British Telecommunications Public Limited Company

Avril Joy Smith

John Leonard Adams

A packet network node and method of operating a packet network node are disclosed. Conventional packet network nodes react to congestion in the packet network by dropping packets in a manner which is perceived by users to be indiscriminate. In embodiments of the present invention, communication sources precede communications with a start packet which contains a communication identifier also carried within subsequent packets of the communication. The packet network node makes an entry in a vulnerable communications table () on receipt of such a start packet. After an amount of time, and often before the cessation of a communication, such entries are removed from the vulnerable communications table. On the onset of congestion, the packet network node disclosed herein deletes packets in communications identified in the vulnerable communications table. This provides a congestion alleviation method which is less annoying to users since communications that have been in existence for longer are less susceptible to component packets being deleted.

Packet communications network congestion alleviation method and apparatus

In a broadband switching system for the switching of asynchronously transferred cells of data, a dynamic bandwidth controller (DBC) controls the application of data cells at an input port of the system, the data cells being supplied by a number of transmitting end-stations. The DBC detects incoming cells, identifies the source of the cells, provides buffering for the cells, and controls the output of the cells to the system switches according to a current cell rate (CR) assigned to the cells from the respective source. The system also includes a connection admission (CAC) module which determines bandwidth available in the system. The DBC and CAC operate together to maintain a permanent virtual path of a predetermined minimum bandwidth through the system and allocate additional bandwidth on demand up to a maximum. The additional bandwidth allocated to the path can be automatically removed or reduced of it is not used by the source. Feedback to the source can be provided to prevent cells being supplied at a rate which would result in significant cell loss due to the limitation of bandwidth available for the path in the system.

Broadband switching network

In a broadband switching system for the switching of asynchronously transferred cells of data, a dynamic bandwidth controller (DBC) controls the application of data cells to an input port of the system. The data cells are supplied by a number of transmitting end-systems. When an end-system begins transmitting data cells, the DBC detects the presence of incoming cells and requests bandwidth from a connection admission control (CAC) forming part of the system. The switching system stores a table associating a number of signal sources connected to the input port with respective predetermined maximum transmission times and maximum transmission rates for the sources. When arrival of cells at the input port from one of the source is detected, the DBC and CAC operate together to allocate sufficient bandwidth in the switching system to allow the respective message size to be transmitted within the respective maximum transmission time. A guaranteed minimum rate of transmission is also guaranteed for the source.

Broadband switching system

A service multiplexer ( ) for connecting a plurality of signal sources to a public switched communication network transfers data in the form of a synchronously transferred data cells from a plurality of inputs ( ) to an output ( ) for connection to the network. The multiplexer ( ) includes a bandwidth control unit which receives a bandwidth control signal from the network representative of available bandwidth for transmission of cells to the network and generates feedback control signals for transmission to the signal sources to cause them to alter their data transmission rates in accordance with the available bandwidth. An activity detector coupled to the bandwidth control unit monitors the bandwidth of data received at the inputs. The multiplexer allows ABR (available bit rate)&mdash;commandable signal sources to be linked to a single port of a public network operating on an ABR basis to provide an efficient and fair allocation of bandwidth for each source.

Service multiplexer

A network for ATM signals includes source end systems SES,SES,connected by a permanent virtual connection PVC,through switch SW,SWN. Dynamic bandwidth controllers DBC,DBC,operate as virtual source/virtual destinations. The individual switches, such as switch SW,have associated rate controllers RC,which determine the available bandwidth for the signal path PVC,Dynamic bandwidth controller DBC,interrogates the rate controller RC,RC,using resource management RM signals which cascade from switching node to switching node along the path in a forward direction and then in a backward direction. The DBC's communicate with the SES's using RM signals which may be of a different format to the RM signals which pass from switching node to switching node.

Rate controller

In a broadband switching system for the switching of asynchronously transferred cells of data, a dynamic bandwidth controller (DBC) controls the application of data cells to an input port of the system. Data cells are supplied by a number of transmitting end-systems. When an end-system begins transmitting data cells, the DBC detects the presence of incoming cells and requests bandwidth from a connection admission control (CAC) forming part of the system. The switching system stores a table associating a number of signal sources connected to the ingress with respective predetermined transmission bandwidths and, preferably also, maximum delay times. When arrival of cells from one of the sources at the input port is detected, the DBC sends a request signal for the relevant predetermined bandwidth to the CAC and delays transmission of the cells until at least the predetermined bandwidth is allocated. This delay is typically effected by sending a cell rate indicator signal back to the input port for placing the source in a halt mode. If no allocation of bandwidth has occurred before the respective maximum delay time, bandwidth is allocated by robbing bandwidth form other signal sources.

A broadband switching network is shown having a plurality of interconnected switching units arranged to transfer cells asynchronously therebetween. A switch control establishes connections for the asynchronous transmission of these cells between ports. A bandwidth control detects the rate at which cells are supplied to an input port; and, in response, requests switch control to allocate bandwidth to the connection. When bandwidth has not been allocated, received cells are downgraded or rejected by a usage control device. The usage control device only allows high priority cells to remain as such when bandwidth has been allocated. The network facilitates logical connections to be established without dial-up procedures. However, customers may be charged in terms of their actual usage made of the network.

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Oxford, United Kingdom

Avril Joy Smith