WO1996019089A1 - Communications system - Google Patents

Abstract

In a telecommunications system employing optical transmission, subscribers are coupled to street ONUs via twisted pair subscriber loops. Traffic is carried across each loop in a service independent digital format at a bit rate appropriate to the bandwidth of the traffic. The arrangement facilitates the introduction of new services and/or changes in a subscriber's service mix.

Description

COMMUNICATIONS SYSTEM

This invention relates to communications systems supporting both voice services and broad band services such as broadcast video and video- on-demand In particular, the invention relates to an apparatus and method for providing subscriber access to those services

BACKGROUND OF THE INVENTION

A wide range of narrow band and broad band services are currently available via telecommunications networks The provision of these services has been greatly facilitated by the introduction of fibre in the loop (FITL) to support these services on a wide band optical carrier At present these services are generally limited to larger business premises where it is economic to provide a direct fibre connection to the network However, in numerical terms the large majority of subscribers are either residential or are small business subscribers with a single line or only a small number of lines These subscribers are coupled to the network via conventional twisted pair subscriber loops and it is generally considered to be uneconomic to replace these wired loops in the foreseeable future with the optical fibre connections that could carry the various services, particularly broad band services directly to the subscriber Twisted pair loops are in fact being installed for most new subscribers on the grounds of low cost and compatibility with existing equipment Arrangements for coupling subscriber loops to optical transmission systems are described for example in specification number US-A-4,768, 188 and by Boulter et al. in Proceedings of the International Symposium on Subscriber Loops and Services, 1986, pp175-180

The availability of new services has introduced the additional problem that different subscribers will require different services, some may require only a basic POTS service Also, as service churn introduces new services and modifies current services, there is a potential added cost to the carrier in the introduction of new equipment and the constant need to change equipment to accommodate different service requirements One approach to this problem has been the introduction of the service adaptive subscriber line card However, these devices are relatively costly in terms of hardware investment and in engineer time to effect the necessary installation, and can be rendered obsolete by the introduction of new services which are outside the current service adaptive line card capabilities and/pr when the subscriber changes his/her service requirements

It is an object of the invention to minimise or to overcome these disadvantages

A further object of the invention is to provide a cost-effective network access to a subscriber via a wired subscriber loop

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided apparatus for coupling a subscriber to a communications network via a subscriber loop, the apparatus including a common transceiver unit for coupling to the network and adapted to serve a plurality of subscribers each via a respective subscriber loop, and a subscriber transceiver unit or network termination unit for coupling to the respective subscriber loop and to one or more subscriber terminals, wherein the common transceiver unit and the network termination unit have means for determining a transmission bit rate that can be supported by the loop, and wherein the common transceiver unit and the subscriber transceiver unit are adapted to provide service independent digital communication over the subscriber loop at downstream and upstream bit rates less than or equal to said determined bit rate

According to another aspect of the invention there is provided a method of providing subscriber access to a communications network via a subscriber loop, wherein there are transceiver units one at each end of the loop, the method comprising determining a transmission bit rate that can be supported by the loop, and effecting communication in a service independent form over the subscriber loop at downstream and upstream bit rates that are less than or equal to said determined bit rate

The technique permits the provision of a wide range of services to a small business or a residential subscriber without the need to replace the conventional twisted pair subscriber loop

Advantageously, the subscriber unjt is programmable via the network so that new services and service changes can be introduced without the need to visit the subscriber premises

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference to the accompanying drawing in which -

Figure 1 depicts in schematic form a telecommunications network providing subscriber access over a wired subscriber loop; and

Figure 2 shows in further detail the subscriber access equipment of the network of figure 1

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to figure 1 , there is shown in schematic form a telecommunications network in which a plurality of services including broad band services are provided over a fibre to the kerb system Typically the network incorporates a trunk network, indicated as a telecommunications network 1 1 , a broadcast/NVOD system 12, broad band services 13, video on demand (VOD) services 14, and a network management system 15 All these services are coupled to a switch node generally depicted as 16 This switch node may comprise the head end of a fibre optic distribution system to subscribers The switch node 16 is coupled to a number of primary nodes 17 each typically housed in a street cabinet Each primary node 17 is in turn coupled to a number of street optical network units (ONU) 18 which function as common transceiver units providing an interface between fibre optic transmission in the network and electrical transmission to subscribers Each street ONU 18 distributes digital traffic to a number of subscriber stations 19 over twisted pairs or coaxial drops 20 using a transmission system which is service independent

Referring now to figure 2, the subscriber's end of the network is shown in further detail The subscriber station is provided with a network termination unit 21 which receives digital traffic from the ONU 18 over the subscriber loop 20 and transmits digital traffic back across the loop to the ONU The downstream and upstream transmissions may be symmetric or asymmetric The network termination unit may be disposed at the customer premises, in a local street cabinet or adjacent the ONU, and serves via a broad band line card 210 various items of customer equipment such as a telephone set 22, a facsimile machine 23 and, via a set-top box 24, a television receiver 25 The unit is controlled by a processor 27 and may be powered, e g from the domestic electricity supply via a power supply 26

The street ONU has an optical transmitter 31 and an optical receiver 32 for interfacing with the fibre optic network Electronic transceivers 33 are provided one for each subscriber A multiplexer (MUX) is interfaced between the optical transmitter and receiver and the electronic transceivers 33 Operation of the ONU is controlled by a processor 34 and electrical power is obtained e g from the primary node via a power supply 35 The ONU may also provide emergency electrical power to each subscriber over the subscriber loop e g to maintain a basic telephone service in the event of a mains power failure In some applications, the ONU may provide the sole power source for the subscriber The ONU may also incorporate a test head (not shown) for performing subscriber loop testing

In this arrangement, the significant power dissipating functions, such as ring tone generation, may be provided in the subscriber's network termination unit so that the ONU has a relatively low power dissipation

The traffic across the subscriber loop between the ONU and the network termination unit is carried in a service independent format at a bit rate appropπate to the nature of the traffic This bit rate may be selected from a set of bit rates comprising e g 1 Mb/s, 5 Mb/s, 10 Mb/s and 25 Mb/s Conversion of the traffic into the form for service independent transmission over the loop and reconversion of signals received over the loop is effected via the ONU and the network termination unit processors which are programmed to perform this function The particular rate to be employed over the loop is agreed between the processors in the network termination unit and the ONU respectively This is determined by transmitting a training sequence, from the ONU across the subscriber loop to the network termination unit at each of the various bit rates A pilot tone is sent from the ONU to the network termination unit immediately prior to transmission of the training sequence to alert the termination unit of the nature of the following transmission This training sequence may be stored in the ONU, or it may be transmitted to the ONU via the fibre network Typically, the network termination unit returns the received sequence back to the ONU where it is compared with a stored sequence to determine the number of errors introduced in the transmission process When this error rate exceeds a predetermined threshold, this indicates that the maximum effective bit rate for that subscriber loop has been exceeded This information is then relayed to the network manager so that an appropriate maximum bit rate can be allocated to the subscriber loop This measurement can be performed on initial set up of the subscriber loop, or it may be performed regularly e g on a daily basis In some applications the measurement may be performed on a call-by-call basis

The bit rate to be employed over the loop is notified to the network termination unit processor by the ONU processor This bit rate is independent of the service required by the subscriber In many applications, each subscriber loop may be operated at its maximum bit rate irrespective of whether the subscriber requires only a narrow band POTS service or a wide range of broad band services In other applications the bit rate can be chosen to match the subscriber's service mix Thus, for a subscriber requiring only a POTS service, the 1 Mb/s rate could be selected as this can easily accommodate a 64 kb/s voice channel On the other hand, a subscriber requiring e g three video channels could be allocated the 25 Mb/s rate if this rate is available on his subscriber loop Advantageously, the customer network termination unit is software programmed via the network according to the customer service demand thereby obviating the need for engineer access to the customer premises when new services are introduced or when a change in service mix is required

The system provides dynamic allocation of both services and bandwidth leading to "service dialtone", and allows equipment in the field and in the customer premises to be independent of service mix This reduces operational costs associated with new service provisioning and customer churn

Claims

CLAIMS:-

1. Apparatus for coupling a subscriber to a communications network via a subscriber loop, the apparatus including a common transceiver unit for coupling to the network and adapted to serve a plurality of subscribers each via a respective subscriber loop, and a subscriber transceiver unit or network termination unit for coupling to the respective subscriber loop and to one or more subscriber terminals, wherein the common transceiver unit and the r etwork termination unit have means for determining a transmission bit rate that can be supported by the loop, and wherein the common transceiver unit and the subscriber transceiver unit are adapted to provide service independent digital communication over the subscriber loop at downstream and upstream bit rates less than or equal to said determined bit rate

2. Apparatus as claimed in claim 1 , wherein operation of the common transceiver unit and the subscriber transceiver unit are controlled each via a respective processor

3. Apparatus as claimed in claim 1 or 2, wherein said bit rate determining means comprises a training sequence generator arranged to transmit training sequences over the loop at a plurality of bit rates, and error detection means for determining a bit rate at which a measured bit error rate exceeds a predetermined threshold

4. Apparatus as claimed in claim 1 , 2 or 3 wherein the subscriber transceiver unit is programmable via the network

5 Apparatus as claimed in claim 1 , 2, 3 or 4 wherein the common transceiver unit incorporates means for supplying electrical power to the subscriber transceiver unit across the subscriber loop 6. A method of providing subscriber access to a communications network via a subscriber loop, wherein there are transceiver units one at each end of the loop, the method comprising determining a transmission bit rate that can be supported by the loop, and effecting communication in a service independent form over the subscriber loop at downstream and upstream bit rates that are less than or equal to said determined bit rate

7 A method as claimed in claim fi, wherein the transmission bit rate is determined by transmitting a training sequence over the loop at a plurality of bit rates, determining the number of errors in the transmitted sequence at each said bit rate, and determining a bit rate at which the number of errors exceeds a predetermined threshold