The invention relates to a bonding circuit for an xDSL line card which, in particular, can be used in a DSLAM (Digital Subscriber Line Access Multiplexer) circuit, and a method for bonding data fragments over a number of line cards.
In the case of an access to a broadband data transmission network, there is a continuous wish for higher data transmission rates and greater ranges for transmitting the data over existing telephone lines. Access to a data network, for example the Internet, is possible via conventional telephone lines by means of xDSL transceivers.
FIG. 1 shows a conventional network access to a broadband backbone data transmission network. The backbone data transmission network, for example the Internet, is connected to a DSLAM (Digital Subscriber Line Access Multiplexer) line via a broadband data transmission line, for example an optical fibre line. The DSLAM circuit is located, for example, in a DSLAM cabinet of an exchange (central office). The DSLAM circuit is the bridge to the data transmission network. The DSLAM circuit represents a combination between an xDSL modem block and a multiplex system for the connecting line to the data network, for example to an Internet provider (IP).
FIG. 2 shows a conventional DSLAM circuit. The conventional DSLAM circuit contains an uplink card for exchanging data with the backbone data transmission network and a number of xDSL line cards connected to the uplink card. Each xDSL line card, in turn, has a number of ports for connecting telephone lines which, for example, are formed by twisted two-wire copper telephone lines. In the example of a DSLAM circuit according to the prior art, shown in FIG. 2, the DSLAM circuit contains N line cards, each line card having M ports.
FIG. 1 is used for illustrating the problems forming the basis of the invention. In the example shown in FIG. 1, a first terminal connection CPEA (Customer Premise Equipment) is connected to ports 1-3 of a line card of the DSLAM circuit, for example via a main distribution frame (MDF). The terminal connection CPE comprises a splitter to which a conventional telephone is connected, on the one hand, and a data modem, on the other hand. The data modem is also connected directly to the DSLAM circuit via two further telephone lines. The three telephone lines, with which the terminal connection CPEA is connected to the DSLAM circuit, form a telephone line bundle BA for increasing the data transmission rate between the DSLAM circuit and the terminal connection CPEA. The data transmission rate on a telephone line is dependent on, among other things, the distance between the DSLAM circuit and the terminal connection CPE. The greater the distance, the lower the maximum data transmission rate of the telephone line. To increase the data transmission rate to a terminal connection CPE, therefore, a number of telephone lines are combined to form a telephone line bundle and are connected to a terminal connection. Each telephone line in the example shown in FIG. 1 has, for example, a data transmission rate of 50 MB/sec and thus an aggregate data transmission rate of about 150 MB/sec can be achieved for the terminal connection CPEA.
FIG. 3 shows a conventional line card which is provided in the conventional DSLAM circuit represented in FIG. 2. The conventional xDSL line driver circuit as shown in FIG. 3 has a transmit signal path and a receive signal path. On the transmit signal path, a transmit data packet buffer for temporarily storing data packets is received from the uplink card of the DSLAM circuit by a bonding circuit (x-bond) provided on the line card is provided. The temporarily stored data packets DP are divided into data fragments DF by a subsequent fragmentation circuit and delivered to a demultiplexer D-MUX which distributes the data fragments DF to different signal lines. The bonding circuit contains a transmit data packet buffer (TX-MEM), the output of which is connected to x-DSL transceivers (PHY). The transmit signal path of the bonding circuit (x-bond) contains a transmit controller for driving the data packet buffer, the fragmentation circuit and the demultiplexer.
The receive signal path of the bonding circuit x-bond comprises a data fragment buffer (RX-MEM) which is connected to the x-DSL transceivers (PHY). In addition, the receive signal path contains a multiplexer (MUX) for combining the various received data fragments DF, the data fragments DF being reassembled to form a data packet (DP) by a reassembling circuit and temporarily stored in a data packet buffer of the receive signal path provided for this purpose before they are transmitted to the uplink card of the DSLAM circuit by the bonding circuit. The receive signal path, like the transmit signal path, has a controller which controls the multiplexer, the reassembling circuit and the receive data packet buffer.
Apart from the bonding circuit x-bond, the line card has for each port an xDSL transceiver PHY for transmitting and receiving data fragments DF which are exchanged with the terminal connection CPE via the associated telephone line.
A data packet DP coming from the data network, for example an Ethernet data packet, is split into smaller data fragments DF on the transmit signal path of the bonding circuit x-bond and distributed to various signal lines via the demultiplexer. The transceivers PHY then transmit the data fragments DF via a bundle B of telephone lines to the corresponding terminal connection CPE.
Conversely, data fragments DF which are received by a terminal connection CPE are delivered by the x-DSL transceivers PHY to the receive signal path of the bonding circuit x-bond and are there combined by the multiplexer. The combined data fragments DF are then reassembled by the reassembling circuit to form a data packet DP, for example an Ethernet data packet, and temporarily stored in the data packet buffer. The temporarily stored data packets are then transmitted by the bonding circuit of the line card to the uplink card and from there to the data transmission network.
However, the conventional bonding circuit shown in FIG. 3 has the disadvantage that it only allows the bundling of telephone lines which are jointly connected to a line card. In the arrangement according to the prior art shown in FIG. 1, for example, the user of the terminal connection CPEB, whose telephone is connected to the DSLAM circuit via a telephone line, would like to use a second telephone line in order to increase the data transmission rate provided for the terminal connection CPEB. This would allow the user of the terminal connection CPEB, for example, in turn to connect a data transmission modem with a high data transmission rate.
Telephone lines are usually run in parallel in cables which, apart from the telephone lines used, contain additional redundant spare telephone lines. In the arrangement shown in FIG. 1, for example, a further spare line is run. The conventional line card, as shown in FIG. 3, has, for example, M=4 ports, ports 1-3 being connected to the first terminal connection CPEA of the first user A via the telephone line bundle BA and the fourth port being connected to the telephone of the second user B. If user B should wish to extend his terminal connection CPEB to form a bundle in order to increase the data transmission rate, this is not possible since the conventional bonding circuit x-bond according to the prior art does not have a further free port for the connection.
If the conventional DSLAM circuit, as shown in FIG. 2, contains further line cards which have unoccupied ports, it is not possible to connect the spare line to such a port since the fragmentation of the data packets DP to form data fragments DF for the second terminal connection CPEB and the reassembly of received data fragments DF from the second terminal connection CPEB takes place within a master bonding circuit and signal delays produced by the data transmission via a different line card and the uplink line card cannot be compensated. The conventional bonding circuit x-bond according to the prior art as shown in FIG. 3 thus only allows telephone lines to be bundled which are connected to the same line card. Bundling subscriber lines which are connected to different line cards or line driver cards is not possible with the bonding circuit according to the prior art shown in FIG. 3. There is thus no possibility for bundling telephone lines for a terminal connection CPE at the DSLAM system level.