 6 along with associated optical terminals 7. The output tributaries carrying data to be dropped or added are shown at 8.
The functionality of the interchange or matrix switch varies between designs; in particular it can vary in the following parameters:
a) the size of the smallest increment of traffic which can be routed, and whether such an increment is fixed in size or is variable in the operation of the multiplex.
b) the routing options which are available, e.g. whether the increments can be transferred between timeslots as they pass through the multiplex, or merely be accessed by the add-drop tributary ports (it is not
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Proceedings IEEE Global Telecommunications Conference & Exhibition, Nov. 28-Dec. 1, 1988, Hollywood, Fla., N. Fujimoto et al: "Experiment broadband drop/insert/cross-connect system: 1.8 GBIT/S optical shuttle bus", pp. 954-959.
Proceedings of International Symposium on Subscriber Loops and Services, Sep. 29-Oct. 3, 1986, Tokyo, Japan, K. Murano et al: "A Flexible and autonomous network configuration for broadband subscriber loop transmission", pp. 187-192.
GPT Limited
Patel Ajit
Safourek Benedict V.
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