Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Patent
1997-09-15
2000-03-28
Bocure, Tesfaldet
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
370395, 370412, H04J 314
Patent
active
060440600
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an asynchronous transfer mode (ATM) network switch. More particularly, this invention relates to a switch having means for controlling the flow of ATM cells constituting an individual virtual connection (VC).
2. Background of the Invention
In ATM data transmission, cells of data conventionally comprising fifty-three bytes (forty-eight bytes carrying data and the remaining five bytes defining the cell header, the address and related information) pass through the network on a virtual connection at an agreed upon rate related to the available bandwidth and the level or service paid for. The agreed upon rate will relate not only to the steady average flow of data, but will also limit the peak flow rates.
Over an extensive network, cells on a connection can become bunched together with different cells having different delays imposed upon them at different stages, so that the cell flow on a VC then does not conform with the agreed upon rates. To prevent rates being exceeded to the detriment of other VC's in the network, the network will include, for example at the boundary between different networks, means for policing the flow. The flow policing means typically includes a "leaky bucket" device which assesses the peak and average flow rates of cells on a VC and if required either downgrades the cells' priority or discards cells. An example of such a device is disclosed in co-owned UK Patent Application No. 9505358.3 which is hereby incorporated herein in its entirety. Since policing can result in the discarding of cells which should not be discarded, it is desirable to effect "traffic shaping" to space out the cells on a VC sufficiently so as to ensure that they meet the agreed upon rates, and in particular the peak rates.
A problem with traffic shaping is that it is desirable to delay the transmission of cells by variable amounts in an attempt to avoid cell loss. In practice, however, variable cell delay has been difficult to implement.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a traffic shaping means for an ATM switch.
It is another object of the invention to provide an ATM switch with a traffic shaping mechanism which delays the transmission of incoming cells by varying amounts of time.
It is a further object of the invention to provide a traffic shaping mechanism for an ATM switch which accounts for both peak and average cell flow rates.
In accord with the objects of the invention, an ATM network switch is provided with a traffic shaping means on the input or output side thereof. The traffic shaping means broadly comprises means for determining for each cell received at the traffic shaping means an onward transmission time dependent upon the time interval between the arrival of the cell and the time of arrival of the preceding cell on the same VC, buffer means for storing each new cell at an address corresponding to the onward transmission time, and means for outputting cells from the buffer means at a time corresponding to the address thereof.
In one embodiment of the invention, the switch comprises a cross-point switch (switch fabric) having a plurality of input ports (cell receiving means for receiving ATM cells from a data link) and a plurality of output ports (cell transmitting means for transmitting ATM cells outwardly on the data link), and one or more controllers (which are often called "slot controllers" or "link controllers") for switching data cells from any input port to any output port. The cell transmitting means of each controller includes the traffic shaping means arranged to set, for each cell presented to the transmitting means, a current onward transmission time when onward transmission at the input rate meets a predetermined flow rate criterion, and a delayed onward transmission time when onward transmission at the current time would cause the traffic on a VC to exceed a predetermined flow rate criterion. The traffic shaping means comprises at least one leaky bucket pro
REFERENCES:
patent: 5381407 (1995-01-01), Chao
patent: 5519689 (1996-05-01), Kim
patent: 5694390 (1997-12-01), Yamato et al.
Bocure Tesfaldet
Gallagher Thomas A.
General DataComm
Gordon David P.
Jacobson David S.
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