Asymmetric digital subscriber line (ADSL) systems enable data to be transmitted over a pair of metallic twisted pair (usually copper) wires to customer premises. It is thought that the maximum transmission performance that is likely to be obtained with modern variants of ADSL is a download data rate of 24 Mbps and an upload speed of about 3 Mbps. Such data rates are dependent on the length of the metallic twisted pair from the customer premises to the telephone exchange and thus many customers will receive services at significantly lower data rates.
To improve data rates optical fibre has been installed into the access network. The greatest data rates are likely to be provided using fibre to the premises (FTTP) networks, such as passive optical networks (PONs), but there is a significant cost involved in providing fibre to customer premises. Fibre to the cabinet (FTTCab) networks are known to provide an attractive solution to providing customers with high data rate services without requiring as much investment as FTTP networks. Typically in FTTCab networks, very high bit-rate digital subscriber line (VDSL) systems are used to provide data rates of 40 Mbps and higher, for both upload and download on the metallic twisted pair cables. It is believed that improvements to VDSL systems may provide data rates in excess of 100 Mbps.
DSL systems work by utilising the frequencies above those which are used by the conventional telephony signals. In particular, VDSL2 defines three frequency windows for downstream data and 2 frequency windows for upstream data. Each of these windows comprises a number of carriers which have a 4.3125 kHz frequency separation. Each of these carriers will transmit one or more symbols with each of these symbols being used to transmit up to 15 bits of data. During a training process the insertion loss and noise level are determined for each of the carriers such that the signal to noise ratio (SNR) for each carrier can be determined. The training process determines the capacity of the upstream and downstream links in accordance with the SNRs of each of the carriers.
According to a first aspect of the present invention there is provided an apparatus having a first digital subscriber line connection to a first communications network and a second connection to a local area network, the apparatus being configured to, in use, transmit data via the local area network in response to the initiation of a training process for the digital subscriber line connection.
The apparatus may comprise a modem or a router. The apparatus may be configured, in use, to transmit data to a device connected to the local area network via a powerline adaptor. Data may be transmitted by the apparatus to a set top box or a router via the powerline adaptor. The apparatus may be further configured to cease transmitting data via the local area network in response to the termination of the training process for the digital subscriber line connection.
According to a second aspect of the present invention there is provided a method of operating a communications network, the method comprising the steps of: a) initiating a training process for a digital subscriber line connection with an apparatus connected to a communications network; and b) in response to the initiation of the training process, transmitting data from the apparatus to a local area network. In step b) the apparatus may transmit data to a further device via a powerline adaptor.
The network may comprise the further step of c) ceasing to transmit data to the local area network in response to the termination of the training process for the digital subscriber line connection.
According to a third aspect of the present invention there is provided a tangible data carrier for use in a computing device, the data carrier comprising computer executable code which, in use, performs a method as described above.