Rate controller

Details Rate controller Rate controller

1998-02-23

2001-12-04

Ton, Dang (Department: 2661)

Multiplex communications

Communication techniques for information carried in plural...

Adaptive

Reexamination Certificate

active

06327269

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a network for signals of different bandwidth, and a rate controller for use in allocating bandwidth to a signal path through the network.
BACKGROUND
It is known to link multi-user systems over large distances through leased telephone lines. For example, a workstation may be linked over a long distance to a host computer through a leased line in a telephone system. The line passes through a number of switching nodes and its bandwidth may be shared by a number of different users connected to the same host or different source end systems. The data is typically transmitted between the work station and host in a bi-directional manner, in bursts. The transmissions may be supported by asynchronous mode transmission mode (ATM) equipment. The bandwidth available to a particular transmission is initially determined by the signal source performing a routine in which the transmitted data rate is progressively increased in a test routine. The system at the destination sends back to the source a signal when the received signals become corrupted due to the data rate becoming too high, and in this way the data transmission bandwidth is set to the maximum value that the path can handle. Another bandwidth allocation technique is disclosed in EP-A-0 603 099.
When a number of signal sources and destinations share the same line, an unfair allocation of bandwidth can occur in which the shortest path tends to grab the most bandwidth because the acknowledgement signal returned during test routine occurs more quickly over a short path, so that the shorter path can acquire bandwidth more quickly. As a result, long paths tend to operate at a slower data rate than short paths. Another disadvantage is that the customer has to lease the telephone lines on a continuous basis, whereas the actual utilisation of the line varies greatly with time. For example, at night, a low utilisation rate may be achieved so that the customer has to pay for time when the line is not actually being used.
Recently, proposals have been made to integrate leased lines into a telephone network system so that the available bit rate (ABR) of the leased line can be used for other purposes during periods of low data transmission so as to permit data users to be charged on the basis of time that data is actually transmitted rather than on a flat rate leasing basis.
One proposal is to use the so-called virtual source/destination (VS/VD) configuration in which a source end system (SES) is connected to a public telephone network through a node which acts as a so-called virtual source (VS) that feeds data from the SES into the network for onward transmission to a destination end system (DES) for example a host computer or another workstation. The DES is connected to the public network through a so-called virtual destination (VD) that receives signals from the virtual source. Also, the DES can communicate back to the SES so that the virtual source and virtual destination operate bi-directionally and each comprise a VS/VD. In PCT GB 95/00502 and EP 94301673.3 a VS/VD system is described in which the bandwidth allocated to a bi-directional ATM transmission path through a public telephone network is controlled by means of a dynamic bandwidth controller (DBC). The DBC acts as a VS/VD and a connection admission control function (CAC) reviews the available bandwidth of switching nodes disposed along the transmission path so that the DBC can optimally allocate bandwidth to the path depending on operational conditions in the public network.
The DBC communicates with the SES using a specially configured form of digital ATM signal known as a resource management (RM) signal, which is used to instruct the SES to transmit at a data rate corresponding to a particular bandwidth determined by the DBC to be acceptable for the network. Also, the DBC reviews data signals received from the SES to police the data transmission rate to ensure that it falls within the acceptable bandwidth. The DBC also buffers signals received from the SES and provides certain data re-shaping and rate control functions.
The use of VS/VD architecture overcomes the contention difficulties associated with prior networks but has the disadvantage that a CAC function needs to be overlaid for all the switches of the public telephone network in order to provide the DBC with bandwidth control information. However, in practice, the network provider may wish to introduce VS/VD facilities progressively through the network and the introduction of a CAC and a DBC function as described in PCT GB 95/00502 and EP 94301673.3 would be initially expensive as it implies that all of the switches of the system would need to be replaced by switches that can handle ABR formatted signals.
SUMMARY OF THE INVENTION
With a view to overcoming the problem, the present invention provides a network for signals of different bandwidth, comprising: an input for signals from a source end system; an output for the signals; a plurality of switching nodes for selectively providing a signal communication path between the input and the output; a dynamic bandwidth controller for controlling the bandwidth allocated to the path for signals from the source end system; and a plurality of rate controllers each associated with a respective one of the switching nodes for determining the bandwidth available for the path through the node; the dynamic bandwidth controller being operative to interrogate the rate controllers such as to determine the bandwidth available for the path and provide a signal to instruct the source end system of the available bandwidth.
By the use of a plurality of individual rate controllers, each associated with a respective switching node, the use of a separate CAC is avoided, which permits the switching nodes of an existing network progressively to be changed to handle ABR signals so that the ABR service can be progressively introduced through the network.
Preferably the rate controllers each include means for transmitting a signal representative of the bandwidth available for the path through its associated node, to the rate controller associated with a next switching node along the path, and bandwidth determining means for determining the bandwidth available for the path through the node as a function of the lowermost of the actual available bandwidth and the bandwidth signalled to be available through the preceding node.
The invention also includes a rate controller for use with one of a plurality of switching nodes connected in a network comprising an input for signals from a source end system, an output for the signals, a signal communication path between the input and the output through the plurality of switching nodes, and a dynamic bandwidth controller for controlling the bandwidth allocated to the path for signals from the source end system, the rate controller comprising: means for transmitting a signal representative of the bandwidth available for the path through the node, to the rate controller associated with a next switching node along the path, and bandwidth determining means for determining the bandwidth available for the path through the node as a function of the lowermost of the actual available bandwidth and the bandwidth signalled to be available through the preceding node.
The invention also extends to a method of allocating bandwidth to a signal path through a network for signals of different bandwidth that comprises an input for signals from a source end system, an output for the signals, a plurality of switching nodes for selectively providing a signal communication path between the input and the output, the method comprising: controlling the bandwidth allocated to the path for signals from the source end system; and successively, for each node in the path, transmitting a signal representative of the bandwidth available for the path through the node to the next switching node along the path, and determining the bandwidth available for the path through the node as a function of the lowermost of the actual available bandwidth and th

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