Broadband telecommunications system

Details Broadband telecommunications system Broadband telecommunications system

1998-01-13

2001-10-23

Patel, Ajit (Department: 2662)

Multiplex communications

Communication techniques for information carried in plural...

Adaptive

C370S235000, C370S236000

Reexamination Certificate

active

06307866

ABSTRACT:

The present invention relates to broadband telecommunications systems and in particular, but not exclusively, to telecommunications systems wherein data is communicated using Asynchronous Transfer Mode.
Telecommunications systems which are arranged to communicate data at rates in the order of megabits per second are known as broadband telecommunications systems. Communication of data at such high data rates is arranged to be provided by telecommunications networks between sources of the data and destinations, via nodes or switches which are interconnected by data transmission means. The data transmission means may be radio links in which case the data is conveyed by microwave signals, or fibre optic systems in which case data is communicated by light, or more conventionally data may be conveyed by electrical signals carried by twisted wire pairs.
In order to effect communication of data at such high rates between a plurality of sources, telecommunications systems must make optimum use of an amount of data communications bandwidth provided by a telecommunications network. To this end, broadband telecommunications systems operate to communicate data in the form discrete packets carrying a predetermined amount of information. An example of such a broadband telecommunications system is an Asynchronous Transfer Mode telecommunications system, wherein data is conveyed in ATM cells. Each ATM cell comprises a predetermined quantity of data as well as a cell header, which contains a Virtual Channel Identifier and a Virtual Path Identifier, which are used by nodes or switches to route the ATM cells across the telecommunications network.
Nodes, exchanges or switches which operate, inter alia, to route cells across a telecommunications network will be hereinafter referred to as telecommunications switches.
To achieve an efficient utilisation of a data communications bandwidth provided by a telecommunications network, telecommunications systems operate to provide a predetermined series of data transport media characterised by pre-defined data transmission parameters such as delay, integrity and cell rate. The telecommunications system is therefore arranged to provide a series of virtual communications paths, each of which is arranged to communicate data in accordance with the predetermined transmission parameters. Such communications paths are known as ‘bearers’ each of which is defined by the attributes of the data which it is able to communicate. Hence, by selecting an appropriate bearer for a certain type of data source, a user of the telecommunications network is provided with a cost effective means for communicating broadband data in accordance with the type and attributes of data the user is generating.
Bearer types which require that data is communicated with a low delay and high integrity, demand that a network links communications bandwidth provided by the telecommunications network is reserved or allocated on demand to such services at a higher priority than data carried by delay tolerant bearers. However, where a data bearer is arranged to communicate data which is delay tolerant, the network links communications bandwidth which remains unused after low delay and high integrity bearer services have been allocated bandwidth, may be allocated for transmission of such delay tolerant data in an efficient manner.
Network links communications bandwidth as used herein refers to a bandwidth provided by a telecommunications network for communication of data of all types whereas, the communications bandwidth, which may be correspondingly represented as a cell rate, which is un-used after the network links communications bandwidth of the telecommunications network has been allocated to low delay or high integrity data sources will be hereinafter known as Available Bit Rate (ABR) bandwidth or, correspondingly an ABR cell rate.
In the case of known Asynchronous Transfer Mode systems, the ATM-Forum have standardised ABR and ABR bearers.
As a result of the tolerance to delays which is characteristic of the data communicated by delay tolerant bearers, the switches of the telecommunications network may be arranged to efficiently utilise the remaining ABR data communications bandwidth by multiplexing data from a plurality of sources arriving at each of the network switches embodied within the telecommunications network. However, in order to provide this efficient bandwidth utilisation, the switches within the telecommunications network must be provided with data storage means arranged to store cells of data received from a particular data source, in order that advantage may be taken of ABR bandwidth as it becomes available on the telecommunications network.
Since each switch in the telecommunications network must be provided with means for data storage, and each switch must provide a facility for data storage for each data source utilising the delay tolerant bearer, the cost of providing such data storage becomes a technical problem.
The technical problem of reducing data storage requirements in a telecommunications system arranged to multiplex data from a plurality of delay tolerant sources onto an ABR data communications bandwidth, is addressed by the present invention.
According to the present invention there is provided a broadband telecommunications system, comprising at least one broadband telecommunications switch, and data transmission means coupled to said at least one telecommunications switch and to each of a plurality of data sources, said system operating to communicate data from said sources to destinations in a form of a plurality of cells, the communication being arranged to satisfy predetermined transmission parameters, which transmission parameters include an initial cell rate representative of a maximum rate at which data from said sources may be initially communicated to said at least one telecommunications switch, when said sources change from an idle to an active state, characterised by the telecommunications switch being provided with a bandwidth allocator which operates to calculate an available bandwidth for allocation between said plurality of data sources in accordance with a number of said data sources which are idle during a predetermined period scaled respectively by each initial cell rate, and operates to allocate said available bandwidth between active data sources, so as to substantially reduce a data storage requirement.
The bandwidth allocator may operate to allocate bandwidth in accordance with a demanded cell rate from each source.
The demanded cell rate may be communicated to said telecommunications switch by a signalling means. The signalling means may be resource management cells communicated between said data sources and said telecommunications switch with the data cells generated by said sources.
The term cells is intended to include packets of data with a fixed or variable size, which packets may also include control or signalling information. ATM cells are one example of such cells.
The calculation of the available bandwidth which may be allocated between sources of delay tolerant data in accordance with the initial cell rate of those data sources which are idle, represents a pessimistic estimate of available ABR bandwidth. This is because this calculation assumes that those data sources which are idle become active at the end of a predetermined period and will transmit at their initial cell rate. However, an effect of this pessimistic calculation is to substantially obviate a requirement for substantial data storage at the telecommunications switch, particularly for data sources which communicate data on the transmission means at cell rates which would otherwise exceed that which can be accommodated by the telecommunications switch. By allocating the pessimistic bandwidth on a basis of the instantaneously demanded cell rates communicated by said data sources delay tolerant data from said plurality of data sources may be multiplexed onto the telecommunications system efficiently utilising the ABR bandwidth without a requirement for a substantial data s

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