Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-08-19
2001-07-17
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C375S222000
Reexamination Certificate
active
06262991
ABSTRACT:
BACKGROUND TO THE INVENTION
This invention relates, in general, to the architecture of a communication system, and is particularly, but not exclusively, applicable to an arrangement of modems in an exchange of a telephone network, such as a public switched telephone network (PSTN).
SUMMARY OF THE PRIOR ART
Telecommunication systems that interconnect subscriber terminals are now capable of supporting broadband data communication on both an inter-subscriber terminal basis (through an exchange) or on a client-server to subscriber terminal basis. In either case, both the subscriber terminal and the infrastructure equipment contain a dedicated modem, which modems are coupled together to support communication between the subscriber terminal and the exchange. In this respect, there is a one-to-one mapping between modems associated with each subscriber terminal and the infrastructure. For example, current broadband access systems that interconnect subscriber terminals and an exchange use copper cabling (usually termed “twisted pair” technology), and conventionally employ two broadband modems, one at each end of the twisted pair.
As will be appreciated, the subscriber terminals may be wire-line telephones that have semi-permanent communication resources assigned between each subscriber terminal and the infrastructure, i.e. the exchange, or may have a dynamically assignable communication resource supported, for example, on a radio frequency (RF) link that is established between a base station sub-system (BSS) of a cellular communication system and the subscriber terminal.
Unfortunately, a significant cost in manufacturing infrastructure relates to the requirement to provide a plethora of modems (provided within line cards) to support the many subscriber terminals that operate within a broadband communication system. As such, it is desirable that the number of modems implemented within a system is minimised.
With respect to the structure of conventional telephony networks and particularly in relation to local telephone exchanges, a saving in each cost-to-customer connection is accomplished by reducing the number of switch-ports needed to service a given number of subscriber terminals. This concentration function is achieved by recognising that, although each subscriber terminal requires a connection to a central switch, the actual connection is discontinuous and bursty and therefore only carries traffic, i.e. information, for relatively short periods of time. As such, for a sufficiently large number of users, the number of switch-ports needed in the exchange is small in proportion to the number of subscriber terminals connected thereto.
For example, if a subscriber terminal, such as a telephone or a computer, utilises a communication resource (i.e. a connection) for only 10% of a peak operating period for the network, a group of subscriber terminals require, on average, only one-tenth the number of switch connections to support all the calls. In this type of system, network operators accept that, occasionally, a subscriber terminal wishing to make a call may not be able to access the switch because all other switch-ports are contemporaneously occupied by other subscriber terminals. However, appropriate dimensioning of the communication system will ensure that a redundancy is built into the communication system, and that switch-port contention (unavailability) only therefore happens very infrequently.
As will be appreciated, the principal of determining an appropriate number of communication resources for the network is based on classic communication theory and is expressed statistically in Erlangs, and it will further be appreciated that optimisation of the system will depend upon the type of traffic supported during each call, i.e. the requirements for video communication systems will differ from those for speech communication.
Like conventional telephony systems, broadband networks achieve a concentration function using an analogous principle. Specifically, while each broadband subscriber is allocated a dedicated modem at both the exchange and at its premises, infrastructure equipment located deeper within the broadband network is shared and therefore dimensioned to provide sufficient capacity to service an expected number of simultaneously active broadband calls. The broadband network cannot therefore provide simultaneous service to all broadband subscriber terminals, and yet broadband modems remain dedicated to a particular subscriber terminal regardless of its usage of the broadband service(s).
As previously stated, the provision of such dedicated modems on a per-line basis is expensive, and is further exaggerated by the increased complexity required in broadband networks. Consequently, there is a significant increase in cost associated with providing a broadband network, which cost is over and above that for a corresponding narrowband telephony system and which therefore discourages wider deployment of broadband systems.
More particularly, a modem is comprised from three functional blocks, with its cost of manufacture heavily dependent upon the processing requirements of the modem. More explicitly, a modem includes line interfaces, digital-to-analog (D/A) converters and a signal processor. The line interfaces provide signals of a suitable amplitude to drive communication signals along the twisted pairs (or the equivalent transmission medium), and also to accept incoming signals. The D/A converter acts to provide an interface between the digital processing functions and the analog signals used on the twisted pairs, and the signal processor provides and implements complex processing logic required to characterise the line and optimise the capacity. It is the complexity of the processor that contributes significantly to the cost of each modem, with this complexity increasing as a function of the number of services (and the information bearing capabilities of each service) supported in the broadband network. Indeed, in relation to broadband communication, generally, types of transmission technology range from simple coding schemes (that are suitable for short distances) to elaborate and complex signalling schemes that achieve greater distance penetration over a communication resource, such as a twisted pair. These more elaborate and complex signalling schemes therefore necessarily require greater processing capabilities and consequently impose additional costs, although very large scale integration can eliminate the necessity for some dedicated, high cost modems.
As such, requirement exists to provide an improved communication infrastructure that supports broadband-type communications but which utilises a reduced number of broadband modems
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided an infrastructure exchange responsive to a plurality of subscriber terminals each having a dedicated modem that supports data transmission, the infrastructure exchange comprising: at least one assignable modem capable of communicating with the dedicated modem of at least some of the plurality of subscriber terminals; and a first cross-point switch having a plurality of inputs and a plurality of outputs, the first cross-point switch arranged to route data transmission between the plurality of subscriber terminals and the at least one assignable modem; wherein the infrastructure exchange has fewer assignable modems than a combined number of dedicated modems in the plurality of subscriber terminals and the first cross-point switch acts to increase a ratio of dedicated modems in the plurality of subscriber terminals to assignable modems in the infrastructure exchange.
In a second aspect of the present invention there is provided a communication system comprising at least one exchange and a plurality of subscriber terminals each having a dedicated modem that supports data transmission, the infrastructure exchange comprising: at least one assignable modem capable of communicating with the dedicated modem of at least some of the plurality of subscriber terminal
Dyke Peter John
Lewis Andrew Paul
Unitt Brian Michael
Boakye Alexander O.
Lee Mann Smith McWilliams Sweeney & Ohlson
Nguyen Chau
Nortel Networks Limited
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