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A method for selecting a mode of operation for at least two modems is described. First, a handshake procedure is performed in order to determine a set of possible modes of operation supported by said modems. From said set of possible modes of operation, a set of favorable modes of operation is deriv

A method for selecting a mode of operation for at least two modems is described. First, a handshake procedure is performed in order to determine a set of possible modes of operation supported by said modems. From said set of possible modes of operation, a set of favorable modes of operation is derived. In case there exist two or more favorable modes of operation, a probing-based selection is performed that comprises evaluating respective performances of said favorable modes of operation. The favorable mode of operation with the best performance is selected as a resultant mode of operation.

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1. A method for selecting a resultant mode of operation for at least two modems that communicate via a communications network, comprising: (a) performing a handshake procedure to determine a set of possible modes of operation supported by the at least two modems, the set of possible modes of operati

1. A method for selecting a resultant mode of operation for at least two modems that communicate via a communications network, comprising: (a) performing a handshake procedure to determine a set of possible modes of operation supported by the at least two modems, the set of possible modes of operation including protocol standards and annexes that are supported by the at least two modems;(b) selecting a first set of favorable modes of operation from among the set of possible modes of operation using a first level of priority-based selection based on priorities assigned to the annexes;(c) selecting a second set of favorable modes of operation from among the first set of favorable modes of operation using a second level of priority-based selection based on priorities assigned to the protocol standards; and(d) in case there exist two or more second favorable modes of operation from among the second set of favorable modes of operation, performing a probing-based selection by evaluating respective performances of each of the second favorable modes of operation and selecting a second favorable mode of operation with a best performance from among the second set of favorable modes as the resultant mode of operation. 2. The method of claim 1, wherein the protocol standard is selected from a group consisting of: G.992.1, G.992.2, G.992.3, G.992.4, and G.992.5. 3. The method of claim 2, wherein step (a) comprises: (a)(i) performing the handshake procedure to determine the set of possible modes of operation supported by the at least two modems, the set of possible modes of operation being related to particular annexes of the protocol standard. 4. The method of claim 1, wherein step (b) comprises: (b)(i) selecting the first set of favorable modes of operation from among the set of possible modes of operation using the first level of priority-based selection based on priorities assigned to different classes of upstream tone usage. 5. The method of claim 4, wherein the different classes of upstream tone usage comprise, in descending order of priority, annex J type, annex B type, and annex A type. 6. The method of claim 4, wherein one or more of the different classes of upstream tone usage are excluded from the first level of priority-based selection. 7. The method of claim 1, wherein the various protocol standards are prioritized in a descending order of priority, at least one of the various protocol standards being selected from a group consisting of: G.992.5, G.992.4, G.992.3, G.992.1, G.992.2, and non-ITU standards. 8. The method of claim 7, wherein the G.992.3, the G.992.4, and the G.992.5 standards are assigned a similar priority. 9. The method of claim 1, wherein step (d) comprises: (d)(i) initialising the at least two modems to a probing mode of operation when the two or more second favorable modes of operation exist. 10. The method of claim 9, wherein step (d)(i) comprises: (d)(i)(A) initialising the at least two modems to a diagnostic mode of operation when the two or more second favorable modes of operation exist. 11. The method of claim 9, wherein step (d) further comprises: (d)(ii) deciding whether to re-initialise the at least two modems before data transmission is started. 12. The method of claim 1, wherein step (d) comprises: (d)(i) measuring a condition of the communications network; and(d)(ii) determining a signal-to-noise ratio of the communications network using the condition. 13. The method of claim 1 wherein step (d) comprises: (d)(i) estimating a condition of the communications network; and(d)(ii) determining a signal to noise ratio of the communications network using the condition. 14. The method of claim 1, wherein step (d) comprises: (d)(i) determining at least one of an upstream bit rate and a downstream bit rate for each of the second favorable modes of operation. 15. The method of claim 1, wherein step (d) comprises: (d)(i) determining a performance index indicating the respective performances for each of the second favorable modes of operation. 16. The method of claim 15, wherein step (d)(i) comprises: (d)(i)(A) deriving the performance index indicating the respective performances for each of the second favorable modes of operation from line conditions of the communications network. 17. The method of claim 15, wherein step (d) further comprises: (d)(ii) selecting the second favorable mode of operation with a highest performance index as the resultant mode of operation. 18. The method of claim 15, wherein step (d) further comprises: (d)(ii) determining a secondary performance index when all of performance indices from among the performance index are equal to a maximum; and(d)(iii) evaluating the secondary performance index for each of the second favorable modes of operation. 19. A method for selecting a resultant mode of operation for at least two modems that communicate via a communications network, comprising: (a) performing a handshake procedure to determine a set of possible modes of operation supported by the at least two modems, the set of possible modes of operation including protocol standards and annexes that are supported by the at least two modems;(b) deriving a set of favorable modes of operation from the set of possible modes of operation; and(c) in case there exist two or more favorable modes of operation, determining a performance index indicating the respective performances for each of the favorable modes of operation according to: PI=αd·(DS−DSmin)+αu·(US−USmin), wherein DS and US denote the downstream and the upstream bit rate, respectively, DSmin and USmin, denote the minimum downstream and the minimum upstream bit rate, respectively, and αd and αu denote weight factors, and selecting at least one of the set of favorable modes based upon the performance index as the resultant mode of operation. 20. A modem unit for transmitting data via a communications network, comprising: a transmission unit configured: (i) to perform a handshake procedure to determine a set of possible modes of operation, the set of possible modes of operation including protocol standards and annexes that are supported the modem unit,(ii) to derive a first set of favorable modes of operation from among the set of possible modes of operation using a first level of priority-based selection based on priorities assigned to the annexes, and(iii) to derive a second set of favorable modes of operation from among the first set of favorable modes of operation using a second level of priority-based selection based on priorities assigned to the protocol standards; anda probing facility configured to perform a probing-based selection that comprises evaluating respective performances of the second favorable modes of operation from among the second set of favorable modes of operation when two or more second favorable modes of operation exist and to select a second favorable mode of operation with a best performance as a resultant mode of operation. 21. The modem unit of claim 20, wherein the modem unit is configured to support a protocol standard selected from the group consisting of at least one of the protocol standards: G.992.1, G.992.2, G.992.3, G.992.4, G.992.5. 22. The modem unit of claim 20, wherein the modem unit is implemented as part of either a central xDSL modem or a remote xDSL modem. 23. The modem unit of claim 20, wherein the first level of priority-based selection for selecting the first set of favorable modes of operation from among the set of possible modes of operation is based on priorities assigned to different classes of upstream tone usage. 24. The modem unit of claim 20, wherein the probing facility is further configured to initialise the modem unit to a probing mode of operation to perform the probing-based selection. 25. The modem unit of claim 20, wherein the probing-based selection comprises: determining line conditions of the communications network; anddetermining a signal-to-noise ratio of the communications network based upon the line conditions. 26. The modem unit of claim 20, wherein the probing facility is further configured to determine a performance index indicating the respective performances for each of the second favorable modes of operation when two or more second favorable modes of operation exist. 27. The modem unit of claim 26, wherein the probing facility is configured to select the second favorable mode of operation with a highest performance index as the resultant mode of operation when two or more second favorable modes of operation exist. 28. The modem unit of claim 20, wherein the probing facility is configured to decide whether the modem unit has to be re-initialised before data transmission is started.