Abstract:
A method and a device for data processing between a first network element connected via several lines to several second network elements. The method includes the following steps: (i) if a line is trained, at least one other line is switched to a first mode; and (ii) if the line has been trained, the at least one other line is free to switch to a second mode.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     DSL (Digital Subscriber Line) is a family of technologies that provide digital data transmission over the wires of a telephone access network. DSL technologies are often referred to as “xDSL”, wherein “x” stands for various DSL variants. 
     Asymmetric Digital Subscriber Line (ADSL, ITU-T G.992.1) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voice band modem can provide. Such fast transmission is achieved by utilizing frequencies that are normally not used by a voice telephone call, in particular, frequencies higher than normal human hearing. 
     ADSL2 (ITU-T G.992.3) and ADSL2plus (ITU-T G.992.5) are variants of ADSL, both providing better performance compared to basic ADSL. 
     VDSL (Very high speed DSL, ITU-T G.993.1) as well as VDSL2 (Very high speed DSL 2, ITU-T G.993.2) are xDSL technologies providing even faster data transmission over a single twisted pair of wires. This is mainly achieved by using a larger frequency range. 
     xDSL technologies exploit the existing infrastructure of copper wires that were originally designed for plain old telephone service (POTS). They can be deployed from central offices (COs), from, e.g., fiber-fed cabinets preferably located near the customer premises, or within buildings. 
     Transmission of signals across a copper access network may cause crosstalk problems. 
     Copper access networks often are designed such that they utilize cables containing a multitude of wires or wire pairs. Wires or wire pairs are often organized in binders within cables. 
     Wires or wire pairs are running in parallel with other wires or wire pairs over significant distances. 
     Crosstalk occurs when wires are coupled, in particular between wire pairs (twisted pair lines) of the same or a nearby binder within the same or an adjacent cable. Hence, data signals from one or more twisted pair lines can be superimposed on and contaminate a data signal of a different twisted pair line. The crosstalk comprises a near-end crosstalk (NEXT) and a far-end crosstalk (FEXT). 
     Based on such crosstalk, data signals transmitted over twisted-pair lines can be considerably degraded by the crosstalk interference generated on one or more adjacent twisted-pair phone lines in the same and/or a nearby cable or binder. With an increasing transmission speed, this problem even deteriorates. Crosstalk may significantly limit a maximum data rate to be transmitted via a single line. 
       FIG. 1  illustrates in particular crosstalk comprising NEXT and FEXT components between a Central Office (CO) comprising several transceivers CO 0  to CO N  and several Customer Premises Equipment transceivers CPE 0  to CPE N  located at different customer locations. CO and CPE transceivers may be connected via a common Cable Binder. 
     The impact of NEXT can be reduced and/or eliminated by utilizing different frequency bands for upstream and downstream directions of transmission. A remaining crosstalk is then mainly based on FEXT. 
     In ADSL2 and ADSL2plus, saving of transmission power can be achieved by an “L2 mode” that allows reducing the power for transmission when the payload data rate which is to be transmitted falls below a predetermined threshold. When the data rate exceeds a certain threshold, transceivers switch back to an “L0 mode” (full power mode). 
     However, operators dislike using said L2 mode in their networks, because it results in significant crosstalk and/or interference issues. 
     A “Signal-to-Noise Ratio (SNR) margin” represents the amount of increased received noise power (in dB) relative to the noise power that the system is designed to tolerate, wherein it still meets the target bit error rate of 10 −7 . 
     A “training” refers to the first phase of setting up the communication link between two DSL transceivers. During a training phase, the transceivers at both ends of the line exchange their capabilities and negotiate a set of parameters. 
     As switching from L2 mode into L0 mode leads to significant non-stationary crosstalk, solutions are required to cope with such crosstalk. 
     Reference is made to  FIG. 1  showing a line  101  connecting the Central Office with CPE 0  and a line  102  connecting the Central Office with CET 1 . 
     With line  101  running in L2 mode, it produces only little crosstalk into line  102  due to its low transmission power. When CO 1  and CPE 1  transceivers perform training, they see a high SNR margin. They adapt themselves to such good line conditions. 
     When line  101  switches to L0 mode, its crosstalk into line  102  suddenly increases, i.e., the SNR margin on line  102  rapidly drops. In a worst case scenario, the connection on line  102  crashes and retraining of CO 1  and CPE 1  becomes necessary. Such retraining leads to an interruption of the service and shall be avoided. 
     Switching into L2 mode and from L2 mode to L0 mode may happen at a rate of less than one second, depending on data bursts. Accordingly, connection crashes of adjacent lines may occur not only once every few hours but at a tremendously higher rate thus leading to an instable overall network. 
     A solution to overcome these disadvantages is to disable Power Saving (L2) mode. This, however, comes at the cost of a high overall power consumption. 
     BRIEF SUMMARY OF THE INVENTION 
     The problem to be solved is to overcome the disadvantages as set forth above and in particular to provide an efficient and stable approach to utilize a power saving mode in a DSL environment. 
     This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims. 
     In order to overcome this problem, a method is provided for data processing between a first network element being connected via several lines to several second network elements comprising the steps:
         if a line is trained, at least one other line is switched to a first mode;   if the line has been trained, the at least one other line is free to switch to a second mode.       

     In particular, the first network element comprises several sub-network elements, each being connected to a second network element. Advantageously, each sub-network element is connected via a line to a second network element. In particular, a line comprises a twin-wire line. 
     The training of a line may be directed towards setting up a communication link between two transceivers, each at either end of the line, wherein the transceivers may be (x)DSL transceivers. 
     The first mode may in particular be a mode of high power and/or full power. In such case, the training takes into consideration a significant or high amount of interference thus allowing the transceivers to adjust to a data rate that can be maintained during operation. 
     It is to be noted that if the line has been trained, the at least one other line may maintain the first mode, e.g., a full power mode, and does not have to switch to the second mode. 
     In an embodiment, the first network element is or is associated with a Central Office (CO) and/or a Digital Subscriber Line Access Multiplexer (DSLAM). 
     In another embodiment, the several lines are Digital Subscriber Lines, in particular Asymmetric Digital Subscriber Lines according to ADSL2/2plus standards or Very high speed Digital Subscriber Lines according to VDSL/VDSL2 standards. 
     In a further embodiment, training of a line comprises setting up a communication link between two transceivers. 
     In a next embodiment, the transceivers at both ends of the line exchange their capabilities and negotiate a setting of parameters. 
     It is also an embodiment that the second network element is a Customer Premises Equipment (CPE). 
     Pursuant to another embodiment, the first mode corresponds to a full power mode. 
     According to an embodiment, the second mode comprises at least one mode of reduced power. 
     The second mode may in particular comprise several modes of reduced power (i.e. not full power), wherein the several modes may differ gradually. 
     According to another embodiment, the at least one other line that is switched to the first mode is locally associated with the line to be trained. In particular, the at least one other line may be locally associated within a cable binder with the line to be trained. 
     In yet another embodiment, the first network element switches the at least one other line to the first mode. 
     According to a next embodiment, the first network element comprises several distributed first network elements, wherein one of the distributed first network elements communicates the training of one of its lines to the at least one other distributed first network element, the latter switching at least one of its lines to the first mode. 
     Hence, a first DSLAM may communicate to a second DSLAM that training of one of its lines is due. The first DSLAM and the second DSLAM both switch their lines to the first mode. This is in particular useful if the first DSLAM and the second DSLAM share lines of at least one cable binder. 
     This concept applies in a similar manner to more than two DSLAMs or to several Central Offices. However, if the (distributed) network elements know which lines are put together in a binder, they may specifically switch those lines to the first mode that are put together in a binder with the line to be trained, because these lines may inflict significant crosstalk on the line in training. 
     The problem stated supra is also solved by a device for data processing comprising a processor unit that is equipped/arranged such that the method as described is executable on said processor unit. 
     According to an embodiment, the device is a communication device, in particular a network element. Said device may in particular be or be associated with a Central Office (CO) and/or a Digital Subscriber Line Access Multiplexer (DSLAM). 
     The problem stated above is also solved by a communication system comprising the device as described herein. 
     Embodiments of the invention are shown and illustrated in the following figures: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 2  shows a table visualizing data rates that can be achieved by utilizing different SNR margin setting options; 
         FIG. 3  shows steps of a method to be run on a device, e.g., a DSLAM, that allow an efficient utilization of a DSL power management. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     According to the approach provided herewith adjacent lines may be connected to at least one DSLAM or to at least one line card in a Central Office (CO). 
     This DSLAM is aware of which lines are currently in a training mode, which lines are currently in a full power mode (L0 mode) and which lines are in a reduced power mode (L2 mode). 
     The DSLAM (and/or the CO) may be supplemented such that they are able to execute the following steps:
         When a line starts its training phase, at least some other lines, in particular adjacent lines, are switched to the full power mode (L0 mode) irrespective of their current status or use. Optionally, all other lines may be switched to the full power mode (L0 mode).   If or when the training of the particular line is finished, the remaining lines may return to their respective previous modes.       

     This approach may be applied to a single line card or to a complete DSLAM with multiple line cards. 
     There are in particular two options after the training phase of a specific line: The other lines may return from the full power mode (L0 mode) to the mode they had before or they can go through an automatic selection of power management modes. 
     Steps of the method that may in particular be run on a DSLAM, at a CO or in a line card are depicted in  FIG. 3 . 
       FIG. 3  shows a first DSLAM  301  and a second DSLAM  302 . The second DSLAM  302  may also comprise the functionality of the first DSLAM  301 , but regarding this example the second DSLAM  302  may be triggered by the first DSLAM  301  via at least one communication channel  311 . 
     It is to be noted that each component  301  and  302  may be realized also as a CO or as a line card at the CO or of the DSLAM. It is also noted that several such second DSLAMs  302  may be provided that can be triggered by said first DSLAM  301 . 
     In a step  303  a training of a particular line k is conducted, e.g., due to a connection or re-connection of the DSL modem. As stated supra, the training may in particular comprise setting up the communication link between two DSL transceivers, one being located at the DSLAM  301 , the other at the CPE. During training, the transceivers at both ends of the line exchange their capabilities and negotiate a set of parameters. 
     In order to achieve an efficient training result regarding potential crosstalk effects from adjacent lines (in particular lines that are in the same cable binder with said line k), training of line k is conducted when all other lines are in full power mode (see step  304 ). As an option, training of said line k may be conducted when a selection of other lines is switched to the full power mode. Such selection may comprise lines that are adjacent to one another and in particular are adjacent to the line k and hence inflict significant crosstalk to the line k during training. 
     When training of line k is finished (step  305 ), the other lines (adjacent lines) are free to switch to a different mode other than the full power mode, in particular to a mode of reduced power to enable power management (step  306 ). Of course, at least one of the other lines may remain in said full power mode. 
     As an option, the DSLAM  301  may indicate to the DSLAM  302  the training of said line k (see step  307 ). This is in particular useful if lines of the same cable binder are attached to ports of the first DSLAM  301  and to ports of the second DSLAM  302 . 
     As a further option, the DSLAM  302  may check in a step  308  whether line k (attached to DSLAM  301 ) has adjacent lines that are attached to said DSLAM  302  and in the affirmative, the DSLAM  302  may switch all its lines that are adjacent to line k (or generally all its lines) to full power mode (in step  309 ). 
     The end of training of the line k is indicated by step  305  and such information may be conveyed to the DSLAM  302  in order to release the lines previously set to full power mode (step  310 ). Hence, the lines attached to the DSLAM  302  are free to adopt a different power management mode. 
     Further Advantages: 
     The concepts can be implemented by modification of the DSLAM only. No change is required at the CPEs. 
     The L2 mode, in particular as specified by ADSL2/2plus, can actually be used. Operators do not face the risk of an instable network. Hence, power saving mechanisms are efficiently applicable. 
     Because training is conducted under noisy circumstances (severe crosstalk and/or interference), in particular by applying a worst case scenario of utmost crosstalk conditions, no spare SNR margin is required or has to be set up. 
     The table of  FIG. 2  shows which data rates can be achieved by utilizing different SNR margin setting options. 
     Cases  201  and  202  refer to a static SNR margin configuration that may be needed in order to anticipate a worst case scenario that may otherwise not be covered during training of a particular line. If during training of a particular line a significant number of adjacent lines are in L2 mode, a normal data rate (target data rate) is achieved (case  202 ). However, if a number of adjacent lines are in L0 mode during such training (case  201 ), the achievable data rate is smaller than the normal target data rate. 
     The approach provided herein significantly improves the data rate that can be utilized (see cases  203  and  204 ): Training is conducted under noisy conditions, in particular under worst case conditions by inflicting crosstalk from adjacent lines that are in the full power mode (L0 mode) during said training. Hence, no spare SNR margin above the target SNR margin is required to anticipate the case of adjacent lines switching to full power mode (L0 mode) thereby producing higher crosstalk during operation. 
     Transceivers can adapt themselves such that a necessary target SNR margin is just reached, but not exceeded. So, the data rate that can be utilized corresponds to the normal (target) data rate.