Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1997-06-05
2001-02-13
Kizou, Hassan (Department: 2738)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C370S398000, C709S244000
Reexamination Certificate
active
06188686
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to switching apparatus for use, for example, in asynchronous transfer mode (ATM) networks.
2. Description of the Prior Art
FIG. 1
of the accompanying drawings shows parts of switching apparatus previously considered for use in an ATM network. The switching apparatus
1
includes a plurality of data units
2
0
to
2
3
, each data unit having an input portion
4
0
to
4
3
and an output portion
6
0
to
6
3
. In
FIG. 1
, the output portion
6
of each data unit
2
is shown separately from the input portion
4
of the unit concerned, so as to clarify the operation of the apparatus, but it will be appreciated that both the input and output portions
4
and
6
form part of the same data unit
2
.
Each data unit
2
is connected to one or more data input/output ports DP
0
to DP
7
of the switching apparatus; for example, as shown in
FIG. 1
, each data unit is connected to a pair of data ports DP.
The apparatus
1
further comprises a cross-connect switching unit
8
having as many input ports IP
0
to IP
3
and as many output ports OP
0
to OP
3
as there are data units
2
. Each input portion
4
is connected to one of the input ports IP and each of the output portions
6
is connected to one of the output ports OP.
The cross-connect switching unit
8
is controllable selectively to provide connections between its input ports and its output ports. Up to four simultaneous connections, each between one of its input ports and one of its output ports, can be provided. For example, if data is received by the apparatus
1
at data port DP
2
(the “source” data port) that is to be routed to data port DP
4
(the “destination” data port), the cross-connect switching unit
8
is configured to provide a connection between the input portion
4
1
of the data unit
2
1
(the “source data unit” having the source data port DP
2
connected to it) to the output portion
6
2
of the data unit
2
2
(the “destination data unit”) which has the destination data port DP
4
connected to it. Thus, the source data unit
2
1
and the destination data unit
2
2
form a data-unit pair and are allocated a data transfer path within the apparatus for use in passing data from the source data unit of the pair to the destination data unit of the pair. At the same time, up to three other such data-unit pairs can be allocated respective data transfer paths by the switching unit
8
to enable data received at source data ports connected with the respective source data units of those pairs also to be routed through the switch to the respective destination data units of the pairs, those destination data units being connected with the relevant destination data ports.
Since it is possible for two (or more) source data ports to wish to communicate at the same time to the same destination data port, it is normal to make provision for some buffering of the data at some point within the switching apparatus, either within the data units
2
or in the cross-connect switching unit
8
, or possibly in both. This buffering holds up the data of one of the two contending source data ports pending transfer to the intended destination data port of the data received at the other of those two contending source data ports.
In practice, switching apparatus for use in an ATM network may require a large number of data ports and hence a large number of data units
2
. For example, it may be desired to provide ATM switching apparatus with several hundred data ports. This inevitably requires a large number of data units
2
and a correspondingly-large number of input ports and output ports on the cross-connect switching unit
8
.
However, the number of input ports and output ports which a switching unit can have is limited when (as is generally desired) the switching unit is formed as an integrated circuit. For example, it is not readily practicable to provide an integrated circuit package with more than 300 connection pins at the sorts of data transfer rate required in ATM switching applications.
It is accordingly desirable to provide switching apparatus in which the above-mentioned restriction on the number of input and output ports of the cross-connect switching unit no longer limits the size of the switching apparatus.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided switching apparatus including: a plurality of data units; cross-connect switching means, having at least one input port and at least one output port, for providing a data transfer path serving to pass data received at the said input port to the said output port; and connection means connected to the said input port and to at least two of the said data units, which data units together constitute a data delivery group associated with that input port, and operable to deliver data from the different data units of the data delivery group, at different respective times, to that associated input port.
In such apparatus the number of input ports of the cross-connect switching means can be reduced because the data units of the data delivery group share access to the same input port on a time-division basis.
Usually, the said cross-connect switching means have a plurality of such input ports, for example 32 or 64 input ports. The connection means are preferably connected to all of the data units of the said plurality and to all of the said input ports and are operable to deliver data from each data unit of the said plurality to at least one input port of the cross-connect switching means.
There is preferably such a data delivery group, made up of at least two of the said data units, associated with every input port of the cross-connect switching means. In this way significant reductions (a halving at least) in the number of input ports required by the cross-connect switching means can be achieved.
The data units of a data delivery group could be connected by a common data bus to the associated input port, with each unit able to send data to the input port when the other units of the group are in an output-disabled condition. Alternatively, in one preferred embodiment the said connection means are operable to provide each data unit of each data delivery group with its own controllable input connection from the data unit to its said associated input port, each said input connection being switchable from a data-passing state, in which it serves to pass data from its data unit to said associated input port, to a data-blocking state in which it is in a high-impedance condition; the switching of the input connections being controlled so that when the input connection of any one of the data units of the group is in the data-passing state the input connection of each other data unit of that group is in the data-blocking state. This avoids the need for the data units themselves to have special output-disabling circuitry.
When the number of output ports required by the cross-connect switching means exceeds the number that can be physically provided on a single cross-connect switching unit (e.g. an integrated circuit) the said cross-connect switching means may include a plurality of individual switching units, each switching unit providing the cross-connect switching means with fewer output ports than there are data units in the apparatus, and being operable to provide such data transfer paths only between the input ports of the unit and the output ports of the switching unit. In this case, it is advantageous that, for each said data delivery group, the said connection means are operable at one time to deliver data from one data unit of the group to the input port associated with that group, which is an input port of one of the switching units, and are operable at another time to deliver data from that data unit to a further one of the said input ports which is an input port of another of the switching units. In this way, the data unit can send data to other data units via the output ports of both switching units so that connection flexibility is enhanc
Fujitsu Limited
Kizou Hassan
Pezzlo John
Staas & Halsey , LLP
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